ML20212J371
| ML20212J371 | |
| Person / Time | |
|---|---|
| Site: | 05000586 |
| Issue date: | 07/01/1977 |
| From: | DAMES & MOORE |
| To: | |
| Shared Package | |
| ML20212J355 | List: |
| References | |
| FOIA-99-369 NUDOCS 9910050130 | |
| Download: ML20212J371 (148) | |
Text
os/n BALTMJRE GAS
~
AND ELECTRE COMPANY PERRYMAN
~
1IMITED V O ll M E 111
]
EARLY
-2~
'1 SITE a-R REVIEW A
36 DR
TABLE OF CONTENTS
(
1.0 INTRODUCTION
AND GENERAL DESCRIPTION OF PLANT 1.0-1
1.1 INTRODUCTION
1.1-1 1.2 GENERAL DESCRIPTION 1.2-1 1.4 IDENTIFICATION OF AGENTS AND CONTRACTORS 1.4-1 1.4.1 Dames & Moore 1.4-1 1.4.2 Gilbert Associates, Inc.
1.4-1 1.6 MATERIALS INCORPORATED BY REFERENCE 2.0 SITE CHARACTERISTICS 2.1 GEOGRAPHY AND DEMOGRAPHY 2.1-1 2.1.1 Site Location and Description 2.1-1 2.1.1.1 Location 2.1-1 2.1.1.2 Description of Site Area 2.1-1 2.1.1.3 Boundaries for Establishing Effluent Release Limits 2.1-2 1
2.1.2 Exclusion Area Authority and Control 2.1-2 2.1.2.1 Authority 2.1-2 2.1.2.2 Control of Activities Unrelated to Plant Operation 2.1-2 2.1.2.3 Arrangements for Traffic Control 2.1-3 2.1.3 Population Distribution 2.1-3 2.1.3.1 Population Within 16 km (10 mi) of Site 2.1-4 2.1.3.2 Population Between 16 km (10 mi) and 80 kr (50 mi) of Site 2.1-5 2.1.3.3 PopuAation Projections 2.1-5 2.1.3.4 Transient Population 2.1-9 2.1.3.5 Low Population Zone 2.1-12 2.1.3.6 Population Center 2.1-14 2.1.3.7 Population Density 2.1-14 2.1.3.8 Residential Development Within 16 km (10 mi) 2.1-14 2.1.3.9 Public Facilities 2.1-15 2.1.4 References 2.1-17
~2.2 NEARBY-~ INDUSTRIAL,. TRANSPORTATION AND MILITARY FACILITIES.
2.2-1 2 2.1 Locations and Routes 2.2-1
- 2. 2.1.1, Industries, Transportation Routes, Pipelines and Transportation Facilities 2.2-1 2.2.1.2
. Aberdeen Proving Ground Military Reservation 2.2-2 2.2.2 Descriptions 2.2-3
- 2. 2. 2. l' Description of Facilities' 2.2-3 2.2.2.2 Description of-Products and Materials 2.2-7 2.2.2.3 Pipelines
.2.2-7 2.2.2.4 Waterways 2.3: 8 2.2.2.5 Airports 2.2-8 2.2.2.6 Projections of Industrial Growth 2.2-8 2.2.3 Evaluation of Potential Accidents 2.2-9 2.2.3.1 Determination of Design Basis Events 2.2-9 2.2.4 References 2.2-21 Appendix 2.2.A Aberdeen Proving Ground (APG)
Operations 2.2.A-1 2.3 METEOROLOGY 2.3-1 2.3.1 Regional Meteorology 2.3-1 2.3.1.1 General Climate 2.3-1 2.3.1.2 Regional Meteorological Conditions for Design and Operating Bases 2.3-2 2.3.1.3 Design Basis Tornado 2.3-9 2.3.1.4 Extreme Winds 2.3-11 2.3.2 Local Meterology 2.3-13 2.3.2.1 Normal and Extreme Values of Meteoro-logical Parameters 2.3-13 2.3.2.2 Effects of Heat Dissipation Facilities 2.3-18 2.3.3 Onsite Meteorological Measurements Program 2.3-34 2.3.3.1 Preoperational PJogram 2.3-24 2.3.3.2 Tower Location 2.3-24 2 3.3.3 Description of Instrumentation 2.3-24 2.3.3.4 Recording Systems 2.3-24 2.3.3.5 Additional Equipment 2.3-25 2.3.3.6 Calibration and Maintenance Procedures 2.3-25 2.3.3.7 Analysis Procedures 2.3-25 2.3.3.8 Data Periods for Analytical Use 2.3-25
(
2.3.4 Short-Term (Accident) Diffusion Analysis 2.3-27 2.3.4.1 Diffusion Model for 0-2 Hours 2.3-27 2.3.4.2' Diffusion Model for 0-8 Hours 2.3-28 2.3.4.3 Diffusion Model for 0-16 Hours, 0-3 Days, and 0-26 Days 2.3-28 2.3.4.4 Results 2.3-29 2.3.5 Long-Term (Routine) Diffusion Analysis 2.3-30 2.3.5.1 Plant Characteristics 2.3-30 2.3.5.2 Atmospheric Diffusion Model 2.3-31 2.3.5.3 Plume Rise 2.3-32 2.3.5.4 Methods of Depletion and Deposition Calculation 2.3-33 2.3.5.5 Results 2.3-34 2.3.6 References 2.3-35 2.4 HYDROLOGIC ENGINEERING 2.4-1 2.4.1 Hydrologic Description 2.4-1 2.4.1.1 Site and Facilities 2.4-1 2.4.1.2 Hydrosphere 2.4-2 2.4.2 Floods 2.4-9 2.4.2.1 Flood History 2.4-9 2.4.2.2 Flood Design Considerations 2.4-14 2.4.2.3 Effects of Local Intense Precipitation 2.4-15 2.4.3 Probable Maximum Flood (PMF) on Streams and Rivers 2.4-18 2.4.3.1 Probable Maximum Precipitation (PMP) 2.4-18 2.4.3.2 Precipitation Losses 2.4-19 2.4.3.3 Runoff and Stream Course Models 2.4-20 2.4.3.4 Probable Maximum Flood Flow 2.4-24 2.4.3.5 Water Level Determinations 2.4-26 2.4.3.6 Coincident Wind-Wave Activity 2.4-33 2.4.4 Potential Dam Failures, Seismically Induced 2.4-34 2.4.4.1 Dam Failure Permutations 2.4-34 2.4.4.2 Unsteady Flow Analysis at Potential Dam Failures 2.4-35 2.4.4.3 Water Level at Plant Site 2.4-44 2.4.4.4 Other Dam Failures 2.4-45 J
n
)
2.'4.5 Probable Maximum Surge and'Seiche Flooding 2.4-46 1
2.4.5.1 Probable Maximum Winds and Associated Meteorological Parameters 2.4-46 2.4.5.2-Surge and Seiche Water Levels 2.4-53 12.4.5.3 Wave Action 2.4-61
)
2.4.5.4 Resonance 2.4-68 2.4.5.5 Protective Structures 2.4-70 2.4.6 Probable Maximum Tsunami Flooding 2.4-72 2.4.7 Ice Effects 2.4-73 2.4.7.1 Historical Ice Effects 2.4-73 2.4.7.2 Ice Effects on Bush River 2.4-73 2.4.7.3 Snow Pack and Winter PMP 2.4-73 2.4.8 Cooling Water Canals and Reservoirs 4-73 2.4.9 Channel Diversions 2.4-74 2.4.9.1 Susquehanna River 2.4-74 2.4.9.2 Bush River Basin 2.4-74 2.4.9.3 Local Drainage 2.4-74
- 2.4.9.4 General Character of Shore and Near-Shore Materials 2.4-74 2.4.9.5 Historical Erosion Rates 2.4-75 2.4.10 Flood Protection Requirements
-2.4-76 2.4.10.1 General 2.4-76 2.4.10.2 Nuclear Island Fill 2.4-76 2.4.10.3 Roof Drainage 2.4-77 2.4.10.4 Site Drainage 2.4-77 2.4.11 Low Water Considerations 2.4-77 2.4.11.1 Low Water in Streams 2.4-77 2.4.11.2 Low Water Resulting from Surges, Seiches or Tsunami 2.4-80 2.4.11.3 Historical Low Water 2.4-80 2.4.11.4 Future Controls 2.4-80 2.4.11.5 Plant Requirements 2,4-80 2.4.11.6 Heat Sink Dependability Requirements 2.4-81 2.4.12 Dispersion, Dilution, and Travel Times of Accidental Releases of Liquid Effluents in Surface Waters 2.4-81 2.4.13 Ground Water 2.4-82 2.4.13.1 Description and Onsite Use 2.4-82 2.4.13.2 Sources 2.4-88
2.4.13.3 Accidents 2.4-99 t
2.4.14.4-Monitoring or Safeguard Requirements 2.4-114 2.4.13.5 Design Bases for Subsurface Hydrostatic Loadings 2.4-115 2.4.15 References 2.4-117 Appendix 2.4.A Ground Water Field Investigations and Laboratory Testing 2.4.A-1 Appendix 2.4.B Relationship of Vertical Datum 2.4.B-1 2.5 GEOLOGY, SEISMOLOGY AND GEOTECHNICAL ENGINEERING 2.5-1
-2.5.1 Geologic and Seismic Information 2.5-1 2.5.1.1 Introduction 2.5-1 2.5.1.2 Geology of the Region 2.5-2 2.5.1.3 Geology of the Area Surrounding the Perryman Site 2.5-14 2.5.1.4 Geology of the Perryman Site 2.5-27 2.5.2 Vibratory Ground Motion 2.5-41 2.5.2.1 Seismic History 2.5-41 2.5.2.2 Geologic Structures and Tectonic Activity 2.5-43 2.5.2.3 Correlation of Earthquake Activity with Geologic Structures or Tectonic Provinces 2.5-51 2.5.2.4 Maximum Earthquake Potential 2.5-54 2.5.2.5 Seismic Wave Transmission Characteristics of the Site 2.5-55 2.5.2.6 Safe Shutdown Earthquake (SSE) 2.5-55 2.5.2.7 Operating Basis Earthquake (OBE) 2.5-57 2.5.3 Surface Faulting 2.5-59 2.5.3.1 Geologic Conditions of the Site 2.5-59 2.5.3.2 Evidence of Fault Offset 2.5-59 2.5.3.3 Earthquakes Associated with Capable Faults 2.5-59 2.5.3.4 Investigations of Capable Faults 2.5-59 2.5.3.5 Correlation of Epicenters with Capable Faults 2.5-59 2.5.3.6 Description of Capable Faults 2.5-59 2.5.3.7 Zone Requiring Detailed Faulting Investigation 2.5-59 2.5.3.8 Results of Faulting Investigation 2.5-59 2.5.4 Stability of Subsurface Materials and Foundations 2.5-60 2.5.4.1 Geologic Features 2.5-61 2.5.4.2 Properties of Subsurface Materials 2.5-62
E
',,,L i
1 2.5.4.3
~ Exploration 2.5-75 2;5'4.4 Geophysical-Explorations 2.5-86
~2.5.4.5 Excavationr, and Backfill 2.5-90 2.5.4.6
-Ground Water-Conditions:
2.5-93 2.5.4.7 Response of Soils to Dynamic Loading 2.5-94 2.5;4.8.
Liquefaction Potential 2.5-98
~2.5.4.9 Earthquake Design Basis 2.5-103
.2.5.4.10 Static Foundation Analyses 2.5-103
'2.5.5 Stability.of Slopes 2'.5-118 2.5.5.1
. Natural l Slopes 2.5-118 2.5.5.2-Manmade Slopes
~2.5-119
-2.5.6 Embankments and Dams 2.5-120 2.5.7 References' 2.5-121 Appendix 2.5.A Pemote Sensor' Investigation of Perryman Site 2.5.A-1 Appendix 2.5.B Structural Analysis of Piedmont Rocks'in the Vicinity of the Perryman Site 2.5.B-1 Appendix 2.5.C Measured Stratigraphic Sections 2.5.C-1 Appendix.2.5.D Pollen Analysis of Selected Samples 2.5.D-1 Appendix 2.5.E Petrographic Analyses of Crystal-line Rocks 2.5.E-1 Appendix 2.5.F Seismic Reflection Survey 2.5.F-1 Appendix 2.5.G Details of 1976 Phase III Sub-surface Investigation 2.5.G-1 Appendix 2.5.H Laboratory Soil Testing 2.5.H-1 Appendix 2.5.I Details of Foundation Analyses 2.5.I-l 3.0 DESIGN OF STRUCTURES, COMPONENTS, EQUIPMENT AND SYSTEMS 3.5
'MISSILC PROTECTION 3.5-1 3.5.1.4 Missiles Generated by Natural Phenomena 3.5-1 3.5.1.5 Missiles From External Activities 3.5-2 3.5.1.6 Aircraft Hazards 3.5-11 3.5.4 References 3.5-19 b.
g' A
E s
11 I
'l9.0
~ AUXILIARY SYSTEMS f
e 9.2 WATER SYSTEMS 9.2-1 9.2.5:
Ultimate Heat Sink 9.2-1 1
- 11.0 RADIOACTIVE WASTE MANAGEMENT' 1
11.1 DESCRIPTION
11.1-1
-15.0 ACCIDENT ANALYSES
15.1 DESCRIPTION
15.1-1 17.0- ' QUALITY ASSURANCE DURING EARLY SITE REVIEW EFFORT l
17.1 ORGANIZATION 17.1-1 l
1 17.2 00ALITY' ASSURANCE PROGRAM 17.2-1
-17.2.1 Baltimore Gas and Electric Company 17.2-1 17.2.2 Dames & Moore 17.2-2 17.2.3 Gilbert Associates, Inc.
17.2-3 17.2.4 References 17.2-4 1
INDEX
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2.5 GEOLOGY, SEISMOLOGY AND GEOTECHNICAL ENGINEERING TECHNICAL REVIEW OBJECTIVES The overall technical review objective of this section is to demonstrate that the site is suitable from the safety viewpoint with respect to geology, seismology and geotechnical engineering considerations, and to supply to the staff sufficient data to permit an independent objective staff assessment.
Specific objectives are detailed in the following paragraphs.
1.
Basic geologic and seismic data pertaining to the region and site are presented.
These data were obtained from literature search; a program of subsurface investigation by drilling and geophysical techniques; a comprehensive surface mapping program; and laboratory and office analyses.
The seismic and geologic characteristics are described as they relate to Appendix A of 10 CFR Part'100.
The objective is to demonstrate that the geologic and seismic data presented are adequate and that these data accurately lead to a con-clusion as to whether the site is acceptable with respect to any geologic features which could potentially affect the safety of the site.
2.
The seismic design basis for vibratory ground motion is established.
Based on a detailed examination of the seismic history of the region, regional and site geology, and seismo-tectonic relationships, the Safe Shutdown Earthquake (SSE) has been determined.
The Operating Basis Earthquake (OBE) has been determined using probabilistic methods.
The vibratory ground motion associated with both the SSE and OBE has been described.
Likewise, design response spectra for the SSE and OBE are presented.
The objective is to demonstrate that a pfant at the site need not be designed for ground displacement, and that the design accelerations for both the SSE and OBE are acceptable as design bases.
3.
Geologic and seismic data have been evaluated in terms of the potential for surface faulting within the site and the surrounding area.
This includes an evaluation of regional and local tectonic patterns and detailed examination of specific features both on the surface and subsurface.
The objective is to demonstrate whether capable faults have been recognized at or in the vicinity of the site.
2.5-1
e
- 4.. The. condition and enginssring. prop 3rtise of both coil and rock at the' site have.been described as1they relate to the support.of nuclear: power plant 1 foundations.
The bearing and ctability;of the. foundation. soil, foundation settlement, Both static coil liquefaction potential have been evaluated.
and dynamic load conditions have been considered.
There:are
< ' no planned slopes or embankments, the failure of.which could affect the safety.of the plant.
The-objective is.to' demonstrate that the soil and. rock t
t the site are adequate for support of nuclear power
.presen a
. plant structures under all operating and design basis conditions.
e s
4 2.5-11
E 2.5 GEOLOGY, SEISMOLOGY, AND GEOTECHNICAL ENGINEERING 2.5.1 Geologic.and Seismic _Information 2.5.1.1 Introduction 2.5.1.1.1 General.-
This section presents the basic geologic and seismic infor-mation that was obtained during a study of geologic conditions relative to the Perryman Site.
The site is located approximately 1
10 (km) (6 mi) southwest of Aberdeen, Maryland, on the eastern l
shore of the Bush River, as shown in Figure 2.5-1.
This information presented herein was obtained during a two-phase investigation.
The first phase was designed to identify, define, and evaluate the general geologic and seismic characteristics of'the site and its surroundings.
The purpose of the second phase was to examine, in detail, specific geologic features and areas, and to provide additional data from outside sources that were not available during the first phase.
The overall purpose of this program was to evaluate the geological and seismic design parameters of the site.
To achieve this purpose, a program of geologic and seismic resdarch and geologic mapping of the site and its environs was carried out, followed by a program of subsurface investigation and laboratory testing.
2.5.1.1.2 Geologic and Seismic Research and Geologic Reconnaissance Prior to the commencement of field investigations, a comprehen-sive program of information acquisition was carried out to obtain all reports, data, and maps pertaining to the Perryman Site.
I Contact was made with representatives of state, federal, and local: government agencies and members of private organizations i
and universities, through which unpublished information concerning this study was obtained.
A list of the published and unpublished literature used in this report, and of the individuals contacted f
for it, appears in Section 2.5.7.
In addition, a study of surface expressions of features l
possibly associated with geologic structures was carried out through the use of aerial photographs and other high-altitude, l
remote-sensing media.
Prominent lineaments and other features
=
were identified and marked for investigation during the subsequent program of field mapping within the area surrounding the site.
The details of'this study and its results are presented in
]
Appendix 2.5.A.
Geological reconnaissance mapping was carried out in all accessible parts of the area enclosed within a circle of 8 km j
l I
2.5-1 4
I 1
(5 mi) radius that was centered on the site, as shown on Figure 2.5-7.
This circular area did not include:
(1) land within the U.S. Army property on Gunpowder Neck; (2) that portion of the
~
crea covered by water; and (3) some parts of the U.S. Army property on the main Aberdeen Proving Ground military reservation.
All stream systems were traversed and other localities in which outcrop was suspected to_ occur, such as artificial cuts and cteep slopes, were investigated by field geologists.
To aid in the location of suspected outcrop areas, aerial photographs and topographic _ maps were studied prior to and during the field l
I investigation.
In addition, target areas that were identified through the remote-sensing techniques described above were given priority for field examination, j
2.5.1.1.3 Subsurface Exploration This-program included geological borings on and near the alte, a seismic refraction survey, a seismic reflection survey, j
cnd a ground magnetometer reconnaissance.
Samples from the borings were analyzed and compared with the seismic data to ovaluate the subsurface stratigraphy of the site.
This program is described in detail in Section 2.5.4.3, and its results are discussed in Sections 2.5.1.4, 2.5.E, 2.5.F, and 2.5.G.
2.5.1.2 Geology of the Region 2.5.1.2.1 General The Perryman Site lies within the Coastal Plain Province, near its surface contact with the Piedmont Province.
The boundary between these two geologic provinces is referred to as the Fall Zone, and it is located approximately 5 km (3 mi) northwest of the site (Figure 2. 5-2).
The proximity of this boundary to the site has important implications for the physio-graphy, stratigraphy, structure, and geologic history of the Perryman Site and its surroundings.
2.5.1.2.2 Physiography of the Region The site is located within the Coastal Plain physiographic Province, but is within approximately 5 km (3 mi) of the Piedmont Province.
These two provinces are characterized by significantly different types of terrain.
The Coastal Plain is typically a low-lying terrain of low to moderate relief.
A large portion of the province near the coast is composed of extensive tracts of nearly flat plain, which lie at elevations of less than 30.5 (100.0 ft) above een level.
This nearly flat plain includes most of Delaware, Maryland, and Virginia, eact of the Chesapeake Bay (the Delmarva Peninsula).
These nearly flat areas are mainly composed of emerged marine terraces of Pleistocene age that are 2.5-2
formed in poorly consolidated sediments.
Although nearly flat and very slightly sloping toward the east, the terrace areas of the Maryland Eastern Shore (east of Chesapeake Bay) have a significantly higher local relief than those of the shore west of the bay (Appendix 2.5.A).
Farther west on the mainland shore, elevations within the Coastal Plain reach 77 m (250 ft) and the terrain is rolling to moderately hilly.
These hilly areas constitute most of the Maryland Coastal Plain west of the Bay and most of the northern, central, and western parts of tidewater Virginia.
Minor tracts of hilly terrain occur in the northern part of the Delmarva Peninsula.
Within the Piedmont physiographic province, the relief is moderately high (as much as 61 m (200 f t) locally), and eleva-tions range up to 122 m (400 f t) within a few miles of the coast.
Landforms reflect a complex, underlying structure of metamorphic and igneous rocks.
The demarcation between the gentler topography of the Coastal Plain and the more pronounced relief of the Piedmont physiographic province is the Fall Zone.
This transition zone is easily visible on topographic maps and in the field, and coincides with numerous cultural features (such as cities, industrial centers, and shipping terminals) which, in turn, reflect the influence of this physiographic feature on the settlement and development of the eastern seaboard of the United States.
This physiographic boundary is also the surface expression of the boundaries between geologically different provinces.
As is discussed in Sections 2.5.1.2.3 and 2.5.1.3.3, j
however, the definitions of the physiographic provinces and their corresponding geologic provinces are not exactly identical.
2.5.1.2.3 Stratigraphy of the Region The rock units of the region surrounding the site are of j
two general categories:
(1) the weakly-to well-consolidated, generally stratiform sediments of the Coastal Plain; and (2) the crystalline, complex 1y structured metamorphic and igneous rock units of the Piedmont (Figure 2.5-3).
The rocks of the Piedmont are the oldest, and form the basement upon which the sediments of the Coastal Plain formations were deposited.
As shown in Figure 2.5-S, the surface of the Piedmont complex of rocks (the basement) slopes from the Fall Zone southeastward and seaward, beneath the Coastal Plain strata..
The latter formations slope less steeply and, at the same time, thicken in the same direction.
Thus, the materials of the Coastal Plain form, in cross section, a wedge-shaped mass that thickens to the southeast from a feather edge in the Fall Zone.
This prism-shaped deposit extends on land from Long Island to Florida, 2.5-3
cnd westward to Texas.
Offshore, it extends as far north as the Continental Shelf-of eastern Canada.
The formations of the Coastal Plain are composed of silt, clay, limestone, sand, and gravel o:f both marine and continental origin.
They range in age from Early Cretaceous to Recent.
Generally, each successively younger formation has a gentler dip than that lying below, resulting in a decrease in slope upward in the cequence.
The decrease in dip is accompanied by the gradual thickening of the individual strata to the southeast.
Although the Coastal Plain deposits are generally stratiform, many of the formations exhibit considerable lateral and vertical variations in mineral composition and texture.
As a rule, however, they generally are finer-grained toward the east.
These characteristics are interpreted as being the results of sedimenta-tion from sources to the west under widely fluctuating deposi-tional conditions.
Precambrian &nd Paleozoic rocks of the Piedmont Province occur at or near the surf ace in a 72 km (45 mi)-wide belt
. northwest of the Fall Zone.
These are. comprised primarily of schists and genisses, with intrusions of younger Paleozoic granitic rocks.
Farther west, Paleozoic slates, schists, gneisses,.and unmetamorphosed sedimentary formations comprise the interior Piedmont rocks.
The Triassic Lowland section of the Piedmont, still farther west, contains unmetamorphosed conglomerates, sandstones, and shales, that have been intruded by igneous sills and dikes of Late and Post-Triassic age (Figure
)
2.5-3).
1 Approximately 90 km (60 m1) northeast of the Lite, in the vicinity of Philadelphia, Pennsylvania, the primarily crystalline belt decrease in width to approximately 32 km (20 mi).
The rock units in the region that are significant to a discussion of the geology of the Perryman Site are:
(1) the Baltimore Gneiss, (2) the Glenarm Supergroup; (3) the Baltimore Mafic Complex; and (4) the James Run Formation.
The Baltimore Gneiss This formation, the oldest in the Piedmont, occurs in the i
cores of domes in Maryland (for examp)e, the Phoenix and Towson Domes), and as fault-bounded blocks that are uplifted into overlying metamorphic rocks in Pennsylvania (for example, the Honeybrook Uplift).
It consists of granite gneiss, veined gneiss, augen gneiss, amphibolite, and migmatite.
It has been i
intruded by post-tectonic, Paleozoic pegmatites.
Isotopic age determinations on zircons and potassium feldspars indicate that the rocks of the Baltimore Gneiss crystallized initially about 1100 million years (m.y.) ago.
2.5-4
Glenarm Sup;rgroup This large group of rock units of Late Precambrian to Lower Paleozoic age includes the Setters Formation, the Cockeys-ville Marble, and the Wissahickon Group (Tillman, and others, 1975; Crowley, 1976).
The Setters Formation is a thick layer of patassium-rich metasediments that are believed to have been deposited in local, inter-connected fault-block basins.
The Cockeysville Marble occurs with the Setters Formation, as thin layers around domes of Baltimore Gneiss, while the Wissahickon Group is a thick, metamorphosed sequence of interlayered sands and muds, partly equivalent to, but mostly younger than, the Setters Formation and the Cockeysville Marble.
The Peach Bottom Member, which is a black phyllite, and the Cardiff Metaconglomerate are within the Wissahickon Group.
The Baltimore Mafic Complex Most of this formation consists of variably metamorphoLad, mafic igneous rocks.
At its base, however, it is made up of serpentinized, ultramafic rock types, some of which appear to be separated from the main body.
The outcrop pattern reflects the structure of the Baltimore-Washington Anticlinorium.
Primary igneous minerals from these rocks hav yielded ages of approximately 600-700 B.P.
(Wetherill and others, 1966), equivalent in age to part of the Glenarm Supergroup (Crowley, 1974, 1976).
The James Run Formation This formation consists of a bedded sequence of interlayered felsic and mafic gneisses which is also thought to be laterally equivalent to parts of the Wissahickon Group at their time of formation.
The age determinations from zircons in these rocks range between 500 and 600 m.y. ago (Higgins, 1972).
2.5.1.2.4 Geological Structure of the Region The main structural elements in the geology of the region are:
- 1) The Salisbury Embayment; 2) The Baltimore-Washington Antinclinorium; and 3) The Tucquan Arch.
The Perryman Site is located on the west flank of the Salisbury Embayment, a northwest-trending depression in the basement rocks, extending from the vicinity of Newport News, Virginia, to Atlantic City, New Jersey, and westward to the Fall Zone (Figure 2. 5-3).
It is marked by a reentrant in the Fall Zone and a thick accumulation of sediments.
The embayment extends oceanward from the Fall Zone from approximately 192 to 256 km (120 to 160 mi).
It is fairly prominent in the basement rocks, but loses form in the younger sedimentary beds.
At the j
6 2.5-5 I
coastline in Maryland, it contains from'1066 to 2250.m (3500 to 7500 ft) of Mesozoic'and Cenozoic. age sediments.
' North of the site, the. crystalline rocks of the Piedmont have~been intricately folded, faulted, and intruded.
The Baltimore-Washington Anticlinorium, a major fold structure, oxtends in a. gentle arc from Washington, D.C.
to approximately.
22 km-(14 mi) northwest of the site. (Figure 2.5.3).
At least teven mantled domes that have cores of Baltimore Gneiss occur
-along.its axial zone.
The axis of the Tucquan Arch coincides with the axis of the Mine Ridge Anticline.in Lancaster,. Pennsylvania, and can be traced southwest.at least as far as south-central York County, Pennsylvania.- Aeromagnetic expression of this' fold extends into northwestern Baltimore' County, Maryland, but the presence of the fold has not been demonstrated there on the ground.
The southeast limb of the arch extends into northwest Harford County,iabout 32 km. (26 mi) northwest of the site.
The Baltimore-Washington Anticlinorium and the Tucquan Arch, as well as other large structures in the region, are thought to be the results of multiple episodes of folding in the Piedmont.
The first period of folding (referred to hence-forth as F ) produced isoclines and nappe structures, such as
{
3 the basement nappe, shown diagramatically in Figure 2.5.B-6, and the Drumore Fold, shown on the regional geologic map (Figure i
2.5-3).
The.second period of folding (F ) resulted in the 7
formation of the Tucquan Arch, the Baltimore-Washington Anticlinor-ium, and the Emmorton Antiform (named and defined in Appendix i
~
2.5.B).
The minimum age of the last folding event (F ), esta-9 blished by isotope dates from post-tectonic pegmatites, is approximately 440 m.y.
B.P.
(Before the Present) (Hopson, 1964; Tilton, and others,.1959).
Aeromagnetic patterns in the region of the upper Chesapeake
'l Bay show a marked lineation that underlies and trends parallel to the bay.
A steep gradient between broad, magnetic low areas under the bay and high areas under the Eastern Shore trends generally northeast.
This pattern is a reflection of bedrock structures of regional scale, the nature of which is unknown at this time.
Speculative interpretations of these features are discussed in the following aubsection.
Faults Numerous faults have been identified or postulated in the
- region, j
The linear magnetic feature in the region of the upper Chesapeake Bay has been interpreted by Higgins and others
)
(1974a) as reflecting the presence of a basement fault of major 2.5-6
F c
I 1
proportions.
Dissimilarities of magnetic patterns on either
]
side of a' steep magnetic gradient suggest.that rocks of dissimilar composition are in sharp contact along the trend of Chesapeake Bay.
This mggnetic feature is aligned along a trend of approxi-mately N. 25 E with fault features in northern Delaware that are described by Spoljaric and others (1973).
Evidence from paleochannel deposits suggest that the trend of the upper reach of Chesapeake Bay is inherited from an ancestral Susquehanna River, the course of which Higgins and others-(1974a) speculate was controlled by a zone of weakness that was associated with the postulated fault.
Although Hansen (1974) questioned the validity of some of the evidence presented by Higgins and others (1974a), he did not dispute their conclu-sion that the magnetic anomaly may represent a zone of basement faulting.
In a later note, Higgins and others,(1974b), cite evidence suggesting that movement along'the postulated fault zone may be continuing.
The alignment of parts of several major streams in the area from Long Island to the Potomac River has been the subject of much speculation (e.g., Darton, 1891, 1894; Hobbs, 1904; Fenneman, 1938).
Higgins and others, (1974a) further speculate that the northeast-south west-trending fault which they postulate beneath the upper Chesapeake
.may be part of a zone of much greater extent, which is expressed by the aligned segments'of the Potomac, Delaware, and Hudson Rivers,'as well as the upper bay.
Studies by Spoljaric (1973) and Spoljaric and others (1976) and Dames & Moore (1973a) report faults in the basement below Coastal Plain sediments in northern Delaware.
The main structurg in this area is reported to be a graben with a trend of N. 25 E.
LANDSAT-1 imagery shows the presence of surface lineations in the same locality, with the same trend (Spoljaric, and others, 1976; this report, Appendix 2.5.A).
Detailed studies on one of the associated faults indicate that sediments younger than early Late Cretaceous have not been affected by the fault.
Spoljaric and others (1976) relate known and postulated fault structures in the Delmarva Penninsula to tectonic patterns on a continental scale, and conclude that, as sea-floor spreading is known to be going on, faults in the Delmarva region are under-going adjustment and are responsible for recent earthquakes in the northern and central parts of the peninsula.
Preliminary results of recently completed, but unpublished, reflection-seismic surveys in Kent, Queen Annes, Talbot, and Dorchester Counties, Maryland, by the U.S. Geological-Survey indicate that block faulting similar to that revealed by Dames & Moore (1973b) in northern Delaware occurs on the Eastern Shore.
Near Seward, Maryland, sediments of Early Cretaceous age appear to be involved in the deformation of the basement.
Interpretations of these data are at present incomplete and the trends of suspected faults are unknown.
2.5-7 i
r The faults in the basement, which involved the overlying Coastal Plair, sediments, were reported near Brandywine, Maryland, by Jacobeen (1972, 1974).
Two en echelon faults with a north-northeast orientation displace Cretaceous sediments, but appear to die out in younger beds.
Jacobeen concluded that movement clong the faults was sporadic into Miocene time, but that other processes, such as micro-slippage or differential compaction clong the fault zone, may have produced surface lineaments which are now apparent in drainage patterns.
The youngest cssociated deformation involves a few inches of offset of Pliocene Upland Gravel.
Southward extensions of these faults studied in detail by Dames & Moore (1973a) reveales the same conclusion.
A similar zone of deformation along a northeasterly trend in the Coastal Plain was reported near Stafford, Virginia, by Mixon and others (Mixon, and others, 1972; Mixon and Newell, 1976; Mixon, 1976; Newell and others 1976).
Detailed studies of this zone by Dames & Moore (1976b) d:monstrated that the latest faulting and/or flexing of Coastal Plain beds occurred before the mid-Miocene.
However, two minor reverse f aults reportedly cut Pliocene (?) Upland Gravels in the vicinity Dames & Moore (1973a).
The displacements along clong these faults are reported as 13 and 46 centimeters (cm) (5 and 18 inches (in)).
The presence of this and similar faulting along the Fall i
Zone, combined with the linearity and other physiographic feature, has lately prompted Hack (1976) to suggest that M3sozoic and Tertiary differential movement along the Fall Zone may be more regionally extensive than has been previously considered.
He emphasized, however, that such offset apparently predates the deformation of the undeformed Miocene strata that locally trangress across the zone.
In the Piedmont near the Perryman Site, many faults of various sizes have been reported.
The Baltimore Mafic Complex, a major rock unit in the region, has been interpreted by Crowley (1976) as being originally emplaced by gravity sliding into a ecdimentary basin.
Contacts around the Baltimore Mafic Complex would be drav.1, following this interpretation, as thrust faults.
This was not done in Figure 2.5-4, which shows the locations of faults that are of possible tectonic concern.
Contacts around the Baltimore Mafic Complex bodies clearly have been involved in the main episode of Paleozoic folding; thus, if the contacts ware originally faults, they have not behaved as faults since the Paleozoic age.
A high-angle fault cutting Pliocene-Pleistocene sediments l
hcs been reported at Upper Marlboro, Maryland, approximately 19 km (12 mi) east-southeast of Washington, D.C.
(Dryden and 2.5-8 i
)
Bradley, 1932).
The throw of the fault is estimated to be between 1. 5 and 4. 5 m (5.0 and 15.0 f t) with the Pliocene-Pleistocene sediments in fault contact with Cretaceous or Tertiary strata.
Other possible small faults were postulated to exist approximately 6 km (4 mi) northwest of Upper Marlboro and at Newtown, Maryland, located approximately 43 km (27 mi) south-southeast of Washington, D.C.
In these areas, however, clayfilled joints in sand strata have been offset up to 15 cm (6 in).
These features may have resulted from dessication; therefore, their origin is questionable.
Hershey (1937) described shear zones, joints, and faults in the Port Deposit Granodiorite Complex hear the Susquehanna River.
As dikes have been intruded along some of the shear zones, Hershey concluded that the formation of the zones predates the close of Paleozoic plutonism.
In the vicinity of Havre de Grace and Port Deposit, normal and reverse faults occur which show of f sets of as much as 1. 2 m (4.0 f t).
According to Hershey, however, mineralization along associated joints is probably of a hydrothermal origin, which suggests that plutonism was still active at the time of formation of the joints and faults.
All of these features trend parallel to the foliation of the rocks.
Dames & Moore (1976d) reported a number of pre-and post-metamorphic faults in the vicinity of the Susquehanna River, between Havre de Grace and the Conowingo Dam.
Most of these were similar to and compatible with the metamorphic shears and faults described by Hershey (1937) and Southwick (1969).
4 Two of them, however, had not been previously reported and are considered to be pertinent to the present study.
One of these is an observable fault, exposed over an outcrop length of about 305 m (1000 ft) in a quarry just The north of U.S. Highwgy I-95, on the west side of the river.
fagit strikes N.
35 W., and dips southwestward at an average of 45.
Field evidence relating to the age of last movement 1
was not observed along the fault; therefore, no conclusions as to the age of last movement were made.
No topographic expression of the fault was noted, however, which suggests that its last movement was not geologically recent.
The other feature is an interpreted fault.
It also trends northwest-southeast, and passes along the northeastern boundary of the former Bainbridge Naval Training Station, over a length of at least 13 km (8 mi).
It is recognizable as a lineament of regional significance in high-altitude imagery (Appendix 2.5.A, Lineament 4).
Although no direct evidence of faulting was observed, indirect evidence in the form of prominent topographic lineaments, abrupt termination of metamorphic rock units, and aeromagnetic patterns all suggest strongly that a regional fault involving significant offset occurs in that vicinity.
No i
evidence suggesting the amount, age, or direction of movement was observed.
2.5-9
E
. The-Mill Green fault,. located about 26.km (16 nil northwest of.the site (Figure 2.5.3), cuts across northwest-striking cchistosity;in :the' metamorphic rocks and brings contrasting
. lithofacies into sharp. contact, over a total distance of about 16 km (10 mi) -(Southwick,1969).
The trend of this age, and follows fcult is parallel to Paleozoic foldsoof F)This relationship them around.the younger folds of F cuggeststhatthefaultisof'loweh, age.
Paleozoic age.
The Martic Line, located approximately 51 km (32 mi) northwest of the site, continuea to the southwest.ta).the vicinity of Frederick, Maryland.
This. feature has been defined as a major thrust fault, although recent work discounts its postulated continuous nature (Southwick and Fisher, 1967; Wise, 1970).
In eP sode of i
any case, the feature has been involved'in the F2 Paleozoic folding, as is'seen in its' map pattern, and, therefore,
'is probably of early Paleozoic age.
A belt of serpentinite bodies in northern Harford County has also been interpreted as being associated with a fault of 80 km (50 mi) in extent- (Southwick,1969).
This feature 1was examined in detail by Dames & Moore (1975d) in the area of Peach Bottom, Pennsylvania.
No' evidence for the existence of the fault was found, nor was any evidence of post-Mesozoic movement along the trend of the serpentinite bodies.
A' zone of Triassic basins of the-Newark group extends from the Bay of Fundy to the Carolinas.
The closest approach of these batins to the site is approximately 72 km (45 mi) to the northwest, near Gettysburg, Pennsylvania.
Triassic dikes that are related to intrusions within the basins are numerous and many extend nearly to the Fall Zone.
Several other similar Triassic basins exist east of this line.
Triassic rocks of the Richmond Basin at Richmond, Virginia, are in fault contact with gneisses of probable Precambrian age on the west and are in depositional contact with granite of Precambrian or Paleozoic cge on the east.
A possible north-northeastward extension of this basin beneath Coastal Plain sediments is suggested by boring data.
Triassic rocks have been encountered in borings at Bowling Green and Edgehill, Virginia, and near Brandywine, Maryland, located 53 km (35 mi), 88 km (55 mi), and 112 km (70 mi) north-northeast of Richmond, respectively.
Triassic rocks have also been encountered in deep wells in the Salisbury area of southeastern Maryland.
A, postulated, major east-west fault zone, named the Cornwall-Kelvin Wrench Fault, has been inferred to extend through southeastern g
Pennsylvania near Latitude 40 N.
On the basis of geophysical data and the interpretation of structural lineations on both the continent and the Atlantic Ocean Basin, this inferred fault has been postulated to extend seaward along the Kelvin Seamounts.
A lateral' displacement on the order of 144 km (90 mi) has been 2.5-10
o I
suggested for the continental portion of the fault (Drake, 1963; Woodward, 1968).
The closest approach to the site of the postulated Cornwall-Kelvin Wrench Fault is approximately 96 km (60 mi) to the north-northeast, between Harrisburg and Reading, Pennsylvania.
It should be noted that evidence for the presence of the Cornwall-Kelvin structure is largely indirect, being based on interpretation of magnetic survey data and the faint suggestion of the continuity of an east-west trending continental fault pattern that, up to the present time, has been mapped as indivi-dual or discontinuous structures.
Other faults have been described in the Piedmont rocks of the area as late faults, and several north-northeast-trending faults have been mapped where associated with the Baltimore Gneiss Domes (Figure 2.5-4).
The faults that border the domes l
appear to be genetically related to the emplacement of the domes, and may be reverse faults (Cloos, 1964).
The late faults are probably Mesozoic in age and related to faulting in i
the Triassic Basins, although no definite age can be attributed to them on the basis of present' evidence.
The faulting in the Triassic Basins of the East Coast has been studied in the Newark Basin north of the site area (Dames & Moore, 1976).
A l
minimum age of last movement for the faults dated there is 1
approximately 70 m.y. ago.
Recently, faults in the bedrock beneath the Potomac River have been found by Bock (1973) during the Washington, D.C.,
subway tunnel construction.
These faults are of a high-angle, reverse nature and generally trend east-west and northeast, with stratigraphic of f sets of from 0.6 to 1.8 m (2 to 6 ft).
Darton (1951) reported the presence of several faults in the bedrock and overlying Coastal Plain sediments in the vicinity of Washington, D.C.
At least two of these faults were described as involving deposits of Pleistocene age.
A minor fault has been identified approximately 96 km (60 mi) northeast of the site, near Gibbstown, New Jersey (Salisbury and Knapp, 1917).
This fault is in the crystalline basement, covered by approximately 91 m (300 ft) of unfaulted Coastal Plain sediments, and is parallel to the general northeast-southwest trend of the Piedmont.
Two small folds have been mapped in Coastal Plain sediments east of Trenton, New Jersey (Minarc and Owens, 1966).
They are from 5 to 6 km (3 to 4 mi) in length, with units as young as Miocene age involved in the folding.
2.5-11
During the remote-sensing study' performed as part of this investigation, a lineament'was identified _which may reflect the presence of.a fault'of regional proportions.
This feature (Lineament 4; Appendix 2.5.A), extends southeasterly from the Piedmont, across' northern Chesapeake Bay, and into the Delmarva Peninsula.
However, no evidence.as to age or magnitude of movement, if sny, was. observed; 2.5.1.2.5 -Geological History Of The Region Although the' complex evolutionary history of.the region is not completely understood, investigations and hypotheses by numerous 1 geologists,over the years. provide an account of the basic geologic history (e.g., Higgins, 1972 ; Crowley, 1973 Dames & Moore, 1976e).
The earliest identifiable evolutionary sequence-started with the deposition of sediments in.the Precambrain era.
These sediments were intruded by igneous rocks which, together with the sediments, were subsequently metamorphosed to schists and gneisses by a major tectonic event (The Grenville Orogeny).
The oldest rocks in the' Piedmont are grouped together in a unit called the Baltimore Gneiss.
Figure 2.5-4 shows its distribution.
Isotopic age determinations on zircons and potassium feldspars from this unit (Tilton and others, 1958, 1960) indicate that they initially crystallized about 1100 m.y.
ago and are, therefore, Grenville in age.
i The rest of the rock units in the area are believed to be the result of the Late Precambrian (Avalonian) rifting of the North American and Eurafrican continental plates and concurrently the formation of oceanic crust and the development of a thick eedimentary' sequence at the continental margin.
The rocks thus formed'can be' separated into two categories, those that were deposited on continental crust (Glenarm Supergroup) and the i
rest which were probably deposited on, or as, oceanic crust (Port Deposit Gneiss, James Run Gneiss, and Baltimore Gabbro).
The initial episode of rifting occurred in Late Precambrian time, approximately 800 m.y. ago, creating fault-bounded basins within the continental crust.
The Setters Formation, the basal unit of the Glenarm Supergroup (Tillman and others, 1975; Crowley, 1976), was deposited in these basins. _This unit consists of a thin layer of potassium-rich clastic sediments which were derived from the local irregular topography and deposited in small, interconnected basins.
When stable conditions returned to the shelf, the Cockeysville Marble was deposited.
Both of these units now
' occur as thin layers that encompass the Baltimore Gneiss Domes.
A thick sequence of interlayered sands and muds, the Wissahickon l
Group of the Glenarm Supergroup, developed seaward from these 2.5-12
s bnains. ?Ths:dsposition of thaco;cediments continued into i
'Ordovicianhtimes, overlapping the. lower Glenarm units and becoming. laterally equivalent to the Cambro-Ordovician Conestoga
' Limestone'to the' west.
The source of most of the sediments in the Wissahickon Group wasLfrom~the east, and the sediments
. became~ coarser with time..
' Between,the spreading continents, oceanic' crust was forming.
- The presently accepted hypothesis for.the origin of the Baltimore
- Gabbro.is that2it formed as part.of this oceanic crust (Crowley, 1973, 1976).
LAt the start'offthe Paleozoic, convergence began with the subduction of oceanic crust beneath the adjacent plate.
An island. arc formed along the East Coast, which supplied volcanic and pyroclastic detritus into the adjoining trough.
The' James Run~ Gneiss ~is believed to have originated as part of this outpouring of volcanic materials.
The' convergent stage ended
- with a' two-stage' collision, resulting {in two periods of deforma-tion.
The'first of:these' involved obduction of the oceanic crust and its emplacement into the Wissahickon Trough as a thrust sheet.
This event resulted in the formation of a diamic-tite facies'of the Wissahickon Group and the partial dismemberment of the thrust sheet.
At a deeper crustal level, remobilization of the Grenville-age basement and the formation of nappes were occurring.
The final stage of collision produced the large, asymmetrical antiforms that are dominant in the area (for example, the Tucquan: Arch and the Baltimore-Washington Anticli-norium)..The up-arching of the Tucquan Arch was accompanied by thrusting along the Martic Line and in the Lancaster Synclinorium.
'The. final closing of the-Proto-Atlantic Ocean apparently occurred later in southern North America than in the northern part of.the contienent.
This resulted in northeast-trending, right-lateral, wrench faulting along'the East Coast.
In Mesozoic time, rifting occurred, with a rotation just opposite to that Jcaused by the uneven: Paleczoic closing.
Left-lateral wrenching resulted in the formation of the Triassic Basins and the brittle deformation of their sediments.
Late in the Triassic period, tensional faulting of the exposed Land eroded crystalline' rocks'resulted in a series of elongated basins'or grabens into which'were deposited non-marine sediments and intercalated lava flows while downfaulting continued.
While spreading of the continents continued early in the Cretaceous period,.the Piedmont rocks were slowly downwarped to the east..This downwarping continued intermittently through Cretaceous and: Tertiary time to form the base for deposition of Coastal Plain sediments.
Several periods of submergence and emergence followed, and resulted in an accumulation of alternating terrestial and marine sediments.
2.5-13
During early Pleistocene time, the ocean' advanced westward to the Fall Zone, completely covering the Coastal Plain.
Fluctu-oting sea levels, which occurred during Pleistocene time, resulted in alternating periods of erosion and deposition along what are now the major terraces and scarps of the region.
A veneer of Pleistocene soils covers most of the Coastal Plain.
2.5.1.3 Geology.of the Area Surrounding the Perryman Site As part of the geological investigation of the Perryman Site cnd its surroundings, detailed surface mapping was carried out in en area of 8-km (5-mi) radius, which was centered on the site.
Additional mapping was done outside this area where it was necessary to determine structural relationships within units of the Piedmont (Figure 2.5-7).
The results of this program, together with cvailable information from other investigations, are summarized in the following descriptions.
2.5.1.3.1 Physiography of.the Area Surrounding the Site The physiography of the area is divided into two major types by the Fall Zone, an abrupt topographic gradient which trends from the mouth of the Susquehanna River at Havre de Grace south-westward through Aberdeen, and north of Edgewood to Middle River.
U.S. Highway 40 and the Baltimore and Ohio Railroad tracks follow the Fall Zone almost exactly through the area (Figure 2.5-6).
From the Fall Zone to the bay, the terrain is low and flat to moderately rolling; on the other side of the Zone, the topography changes abruptly, being higher and exhibiting greater local relief.
The latter, more rugged terrain reflects the presence of complexly structured, crystalline rocks of the Piedmont Province at the surface or shallow depths, while the lower country is underlain by relatively flat-lying deposits of poorly consolidated cediments of the Coastal Plain.
The major portion of the circle of 8 km (5 mi) radius around the site lies withi'n the Coastal Plain.
In the Piedmont, the land is well drained and, where not cleared for settlement or farming, is heavily forested with a dominantly broadleaf vegetation.
A series of well developed streams flow generally southeastward across the area and into various arms of Chesapeake Bay.
The drainage patterns reflect ctructural trends in the underlying metamorphic rocks and often have rectilinear courses (Appendix 2.5.A).
The Coastal Plain of the area is dominated physiographically by three wide embayments which follow the courses of drowned : tream valleys.
These embay-ments are:
the mouth of the Susquehanna River on the northeast; the Bush River-just west of the site; and Gunpowder River on the j
couthwest.
The Aberdeen Peninsula and Gunpowder Neck project j
into the Chesapeake Bay system between these deep reentrants.
Rectilinear courses in the Bush and Susquehanna Rivers suggest otrongly that the underlying Piedmont rocks have influenced their development.
The terrain becomes lower and flatter toward the 2.5-14
southeast and Chesapeake Bay.
Near the Fall Zone on the west,,a mature topography of low hills (up to 37 m (120 ft) in elevation) is underlain by sandy, clayey, and gravelly beds of the Potomac Group.
This terrain becomes flatter to the southeast and east.
By contrast, most of the Aberdeen Peninsula is of low relief, with maximum elevations of less than 18 m.(60 ft).
- Flat, gently sloping terrace deposits cover the entire Aberdeen Peninsula and parts of the lower portion of Gunpowder Neck (Figure 2.5-6).
These surfaces slope gently to the shore of Chesapeake Bay, where the terrain becomes very low and marshy.
Drainage patterns and other physiographic features in the area are discussed further in Appendix 2.5.A.
2.5.1.3.2 Stratigraphy of the Area Surrounding the Site The area of 8 km (5 mi) radius around the Perryman Site is underlain by crystalline rocks of the Piedmont Province and unconsolidated sediments of the Coastal Plain.
The Fall Zone, which divides these two provinces, lies about 5 km (3 mi) northwest of the site.
The Piedmont rocks occur at or near the surface northwest of the Fall Zone.
Their upper surface dips gently to the southeast and passes into the subsurface at the Zone.
The sediments of the Coastal Plain comprise a wedge-shaped aggregate of deposits, which thins to a feather edge at or slightly west of the Fall Zone and thickens to the southeast.
The maximum thickness of the Coastal Plain section within the area is not known.
Information from drill holes and geophysical surveys, however, confirms that the rocks of the Piedmont extend beneath the Coastal Plain at increasing depths toward thr, southeast (Section 2.5.1.3.3).
The Piedmont Crystalline Complex The Piedmont consists largely of Late Precambrian and Early Paleozoic rocks that have been multiply deformed in Late Precambrian, Paleozoic, and Mesozoic times.
The intensity of the deformation has decreased with time since the early Paleozoic.
The Paleozoic deformation resulted in the formation of all of the (Post-Grenville) ductile structures that have been observed in the Piedmont.
A dominant Paleozoic feature in the Maryland Piedmont is the Baltimore-Washington Anticlinorium (Figure 2.5-4).
The rocks adjacent to the site that were studied during this investi-gation lie on the eastern limb of this complex antiform.
The part of the Piedmont that was studied in this investi-gation offers many good exposures of rock along northwest-trending streams.
The streams (James Run, Grays Run, Winters The Run, and Bynum Run)'are deeply incised west of the Fall Line.
relatively fresh rock, associated saprolite, and stratified.
Recent alluvium were studied for evidence of faults that were postulated by earlier workers (Southwick 1969 ; Crowley, 1976) and to evaluate relationships between ductile and brittle structures and the ages of last movement of all known or suspected faults.
i i
2.5-15
i The earliest mapping of this area was performed by the Maryland Geological Survey (Maryland Geological Survey, 1904).
Several later studies have dealt with selected topics; these include, for example, Hershey's (1937) study of the Port Deposit Gneiss, Cohen's (1937) paper on the Baltimore Gabbro, and Pearre end Heyl's study (1960) of the chromium deposits of Maryland, Pennsylvania, and Delaware.
A geologic map of Harford County, in which the site is located, was compiled by Southwick cnd Owens (1968) and followed by reports (Southwick, 1969; Owens, 1969).
More recent' reviews and interpretations of the region by Higgins (1972) and Crowley (1976) are based on this map cnd their own geologic mapping of Cecil County (Higgins, in progress) and Baltimore County (Crowley, 1976).
Detailed studies oj br.d ttle structures outside the area that are pertinent to the Perryman Site were carried out by Dames & Moore (1975d).
As a result of the field investigations of this study, four main rock divisions are recognized in the Piedmont of the area currounding the site.
These are:
- 1) a massive gneiss, probably the Baltimore Gneiss; 2) the Wissahickon (Schist) Group of the Glenarm Supergroup; 3) the James Run. (Gneiss) Formation; and 4) the Baltimore Mafic Complex.
Descriptive terms such as gneiss, schist, and gabbro are used throughout this report for clarity even though more formal names exist (such as James Run Gneiss for James Run Formation).
The spatial distribution of these rocks is shown on the geologic map of the area, Figure 2.5-7.
Each of the above rock divisions is described in detail below.
Baltimore Gneiss This unit crops out along Bynum Run.
It is a porphyritic, microcline-biotite-quartz-plagioclase gneiss that occurs as discret lenses, infolded within an interlayered mafic and felsic paragneiss sequence (the James Run Gneiss).
This gneiss is distinct from all other rock types in this area, and its description is similar to that of the Baltimore Gneiss, as defined elsewhere (Southwick, 1969; Hopson, 1964).
Therefore, the correlation of the unit that is proposed by Southwick (1969) is accepted here, and these rocks will be referred to as " Baltimore Gneiss".
If this rock type is correlatable with the Baltimore Gneiss, then it also is Grenville basement, because isotopic age determinations of zircon and potassium feldspar (Tilton and others, 1958) from Baltimore Gneiss to the southwest indicate crystallization ages of 1100 m.y. ago.
Data from the map area suggest that during the Paleozic deformations, it was remobilized and experienced ductile deformation similar to the supracrustal rocks of younger age.
Higgins (1972) and Crowley (1976) do not believe that Baltimore Gneiss occurs in this area, the former including these rocks in the James Run Formation and the latter in the lower parts of the Wissahickon Group.
2.5-16
m 5
i Wissahickon Schist Associated with the " Baltimore Gneiss" in Bynum Run are schists interbedded with minor quartzites and metagraywacke.
The rocks also occur in Winters Run and are lithologically identical to members of the Wissahickon' Group that occur in a broad band to the north.
.These schists (along the Fall Zone) grade from fine-grained, biotite-muscovite-quartz schist to very coarse-grained garnet and tourmaline-biotite-muscovite-quartz-feldspar schists.
1 Many concordant quartz veins and pods occur in this unit.
Jl This Wissahickon group forms the major part of the Glenarm l
Supergroup (Tillman and others, 1975; Crowley, 1976), which includes. rocks from Late Precambrian through Lower Ordovician age.-
These rocks overlie the Baltimore Gneiss, Setters Formation, and the Cockeysville Marble, and are probably laterally equivalent
]
(in age) to the' James Run Formation.
Southwick (1969) has divided
]
the rocks mapped here as.Wissahickon into several other units because of their stratigraphic positions, even though such litho-logic variety is characteristic of the Wissahickon Group.
James Run Gneiss The James Run Gneiss is best exposed along James Run and at its type locality, the Gatch Quarry, as defined by Southwick and j
Fisher (1967).
It also crops out in Bynum Run, Winters Run, and their tributaries.
It is a distinctly layered gneiss, with mafic layers (amphibolite) interbedded with felsic layers (quartzo-feldspathic gneiss) and minor intermediate layers (dioritic in composition).
The layers are commonly on the order of a few inches or feet in thickness, but larger units of either end member composition may occur.
These rocks have been interpreted as metamorphosed volcanic and pyroclastic rocks that belong to the James Run formation (Higgins, 1972).- Higgins shows that concordia ages of zircons
)
from these rocks range between about 500 to 600 m.y.
No contact j
metamorphic effect that is attributable to the adjacent Aberdeen Metagabbro was detected within these rocks.
Aberdeen Metagabbro A large body of variably metamorphosed and defermed, mafic 3
igneous rock (" gabbro") occurs along the Fall Zone in Harford County.
This body, along with other, similar, mafic igneous rocks and associated ultramafic rocks to the southwest, northeast, i
and northwest has been designated the Baltimore Mafic Complex by Crowley (1976).
The particular body that lies partly within the map area has been named the Aberdeen Metagabbro (Crowley, 1976).
Its expression can easily be seen on high-altitude imagery.
Aeromagnetic maps of this area, compiled by the U.S.
Geological Survey and summarized in Figure 2.5-8, also show a 2.5-17 i
i
n dictinctive magnetic' feature that coincides with the, mapped portion of the body northwest;of the Fall Zone.
This magnetic cignature extends to the southeast beneath.the Coastal Plain.
The term metagabbro is partially a misnomer for the composi-
- tional range of rocks that occurs in this body.
The center of f
tha-body, exposed in the_Stolzfus Quarry on Grays Run,-offers good exposures of a layered gabbro with well-preserved,' original-textures, such as cumulate layering, with graded beds and channel ccour, features.
A variable, but low degree of metamorphism or sutometamorphism has affected some of the gabbroic rocks, locally causing the breakdown of'pyroxenes to a fibrous amphibole.
This alteration was well described by Williams (1884, 1886, 1890).
Near.the western border of this poorly exposed, mafic igneous body lies a zone that-has been strongly deformed.
A recrystallized fabric obliterates all primary textures.
This local recrystalli-zetion was contingent on intense shearing that appears to be restricted to the edge of the body.
This. rock is a true metagabbro at the contact, where it~ resembles amphibolite,.whereas homogenous, wsakly foliated gabbro occurs away from the border.
Wetherill cnd others (1966) date primary igneous minerals from the " Baltimore G bbro" and obtained Late Precambrian ages (pyroxene, 702 m.y.
and plagioclase, 580 m.y.).
Their data from hornblende were considerably younger (372 m.y.).
In view of the secondary nature
~
of most of the hornblende, this age probably reflects a later pariod of metamorphism.
. Hopson-(1964), Southwick (1969), and previous workers bnlieved that the Baltimore Gabbro is the oldest' intrusive rock in the area.
More recently, Crowley (1976) and Hannan (1976) have presented stratigraphic and geochemical evidence that suggests an ocean floor origin for these mafic bodies.
Saprolite The rock units described above have been affected to various degrees by saprolitization, or decomposition through severe-l chemical weathering.
This has produced a mantle of saprolite, or I
decomposed rock, over most of_the area that is shown in Figure 2.5-7 as outcrop.
In much saprolite, original textures and atructures can be discerned'and, hence, it can often be related to its parent rock type.
Where soil-forming processes have been more effective, however, rock structures have been obliterated, and the saprolite is a mixture of clay and sand and pebble-size grains of chemically resistant minerals and incompletely decomposed fragments of parent rock.
The extent of saprolitization in any locality is, among other things, a function of mineral composition cnd permeability to ground water of the parent rock.
Therefore, great variation in thickness of the saprolite mantle over a large area can be expected.
The interface between relatively unweathered rock and saprolite is usually a zone of transition which is 2.5-18 1
l
n difficult to define.
However, the base of this zone is a useful stratigraphic feature and can be recognized both in outcrop and in drill holes.
Within the area, the thickness of saprolitization varies from 0 to as much as 30 m (100 ft).
goastal Plain Sediments Coastal Plain sediments in the region within and immediately adjacent to the 8 km (5 mi) radius around the Perryman Site were mapped from surface outcrops in road cuts, railroad cuts, streams, and sand and gravel quarries.
With a few minor exceptions, the stratigraphy appeared to agree with Owens' (Southwick and Owens, 1968) map of the geology of the. Coastal Plain of Harford County.
Figure 2.5-7 is the geologic map of the area within and adjacent to the 8-km (5-mi) radius around the site, and is based on both Southwick and Owens' (1968) map and Dames & Moore's geologic mapping program.
The Cofstal Plain sediments were deposited on the irregular surface of the metamorphic crystalline basement rocks of the Piedmont, and they crop out in an arcuate pattern in the zone between the Fall Zone and the shore.
The basement beneath the Coastal Plain in the Maryland-Delaware-Virginia area forms a deep, southeasterly plunging trough whose axis is roughly perpendicular to the structural trend of the Appalachian Mountains (Owens, 1969).
This trough is known as the Salisbury Embayment.
Coastal Plain sediments fill this trough, forming a wedge that dips and thickens to the southeast.
Two major units of Coastal Plain sediments, the Talbot Formation and the Potomac Group, occur in the area at and adjacent to the site, and are described below.
Potomac Group The Potomac Group, generally considered to be Lower Cretaceous in age (Owens, 1969), is divided into three formations, from oldest to youngest: the Patuxent, the Arundel, and the Patapsco.
The Patuxent Formation consists of light-colored arkosic sand and gravel with small, interbedded, light-colored clay lenses.
The Arundel Formation consists of dark gray, lignitic clays, with nodules and lenses of iron ore.
The Patapsco Formation, at higher elevations than the othe2 two formations, is composed of highly colored and variegated clays, cross-bedded sands, and gravels (Berry, 192 9 ; Owens, 1969).
Division of the Potomac Group of the study area into these three formations is questionable because of the extreme lithologic variation, both laterally and vertically, within the whole Potomac Group.
This variation'was confirmed in the field mapping program, and it was not found practical to distinguish among the formations of the Potomac Group.
At the site, however, broad lithologic zones are recogni-zable within the Potomac, (Figure 2. 5-10).
These zones are not equivalent to the formational units described above.
2.5-19
m According to Owens (1969), the Potomac Group in Earford County was apparently deposited in a continental, alluvial environment, with fluviatile channel fill, overbank, and possible piludal deposits represented.
The fluviatile origin can be supported by evidence, such as extensive crossbedding in the cends, the presence of channels with fillings of sand and gravel, the wide range of thicknesses of beds, the erratic distribution of lithofacies, and the abrupt variations of lithologies.
A number of sand and gravel quarries in the map area provide extensive exposures of Potomac Group sand, gravel, and clay beds, cnd demonstrate the lack of both lateral and vertical lithologic continuity.
Sections were measured in Stancill's Quarry, at Joppatowne, Maryland, and in the Harford Sand Quarry, at Magnolia, M2ryland, and are presented, along with twelve other measured ccctions, in Appendix 2.5.C.
'Talbot Formation The Talbot Formation, Pleistocene in age, was mapped in Harford County by Owens (Southwick and Owens, 1968) as two separate lithofacies: a gravelly sand facies of fluviatile origin, as evidenced by its restriction to channel filling and its extensive crossbedding, cnd an overlying, silty clay facies of uncertain depositional environment (Owens, 1969).
The lower, gravelly sand facies is thick-bedded, with irregular cross stratification and local bouldery gravel.
The gravel contains a high proportion of matamorphic rocks.
The upper facies is massive to thin-bedded clayey silt or silty clay.
The greatest portion of the Talbot Iurmation in Harford County lies within the Aberdeen Proving Grounds, which is largely inaccessible for study.
- However, one 15-m (50-ft) high bluff on the Aberdeen Proving Grounds was msasured (Section XII) and is included in Appendix 2.5.C, along with a measured section of Talbot sediments from the bank of the Bush River at the Perryman Site (Section XIII).
2.5.1.3.3 Structural Geology of the Area Surrounding the Perryman Site Gsneral Structural Setting The area of 8-km (5-mi) radius that is centered on the site lies within the Inner Piedmont and Coastal Plain tectonic provinces (Dames & Moore, 1976).
Although the surface of most of the area ie underlain by deposits of the Coastal Plain, the crystalline rocks of the Piedmont Province form a basement at relatively challow depths (approximately 122 m (400 f t) beneath the site).
Therefore, the structural properties of the Piedmont influence
{
vary strongly the overall structural setting of the, site and its curroundings.
As tectonic structures in the poorly consolidated, crdimentary deposits of the Coastal Plain can logically be related to the tectonic characteristics of the Piedmont basement, stress 2.5-20 u-
m was laid on identifying and evaluating the tectinic character of tne Piedmont both adjacent to and underlying the Coastal Plain beds.
Because of their geometric relationship and probable interaction, it is implicit that, in this area, the two tectonic provinces must be considered jointly, rather than as separate entities.
Linear features that are visible on the surface through the use of remote-sensing techniques are discussed in Appendix 2.5.A.
A total of 122 linear features were identified, in which three prgmingnttrenddirectionswgregetected.
These are:
(1)gaN6 30 -60 E.
trend; (2) a N.
15 -30 E.
trend; and (3) a N.
35.-40 W.
trend.
It was also noted that regionally prominent, north-south linear patterns are subdued by these three trends in the area of the site.
The magnetic characteristics of the a'rea surrounding the site are shown in generalized form in Figure 2.5-8.
It is evident from this map that a strong, northeasterly magnetic trend passes through the site area.
This trend is best exemplified by the large, trough-like area of relatively low intensity under Chesapeake Bay, but also is evident in patterns between the Bush and Susquehanna Rivers.
Coincident with and west of the Bush River, a more northerly trend occurs.
North of the Fall Zone (delineated by U.S.
Highway 40), the magnetic patterns are more complex, generally of higher intensity, and coincident in most areas with surface outcrop patterns.
ruperimposed upon the northeasterly trend described above, a northwesterly trend is evident in the contour patterns along the upper Bush River.
The combination of northeasterly and north-westerly trends in that vicinity produces a steplike, rectilinear pattern that agrees closely with shorelines of the river.
In the vicinity of the site, both orientations can be seen.
A magnetic plateau occurs beneath the site, but is broken by high and low areas which, at the eastern boundary of the site, assume very linear proportions and a strong, northeasterly orientation.
Contacts between the stratigraphic units in the Piedmont (described in Section 2. 5.1. 3.2) are closely related to the patterns of magnetic contours that are depicted in Figure 2.5-8.
For example, the generally north-south-oriented contact between the Aberdeen Metagabbro on the east and the James Run Gneiss on the west, as well as the overall pattern of the Emmorton Antiform (described in Appendix 2.5.B) are faithfully recorded in the magnetic patterns north of the Fall Zone.
Similarly, a surface contact between the Metagabbro and the Port Deposit Gneiss, just northwest of Havre de Grace, is coincident with a steepened gradient on the contours in that area.
Minor variations in the directions of trends along these contacts agree well with the orientations of foliation and fractures that were observed on surface outcrops.
Thus, the characteristic associations between 2.5-21 8
ceromagnetic contours and rocks, as observed on the surface, may be recognizable for some distance into the subsurface southeastward from the Fall Zone, where the basement is covered by beds of the Coastal Plain.
A structural lineament of regional significance has been postulated in association with the large, linear, magnetic low crea uncer Chesapeake Bay (Higgins and others, 1974a, 1974b).
The tectonic implications of this lineament, which is described in more detail in Section 2.5.1.2.4, are at present speculative.
A boring has recently been completed on Spesutie Island, located cpproximately 13 km (8 mi) east of the site, by the Maryland Geological Survey, to further investigate the nature of this magnetic feature.
Bromery (1968) collected and compiled gravity data in the region of Baltimore and parts of Carrol and Harford Counties.
Figure 2.5-9 shows part of his interpreted map that covers the area around the Perryman Site.
A northeast-southwest trend is evident in the gravity contours north of and west of the site; near the site, however, gravity gradients are less steep and a nearly flat area extends from the site southward for approximately 4.8 km (3 mi).
Interpretations by Bromery on the basis of this map and magnetic patterna in the area suggest that a domal structure of Baltimore Gneiss, sir >.ilar to others known in the exposed Piedmont rocks of the region, may underlie the Coastal Plain in the vicinity of the northern end of Gunpowder Neck, the peninsula immediately west of Bush River.
This interpreted feature, outlined by the closed, magnetically low contours in Figure 2.5-9, has been designated the Magnolia Dome by Bromery (1968).
A large, nearly circular gravity high in the southwest corner of Figure 2.5-9 was interpreted by Bromery as possibly being a buried, funnel-shaped mass of Baltimore Gabbro.
The northeast-trending, linear high feature in the center of the figure was correlated by Bromery with the Bellair Gabbro Belt, composed mainly of the Baltimore Gabbro.
The broad, somewhat elliptical gravity high north of the site correlates generally with the outcrop pattern of the Aberdeen Metagabbro (Figure 2.5-7).
Gravity values decrease steeply southward toward the site; this steep gradient may therefore represent the southward boundary of the metagabbro.
i A series of folds has deformed the exposed metamorphic rocks of the Piedmont in the area around the site.
These folds are defined by mineral foliation within the rocks, and are oriented generally north-south and north-northeast.
Two generations of folds were recognized:
(1) an earlier, isoclinal set (referred
)
to subsequently as F folds) and (2) a later, asymmetric set that
{
hasdeformedtheearkierfolds (referred to henceforth as F folds).
These folds and their structural significance are discussed in detail in Appendix 2.5.B.
2.5-22
r Faults Faults,' shears, and other deformational structures that are possibly associai.ed with faults in the area surrounding the site are described in the paragraphs below and depicted in Figure 2.5-7.
Evidence supporting the interpreted structural significance of faults in the Piedmont is presented in Appendix 2.5.B.
Northwest-Striking, Left-Lateral, and East-West Striking, Right-Lateral Faults These faults are best exposed in the James Run Gneiss.
They appear to form a conjugate set and have mutually offsetting geo-metries.
They are the most common faults in the area.
Their orientations and senses of movement suggest that they formed in association with the younger folds of the area, which are believed to be associated with the main episode'of Paleozoic metamorphism.
1 Northeast-Striking, Right-Lateral Faults These faults are the next most-common in the area and clearly postdate those described earlier.
They are particulatiy well-exposed along James Run.
Their orientation and sense of movement, in context with the regional tectonics, suggest that they may have formed during Late Paleozoic time.
North-South to Northeast-Striking, Thrust and Reverse Faults These faults were observed in the James Run Gneiss and Aberdeen Metagabbro.
Their geometries suggest that they are related to the episodes of folding in these rocks, and, hence, are probably middle Paleozoic or older in age, j
1 Northeast, Northwest, and East-West-Striking, Normal Faults These faults occur along the contact between the Metagabbro and the James Run Gneiss, in both formations, and on the west limb of the Emmorton Antiform in the James Run Formation.
They commonly contain gouge which is possibly unhealed.
This possibi-lity and the geometries of the faults suggest that they may not be associated with Paleozoic deformations.
Some of them, however, may have formed as a result of Mesozoic, left-lateral rifting, although no definite age of last movement can be assigned them.
North-Northeast-Striking, Lef t-Lateral Fault This fault is located in the Aberdeen Metagabbro, approximately 4.0 km (2.5 mi) north of the site, on Grays Run.
It is the closest known surface fault to the site.
Although the rock is highly soprolitized, numerous planes with near-horizontal slicken-sides trending N. 20 E. were observed.
Its orientation and sense of movement agree with those of fcults associated with Mesozoic, left-lateral rifting, but no definite age of last movement has been assigned to this fault.
2.5-23 A
~
y
'x o,:
y
- f., '
I
- Gravitational Gliding": Faults LCrowley f(1976) suggested' the occurrence of a group' of thrust ifaultsiat'the contact between the Baltimore Mafic _ Complex rocks'
< end!other units.: lThis1 suggestion is based onLa. regional, strati-l z graphic,/(and structural analysis of the Maryland Piedmont.1976) interpreted;t 1
Crowleyl clides.z
-However,Lin our analysis;of the contact of'the Aberdeen Metagabbro with the. James:Run Gneiss', al strong indication of:
deformation wasiobserved;inithe metagabbro.-
The contact, the recrystallized fabric,-and:a series ofl thrust-faults (which are Lcmongfthose; discussed'previously, under Thrust and Reverse
^
Faults) allLstrike north-south 1and dip beneath the Metagabbro
-(Figure 12.5-7).: These observations.suggest thrusting under'high confining pressureEin a' stress' regime.similar:tofthat believed to, time.
Regardless of'modefof. origin, the bel operative during F y faults resultingLfrom the emplacement of:the metagabbro have antiforms in the area.
No-cince been~ folded ~by theElarge F7 reactivation of movement since that time is apparent.
.Bynum:Run Fault on the' basis of inferred stratigraphic' relationships, a north-south-striking fault has been postulated about 56 km (3.5 mi) northwest ofithe' site, on Bynum Run (Southwick and Owens, 1968).
- This fault was'shown as occuring_in Piedmont rocks, but not I
offsetting Cretaceous or younger sediments.
Conclusions from a later ' study ; (Higgins,. ' 1973 ) disagreed with this stratigraphic interpretation.
In.the'present investigation ~, both remote-sensing and field investigations were concentrated in the area of the presumedLfault; neither approach, however, produced any geomorphic,nstructural,-or stratigraphic evidence of the existence of such a feature.
It is concluded, therefore, that the fault shown on-Bynum Run on the ' geologic map.of Harford County (Southwick and Owens, 1968) does not exist.
Haha Creek Feature TA deformational structure occurs in a low bank of one of the branches of Haha Creek where a-thin layer of_the Cretaceous PotomactFormation overlies.the Aberdeen Metagabbro..The structure involves beds.of. cemented, sandy gravel which either compose a steep, tightly folded anticline or have been juxtaposed as steeply
-tilted, faulted blocks.
The plastic nature of clay beds below these units makes the exact nature of the structure unclear (Figure 2.5-11). _ The removal of alluvium from the creek bed uncovered lateral extensiong of these units, which indicated an approximate strike of N. 20 E.
2.5-24 L
The Haha Creek Feature is intersected by the trace of Linear J, which was detected by remote-sensing techniques (Appendix 2.5.A).
The ages of the materials involved in the structure are not known; however, on the basis of lithologic similarities, it is believed that they are all Cretaceous.
The samples taken for pollen analysis proved to be barren of pollen (Appendix 2.5.D).
Whether it represents a true tectonic structure or a post-or syndepositional slump feature, the coincidence of the Haha Creek Feature with a promient lineament and anomalous drainage features (Appendix 2.5.A) suggests that its origin may be associated with the tectonic development of the Piedmont basement.
Fractures Observed in Sand and Gravel Quarries Spencer's Quarry is an active sand and gravel quarry that is operated by N.G. Spencer and Son at Abingdon, Maryland, located l
6.2 km (3.8 mi) from the site, on Abingdon Road between Interstate Highway 95 and Norris Corner.
The Potomac Group lithologies there consist of orange and brown, iron-stained, gravelly sand overlying white sand, with local clay pods nd layers, and iron l
concretions.
Most of the quarry faces are near-vertical, with considerable slumping of large blocks of material.
Numerous small, normal faults and grabens were observed in the sand and gravel units (Figures 2.5-12 and 2.5-13).
The
{
maximum displacement observed along any of these faults is 30 cm
)
(12 in), decreasing upward in the unit so that no displacement is traceable into the overlying gravels at the top of the unit.
/
85 W.,
N.
20 W. thgough N6 Trgnds on the faults vary from N.
25 E.,
and' east-west, with dips of from 60 to 75.
A airphoto lineament trending N.
20 E. was identified on airphoto imagery that showed it to pass through the western edge of Spencer's Quarry.
However, extensive searching on the ground, both in and near the quarry, revealed no evidence of the lineament.
]
It can be reasonably concluded that the numerous small faults and grabens are depositional and early post-depositional features that overlie an irregular depositional surface and are attributable to slumping and dif ferential colapaction.
No large-scale faulting was observed, and none of the small normal faults or grabens could be correlated with the airphoto lineament.
One fairly large fault is apparent in the gravel beds exposed on the bank of a cut terrace at the top of the quarry (Figurg 2.5-o 14).
The fault trends N.
75 W. with a maximum dip of 40 northeast that flattens out with depth, and it has a displacement of approximately 0.9 m (3 ft) down to the northwest.
A channel is located immediately below the fault plane.
The fault appears to be due to post-depositional compaction of the thicker and heavier channel sediments.
2.5-25 w ---
Another feature of interest in the quarry was a fairly irrge, overturned fold just below the original ground-surface lovel in an active face (Figure 2.5-15).
Slumping obscured the lower half of the feature, and it was not possible to get close enough to examine the feature in detail.
Loaders digging out the fcce as it was being observed, destroyed the entire feature bafore any more information could be obtained.
Minor anticlinal folding of form '0.3 to' O.6 m (1 to 2 f t) of relief was visible in the clay strata, following the quarrying of the larger fold fcature.
Stancill's Sand Quarry, located approximately 0.3 km (0.2 mi) orst of Joppa Road, and 0.3 km (0. 2 mi) south of U.S. Highway 40, et the end of Oak Avenue in Joppatowne, Maryland,_is an active cend quarry in the Potomac Group.
A detailed description of the lithologies is presented in Appendix 2.5.C.
In the very clean, white and yellow, iron-stained, massive, crossbedded sand units, there are numerous, very thin limonite etained fractures (Figure 2.5-16).
These stained fractures crisscross each other, some following the bedding, but most being independent of the bedding.
The traces of the fractures are enhanced by the limonite staining and weak cementation that renders the stained cracks alightly more resistant to weathering.
No offsets of any kind were observed.along any of the fractures.
i Overlying the crossbedded sand units in Stancill's Sand Quarry are red and white clay layers, which are overlain in turn by soil.
As one face of the quarry was being mined by the loader, a fold in the clay became visible (Figure 2.5-15).
Close examina-tion of the feature revealed no disturbance to the sediments beneath the clay.
The feature does not appear to be tectonic, cnd could have been formed at the time of deposition or as a result of differential compaction.
{
2.5.1.3.4 Geological History of the Area Surrounding The Perryman Site i
The geological history of the area within a 8-km (5-mi) radius of the site is discussed in Section 2.5.1.2.4, Geological History of the Region.
I 2.5-26
2.5.1.4 Geology of the Perryman Site 2.5.1.4.1 Introduction The Perryman Site is located on the east shore of the Bush River approximately six miles southwest of Aberdeen, Maryland.
The site area is irregularly shaped and measures approximately 1825 (6000 ft) by 1525 m (5000 f t).
It is bounded by the CONRAIL Railroad tracks on the northwest, the Aberdeen Proving Grounds on the east, Sod Run to the southeast, and the Bush River on the southwest.
The proposed construction area is located approxi-mately 700 m (2300 f t) east of the Bush River with an average existing ground elevation of about 7.6 m (25 f t).
The location of the site relative to surrounding topographic and cultural features is shown in Figure 2.5.7.
The geologic section at the site consists generally of up to 20 m (65 ft) of unconsolidated, granular sediments of Pleistocene age, underlain by as much as 113 m (370 ft) of sands and gravels of Cretaceous age that, in turn, are underlain by Precambrian and/or Palezoic metamorphic and igneous rocks which are weathered to various depths.
A detailed interpretation of the subsurface geology has been made using information from borings, geophysical surveys, geologic mapping, palynological analysis, and petrographic analysis of samples from rock cores.
2.5.1.4.2 Physiography The topography of the area is formed by a slightly dissected, relatively flat plain that slopes gently westward to the Bush River.
Ground surface elevations at the site range from sea level to about 13 m (42 ft) above sea level.
Minor, low irregu-larities occur in the nearly flat surface as a result of intermit-tent stream erosion.
-In areas of active cultivation, these depressions are maintained as grassed waterways in order to control erosion.
The shoreline consists of a northwesterly-trending line of steep cliffs up to 6 m (20 f t) high and a narrow beach of cobbles and sand.
Figure 2.5-17 shows the general topography of the site.
2.5.1.4.3 Stratigraphy A total of 136 borings have been completed at the site.
Of these, thirteen were drilled into the basement and ten penetrated the unweathered rocks beneath its mantle of saprolite.
Results of refraction and reflection seismic surveys carried out at the site allow the interpolation of information observed in the deep borings.
Palynological analyses of selected samples were carried out during the Phase I and Phase III studies.
A stratigraphic model based on these sources of information is described below and depicted in Figures 2.5.-19 through 2.5-26.
2.5-27 l
Bedrock, consisting generally of gneiss and schist but locally of plutonic, igneous rock, underlies the site at elevations ranging between -99 and -116 m (-324 to -387 f t).
The metamorphic rock generally is strongly foliated and fractures are abundant in the core samples.
For a precise determination of composition, representative samples of basement rock were analyzed petro-graphically.
The results of these analyses are presented in Appendix 2.5.E.
Rocks encountered in Borings 104, 105, 107, 110, 309, 310 cnd 322 are quartz, feldspar and mica-rich gneisses and schists.
Rocks from the first four borings are desc'ribed on the basis of thin-section analysis (Appendix 2.5.E) as being metasedimentary cnd constituting a peligic assemblage.
Foliation has an average dip of approximately 45.
Augen of feldspar and veins of quartz cre common and are oriented parallel to the foliation.
Rock from Borings 104, 105 and 110 was examined petrographically and described as schist, composed of various proportions of quartz, feldspar and mica.
Rock encountered in Boring 107 is markedly different from that in the other deep borings in that it is biotite-rich (content approximately 45 percent), quartz-poor, and less foliated.
It is classified petrographically as a biotite-microcline-plagioclase-calesilicate-paragneiss, and interpreted as being derived from a quartz-poor, calcareous pelite.
Pyrite, apatite, sphene, zircon, epidote, garnet and carbonate minerals occur in various relative aboundances as cccessory minerals in all these rocks.
Chlorite, in particular, i
is common in fracture planes.
Near the center of 'he site, Borings 321, 323 and 324 encountered rocks of igneous origin, beneath metamorphic schist and gneiss.
These rocks are described petrographically (Appendix 2.5.E) as quartz-dioritic to grano-dioritic in' composition and as having experienced strong (Samples 321a and 321b) to virtually no (Sample.324a) cataclastic deforma-tion.
Secondary mineralization in the form of siderite and evidence of hydrothermal alteration occurs in samples from Boring 323.
These igneous rocks occur in units of about two meters (7 ft) thick _in Borings 321 and 324 and at least 0.5 m (2 ft) thick in Boring 321.
In all these borings, the igneous rocks were overlain by metamorphic rocks.
Contacts were fracture zones in Borings 321 and 323 but intrusive in Boring 324.
Mineralogical relationships in thin-sectioned samples indicate that intrusion of these rocks occurred after the peak of meta-morphism for the region (Appendix 2.5.E).
The basement beneath the site appears to be generally comparable to rocks exposed on the surface in the nearby Piedmont Province.
Lithologically, the gneiss and schist samples from the borings are generally similar to outcrops of the lower pelitic schist unit of the Wissahickon Group and, to a lesser sxtent, parts of the James Run Gneiss (Southwick, 1969).
These petrologic similarities, however, are insufficient to warrant definite correlation of the samples from the borings with specific 2.5-28
formations.
The granodiorite and quartz-diorite samples closely resemble descriptions of parts of the Port Deposit Gneiss as given by Southwick (1969), although igneous textures in some thin sections appear to be better preserved and less deformed than is characteristic from the Port Deposit.
No other mappable units in the area contain such lithologies; thus, it seems probable that the intrusive rocks in the vicinity of Borings 321, 323 and 324 belong either to the Port Deposit Gneiss or to a hitherto unknown lithologic unit.
The upper portion of the crystalline basement is weathered to saprolite, a residual soil formed by the chemical decomposition of rocks in situ.
Saprolite thicknesses measured in borings ranged between 7 and 26 m (23 and 85 ft).
The saprolite is composed generally of clay, quartz, and weathered remnants of feldspar, mica and chlorite.
Textures range from silty sand to sandy clay.
It commonly exhibits the original fabric of the crystalline parent rock; however, the upper portion of the saprolite in several borings has been weathered or reworked to the extent that original structures are no longer visible.
The contact between the saprolite and " fresh" or " crystalline" basement rock is gradational over several feet in most borings.
Therefore, the determination of " basement" as defined by the uppermost occurrence of unweathered rock is somewhat subjective.
The upper surface of the saprolite, however, is recognizable in a horizon or thin zone as an erosional unconformity between the basement rocks and the overlying sediments.
" Basement" as a stratigraphic indicator is interpreted from the recognition of this unconformity in boring samples.
" Basement" as determined from seismic surveys, however, reflects the bottom of the saprolite,,
where a large increase in seismic velocity occurs at the interface with unweathered rock.
As the variation in thickness of the saprolite is partly a function of rock permeability, thickness of the saprolite may be an indirect. indicator of structural characteristics of the rcok.
Sedimentary Deposits of Cretaceous Age Sediments of the Potomac Group, of Lower Cretaceous age, lie upon the eroded surface of the basement as defined by the j
top of the saprolite.
These sediments are poorly-consolidated j
clastics of very irregular textural makeup, distribution and extent (Figures 2.5-19 through 2.5-25).
The thickness of Potomac Group sediments at the site ranges between about 82 and 99 m (250 and 300 ft), being exposed at the surface along the shoreline and covered by younger sediments toward the center of the site.
The Potomac Group in the region is variously composed of f
the Patuxent, Arundel and Patapsco Formations, in order from
]
oldest to youngest and all of Lower Cretaceous age.
Lithologic I
distinctions among these units are not clear in the area around the site, and the Potomac Group is not differentiated there (Owens, 1969).
2.5-29
1 i
Samples of various units within the sedimentary section at the' site were subjected to palynological analysis in order to datermine their geologic age; most of these samples, however, proved barren of fossil pollen and, of the samples from the i
Potomac Group, ages were determined for only eight (Table 2.5-1 and Appendix 2.5.D).
All of these were found to be of Albian (Lower Cretaceous) age and stratigraphically equivalent to a florizone within the Patapsco Formation (Appendix 2.5.D).
These samples ranged in vertical distribution from the surface, clong the shore of the Bush River (Table 2.5-1), to a maximum d:pth of 61 m (185 ft) beneath the surface in Boring 309, (Appendix 2.5.D).
It is not known whether sediments of the older Arundel and Patuxent Formations occur in the remaining caction of approximately 43 m (130 f t) celow that level.
Lithologic units within the Potomac Group are very dis-continuous laterally and the sediments are generally similar throughout the vertical section at the site.
Nevertheless, three general lithologic divisions were observed during the sub-curface investigations and were utilized for descriptive purposes.
The boundaries of these units probably do not coincide with formational boundaries within the Potomac Group.
These lithologic units, as recognized at the site, are described below.
The basal unit (Pl in Figure 2.5-10) is made up of light to dark gray, red and brown clay and clayey silt, with frequent layers of fine sand.
In some borings lignitic layers, cemented sand, and thin beds of basal gravel were observed.
Generally, the sand layers become thicker to the south and west.
The unit ranges between 16 and 34 m (52 and 110 ft) in thickness.
The middle unit (P2 in Figure 2.5-10) consists predominantly of fine to medium sand and is 24 to 44 m (80 to 144 ft) thick.
This zone contains occasional lenses of silt, clay and gravel.
The upper unit (P3 in Figure 2.5-10) is made up of interbedded cand, silt and clay layers.
Its thickness ranges between 21 and 37 m (70 and 123 f t).
Although the three lithologic units are recognizable on a broad scale, lithologic differences between beds in the units are not sufficiently distinctive to allow the recognition and cesignment of individual, small samples to any one unit.
The ecnd layers are generally very fine grained, occasionally grading into medium to coarse sand or fine gravel.
The sand is rounded quartz, frequently micaceous and with trace accessory minerals.
Sand layers typically grade from coarser at the base to very fine, silty sand at the top, although the lower material may be only fine sand.
Occasionally, sand layers grade upward into silt or clay; these transitional zones are thin, however, and may be more abundant than is indicated by the samples obtained.
2.5-30 1
F
'Beddingistructures'in silt and-clay layers range from massive to laminated.
Thel thinly bedded to: laminated clays are
-sometimes interbedded with silts or'very fine sands in a cyclic sequence.
The dark gray: to black silts and clay occasionally
.are lignitic, frequently.being recognizable as marker horizons between' borings.
In: cases where the lignite was.not seen in an adjacent boring,.the zone usually could be correlated with.non-lignitic, but gray-colored, silt or clay at"the_ appropriate level.
At the' surface, red and brown clay crops out'in the bank of lthe Bush River along,the north edge,of the site, where it is overlain by a-iron-cemented. sand.
This clay is encountered 1above an elevation of +3 m (+10 ft) as far as 305 m (1000 ft) east of the river:(see Figure;2.5-23).-_In this section, the sand and gravel unit'is missing and only a thin layer of the upper silt, facies of the Pleistocene Talbot formation caps the
~
. cretaceous sediments.
The clays become thinner to the east, undergoing facies changes'and finally lensing out.
Farther to theLnorth, white to gray and red-brown silt and silty clay crops out on the' beach on the north and south sides of the_ Pennsylvania Central Railroad tracks.
~
Correlation of the sediments required detailed examination of. boring logs and. samples.
A careful' log of the behavior of the drill machinery and mud was kept to aid in correlation of units between drill holes.
As similar sands, clays and silts wereLfrequently encountered at various depths within a single boring,. correlation to nearby borings required that very minor variations in character be noted.
Due to*dist'urbance in samples and a lack of visible sedi-mentary structure, the basal clay frequently resembles the very highly weathered, unstructured saprolite.
However, frequently a thin zone,of basal gravel, ranging from fine pebbles'to cobbles in texture, was encountered at the base of the Cretaceous section.
This. zone was generally noted because of drill chatter and was Leonfirmed'by sampling in several borings.
A cemented sandstone 15 to 25 cm thick was encountered at an approximate elevation of
-91 (-3'00 ft) _(Figure 2.5-23).
Samples indicate that this layer grades upward ~into a gray sandy silt.
This silt layer extends to the southwest from Boring 310,-becoming sandiers it is probably an uncemented facies of the sandstone.
A gravelly zone
-was-sampled at an approximate elevation' of 59 m (180 f t).
Although the matrix varies somewhat among borings, the gravel is continuous on cross sections between Borings 309 and 323 and 321 Land 324 (Figures 2.5-23 and 2.5-24).-
Higher in the saction between borings.309 and 323 a thin silt layer dips from elevation
-3 3 - (-110. f t) _in Boring 309 to elevation -43 (-140 ft) in Boring 310.-
2.5-31
~
,n vs
/[
The hiihly discontinuous naturesof' lithologic units within the; Potomac Group, the juxtaposition of' depositional units.
(rcsultingifrom;widely-differing hydraulic regimes, the oxidized
-ctate of: iron-bearingLminerals in'the sediments, the. absence of lmnrine fossils, and~the.overall geometry of the' sedimentary iocctionLall'auggestLstronglyfthat the Potomac Group beds were cdsposited in.a mature alluvial or. deltaic environment of moderate to/ low energy. -Analysis'of floral remains in the upperL61 m..
(185 ft) of Potomac section' yielded evidence (Appendix 2.5.D).
which further supports 1this conclusion.
'Shdiments'of-Pleistocene Age Lover most'of the site,,the Talbot Formation of' Pleistocene age overlies.the-Cretaceous materials.
The Talbot Formation as dascribed by; Owens - (1969) is a' terrace deposit,.primarily con -
n
- cisting:of a basal sand and'gravelLlayer, with minor interbeddedi
=cilt and clay, and an overlying' silt layer.
The composition of-
'thefsand and gravel layer is. silty,. fine tol coarse sand and fine-to coarse gravel composed'of subrounded quartz, chert, sandstone and metamorphic rock.
The sand and gravel layer is.approximately
- 2. 5 to: 15 m - (8 to 50 f t) thick, but pinches out near the. Bush River along the northwestern edge of the.. site.
The relative proportions of sand and gravel change rapidly-both with depth d laterally,'with lenses and thin layers of' silt and clay.
c
- an Texisting locally within sand and gravel layers.
The upper portion of the Talbot Formation is a sandy,; clayey silt up to 8.2Lm (27 f t) thick.
The texture changes laterally., becoming more or-less sandy and clayey, and pinches out in the' bank of the Bush River along!the northwestern edge of the site.
The' Pleistocene Talbot beds overlie:the Cretaceous Potomac Group.on.an unconformable erosion surface of moderate relief-
.(Figure 2.5-27).
During this investigation, the contact between
'the:two units was defined as the base of coarsely clastic beds
-where they extend:from or near the surface to contact with
' finer-grained:lithologies below, or,' where the gravel facies of the Talbot is missing, the contact between the silty unit and underlying sand of characteristic Potomac lithology.
'An analysis of' fossil wood from.the lower part of the Talbot near Oakington (approximately 8.8 km, or 5.5 mi, east of
'the site) carried out by Owens (1969, p. 99) yielded a radiocarbon age'of1 more.than.35,000 years B.P.. OwensLeoncluded, on the basis of this, thatithe Talbot may be pre-Wisconsin in age.
~
-Fossil remains in the Talbot Formation at the site are rare,2due to the highly oxidized nature of most of the sediment.
Only two samples of those examined proved to contain identifiable Pleistocene : flora - (Table 2. 5-1 and Appendix 2. 5.D).
These were 1taken from the cliffs at the shoreline approximately 330 m (1000
'f t) ' north of Sod Run,- and from Boring 106 at an elevation of ' -10. m - (-30 f t).
2.5-32
t j
Recent Sediments Recent sediments consisting of very soft, organic silt and clay were encountered in nine of ten borings located in the Bush River, to depths ranging up to 15.2 m (50 ft) below sea level (Figures 2.5-20 and 2.5-25).
No recent sediment was encountered in Boring 118; this anomalous condition is possibly the result of dredging operations associated with the emplacement of a sewer pipeline crossing in the area, as well as the possible existence of a ridge formed on a resistent clay bed of the Potomac Group.
In general, the thickness of organic sediment decreases upstream (Figure 2.5-25).
A thicker section of recent sediment in the central portion of the river, at Boring 111 (Figure 2.5-20), suggests that the axis of a paleochannel of the river may lie near that point.
2.5.1.4.3 Geological Structure of the Perryman Site The following descriptions of geological structures at the site are based largely on inferences drawn from sources of indirect information, as very little evidence of structure is directly observable at the site.
These sources include the results of:
- 1) surface mapping of the site and surrounding area; 2) exploratory borings; 3) a seismic refraction survey; 4) a seismic reflection survey; 5) a ground magnetometer reconnais-sance; 6) an assessment of aeromagnetic data; and 7) a study of features on remote-sensing imagery.
General Structural Setting Unconsolidated sediments of the Coastal Plain Province lie unconformably upon a basement of complex 1y-structured, crystalline rocks at the Perryman Site.
Toward the Coast (eastward), the thickness of the sedimentary section increases, while it decreases to a feather edge inland (toward the west).
The feather edge lies in contact with outcropping crystalline rocks in the vicinity of the Fall Zone, which passes northwest of the site as close as 5.6 km (3.5 mi).
At the site, the thickness of the sedimentary section averages about 132 m (400 f t).
The nearest outcrops of crystalline rock are on Grays Run, about 4.8 km (3 mi) to the NW, and Swan Creek, about 9.6 km (6 mi) to the NE.
At both localities, the outcrops are composed of strongly foliated Aberdeen Metagabbro.
From 3.2 to 6.4 km (2 to 4 mi) away, in the Perryman Test Well Field, a series of wells drilled to basement encountered crystalline rock at elevations of -19 to -87 m (-60 to -265 ft) showing an apparent gradient of the basement surface toward the coast of about 1 in 100 with a local sharp increase of 1 in 10 (Figure 2.5-7).
2.5-33
B* Cement Topography The topography of the basement beneath the site, as inter-proted from data obtained by seismic surveys and borings, is d:picted in Figure 2.5-17.
The " basement" as defined in the figure is the top of continuous unweathered rock, and not the otratigraphic basement immediately underlying the Potomac Group thnt is defined by an ancient erosion surface.
The upper surface of unweathered crystalline rock is seismically anomalous and, ov r most of the site, is readily recognizable on the seismic rccords.
Where seismic lines cross borings, agreement between tha depth of fresh, unweathered rock as described in the boring logs, and a prominent seismic reflector that can be traced between holes, is good.
Seismic data obtained by the refraction method during Phase I etudies (Figures 2.5.G-96 through 2.5.G-102) and by the reflec-tion method during Phase III studies (Figures 2.5.F-2 through 2.5.F-9) were used to compile the structure contour map of Figure 2.5-17.
While agreement among the borings and the two acts of seismic data was good over most of the area, disagreement b: tween the refraction and reflection profiles occurred in the vicinity of the junctions between Seismic Lines A, F, and J (Figure 2.5-17).
In that locality, information from the reflection survey was given precedence over that from the refraction survey because 3
of the greater precision of the reflection method in this instance.
With the stated exception, contour lines drawn on the refraction end reflection lines, separately, agree within approximately five percent of depth values when combined in a single map and the resultant patterns are compatible.
Where two or more seismic lines cross, data control is b ct; consequently, the contour patterns were developed in those arcas first.
Progressing outward from those areas, control d: creases and the contour patterns are necessarily more inter-pretative.
In those areas, standard procedures were used to produce a reasonable pattern in light of the geometry established in areas of good control.
While the structure contour map in Figure 2.5-17 is interpretative in its entirety, information control in the form of crossing lines and borings is sufficient over much of it that it represents a good approximation of the probable morphology of unweathered, crystalline basement rock b: neath the site.
{
i It is demonstrable from stratigraphic correlations among j
Borings 309, 310, 321, 322, 323 and 324 (Figures 2.5-23 and j
2.5-24) that the surface of the basement as defined by the l
uppermost occurrence of in situ saprolite, and the basement established on the basis of seismic velocity at the interface l
2.5-34
w L
between'the saprolite and unweathered rock, have'very different surface morphologies.
The seismic basement, which is approximately equivalent.tolthe base'of the saprolite, describes a surface which has been; formed by' differential, chemical-weathering.
Although several environmental factors control the development
.of,saprolite, one of the most important ones governing depth of weathering'is' permeability..This factor, in turn, in crystalline rocks may be directly relatable to fracture and foliation charac-teristics.
Thus, the structure contours. drawn-on the basement
.in Figure 2.5-17 may:be-representative of " grain", or fracture-geometry in the basement rocks.
.On'this premise, at least.two areas.of rocks with contrasting
~
" grain" characteristics appear.to exist beneath the site.
Jut area of apparent ridge; topography with a N-S orientation occurs in the northeast part of the site, between Seismic Lines J, Ki and L.
South and west of.this area, a less rugged area with both northwesterly and northeasterly' trends is apparent, and, in the vicinity of; Seismic Lines E, H, and~I, a strong, nearly E-W
~
trend-appears.- Boring 104 was drilled into the rugged, ridge topography.on the northeast and recovered gneissoid and schistose rocks similar to those encountered in the gentler topography in the central part of the site.
Similarly, the basement rocks q
encountered in' Boring 107, although they have a higher. biotite content than those of the other deep borings, are compatible with the other gneiss and schist samples from elsewhere under the site;'therefore, it appears that the difference in " grain",
as shown in the interpreted structure contours, may be due to differing structural characteristics of rocks of similar composi-tion, rather than to differential weathering of dissimilar lithologies,.
Inferred structural patterns as interpreted in Figure 2.5-17.are generally compatible with magnetic trends in the area around'the site as depicted in Figure 2.5-8, in that northeasterly, northwesterly, and transitional N-S' trends are evident =in the aeromagnetic contour lines.
The site.itself, however, appears in the aeromagnetic map-(Figure 2.5-8) as an isolated magnetic low areai without internal distinguishing features.
In an effort to define subsurface structural trends, a ground magnetometer reconnaissance was conducted at the site.
Graphic summaries of.the observed data are depicted in Figure 2.5-18.
The locations of survey lines are shown on Figure
.2.5-17.
The; magnetic data reflect generally the relative overall magnetic characteristics of the rocks underlying the site.
Because of the depth to basement, details of the basement are not, discernible on the basis of this information.
However, the results of the magnetometer reconnaissance at the site, considered 2.5-35
in the context of supporting data, show that the basement is divisible into magnetic domains, and that these domains probably represent variations in basement rock types.
Magnetic profiles W, X, Y, and Z (Figure 2.5-18) all show contrasting areas of magnetically high and low intensities.
A gcnerally elongate area of relatively low magnetic intensity i
occurs in the central part of the site with a northwest-southeast orientation, and is flanked to the northeast and southwest by arcas of higher intensity.
The magnetically high area to the northeast appears to coincide generally with the strongly linear, rugged basement topography that is interpreted as existing in that area.
Magnetic profile W, (Figure 2.5-18), in particular, shows a sharp change in gradient about 131 m (400 ft) NW of Boring 104 that coincides closely with the basement structure contours as interpreted from the seismic data on Lines J and K (Figure'2.5-17).
Borings 321, 323, and 324 recovered samples of quartz-diorite and diorite with gneiss and schist.
The presence of these igneous rocks in that area may be related to the magnetically low zone that also occurs there.
If this is the case, it is possible that similar rocks extend along the low trend to the northwest and southeast and that, therefore, a petrologic discon-tinuity in the basement passes through the site with a strong NW-SE orientation.
At the west ends of magnetic profiles Y and Z, magnetically low values also occur (Figure 2.5-18).
On profile Z, this low coincides with an interpreted low area on the seismic basement and the two features may therefore be related.
On profile Y, a
steep gradibnt downward toward the Bush River is interrupted by a charp upward deflection of the magnetic profile; these features are coincident with a nearly E-W oriented, steep basement scarp and associated fault as interpreted from the seismic profiles in that area.
Faults Fault features in the basement were encountered in Borings 310, 321, 323, and 324.
Four probable faults were identified from seismic relfection data:
- 1) between Borings 310 and 323;
- 2) between Borings 309 and 105; and 3) near the east end of Line H.
In addition, twenty-three anomalous features were identified in the basement from the reflection data.
The origin of the latter features may be due to any one of several causes, only onn of which is faulting (Appendix 2.5.F).
None of the features dicplay disruption or offset of reflectors in the sedimentary beds overlying the basement.
Locations of seismic line crossings of interpreted faults and other basement anomalies are shown in Figure 2.5-17.
2.5-36
c d
Fault.in the Vicinity of Boring 310 During the drilling of Boring 310, indications of postible faulting in the. basement rocks were encountered.
These indications include the presence of apparent breccia, high secondary per-meability and associated poor core recovery, and possible gouge.
To investigate this feature further, Borings 321, 322, 323, and 324 were drilled at 65 m (200 ft) spacings in a cruciform pattern around Boring'310, with an orientation that was keyed to the existing line between Borings 309 and 310.
Further evidence of faulting in the form of definite breccia, strong slickensiding, and open fractures,Lwell below the basement surface, were encountered in Borings.321 and 324.
Cores from Boring 323 exhibited only slight slickensiding on chlorite seams and, in general aspect, appeared less affected by ca+.aclastic processes.
The presence of quartz'and feldspar-rich rocks of probably igneous texture was noted in Borings 321, 323 and 324 and samples of these rocks were examined petrographically (Appendix 2.5.E).
Thin sections of this rock from Boring 321 were found to be strongly affected by faulting, while rock from Boring 323 was found to have been affected to a lesser degree and from Boring 324,.only very'slightly.
It is concluded from these data, therefore, that the trend of this basement fault is oriented generally NW-SE, with lateral boundaries lying between Borings 322'and 310 and in the vicinity of Boring 323.
The fault "ay be associated with the contact between basement rock units as interpreted from the structure contour map (Figure 2.5-17) and the ground magnetometer profiles (Figure 2.5-18).
Close-order correlations were established among stratigraphic horizons in' Boring 310 and the surrounding borings.
The eroded surface of the saprolite, a basal gravel zone, lignite zones, and other marker horizons provided means of establishing that, within the resolution of the sampling method, the surface of the j
basement and the sediments immediately above it apparently are not vertically offset by faulting (Figures 2.5-23 and 2.5-24).
While relief is evident on the saprolite surface, gradients are very gentle and it was concluded, on this basis, that the fault in the vicinity of Boring 310 has probably not experienced significant vertical movement since the deposition of the Cretaceous sediments which overlie it.
Further, petrographic studies suggest that faulting associated i
with the igneous rocks in Boring 323 took place under conditions of elevated temperature and/or pressure conditions (Appendix 2.5.E) and therefore are probably related to the closing stages i
of. metamorphism in the basement complex, which far pre-dates the Cretaceous sediments.
However, a seismic anomaly identified on Line M is described (Section 2.5.F.5.8) as showing strong indications of displacement of the seismic basement, and possibly, of the sediments overlying 2.5-37 4
O!
- thh basement.: This interpreted 1 fault occurs in the~ basement' b3 tween Borings!310.and 323',Lapproximately.24.m-(75 ft) west of
- Boringi323._JAlthough the seismic line agrees'well with the-
.information from the borings;at the.-locations of the' borings, f
'tha' reflection: data on Line[M-(Figurci2.5.F-7) strongly1suggest thtt disruption ofiat least-the lower part'ofithe Potomac Group
' ' 'esdimentsrhas2 occurred between those~ locations, andLthat the caismic basement' hasL beenl displaced vertically by about'13 m ~(40 ft).'(Section 2.5.F.5.8.).i.The occurrence of this seismic Tenomaly'in;the' vicinity,of'aiknown fault zone dictates.the conclut. ion. that parts ' ofi that : zone. appear. to. have been active "after early(?)1 Lower Cretaceous time,.approximately 100 million Lycars:.ago.
- FaultBetweenBoringsj309? ann: 105 A fault.istinterpreted as occurring on-Seismic Line'0, approximately half-wayf between Borings 309 and 105 (Figures 2.5-17,-2.5.F-9).
. ApproximatelyL 24: m"(75 f t) of displacement is tinterpreted on the' surface of the seismic basement,'but no-disturbance-of the overlying. sediments was noticeable.. The orientation of'this fault:is not known.
Inferred structural contour line patterns on topLof the seismic basement.(Figure
.2.5-17), however,-show1possible presence-of a NE-SW trending low
-area-in that. vicinity, which may possibly be associated with fracturetpermeability in the fault zone..
I Faults.on Line H Two faults are interpreted'at the east end of Line H, near.
'itsfjunction with Line I (Figures 2.5-17, 2.5.F-2 and 2.5.F-3).
The~more easterly of these shows a'possible-displacement of the crystalline basement of.up.to 24 m (75.ft), with evidence of-disturbance.and abrupt relief features in the overlying sedimentary section.-
Structure contour lines. interpreted on the seismic basement
-(Figure 2.5-17) show a'strongly. oriented, WNW lineation in the vicinity of'the junction of seismic lines H and I.
On both
~
lines,1 a' steep increase in gradient of the basement shows a scarp-like feature with a local relief of about 39 m (120 ft) in less than -33 horizontal meters -(100 f t).
Where this subsurface
- topographic feature crosses.Line H, it passes ~within 16 m (50 L f t) c of the. easternmost interpreted f ault.
Where the feature crosses'Line I, it coincides _with a possible disruption of the l
crystalline' rock surface that is considered to be questionable
'bacause of.the somewhat lower quality of the data on Line I
- (Saction 2. 5.F. 5. 5)..'Another abrupt increase in gradient of the 1
surface of the crystalline rock occurs on Line I about 33 m 1
(100.ft) NE of the one described'above, i
2.5-38
\\
~
A
R 1
If'a lint is projected from this'second topographic feature Lon'Line I in.the direction of' trend of the first feature, the U.....
projected line crosses Seismic Line H at the more westerly of the two interpreted faults.
Thus, it appears probable that the morphologyLof the surface of crystalline rock-in this. area is strongly. influenced by the coincident occurrence of faults in the basement, at least one of which may be. associated.with-structural relief in the overlying Lower Cretaceous sediments.
.Other Possible Faults Numerous other. anomalies on.the surface of the crystalline rock that could possibly be associated with; faulting are identified on Figure 2.5-17...It is considered that theLinterpretations of these. anomalies.has.been done:in a conservative manner and that,
- with the exception of the areas described in detail above, all of these interpreted anomalies'may have explanations other than
-faulting..
'The Potomac Group As mentioned before, sedimentary deposits of the Potomac-Group at the site have a laterally-discontinuous, lithologically, j
varied aspect that is typical of the unit as it is exposed elsewhere in Harford County.
Correlation.of lithologic units is difficult because of this characteristic.and, among the more wide-spaced borings, is somewhat speculative.
Although numerous local variations in apparent dip can be seen on the subsurface section-(Figures 2.5-19 through 2.5-26), a general dip toward the southeast is evident through the site area.
Extensive exposures of Potomac sediments in sand pits within-a few miles of the-Perryman Site.show faulting, slump-structures, and structures due to differential compaction of water-saturated sediments (Section 2.5.1.3.2).
Most of these structures'have stratigraphic associations that strongly suggest origins penecontemporaneous with deposition.
Faults observed in these exposures were generally limited in vertical extent by undisrupted strata passing either above or below the fault trace.
On the basis of.these observations, it is to be expeited
]
that such structures as slumping, gravitational folding, and j
small scale, syndepositional-faulting may exist in the Potomac beds at the.Perryman Site.
The Bush River is incised into beds of the Potomac Group
'along part of the modern channel.- Upstream from Boring 120, the Potomac beds either crop out in the river bottom or are overlain
.by Recent sediments (Figure 2.5-20).-
Steep bluffs along the i
northern half of the' shoreline adjacent to the si.te are held up Lby Potomac Group-sediments.
These bluffs form parts of prominent i
2.5-39
[i y
.linzarl features in the'arealthat'have been described elsewhere (Saction.2.5.1.3.3.and; Appendix 2.5.A) and which agree'in oriGntation withLregional structural trends.: The. interpreted, NW-SE trends of the. fault under Boring 310 and the associated
- contact between' metamorphic and igneous rocks appear to agree
- with the trend of1this' segment of shoreline. ' Indications of possible disturbance:of the Potomac Group beds in the vicinity of the' junction.offseismic. lines-H and I lie within 99 m (300 f t)' of;the. shoreline; however, the trends-of the. interpreted basement topographic feature and possible associated fault at that' locality do not agree with the trend:of the shoreline and tha geometric 1or, structural relationships between these' features, if any, are-unclear.
'The Talbot Formation Beds of'the' Pleistocene Talbot Formation are deposited upon end incised'into the Potomac Group at the site.
The thickness of the formation. varies from zero along a line which trends Japproximately NNE,through the center of the site, to much as 16 m (50 f t) tin areas of channel deposition.
The configuration of the upper surface of the Potomac Group, upon part of which the Talbot beds lie, is depicted in Figure 2.5-27.
These contours'are drawn.at the base of the lowest beds believed,-on the basis of lithology or pollen dates, to be of Pleistocene age. ~ A system of curvilinear topographic lows and' associated highs trends generally southward through the center of'the. site and into the Bush River.
The interpreted geometry of these features indicates strongly that an ancestral arm of the drainage system now represented by the Bush River flowed across the-site during Talbot time.
Strongly recurved low areas connecting with the present axis of the channel in the Bush River suggest that this stream once meandered over a wide floodplain; possible terraces and incised meander features may record subsequent periods of lowered baselevel associated with late-Pleistocene changes of sea level.
Near the-center of the site boundary along the Bush River, a northeasterly-trending, local increase in gradient passes into tha river at nearly right angles.- This feature appears to be parallel to'the segment of the present shoreline just north of the railroad tracks and south of the site, along the boundary of the Aberdeen Proving Grounds, and may reflect the influence of the same factors that' control the present rectilinear drainage
-along the Bush River.
Much of the interpreted drainage pattern, howsver, does not have a, linear aspect, but rather one of a wall-adjusted stream system flowing over an essentially homogeneous substrate.
2.5-40
2.5.2 Vibratory Ground Motion This section presents an investigation of the seismotectonic characteristics of the Perryman Site and the surrounding region
' intended to develop seismic design' criteria for major structures at the proposed facility in conformance with the guidelines outlined in USNRC Regulatory Guide 1.70, Standard Format and Content of the Safety Analysis Reports for Nuclear Pcwer Plants, Revision 2 (U.S. Regulatory Commission, 1975) and 10 CFR part 100, Appendix A, Seismic and Geologic Siting Criteria for Nuclear Power. Plants (General Services Administration, 1973).
A description and the results of the field investigation and laboratory testing
- program which provided background informa-tion for this investigation are presented in detail in Section 2.5.1.
2.5.2.1 Seismic Hir, tory The site is situated in a region-which has experienced a moderate amount of minor earthquake activity in historic time.
The record of earthquake occurrences in the Maryland-Virginia-Delaware-New Jersey area dates back to the early 18th century.
Many earthquakes have been reported since that time, and minor structural damage has been associated'with several of the. events.
None of these earthquakes are considered to have been of major or catastrophic proportion.
Because this region has been fairly heavily populated since the early 18th century, it is quite certain that any major earthquake activity (Intensity VIII or greater, as defined by the Modified Mercalli (MM) Intensity Scale, 1931, Table 2.5-2) would have been reported in local newspapers, private journals, or diaries.
The lack of any such documentation is indicative of the absence of major earthquake activity in the region during this period.
Structural damage is the rating criterion for larger shocks.
The effects of earthquakes on the rather large variety of con-struction materials used to build older structures, such as chimneys and rock walls, are highly variable, making the intensity evaluations based on such reports imprecise.
However, the rather long period of record and the evenly distributed population provide a reasonable basis for estimates of future activity.
Table 2.5-3 lists all events within 320 km (200 mi) of the site area with Richter magnitude greater than 3.0 or intensities greater than III.
All seismic events within 80 km (50 mi) of the site are also listed.
Figure 2.5-28 displays these seismic events on the regional structure of the area around the site, as well as the significant earthquakes (Intensity V and greater) which have occurred in the northeastern United States.
The closest, significant regional event to the Perryman Site was the Intensity VII shock which occurred in the vicinity of Wilmington, Delaware, on October 9, 1871, approximately 68 km 2.5-41
(42 mi) tx) the northeast of the site.
Ground motion at the site oc a result ofLthis event was approximately Intensity'IV-V, probably as high as any experienced from any other earthquake in the region.
This shock was as large as any recorded earthquake within 320 km (200 mi) of the site.
Accurate location of its epicenter 10 difficult because of limited available inforination.
Based on d mage reports and intensities felt, the epicenter has been located near Wilmington, Delaware, whereas the shock was felt from near Chester, Pennsylvania. on the north; to Middletown, Delaware, on the south; and from Salem, New Jersey, on the east; tx) Oxford, Pennsylvania, on the west.
The initial shock was followed by a much smaller shock just after midnight on October 10.
A contemporary newspaper account indicates that the initial chock was felt at Wilmington "with great distinctness."
Buildings ware shaken severely, and a number of chimneys were damaged in tha surrounding towns of Oxford, Pennsylvania, and New Castle End Newport, Delaware.
An interesting aspect of this earthquake is the fact that is was accompanied by a very loud sound, as of en explosion.
This loud noise, in fact, led to the belief that ths shock as caused by an explosion, probably at the powder mill of the E.I. DuPont deNemours Company, near Wilmington.
This poesibility was carefully investigated at the time, and it was
~
concluded that the shock was a legitimate earthquake.
Five shocks of Intensity V have occurred within 80 km (50 mi) of the site.
Two of these, the Harford County events of M:rch 1883, occurred approximately 24 km (15 mi) northwest of the site, near Fallston, Maryland.
The maximum ground motion experienced at the Perryman Site was probably no greater than Intensity III.
Both of these shocks were local in extent and there were no reports of damage.
In the Fallston area, clocks were reported stopped and crockery rattled on shelves.
The following are three other Intensity V shocks which have occurred no closer than approximately 72 km (45 mi) from the site:
1.
The Delaware event of March 25, 1879; 2.
The Pennsylvania event of March 8, 1889; and 3.
The Wilmington, Delaware-Penns Grove, New Jersey event j
of February 28, 1973.
i The Wilmington-Penns_ Grove shock (1973) appears to be the strongest of the Intensity V events, and was reportedly felt naar the site with an Intensity of IV.
As many as 11 smaller events (Intensity II to IV) have been reported within 80 km (50 mi) of the site, although none have occurred as close as.the two Harford County shocks of 1883.
i 2.5-42
i i
Although it is probable that several of the shocks mentioned previously were felt at the site, no damaging effects were experienced.
Ground motion at the site associated with larger, more distant earthquakes, such as the Charleston, South Carolina, shocks of 1886, or the St. Lawrence River Valley shocks near Quebec in 1663 and 1925, would not have been greater than the 1871 Wilmington shock.
2.5.2.2 Geologic Structures and Tectonic Activity 2.5.2.2.1 Tectonic Provinces The area within a 320-km (200-mi) radius of the Perryman Site includes parts of seven tectonic provinces (Figure 2.5-28).
The provinces are, from west to east, Stable Interior, Fold and Thrust Belt, Blue Ridge-Highlands, Conestoga Valley, Inner Piedmont, Outer Piedmont, and Coastal Plain.
The tectonic province concept used to define these provinces is based on an evolutionary model of the Appalachian orogen (Dames & Moore, 1976c).
This concept was used in this study to provide the province boundaries of significance to the site.
2.5.2.2.2 Tectonic Differentiation of the Appalachian Orogen The outline presented below summarizes the relationships and derivations of tectonic provinces of the Appalachian orogen, as displayed in Figure 2.5-28.
1.
Craton 1
a.
Eastern Belt (Blue Ridge-Highlands) b.
Western Basin
{
(1)
Stable Interior j
(2)
Fold and Thrust Belt 2.
Mobile Belt a.
Eastern Cratonic Margin (1)
Conestoga Valley (2)
Inner Piedmont (3)
Outer Piedmont (4)
Coastal Plain Considering the tectonic evolution of the Appalachian orogen, it is subdivided as above into two fundamental areas:
craton, the part affected only by convergent diastrophism, and mobile belt, the part affected by initial divergent, convergent, translational, and final divergent diastrophisms.
The mobile belt, as defined in this report, is situated east of the great anticlinoria cored by Grenvillian rocks; i.e.,
east of the Long Range (Nova Scotia), the Green Mountains, the Berkshire Highlands, the Hudson-New Jersey Highlands-Reading Prong, and the Blue Ridge Mountains. The mobile belt thus corresponds to the Appalachian 2.5-43
cugeosyncline ard irclndes the quasi-cratonic mergins.
The wastern edge of the motile belt parallels and lies to the west of what was originally the eastern edge of the North American continent during Cambro-Ordovician time, as defined by Rodgers (1968).
2.5.2.2.3 Tectonic Differentiation of the Craton The cratonic portion of the Appalachian Highlands is underlain by continental crust composed of 1000 million-year (my)-crystalline rocks which were deformed during the Grenvillian orogenic cycle.
On the eastern edge of the craton, these rocks crop out at the curface as great anticlinoria.
West of these elevated anticlinoria, lies an elongated, downwarped segment of the continental crust which forms the asymmetric Appalachian basin.
The floor of this basin is formed of Grenvillian rocks that are greatly depressed in-the east (up to 40,000 feet below sea level) and gradually rising toward the west.
The basin is filled with largely unmeta-morphosed sedimentary rocks (both clastic and carbonate), ranging in age from Early Cambrian to Carboniferous.
These rocks form a ecdimentary wedge, thickening to the southeast, that reflects the asymmetry of the basin floor.
Blue Ridge-Highlands Tectonic Province The eastern portion of the craton, termed here the Blue Ridge-Highlands, constitutes a tectonic province and is charac-tarized by Grenvillian rocks deformed during the paleozoic convergence stage (dermal or thick-skinned deformation).
J Characteristically, the terrain is mountainous and exhibits exposure of some of the oldest rocks in the eastern United States (1000-1100 my old).
Earthquakes no greater than Intensity VI are characteristic of this tectonic regime, and none have b:en related to specific structures.
Stable Interior Tectonic Province The Stable Interior tectonic province of the western basin io characteris.ed by the absence of intense deformation and the presence of shelf-delta type Paleozoic sediments.
The rocks display gentle folding, as opposed to the intensely folded and fculted rocks of the Fold and Thrust Belt located immediately to the southeast.
The largest significant earthquake to have occurred in this province (within the regional scope of this etudy) was the 1929 Attica, New York, event (initially cataloged cs Intensity VII-VIII), approximately 420 km (260 mi) from the site.
This shock, and an accompanying concentration of lesser cvents, has been spatially related to the Clarendon-Linden Fault, an anomalous structure in the essentially untectonized rocks making up this portion of the Appalachian Plateau.
Other emaller,, random events are not correlated with specific structures.
2.5-44
r~'
~
Fold and Thrust Belt Tectonic Province The Fold and Thrust Belt tectonic province is characterized by tightly folded and thrust-faulted Paleozoic sediments developed as flysch, or molasse.
The northwestern boundary of this province generally marks a transition between gently folded rocks on the northwest (Stable Interior) and intensely folded and faulted rocks on the southeast, thus marking the western limit of Paleozoic thrusting (Bryant and Reed, 1970).
The largest earthquake which has been recorded in the Fold and Thrust Belt tectonic province was the Giles County, Virginia, Intensity VIII shock of 1897, approximately 450 km (280 mi) from the site.
Other earthquakes in this province are widely scattered, with none exceeding Intensity VI in the area of tha site (Intensity VII's are noted near Ashville, North Carolina, approximately 640 km (400 mi) from the site) and none correlatable to specific structures.
The recorded Intensity VII event at Wilkes-Barre, Pennsylvania, has been related to a mine collapse (Dames &
Moore, 1972).
The tectonic differentiation of the cratonic portion of the Appalachian orogeny largely follows the tectonic subdivisions propose 6 by Rodgers (1970), with only a modification of the eastern boundary of the Blue Ridge-Highlands tectonic province.
This tectonic subdivision is also similar to that recognized by the regulatory agencies (AEC, 1974), with the Stable Interior tectonic province being an equivalent to the NRC's Appalachian Plateau, and the Blue Ridge-Highlands and the Fold and Thrust Belt tectonic provinces constituting the NRC's Blue Ridge and Valley and Ridge provinces, respectively.
2.5.2.2.4 Tectonic Differentiation of the Mobile Belt The mobile portion of the northern Appalachian orogen within the region of interest for this study includes the eastern cratonic margin, which is underlain by continental crust of predominantly Grenvillian age (Inner Piedmont and Conestoga Valley tectonic provinces).
The mobile belt of the southern Appalachian orogen can be divided into the following three areas:
1.
The eastern continental margin, herein called the
{
Inner Piedmont;
)
{
2.
The Outer Piedmont (due to the less understood nature of the Outer Piedmont this province cannot be further subdivided at this time); and 3.
The Coastal Plain.
2.5-45
)
3 Th3 anctcrn cratonic m rgin is bord 0 rcd on its western aids
)
by the Blue Ridge-Highlands tectonic province and on its eastern aide by.the easternmost extent of the Grenvillian basement, q
This eastern boundary is interpreted principally from a line of gneiss domes of one-billion-year-old continental crust, which includes the Pine Mountain' belt, the Sauratown Mountains anti-clinorium, the Baltimore gneiss domes and, possibly, the Chester dome of Vermont.
This boundary corresponds to the eastern limit of the ancient continental margin of North America (Williams and Stevens, 1974; Rankin, 1975).
It also coincides with several cignificant geological and geophysical changes (Williams and Stevens, 1974).
First, it parallels the main gravity high of the Appalachian Mountains (Mayhew, 1974).
Second, it is marked by contrasting seismic refraction profiles that reflect deep crystal contrast.
Finally, it is a zone of faulting, contrasting otructural style, and contrasting metamorphic facies.
This cratonic margin is divided into two tectonic provinces north of Virginia, the Conestoga Valley province and the Inner Piedmont province.
The boundary between these provinces corres-ponds.to the Martic Line in Pennsylvania (Wise, 1970) and the couthward extension of Cameron's Line in western connecticut (Stanley, 1966).
Conestoga Valley Tectonic Province The Conestoga Valley tectonic province is characterized by c miogeosynclinal assemblage overlapping an older clastic assem-blage.
Triassic basins of the Newark Group are characteristic of the Conestoga Valley province (and, to a lesser extent, the Inner Piedmont and Coastal Plain) and are found in the area b$ tween Massachusetts and South Carolina.
The closest approach to the site of these basins is approximately 72 km (45 mi) to the northwest, near Gettysburg, Pennsylvania.
Triassic rocks hcVe been encountered in borings at Bowling Green and Edgehill, Virginia, and near Brandywine, Maryland.
These basins were formed during Triassic time as down-fculted and folded, elongate, graben structures.
Nonmarine, crkosic sediments and intercalated lava flows filled these basins as they were down-faulted and tilted.
At the close of the period, the process of erosion continued to modify the topography of the eastern section to form the base for deposition of Coastal Plain sediments.
In the Triassic basins and associated down-faulting, intru-cions of Juro-Triassic age are cut and displaced, indicating a post-Juro-Traissic age for some of the faulting.
Similar intru-cions in the Inner Piedmont adjacent to the Perryman Site are not disrupted or offset in this manner.
Earthquakes no larger than Intensity VI have been noted in the Conestoga Valley province, 2.5-46
although some small events, up to Intensity VI, are reported and have been tentatively associated with Triassic basin border faults.
Inner Piedmont Tectonic Province The Inner Piedmont tectonic province is characterized by a
]
eugeosynclinal assemblage over an older clastic assemblage, which is characterized in this region by a northeast-southwest-3 trending belt of Precambrian to Early Paleozoic schists, gneisses, j
slate, metaconglomerates, and some igneous intrusions.
These rocks are interrelated in a complex manner by fculting and folding.
The faulting in the Inner Piedmont north and west of the site is thought to be controlled in part by a northeast-l southwest-trending set of dome-like structures of Precambrian gneiss associated with the Baltimore-Washington Anticlinorium.
A discussion of the prominent tectonic structures is presented in Section 2.5.1.
l Earthquakes ascribed to the Inner Piedmont should include the boundary Intensity VII events at Wilmington, Delaware (1871) and Asbury Park, New Jersey (1927), as well as several Connecticut i
valley events of Intensity VII which occurred well over 320 km (200 mi) from the site, albeit in the Inner Piedmont province l
(Dames & Moore, 1976c).
No larger events have been recorded in j
this province, and none of the historical shocks can be satis-i factorily related to specific structures.
The Inner Piedmont is, in general, apparently the most seismically active portion of the area within 320 km (200 mi) of the site.
Concentrations of moderate events are apparent in the New York City area and in the central Virginia seismic zone near Charlottesville, as described by Bollinger (1973).
Both of these zones are more than 160 km (100 mi) from the site area, and both are characterized
~
by low to moderate seismic activity.
Seismicity elsewhere in the province is relatively rare and apparently random, although several Intensity VI events north of the site area appear to be at least spatially related to Triassic basin border faults (Figure 2.5-28).
Outer Piedmont Tectonic Province The Outer Piedmont tectonic province occurs south of Maryland and lies east of the easternmost exposures of the Grenville continental crust and the Inner Piedmont.
This border is also defined by the contrast between the gravitic plutons of the migmatitic Inner Piedmont and the calc-alkaline mafic and felsic plutons of the Charlotte belt (within the Outer Piedmont).
The southeastern border of this province coincides with the Fall.Z7ne that defines the westward limit of the Coastal Plain tectonic province overlap.
2.5-47
The Carolina slate belt, which makes up much of the northern portion of the Outer Piedmont, consists of Late Precambrian to Middle C mbrian volcanic and plutonic rocks (Glover and Sinha, 1973; Odom and Fullagar, 1973; St. Jean, 1973).
Higgins (1972) has correlated the rocks of the Carolina slate belt with the Chopawampsic Formation in Virginia and the James Run Formation in Maryland end named this belt the Atlantic Seaboard volcanic Province.
The rocks of the Outer Piedmont were formed during the initial convergent stage in Late Precambrian to Cambrian time as an icland arc assemblage.
Parts of this province were also possibly related to an Avalonian or African continental margin.
The Outer Piedmont province encompasses the relatively frequent seismic activity around the Richmond-Petersburg, Virginia crea south of the site.
Earthquakes occur most frequently in this eastern portion of the Central Virginia seismic zone described by Bollinger (1973), but have not exceeded. Intensity VI.
Coastal Plain Tectonic Province The Coastal Plain tectonic province is characterized by the development of a miogeosynclinal wedge during the advanced phases of the final crustal divergence.
In the region surrounding the site, this province is characterized by a stratigraphic c quence of interbedded. sands, gravels, clays, and silty sands of both umrine and continental origin.
These materials were deposited on the downwarped basement complex from Early Cretaceous to Quaternary time.
The strata crop out at the Fall Zone and form a wedge-shaped mass that thickens to the southeast.
The everage dip of these strata varies from 14 m per km (75 ft per mi) within the Cretaceous sediments to approximately 2 m per km (10 ft per mi) in the upper Tertiary formations.
Few geologic structures are known in the Coastal Plain province.
The Salisbury Embayment, within which the Perryman Site is located, is a structural low in the basement rocks j
bstween Newport News, Virginia, and Atlantic City, New Jersey.
{
The Embayment is marked by a deep accumulation of Mesozoic and Cenozoic sediments, which approaca a thickness of from 1100 to 2300 m (3500 to 7500 ft) at the Maryland coastline.
The feature
]
is fairly prominent in the basement rocks, but loses form in the i
younger sedimentary sequences, suggesting that it is predominantly a pre-Tertiary feature.
The Coastal Plain underwent regional cpeirogenic movements from Pliocene to Quaternary time, which 1
lifted a portion of the continental terrace above sea level f
(Southwick and Owens, 1969).
Recent studies of leveling data suggest that the east coast io presently tilting eastward, with smaller scale' local perturba-tions (Brown and Oliver, 1976).
The Delmarva peninsula is thought to be tilting south and southeastward, as evidenced by subsurface geology, drainage patterns, and coastal geomorphology (Spoljaric 2.5-48 i
cnd othora, 1976).
Higgine and othnrs (1974) po3tulcto o couthwsst-trending fault along the Fall Zone is southern New Jersey, 5
northern Delaware, and the northern portion of the Chesapeake Bay.
Their interpretation is based on linear, magnetic anomalies and the consistent directional changes in the courses of major i
rivers.
However, geologic evidence for the presence of a fault i
is inconclusive; thus, the significance of the lineament is unknown (Spoljaric and others, 1976).
Two small folds have been mapped in Coastal Plain sediments east of Trenton, New Jersey.
They are from 5 to 6.5 km (3 to 4 mi) in length, with strata as yound as Miocene involved in the folding (Minard and Owens, 1966).
Several faults, originating in the bedrock and cutting Coastal Plain strata as young as Pleistocene, have been documented in Washington, D.C.
These faults are of a reverse nature and generally trend east-west.
Their displacements are on the order of from 0.5 to 1 m (2 to 3 f t) and, therefore, are considered minor structural features (Darton, 1950).
A series of reverse faults affects Coastal Plain materials near Brandywine, Maryland, approximately 97 km (60 mi) southwest of the Perryman Site.
The faults trend northeast-southwest, with
{
a maximum displacement of 76 m (250 ft).
This displacement decreases upward from the basement rock through the overlying sediments in a vertical direction.
Movement along these faults has been intermittent from the Cretaceous to the Miocene time (Jacobeen, 1971; Dames & Moore, 1973a).
The fault zone has been proven by a detailed boring and geophysical program.
Near Stafford, Virginia, a series of faults occurs in the Coastal Plain near the Fall Zone.
There, basement rocks of the Piedmont have been offset along a northeasterly trend and have, significantly affected overlying sedimentary formations as young as the Eocene.
These faults are described by Mixon and Newell,(1976);
Newell and others (1976); Mixon (1976); and Dames & Moore (1976). Neither Brandywine nor the Stafford Fau?ts are considered to be of significance in determining the Safe Shutdown Earthquake (SSE).
Several other faults have also been identified in the Coastal Plain of the Mid-Atlantic region and are described in Section 2.5.1.2.4.
In the region around the site, two earthquakes as large as Intensity VII have been recorded at or near the Coastal Plain province boundary; one in Wilmington, Delaware, in 1871, and another near Asbury Park, New Jersey, in 1927.
The Charleston, South Carolina events of 1886 are the only major historical 2.5-49
shocks to hcvs occurrcd in tha Constal Plcin province, but ths ottendant concentration of over 400 events (mostly aftershocks of the main events) in a small geographical area is anomalous with respect to all other areas of this province.
2.5 ' 2.5 Central Appalachian Salient The previously mentioned provinces are based on tectonic ecsociations resulting from longitudinal subdivisions of the Appalachian orogeny.
These northeast-trending provinces can also be segmented by east-west or northwest-southeast cross The New England Salient is a fundamental feature in otructures.
the Northern Appalachian Mountains and separates tectonic provinces of different character (Dames & Moore,1976b; Cady,1964).
'The most striking salient of the Appalachian orogeny is the C;ntral Appalachian Salient in Pennsylvania.
This feature was probably initiated during early crustal divergence in Late Precambrian time (Wise and Werner, 1969; Dames & Moore, 1976b),
resulting in a profound difference between the northern and touthern portions of the Appalachian orogeny.
The Central Appalachian Salient occurs where the north-northeast to northeast trends, common to the Appglachian mountains, change to east-west trends in the vicinity of 40 N latitude.
The east-west trend has been interpreted to be a major crustal structure by several authors (Woodward, 1961, 1963, 1968; Drake and Woodward, 1963) based largely on circumstantial evidence of interpreted offsets of geophysical anomalies, isopach contours, I
cnd geologic map patterns.
Drake and Woodward (1963) have cuggested that from 130 to 145 km (80 to 90 mi) of dextral offset has occurred on this feature, and that no evidence of post-Cretaceous movement has been found.
Figure 2.5-28 shows the approximate location of this feature, as defined by Woodward (1968).
Even though its surficial expression can not be well defined,
'the Central Appalachian Salient clearly divides the northern and southern portions of the orogeny.
This is supported by inspection of the historical seismicity shown in Figure 2.5-28, wherein consistent changes.in the seismicity within the described provinces are noted from north to south.
Having considered the tectonic development, the inferred geological and geophysical evidence, and the seismicity, the existence of a fundamental boundary between the northern and couthern orogeny has been shown and is illustrated as a zone in Figure 2.5-28.
2.5.2.2.6 Further Possible Subdivisions Continued geophysical examination of the Coastal Plain tectonic province and further work in the Outer Piedmont tectonic 2.5-50
r_
province may reveal additional criteria on which to base sub-divisions of these provinces.
Much of the diagnostic evidence available in the northern Appalachians east of the Inner Piedmont tectonic province has been complicated in the southern Appalachians by more severe thrusting of the mobile belt onto the continent.
Thus, surficial boundaries may not be significant and the major contacts may be obscured.
2.$,2.3 Correlation of Earthquake Activity with Geologic Structures or Tectonic Provinces only a few of the historical earthquakes in the northeastern United States can be satisfactorily related to specific structures at this time.
Therefore, a consideration of the significant events which could influence the seismic design for the Perryman Site will rely, for the most part, on an approach based on the provinces already discussed.
The following are those events which constitute the largest earthquakes of record in the eastern United States, and which embrace all significant considerations for the Safe Shutdown Earthquake for the site; 1.
The large events (Maximum Intensity IX), such as those in the St. Lawrence River Valley and Ottawa-Bonnechere graben area; 2.
The large events (maximum Intensity VIII), such as those which occurred in the Boston-Cape Ann, Massachusetts, area; 3.
The shock (originally categorized as Intensity VII-VIII) of 1929 in western New York State; 4.
The Intensity IX-X Charleston, South Carolina, earthquake
]
i in the Coastal Plain; 5.
The Intensity VIII Giles County, Virginia, shock of 1897; and 6.
The Intensity VII events near the site, such as those shocks which have been recorded in and around New York City, New York; Wilmington, Delaware; and Asbury Park, New Jersey.
St. Lawrence River Valley The St. Lawrence River Valley and the Ottawa-Bonnechere graben area are contained in the Ottawa Basin tectonic province (Dames & Moore, 1976c).
Earthquakes as great as Intensity IX are reported in this region.
The structural interpretation shows that this area is the extension of a transverse trough and 2.5-51
c mobile zona into the Stable Interior (Dames & Moore, 1976c).
B cause of the obvious historical confinement of seismic activity to this region, marked by an intraplate weakness, recurrence of cuch large shocks are expected to remain in the area, and are, thus, not translatable to the Perryman Site.
Boston-Cape Ann The large, maximum Intensity VIII events in the Boston-Cape Ann area have been historically associated with the Boston-Ottawa trend of earthquake activity (Sykes and Sbar, 1973),
which included the Ottawa-Bonnechere graben area described ccrlier.
However, a recent reevaluation (Dames & Moore, 1976c) has resulted in the identification of tectonic regimes which Osparate the former Boston-Ottawa seismic trend into specific tcctonic provinces.
On the basis of this model, the Cape Ann Intensity VIII event, being the largest event to have occurred in the Avalon Platform province, can be restricted to a distance from the site of no less than 400 km (250 mi).
Moreover, according to Ballard and Uchupi (1975), it is possible that the significant Boston-Cape Ann seismic activity is associated with the faulted
{
northwestern boundary of the Avalon Platform province (Figure 2.5-28).
For these reasons, it is not deemed necessary to translate this activity to the site.
Western New York The shock of 1929 near Attica, New York, is anomalous with respect to the seismicity of this portion of the Stable Interior.
j It does mark, however, a noted concentration of earthquakes which have been satisfactorily related to the well-recognized feature of the immediate area, the Clarendon-Linden structure, f
It is generally accepted that any recurrence of a similar event 4
would be confined to the structure.
Therefore, the postulation f
of a recurrence of this shock nearer to the site is not warranted.
j A recurrence of the largest event at any location along the Clarendon-Linden structure, or at the nearest approach of the Stable Interior tectonic province, would result in only minimal ground motion at the site (less than Intensity IV).
I Ch_,arleston, South Carolina The largest events to occur in the eastern United States
{
were the events of approximate Intensity X, at Charleston, South j
Carolina, in 1886.
]
The concentration of seismic activity (over 400 events) in the immediate vicinity of Charleston is unique to the Atlantic Coastal Plain; moreover, such a confined density of epicenters is unmatched anywhere in the central and eastern United States, with the possible exception of the New Madrid, Missouri, region.
2.5-52 l
on the strength of this areal distribution alone, it would be
{
concluded that a specific tectonic anomaly is responsible for this localized activity.
However, independent lines of investigation have recently suggested a structural regime which may be responsible for the observed seismicity.
On the basis of seismic reflection profiles parallel to the coast of South Carolina, Dillon (1974) has reported evidence of northwest-trending faults in the continental j
shelf along the South Carolina coast, and states that this would seem to be the only zone of active faulting in the United States
]
south of Cape Hatteras and east of the Appalachians.
Possible evidence of faulting is noted in the basement rocks offshore and j
in the Tertiary rocks of the continental margin.
This possible faulting aligns with the northwest-trending seismic zone (Bollinger, 1973) and has been postulated to be the extension of an active oceanic fracture zone into the continental block (Dillon, 1974; Harrison and Ball, 1973; Sykes and Sbar, 1973).
More locally, a mild, breached fold in the shallow sediments several miles west-southwest of Charleston has been identified by Colquhoun and comer (1973) as the Stono Arch.
The axis of I
this arch trends west-northwest and has possible, associated faulting.
The trend of this structure is aligned with, and grossly parallel to, the seismic zone and the offshore structure j
discussed above, and represents the only known deformation in the immediate vicinity of Charleston.
Thus, it may be a near-surface expression of the more regional (and deeper) anomaly suggested by offshore reflection surveys and magnetic anomaly trends (Zietz and others, 1976).
j l
Transverse to the strike of these structural features are the northeast-trending axes of two structural highs which are identified along the coast, from Savannah, Georgia, to just south of Charleston, at the Beaufort-Burton High and the Yamacraw Ridge (Dillon, 1975).
According to Dillon (1975), the Beaufort-Burton High may be a shallow expression of the deeper lying Yamacraw Ridge.
The intersection of these structures with the suggested northwest trends in the vicinity of Charleston may, at least, be an expression of deeper basement complexity in the
)
area, and lends support to a definition of structure responsible j
for the well-defined cluster of seismic activity in the Charleston area-No other structural anomalies of significance are known in this area of the Coastal Plain.
1 Therefore, the unique density of earthquake activity in the Charleston area is considered to be associated with localized 1
structure, the character and extent of which are only grossly suggested at the present time.
In this respect, an earthquake similar to the largest Charleston shock would be expected to recur in the sarue locale, and would not be subject to translation throughout the Atlantic Coastal Plain tectonic province.
2.5-53 4
Giles County, Virginin-(Southern Appsicchien Soismic Zone)
The'Giles' County, Virginia, earthquake of 1897 is possibly
.the largest: shock to have occurred in the southern Appalachian region.
It is liJted (Coffman and. Von Hake, 1973) as Intensity VIII, and occurred in;the Southern Appalachian seismic zone, naar its intersection with the Central Virginia seismic zone
,. ( Bollinger, 1973).
This intersection is marked by a definite break in-the continuity.of the activity of the northeast-trending j
Southern Appalachian zone, and also-corresponds to an' area of 1
'Gpparent Jurassic differentiation of the system of tectonic
-stresses.along~the Appalachians.
However, in the interests of conservatism, the Giles County Levent~will be considered as a random occurrence within the couthern portion of the Fold and Thrust Belt province, whose nsarest approach to the site is approximately 113 km (70 mi).
Based on the discussion in Section 2.5.2.2;5, such an event should not. occur further north than southern Pennsylvania.
Local Site Area Finally, consideration must be given to the likelihood of Intensity VII events which are known to occur within the Piedmont and Coastal _ Plain provinces.
None of these shocks has been assigned to a specific structure within these provinces at this time, and, therefore, these shocks'should be considered as
- rendom events, capable of occurring adjacent to the site.
2.'5.2.4 Maximum Earthquake Potential' A review of the significant earthquakes in the eastern United States, based on the association with tectonic provinces (or, in two cases, discrete structure) discussed herein, results in the following' listing of possible candidates for the maximum design event..The' site intensity listed is based on conservative estimates of attenuation for central and eastern events, as
. presented by Gupta and Nuttli (1975).
2.5-54
]
I Maximum Proximity 1
Candidate Epicentral Epicentral to site Site j
Event Location Intensity (mi) (km)
Intensity Oct. 20, St. Lawrence IX 640 (400)
Less than IV l
1870 River Nov. 15, Cape Ann, VIII 350 (220)
Less than V 1755 Massachusetts I
Aug. 12,
- Attica, VII-VIII 400 (250)
IV 1929 New York Aug. 31, Charleston, X
800 (500)
IV-V 1886 South Carolina (Reported)
May 31, Giles County, VIII 110 (70)
V-VI 1897 Virginia Oct. 9, Wilmington, VII Adjacent VII 1671 Delaware to site From inspection of the list above, it can be concluded that:
(1) the recurrence of major events (Intensity VIII or greater) can be confined to structures or tectonic provinces which occur no closer than 110 km (70 mi) of the Perryman Site; and (2) conservative, empirical, attenuation characteristics would confine the ground motion experienced at the site caused by these major events, to Intensity VI or less.
In the interest of a conservative, deterministic appraisal of the design earthquake for the Perryman Site, the Safe Shutdown Earthquake for the site is specified as an Intensity VII event occurring near the site.
Such an event would supersede the Site Intensity generated by any considerations of greater events as given above, and is preferred because of the apparently random occurrence of Intensity VII events in, or near the boundary of, the Inner Piedmont province.
2.5.2.5 Seismic Wave Transmission Characteristics of the Site The static and dynamic properties of the subsurface materials at the site are presented in Section 2.5.4.
The analyses presented in this referenced section are based on characteristic ground motion and significant frequencies generated by the maximum potential earthquake described above.
2.5.2.6 Safe Shutdown Earthquake (SSE)
As a result of the derivations discussed previously, an SSE of Intensity VII is tne maximum intensity allowed, consistent with tectonic models presented for the site.
2.5-55
RacCnt corrslations b tw ;n int 0noity end pack ground ccceleration have made use of all applicable data currently cvailable, the bulk of which is collected from seismic instrumen-tation in the western United States (Trifunac and Brady, 1975; Trifunac, 1976).
As more of these strong motion data are collected, maximum peak motion values increase.
This is due not only to the expanding sample, but to the increasing coverage of instrumen-totion, which implies that more ground motions are being recorded ct closer epicentral distances wherein near-field phenomena may predominate.
Such studies' indicate that the mean value of peak horizontal cccelerations is approximately 13 percent of gravity for recording cites where Intensity VII damage was sustained.
This mean value io derived from recordings taken on various types of foundation m:dia, from alluvial valley fill to competent hardrock.
Trifunac cnd Brady (1975) also noted that there is no significant difference (considering the scatter) between the peaks of acceleration recorded on different geologic materials.
This would seem to contradict the accepted engineering premise of amplification of vibratory ground motion by less competent foundation media.
However, greater damage on less competent media has been well catablished by historical damage reports from earthquakes, and cppears to empirically confirm the engineering postulation that, from a practical standpoint, peaks of acceleration are not a rollable indicator of damage potential.
By virtue of the dependence of the correlations utilized above on peak ground motions, the relationships are considered conservative, because the level of sustained acceleration signifi-cent to structural design will be of a somewhat lower level.
On the basis of the relationships discussed above, it is recommended that the design acceleration for the Perryman Site be considered ac 15 percent of gravity at foundation level, resulting from the occurrence of the SSE adjacent to the site.
There are no strong motion records of comparable earthquakes rccorded in the eastern United States.
Thus, the spectral characteristics of eastern events must be assumed on the basis of the gross information available.
Events in eastern North America may be interpreted as intraplate events, seismograms of which are impulsive and richer in high frequencies, as opposed to the events at plate margins (Sykes and Sbar, 1973).
The greater high-frequency content and large felt areas of eastern J
svents may be explained by variations in attenuation (Nuttli, 1973), although the presence of in situ compressive stresses cuggests that source parameters may differ for eastern events; that is, stress drops may be higher (Sbar and Sykes, 1973),
i However, the response spectra shown in Figures 2.5-29 and 2.5-30 chould adequately envelope the effective accelerations generated by the SSE at the site, or the recurrence of larger, more distant events, such as the shocks at Charleston, South Carolina, and in I
2.5-56
the St. Lawrence River Valley.
These spectra are developed in compliance with the guidelines set forth in Regulatory Guide 1.60, as revised.
The duration of strong motion would not be expected to exceed 5 seconds (Donovan, 1974; Seed and others, 1975) and, in all probability, would be less.
Duration of motion from a larger, more distant event, such as the Charleston, South Carolina, event of Intensity X, would be relatively longer than that from the design event; however, the low accelerations attributed to long period motion from a distant, large event would be adequately enveloped by the response spectra.
I 2.5.2.7 Operating Basis Earthquake On the basis of the historical seismicity described earlier,
)
wherein a maximum intensity felt at the site from historical earthquakes was no greater than V, an Operating Basis Earthquake
'(OBE) is recommended which would, during the life of the facility, generate a ground acceleration at the site of no higher than 5 percent of gravity.
This level of acceleration should not be exceeded by the recurrence of an Intensity V event adjacent to the site.
For a felt Intensity of V, Trifunac and Brady (1975) show a mean maximum peak horizontal acceleration of approximately i
4 percent of gravity.
l To further quantify the level of risk of the site experiencing an acceleration as large as 5 percent of gravity during its operating life, an engineering seismic risk analysis, utilizing probabilistic techniques, was performed.
Earthquakes of Intensity V or greater within 320 km (200 mi) of the site were used an a data set to assess the risk levels associated with the recurrence of various intensity levels of earthquakes.
For purposes of this investigation, a case utilizing a limiting event greater than Intensity VII was chosen as appropriate for the area.
The results of this analysis are shown graphically on Figure 2.5-31 through 2.5-33.
Figure 2.5-31 shows the return period (defined as the time interval during which one earthquake occurrence is expected) for various intensity levels-Figure 2.5-32 shows the risk level (which is defined as the probability of at least one earthquake occurring during a 50-year life expectancy of the structure) for various levels of intensity.
Figure 2.5-33 identifies the corresponding risk level for various return periods chosen for design purposes.
To illustrate the application of these figures to design decisions in the case of the proposed plant facility, two examples are addressed:
(1) an operating basis earthquake (OBE) is chosen through deterministic evaluation, and then the risk of that event occurring is identified; and (2) an appropriate risk level is chosen by the owner to represent a reasonable liability against damage by the occurrence of an earthquako; and then, from the risk level, a design earthquake may be identified.
2.5-57
y Example 12 As discusOcd Carlior, cn Carthqunko of Intensity V was conservatively identified as the maximum event which might be expected'to be felt at the site during the operating life of
'the facility. _This value was chosen by assessing the greatest felt intensity.at the site resulting from historical seismicity.
Utilizing Figure 2.5-32, it can be seen that for an Intensity V chock, there is a 26 percent chance-that, during a 50-year dasign life, the facility will experience the maximum expected ceceleration from this intensity of approximately 4 percent of gravity, based on the mean value of Trifunac and Brady (1975).
Example 2:
In the event that the project was to be assigned a 20 percent risk level as representing a reasonable liability of loss or damage due to' earthquake occurrence, one can find the cppropriate design earthquake by using Figures 2.5-31 and 2.5-33.
Should the level of 20 percent risk in a 50-year design life be identified, one can use Figure 2.5-33 to find the corresponding dcsign return period in years - in this ca'se, about 200 years.
Transposing this number to Figure 2.5-31, one finds that the design earthquake having a return period of 200 years at 20 parcent risk would be a low Intensity V.
On the basis of the observations above, the OBE is considered to be an adequate representation of maximum ground acceleration expected at the facility during its operating life.
Horizontal and vertical response spectra for this OBE acceleration level are shown in Figures 2.5-34 and 2.5-35.
i 1
t 2.5-58
m 2.5.3 Surface Faulting A detailed analysis of the geologic investigation to determine surface faulting in the site vicinity is given in Section 2.5.1.4.
No. surface faulting at the site has been determined to date.
Surface faults occurring within 8 km (5 mi) of the site are believed to be Paleozoic, Mesozoic, or possibly Tertiary in age.
2.5.3.1 Geologic Conditions of the Site The lithologic, stratigraphic, and structural geologic conditions of the site and surrounding area are detailed in Section 2.5.1.4 and summarized in Section 2.5.2.2.
2.5.3.2 Evidence of Fault Offset Geologic field investigations'have been carried out to determine evidence for fault offset at or near the ground surface in the site area.
Current information is discussed in detail in Section 2.5.1.4.
No evidence for the existence of capable faults has been revealed at this time.
2.5.3.3 Earthquakes Associated with Capable Faults No reported earthquakes exist within 8 km (5 mi) of the site that can be satisfactorily correlated with faults.
2.5.3.4 Investigations of Capable Faults.
Investigations of faulting near the site have not determined that-capable faulting exists within 8 km (5 mi) of the site.
2.5.3.5 Correlation of Epicenters with Capable Faults No capable faults have been identified in the site area or region surrounding the site.
2.5.3.6 Description of Capable Faults No capable faulting has been identified in the area.
2.5.3.7 Zone Requiring Detailed Faulting Investigation No zone requiring detailed faulting investigation, as specified in Appendix A to 10 CFR, Part 100, has been identified.
2.5.3.8 Results of Faulting Investigation Detailed results of fault investigations are discussed in Section 2.5.1.
I 2.5-59
L' 2.5.4 Stability of Subsurface Materials and Foundations This section presents an evaluation of site conditions and y
geologic features at the Perryman Site that may affect nuclear powerplant. structures or their foundations.
Information has b:en provided that defines the conditions and engineering proper-ties of both the soil and rock supporting the powerplant founda-tions.
The stability of the soils underlying the plant has been ovaluated for both static and dynamic loading conditions, including en evaluation'of the ability of these materials to support the foundations of all Category I structures without incurring oither a loss of stability or excessive subsidence, The Perryman Site has been investigated through a three-phase program, the first two phases of which were performed in 1972, and the third phase was completed during August and September of 1976.
Phases I and II were not performed under a formally organized Quality Assurance Program.
The Phase III investigation was completed under a Quality Assurance Program consistent with the requirements of American National Standards Institute (ANSI)
N45.2, Quality Assurance Criteria for Nuclear Power Plants.
The Phase I field investigation consisted of:
(1) a geologic rcconnaissance of the site and environs; (2) the drilling of 21 borings; (3) the installation of five piezometers; and (4) the parformance of geophysical studies.
Phase I borings were widely spaced over the site and included deep rock coring and offshore drilling in the Bush River.
The geophysical explorations consis-ted of refraction, up-hole velocity, down-hole shear wave, and cmbient ground motion surveys.
The Phase II field investigations consisted of:
(1) the drilling of 45 disturbed soil sample borings; (2) the drilling of 25 undisturbed soil sample borings; (3) the drilling of 21 bulk sample borings; (4) the installation of six piezometers; cnd (5) the performance of a cross-hole geophysical survey.
Phase II borings were drilled for the foundation investigation of the powerplant structures that were planned at that time.
The Phase III field investigations consisted of:
(1) the drilling of 24 borings which included both disturbed and rela-tively undisturbed sampling and rock coring; (2) the installation of eight piezometers; (3) in situ permeability testing in boring holes; (4) the performance of a seismic reflection survey; and (5) a ground magnetometer reconnaissance.
Phase III borings ware drilled at or near the proposed locations of plant structures for the purpose af investigating the soil and rock conditions that would potentially affect foundation performance.
2.5-60
i j
2.5.4.1 Geologic Features I
The geologic character of the site is discussed in detail in Section 2.5.1.4.
Major geologic features at the site are briefly summarized here.
The site is underlain by approximately 122 m (400 ft) of laterally discontinous beds of poorly-consolidated clay, silt, quartzose sand, and gravel, which have been deposited upon a j
basement of complexly-structured, metamorphic and igneous rocks.
The contact between the sediments and the crystalline rocks, slopes eastward from the surface about 4.8 to 6.4 km (3 to 4 mi) north of the site, to thousands of feet under the Delmarva Peninsula (Figure 2.5-5).
The structure of the basement is known from regional considerations to be complex and at least one fault zone is known to exist under the site, in the vicinity of Boring 310.
Three others have been interpreted from the results of seismic surveys at the site.
Two of these may affect the overlying sedimentary materials (Section 2.5.1.4.3).
Beds within the Potomac Group, of Cretaceous age, which directly overlies the basement, are similar in lithology and stratigraphic geometry to beds of the same formation exposed at the surface in the area within a few miles of the site.
At several localities in sand quarries, these beds were observed to have a very laterally discontinous character.
Lithofacies changes are extremely abrupt within the group and correlation of depositional or other stratigraphic units on the basis of lithology is therefore very difficult.
At many of the same localities, faults, joints, and other deformational structures were noted in beds of the Potomac Group (Section 2.5.3.3).
These fehtures are believed to be due directly to penecontemporaneous sedimentary phenomena such as slumping, gravity sliding, differential compac-tion, and excess pore-fluid pressure effects, rather than to tectonic causes.
However, the proximity of these localities suggests that similar structures may be present in the Potomac Group at the site as well.
Approximately half of the site is overlain at the surface by silt and sandy gravel beds of the Talbot Formation, of Pleistocene age.
This unit thickens from a feather edge trending generally N-S through the middle of the site to more 15 m (50 ft) in the southeast corner of the site. Contour lines drawn on the base of this formation (Figure 2.5-27) show that it is largely a result of deposition from a stream system which flowed across the site during Pleistocene time; therefore, its geometry may be expected to be linearly continous on a local scale.
No evidence of deformational structures within the Talbot Formation was observed during this investigation.
2.5-61
2.5.4.2 Properties of Subsurface. Materials 2.5.4.2.1 Laboratory soil. Testing 2.5.4.2.1.1 -Introduction Numerous: tests were performed on selected samples of sub-surface materials in-order to' evaluate the pertinent physical properties.
The laboratory testing of soil samples.from the Phase I investigation' included particle size analyses, Atterberg-limits tests, and moisture content measurements.
This testing was performed'by Dames & Moore at their Cranford, New Jersey, icboratory.
The results of these tests are included in summary form in Table 2.5-4 and 2.5-5.
During the Phase II investigation, all icboratory' soil tasting, except the cyclic triaxial compre.ssion testing, was done by Green Associates, Inc. in their soils and materials leboratory in Towson, Maryland.
The cyclic triaxial compression testing on reconstituted samples was carried out by Geo-Testing, Inc. of San Rafael, California, under a testing program developed by the Bechtel Corporation.
The-Phase II static soil test results are summarized in Tables 2.5-4 through 2.5-9.
Consoli-dation curves from this phase of the laboratory testing appear in Appendix 2.5.H.
The' Phase III investigation included additional laboratory testing to evaluate static and dynamic properties of the sub-surface materials.
The majority of tests were performed at the i
Dames & Moore laboratory at Cranford, New Jersey.
The constant rete of strain consolidation (CRSC) tests were performed at Ardaman & Associates, Inc., in Orlando, Florida.
The organic content tests were performed at Haller Laboratories in Plainfield, New Jersey.
Cation exchange and X-ray diffraction tests were parformed at Rutgers University, Department of Soil.s and Crops.
The details of all laboratory testing procedures are presented in Appendix 2.5.H.
The results of some laboratory tests are presented on the Logs of Borings.
The information presented on the logs include Atterberg limits, dry density and moisture content, and shear strength test results, which indicate the type'of test run, confining pressure used, and shearing strength.
All other test data are presented separately in the form of tables or figures, as appropriate.
2.5.4.2.1.2 Identification-Classification Tests Particle Size Distribution During Phase I, particle size tests were performed on esveral soil samples for identification and classification purposes.
2.5-62 l
During Phase II, particle size tests of site soils were made on representative samples for classification purposes.
Numerous particle size tests were run on samples from the upper sands and gravels for permeability and liquefaction potential evaluations.
During Phase III, sieve tests were performed for classifi-cation and correlation purposes, largely on samples that also.
underwent strength testing.
The results of these tests are presented on Table 2.5-5.
Moisture Content and Dry Density Moisture content and dry density measurements were performed on' samples from all three phases of investigation.
These data are principally used for purposes of correlation of strength and consolidation test results.
Phase I testing included moisture content tests on samples taken with the Dames & Moore type U sampler.
The moisture content values are listed in Table 2.5-4.
In Phase II, moisture content and dry density tests were made for nearly all undisturbed samples.
For 10 borings, moisture content tests were run on all split-spoon samples that had sufficient recoveries of the hard bearing-stratum soils.
Repre-sentative soil types from other borings and all plasticity test samples were tested for natural moisture content.
Additional nylsture content and dry density tests were performed on many of the undisturbed samples recovered in the Phase III investigation.
These moisture content and dry density data are presented on the Logs of Borings and appear on Table 2.5-4.
Atterberg Limits Plasticity characteristics of representative clay and silt samples were measured in each phase by performing Atterberg limits tests.
These tests were performed to identify and classify the onsite soils.
The Plasticity Index (PI) of a soil is repre-sentative of its plasticity, and is defined as the difference between the Liquid Limit (LL) and the Plastic Limit (PL).
The LLs and PIs from the Phase III investigation are presented on the Logs of Borings.
A summary of all-Atterberg limits test data is presented on Table 2.5-4, and shown graphically in Figure 2.5.H-2.
Specific Gravity Specific gravity tests were made on all soil samples that were subjected to triaxial compression and consolidation tests, as well as on other representative samples of the onsite soils.
The test results are presented on Table 2.5-4.
2.5-63
I i
i C^mpaction In Phase II, representative bulk samples from the proposed Cxcavation areas were tested to evaluate the soil compaction chnracteristics for possible use as earthfill material.
Standard cnd Modified Proctor compaction tests were performed in accordance with American Society for Testing and Materials (ASTM) Standards D698-71 and D1557-70, Method C, respectively.
These tests are cummarized on Table 2.5-6 and on Figure 2.5.H-3.
Organic Content A thin, slightly organic soil layer was encountered at a d:pth of approximately 30 m (100 ft) in some borings.
During the Phase II investigation, samples of this and other layers within the site and along the Bush River shoreline that appeared to be organic were tested to determine the. percentage by weight of organic matter.
Two additional samples were tested as part of the Phase III work.
The results of the organic content tosting are presented on Table 2.5-7.
X-Ray Diffraction Representative clay samples were examined by X-ray diffrac-tion methods to identify the minerals in the soil.
The tests ware performed at the Georgia Institute of Technology, School of Geophysical Sciences during Phase I, and at Johns Hopkins Univer-city during Phase II.
As part of the Phase III program, samples of cohesive soils were selected for X-ray diffraction analyses cnd examination by electron microscope techniques at Rutgers University, under the direction of Dr. L. Douglas.
The results of all tests are presented on Table 2.4.A-13.
2.5.4.2.1.3 Static Strength Tests Unconfined Compression During the Phase II program, unconfined compression tests ware performed on cohesive soil samples obtained from zones above and below the foundation level of the various plant struc-tures.
Results of these tests are summarized with the triaxial t st data on Table 2.5-8.
Triaxial Compression Triaxial compression tests were performed as part of the Phase II and Phase III programs, on representative undisturbed cnd recompacted samples to measure the soil strength parameters for une in stability calculations.
Tests were made at different confining pressures to develop the Mohr strength envelopes.
The Mohr's circles, however, are not included in this report, although the data are presented on Table 2.5-8.
2.5-64
P I
4 Unconsolidated-undrained (UU) triaxial compression tests
{
were performed on several different cylindrical soil specimens.
1 Each specimen was loaded by an all-around confining pressure and axial load, so rapidly that no water could drain from the specimen.
This procedure simulates rapid loading of the soil with no drainage in its existing state of stress.
Isotropically consolidated-undrained (CU), triaxial compres-sion tests were made on undisturbed and recompacted samples to construct the consolidated Mohr strength envelopes.
In the CU triaxial test procedure, soil specimens were loaded to different confining pressures and allowed to consolidate.
Then, each specimen was sheared rapidly by increasing the axial load while permitting no water drainage.
Pore water pressure measurements were made during some CU triaxial compression tests to permit the evaluation of the drained Mohr strength envelopes.
Isotropically consolidated-drained (CD), triaxial compression tests were performed on the sandy soils to determine the drained Mohr strength envelopes.
In the CD triaxial compression test, soil specimens were loaded both laterally and axially, and allowed to consolidate.
Several different confining pressures were imposed.
Each specimen was then sheared slowly, allowing drainage to occur so that no pore water pressure developed.
For all triaxial shear tests, the magnitudes of the confining pressures were chosen to simulate the anticipated field conditions.
All soil specimens were loaded at a constant rate of axial deflection, and the resulting stresses were recorded.
Plots of major principal stress versus strain and pore pressure versus strain were made, and the principal stresses for each specimen were plotted as Mohr's circles.
The effective cohesion, total cohesion, and angle of internal friction values for each sample were evaluated from Mohr's circle plots of selected strain-dependent stress.
Sections 2.5.4.2.3, Description of Principal
{
Soil Layers, and 2.5.4.10.3, Bearing Capacity: Category I Struc-tures and Turbine Generator Buildings, contain further discussions of strength parameters used in the analyses.
2.5.4.2.1.4 Dynamic Testing During the Phase II investigation, triaxial compression tests, incorporating cyclic, dynamic loading under controlled stress conditions, were performed on saturated test specimens of 1
the remolded upper sands and gravels.
These tests are now I
considered to be inappropriate for evaluation of the liquefaction potential of in situ soils.
Therefore, the results of these tests are not presented in this report nor were they used in the analysis of liquefaction potential that is presented herein.
As part of the Phase III program, a total of 16 stress-controlled, cyclic-triaxial tests were performed on relatively 2.5-65 l
undisturbed samples.
Reasonably homogeneous specimens of poten-tially liquefiable, cohesionless samples were chosen for testing.
Samples that appeared to have baen subjected to disturbance during field investigation, transportation from the field, or handling in the laboratory were rejected.
ASTM specifications were followed whenever available and cpplicable; otherwise, the procedures and specifications that cre detailed in the Soils Laboratory Manual of Technical Practice prepared by Dames & Moore (1975c) were used.
Test specimens were saturated with back pressure and consolidated isotropically to an effective pressure that is approximately equal to_the cstimated in situ overburden pressure.
The samples were then cubjected to failure under cyclic loading.
A prespecified deviator stress was used in each test.
Details of the procedures for specimen selection and preparation are presented in Appendix 2.5.H.
2.5.4.2.1.5 Oedometer Tests Step-Loaded Consolidation During the Phase II and Phase III investigations, conventional step-loaded consolidation tests were performed on undicturbed camples from bearing strata and near-surface silts and clays.
The tests were completed in accordance with ASTM Standard D2435-70 (ASTM, 1975).
In the Phase II work, these data are presented in the form
)
of void ratio versus log-effective stress plots, Figures 2.5.H-Sa through 2.5.H-5j.
The results of the deflection versus log-time plots have been summarized on Table 2.5.H-1.
For the Phase III program, the results are presented in the form of strain versus log-effective stress plots, together with deflection versus log-time plots for selected (usually alternate) loads.
Constant Rate of Strain Consolidation Two tests were performed at a constant rate of strain at Ardaman & Associates, Inc. under the direction of Dr. A. Wissa, in Orlando, Florida in accordance with procedures established by Wissa (and others, 1971).
Constant rate of strain consolidation (CRSC) tests generally provide a better definition of the maximum past pressure (the greatest pressure experienced by the deposit j
in its geologic past) and a more complete examination of the coefficient of consolidation, c.
As a result of the high degree of overconsolidation of Ehe samples from the 3erryman 1
(kN)/m (100,000 Site'2)oading the samples to 4790 kilonewtons lb/ft did not firmly establish the virgin portion of the i
consolidation curve.
The results of the CRSC tests appear in Appendix 2.5.H.
l 2.5-66 i
I L
s.
.j '
Constrained Modulus
.During.the PhasefIII. investigation, tests were performed, iusing a conventional oedometer, on_ undisturbed soil samples to L evaluate.the constrained modulus. (D)l of - the soil.
Each sample was verticallytloaded to a confining pressure equal to its estimated in situ overburden pressure, land then unloaded and-reloaded'several times while deflection measurements were recorded.
The constrained modulus was calculated from the'resulting stress-strain plot of test data and used to evaluate the elastic settle-ment within sandy. soils.
The test results are presented in
, Figures 2. 5.H-7a' and 2. 5.H-7b.. Moduli are listed on. Table 2.5-9.
' Modulus of Elasticity The static modulus of elasticity (E) of the bearing stratum soils was evaluated,.in accordance with the procedure discussed by Wilson-and~Dietrich (1960) during the Phase II program.
Each undisturbed = specimen was loaded laterally andivertically'to a confiningLpressure equal to.its existing overburden pressure and
' allowed to' consolidate.
Then, each specimen was loaded axially to approximately'70'to 90 percent of the peak failure load.
This. cycle was repeated several times, while load'and deflection measurements were made,Luntil.a constant slope was obtained for the. stress versus strain plot..Then,.the specimen was loaded to failure.. The moduli are. presented on. Table 2.5-9.
I 12;5.4.2.1.6 Other Tests-Permeability
- Falling-head and constant-head, laboratory permeability
- tests were. performed 1on' selected undisturbed soil samples.
Coefficients of permeability were calculated from the test data.
All test results are shown on Table 2.4.A-10.
' Ion Exchange-Cation exchange capacity and exchangeable ion tests were performed, under the direction of Dr.
D.K. Markus of Rutgers University, on' selected Pitcher tube samples and Dames & Moore type U samples of both cohesive and'cohesionless soils.
These tests were performed as part of the accidental spill analysis.
The-test results'are' presented on Table 2.4.A-12.
4 2.5.4.2.2 ' Description.of Generalized Profile I
For purposes of assessing the suitability of the Perryman Site-for nuclear powerplant construction, a generalized profile of subsurface materials has been developed.
This profile consists of five idealized soil strata (Layers A through E), highly 2.5-67 j
j I
.y t wrashered rock /(saprol'ite)", and jrelatively hard' rock.
AJvariation g
TofJmaterialiproperties exists [withinLeach layer.: For some of 1the1 engineering analysesLpresented in:this_ report, a1slightly
.eltered0 soil profile was assumed <thatEincluded the same principal; Icyers,tbut.with different'dir.ansions'as to' vertical.or-lateral'
" extent.. 'In-these instances', the1 modified profile presents; faither a:more: representative' condition:for;the'particular structure
-under considerationbor?a:more conservative representation of cite / conditions lthan'does?the generalized profile.
Five. cross scsctions;(Figures 2.5-38a through 2.5-42)- have been prepared'
- which illustrateLthelrelationshipLof theffoundations of seismic,
~ Category IEfoundations'tosthefsubsurface materials.
The~ locations of1these-sections'are shown in Figures-2. 5-36,: 2. 5-37a, ;and 2.5-37bi Layer?A consists of Pleistocene. deposits.of brown.and grayish-brown, stiff,-clayey' silt-and silty. clay, with occasional
.lsnses of finedsand.
This layer'blanketsithe site and; varies in thickness from 1 ~ to 8 m (3:.to 26 f t).
Layer'B underlies' Layer A,.and consists of Pleistocene 1 fine and fine-to-coarse. sands,-
and~ fine-to-coarsefgravels'with varying' percentages'of' silt.
!:Some' local pockets and/or lenses.of stiff clayey silt were also noted.
Layer;B varies in thickness from 5'to 14 m (17'to 45 f t), and extends to an elevation.of -8. 5 m ~ (-28 f t) infthe' 1powerplant= area..In the western portion of the~ site, along the
. Bush River,vthe Layer B' sands iand: gravels seem to be nearly replaced by' brown, very stiff-to-hard, micaceous silty clay.
This condition is somewhat typified by Log of Borings 316B, 239,
- 233,; and; 236.-
No Category I structures will be founded on oitherLLayer Afor Layer B soils.
However, some portions ~~of the oLayer A(soils may be used'as compacted fill'to' raise the general
' plant; grade,---and some' Layer B soils may be selected for-the
- CategoryLI' compacted fill, immediately below the foundation mat.
of the Category.I structures.
Layers C and C', of Cretaceous age, underlie L'ayer B and consist of interbedded fractions'of dense-to-very dense sands (and hard silty clays, respectively..
The relationship'between these two:sublayers is represented by subsurface cross sections A-A'1and~B-B' (Figures 2'.5-38a through 2.5-39b) between approxi-mmte elevations -5 and -15 m '(-20 and -50 f t). 'The sands of i
Layer 1Clare. generally fine to medium in gradation, with a trace 4
/
to'~a little silt.
Layers C.and C' extend as deep as elevation -
28 m (-90 f t) in the' vicinity of the powerplant, as indicated by
~
Logs of Borings 222 and 105.
.Because.the proposed Category I fill will be founded at elevation -9.8 m (-38 ft), Layer C and
.C.'
will be'theLnatural deposits which will directly' underlie the JCategory:I fill.
Layer D is,a Cretaceous deposit, which underlies Layers C
.and'C', consisting of'hard.to.very hard red, gray, and brown L
clayey'siltLand silty clay, with_a little fine sand.
Layer D
-2.5-68 f,_
r i
varico in thickness from 3 to 21 m (10 to 70 ft) in the vicinity of the powerplant structures.
Some portions of this layer contain relatively small amounts of organic matter, including black, carbonaceous fragments (Table 2.5-7).
Layer E underlies Layer D and consists of Cretaceous sedi-ments of very dense, red and brown, silty fine and fine-to-medium sands.
This layer varies in thickness from approximately 12 to 23 m (40 to 75 ft) in the vicinity of the powerplant J
structures.
The remainder of the underlying soils consists of alternating I
strata of very hard clays and very dense silts and sands of the Cretaceous age.
These soils extend to approximate elevation -92 m
(-300 ft), where residual soils are encountered.
This weathered rock (saprolite) is of Precambrian and/or Paleozoic age, and generally overlies the parent bedrock.
Within the vicinity of the powerplant structures, the thickness of the saprolite ranges j
from 4 to 15 m (14 to 50 ft).
Bedrock is initially encountered I
at elevations varying from -99 to -106 m (-324 to -347 f t).
A detailed description of the bedrock is provided in Section 2.5.1.4.2.
Detailed discussions of the physical properties of each layer as these properties relate to foundation performance are provided in the paragraphs that follow.
2.5.4.2.3 Description of Principal Soil Layers This section presents detailed descriptions of the physical properties of each of the five idealized soil strata (Layers A through E).
In addition to the vertical and horizontal extents i
of each stratum, index, strength, consolidation, and compres-sibility properties are described as they relate to foundation construction and performance.
The details of the field and laboratory tests that measured these physical properties are included in Appendix 2.5.G and 2.5.H.
The subsurface cross sectionu, Figures 2.5-38a through 2.5-41b illustrate the relation-ship of the five idealized layers to the proposed Category I foundations.
The locations of these cross sections, with respect to the proposed structures, are shown in Figures 2.5-36, 2.5-37a, and 2.5-37b.
More detailed subsurface information is provided in the Logs of Borings in Appendix 2.5.G.
Layer A Layer A consists of Pleistocene deposits of brown and grayish-brown, stiff clayey silt and silty clay, with occasional lenses of fine sand.
This layer blankets the site and varies in thickness from 1 to 8 m (3 to 26 ft).
Figure 2.5.H-la presents a graphic illustration of Layer A in the form of a band width on the particle size graph.
The amount of sand, by weight, that is typically found in a Layer A sample is approximately 25 percent.
2.5-69
P rticle size indices are summarized on Table 2.5-5.
The i
rcsults of Atterberg limits tests, plotted on the plasticity chart in Figure 2.5.H-2, indicate that the fine-grained soils of Layer A are predominantly inorganic silts and clays of low to medium plasticity.
These results may be interpreted as further indicating that the inherent swelling capacity of the clays is low to medium (Terzaghi, 1967).
This characteristic subsequently implies that the soils may be suitable for use as compacted fill.
The moisture contents of the soils of Layer A at the time of the Phase III investigation commonly ranged from approximately 15 to 25 percent and averaged approximately 20 percent.
A cummary of the index properties of the soil is presented on Trble 2.5-4.
The shear strength of the soil in Layer A was evaluated in the laboratory by performing triaxial compression tests.
Table 2.5-8 presents a summary of these tests, which include yield, paak, ultimate, and residual shear strengths obtained from d;viator stress versus axial strain plots.
Section 2.5.4.10.3, B aring Capacity: Category I Structures and Turbine Generator Buildings, describes the strength parameters, & and c, which w:re utilized in the analyses.
These strength parameters were ovaluated using Mohr's circle stress diagrams that were plotted for selected strength data from Table 2.5-8.
The strength data colected were the most meaningful to the particular analysis.
For Layer A soils, yield strengths that occurred at relatively low strain levels and ultimate strengths at high strain were of principal concern.
In addition-to laboratory tests, field utandard penetration tests were utilized as a guide to evaluate the approximate shear strength of the scil (Meyerhof, 1956).
Standard penetration test blow counts are presented on the Logs of Borings (Figures 2. 5.G-5 through 2. 5.G-95), and on the cubsurface cross sections (Figures 2. 5-38a through 2.5-42).
Average standard penetration test blow counts in Layer A ranged from approximately 15 to 30 blows per foot.
A comparison of laboratory strength test results with field atandard penetration test results yields a fairly good correlation bstween undrained shear strength and blow counts.
However, a considerable amount of scatter or variation in data exists, b:cause these soils are heterogeneous.
Generally, the correlation of standard penetration test resistance with the undrained shear etrength of cohesive soils is less reliable than the correlation of standard penetration test resistance with the relative density of cohesionless soils.
The consolidation characteristics of the Layer A soil were m:asured with conventional, laboratory, step-loaded oedometer tosts.
A swnmary of the deflection versus logarithm of time curves is presented on Table 2.5.H-1, and the strain, or void-rctio versus logarithm of pressure plots are presented in Figures 2.5-70
The test results indicate that Layer A-soils are overconsolidated and will.likely be suitable for support of foundations of some of the non-Category I structures.
l The soils of Layer A may be'used as compacted fill to raise
-the general plant grade to elevation +10.7 m (+35 ft).
As a result, some non-Category I structures and other facilities, such as service roads, access roads, and parking areas, may be founded on this fill in the vicinity of the major plant structures.
Elsewhere, structures may be founded on undisturbed Layer A soils,at the site. :The results of compaction tests that were performed according.to the ASTM D-1557-70C standard test designa-tion are shown in Figure 2.5.H-3.
The compaction tests that were performed according to both ASTM D-1557-70C and ASTM D-698-71C are smnmarized on Table 2.5-6.
The physical properties of laboratory-compacted samples of Layer A soils are discussed in Section 2.5.4.5.4, Description of Fill. Properties.
Layer B Layer B underlies Layer A and consists of Pleistocene deposits of medium dense to dense, brown, fine-to-coarse sands and fine-to-coarse gravels, with varying percentages of silt.
Local pockets and/or lenses of stiff clayey silt were also noted.
In the powerplant area, Layer B varies in thickness from 5 to 14 m (17 to 45 f t), and extends to elevation -8.5 m (-28 ft).
In the western portion of the site, along the Bush River, the Layer B sands and gravels are nearly replaced by brown, very stiff-to-hard, micaceous silty clay. Logs of Borings 316B, 239, 233, and 236 are examples of this condition.
The gradation range of Layer B soil is shown in Figure 2.5.H-la.
The coarser portions of Layer B consist of 50 percent gravel, 40 percent sand, and 10 percent silt.
Typical percentages of gravel, sand, and silt in the remaining soils ar,e 25, 65, and 10 percent, respectively.
Particle size indices are summarized on Table 2.5-5.
The dry densities of samples taken from 76 mm3 (95 (3-in) diameger tubes were measured to be 1520 to 17j0 kg/m and averaged approximately 1600 kg/m (100 to llg)lb/f t ), Table 2.5-4 summarizes the index properties of the lb/ft soil.
The shear strength of Layer B soils was measured by triaxial compression tests on relatively undisturbed samples.
Most of the samples tested contained only fine gravel, rather than fine and coarse gravel, because most samples with large gravel were judged unsuitable for testing.
Table 2.5-8 summarizes those triaxial compression tests.
Section 2.5.4.10.3, which presents the bearing capacity analyses, also describes the strength parameters, & and c, that were evaluated from these test results.
Generally, two sets of values were chosen:
yield strengths, which occur at low strain, and ultimate strengths, which occur at much higher strain levels.
I 2.5-71
o Standard penetration test resistances in Layer B range from cpproximately.20 to 50 blows per foot.
Gravelly soils generally cxhibit higher blow counts than soils without gravel that have cimilar strength and density.
Correlations developed in order to relate standard penetration test resistance to relative d:nsity are not generally applicable to gravelly soils because these relationships (Gibbs and Holtz, 1957) were developed from t sts.on fine sandy soils only.
However, by correlating blow counts from standard penetration tests that were performed at different locations with relative densities, the minimum relative d nsity of sandy soils in Layer B is estimated to be on the order of from 70 to 75 percent.
The actual liquefaction potential 10 addressed in Section 2.5.4.8.
The soils of Layer B will be cxcavated in the vicinity of the major Category I plant structures.
Portions of this material may be used as the compacted fill which will support the Category I mat foundations.
Other portions of the Layer B soils may be used as non-Category I b ckfill around the major plant structures.
The results of compaction tests (ASTM D-1557-70C and ASTM D-698-71C) are cummarized on Table 2.5-6.
Figure 2.5.H-3 presents the compaction curves from the ASTM D-1557-70C tests.
To evaluate the shear atrength of the structural fill, triaxial compression tests were parformed on laboratory-compacted samples of Layer B.
A summary of the results of these tests is presented on Table 2.5-8.
S3ction 2.5.4.5.4, Description of Fill Properties, discusses the physical properties of the soil that are indicated by these tests.
LSyers C and C'
)
Layers C and C',
of Cretaceous age, underlie Layer B and consist of fractions of brown, dense-to-very dense fine to m:dium sands and red and brown hard silty clays.
These two lnyers compose the uppermost region of the bearing strstum.
The Category I structures will be founded on structural, fill placed directly upon these bearing strata.
In the vicinity of the powerplant, the combined thickness of Layers C and c' ranges b3 tween 7.6 and 21 m (25 and 70 ft).
These layers extend as deep as elevation -29 m (-95 ft), as indicated by Logs of Borings 222 and 105.
Beneath powerplant Unit 2, the portions of Layer C'
remaining after excavation to elevation -9.8 m (-32 ft) will b3 as thick as approximately 7.9 m (26 ft).
The greater thickness of this clay layer underlies the northern portion of Unit 2 (see cubsurface cross sections B-B' and C-C').
These characteristics hnve been incorporated in the appropriate settlement analyses.
Particle size tests indicate that Layer C typically consists of 1
90 percent fine sand, with approximately 10 percent of the soil j
pnssing through the number-200 standard sieve.
Layer C' is a l
silty clay, containing approximately 10 percent sand.
The l
pnrticle size bands for both sublayers are shown in Figures 4
2.5.H-la and 2.5.H-lb.
The particle size indices of Layer C and l
C' are summarized in Table 2.5-5.
The results of Atterberg l
I 2.5-72 O
c i
r.
limits tests, plotted on the plasticity. chart, (Figure 2.5.H-2),
)
indicate that Layer C' is predominantly comprised of inorganic clays of low to medium plasticity.
A comparison of the natural moisture content with the liquid limits of samples from Layer C' implies that this silty clay has a relatively low sensitivity I
(Leonards, 1962).
Relationships of liquidity index with effective consolidation stress (Department of the Navy, 1971) also tend to support this conclusion.
Results of X-ray diffraction analyses show these clays primarily consist of the non-expanding clay i
minerals, kaolinite and illite (see Table 2.4.A-13).
The moisture contents of Layer C' range from about 15 to 25 percent and average about 20 percegt.- Dry densities 3)f Layer C range from about 1520 tg 1760 kg/m 3(95 to 110 lb/ft and j
average about.1600 kg/m (100 lb/ft ).-
A summary of the index properties of Layers C and C' is presented in Table 2.5-4.
Triaxial compression tests were performed to measure the shear strength of soil samples from Layers C and C'.
Table 2.5-8 summarizes ~these tests.
In the analyses described in Section 2.5.4.10.3, Bearing Capacity: Category I Structures and Turbine Generator Buildings, the strength parameters, (o and c), were evaluated at relatively low strain levels, generally employing peak strengths for Layer C soils and. yield strengths for Layer C' soils.
At higher strain levels, residual strengths for Layer C soils and ultimate strengths for Layer C' soils were used to develop the parameters.
Field standard penetration test blow counts were used as a point of comparison in evaluating some of the laboratory shear strength data of Layer C'.
Standard penetration resistance was also used as an approximate indicator of the in situ relative density of Layer C.
Standard penetration test blow counts are presented on the Logs of Borings (Figures 2.5.G-5 to 2.5.H-95) and the subsurface cross sections (Figures 2.5-38a,to 2.5-42).
Average standard penetration test blow counts in Layer C' vary from 30 to 70_ blows per foot.
In layer C, standard penetration test blow counts generally exceed 100 blows per foot, which implies relative densities in the neighborhood of 100 percent.
Layer C' consists of soils that are predominantly fine-grained and cohesive in nature and are generally considered nonliquefiable.
A detailed discussion of the liquefaction potential of these soils is presented in Section 2.5.4.8.
Consolidation character-istics of Layer C' were measured with laboratcry step-loaded oedometer tests.
Deflection versus logarithm of time curves are summarized in Table 2.5.H-1 and strain or void ratio versus
-logarithm of pressure p. lots are presented in Appendix 2.5.H.
Constrained modulus tests were performed on samples from Layer C to provide moduli for use in estimates of elastic settlement.
Constrained modulus test curves are presented in Figures 2.5.H-7a and 2.5.H-7b; moduli are listed on Table 2.5-9.
2.5-73
Layar D Layer D is a Cretaceous deposit that underlies Layers C and C' and consists of interbedded red, gray, and brown, hard-to-very hard clayey silts and silty clays, with a little fine sand.
In the vicinity of the powerplant structures, these soils vary in thickness from 3 to 27 m (10 to 90 f t), and extend as deep as clevation -4 3 m (-140 f t).
Occasionally, dark grty, hard, organic, silty clay, with carbonaceous material, was discovered near the bottom of Layer D, as shown in subsurface cross section D-D'.
The results of At' 5 erg limits tests, plotted on the plasticity chart in Figure 2.5.H-2, indicate that Layer D is comprised predominantly of inorganic silty clays and clayey oilts of low to medium plasticity.
X-ray diffraction tests (Table 2.4.A-13) indicate that the clay minerals kaolinite and illite make up 90 percent or more of the clay fraction in those camples tested.
Organic content test results, displayed in
)
Tcble 2.5-7, indicate that a few samples have significant
{
organic content, while most samples tested showed less than 10 parcent organic material.
Consolidation and strength tests show j
that these organic soils will behave as well as other Layer D coils with regard to foundation stability or settlement.
The I
moisture contents range from approximately 15 to 22 percent, with the average at approximately 17 percent.
The index proper-ties of Layer D are summarized in Table 2.5-4.
Triaxial compression test strength data for Layer D soils are presented on Table 2.5-8.
For the bearing capacity analyses, Saction 2.5.4.10.3, a relatively conservative soil strength (occurring at low strain) was selected for Layer D.
Field 4
ctandard ranrt. ration test resistance generally exceeds 100 blows per foot.
- minimum observed standard penetration test resistance w.c.hin the organic zone was 69 blows per foot.
Step-loaded oedometer and constant rate of strain consolida-tion tests show that Layer D soils are overconsolidated, with an overconsolidation ratio in excess of 2.
The results of these tests are presented in Appendix 2.5.H.
The modulus of elasticity wns measured in laboratory tests on samples from Layer D.
Table 2.5-9 lists these moduli.
Layer E Layer E underlies Layer D, and consists of Cretaceous cediments of red and brown, very dense, silty, fine and fine-to-i medium sands.
This layer varies in thickness from approximately 12 to 30 m (40 to 100 ft) and extends as deep as elevation -73 m
(-240 ft) in the area of the powerplant structures.
i 2.5-74
I I
The range in gradation of Layer E is presented in Figure 2.5.H-lb.
.These soils typically contain approximately 70 percent sand, with approximately 30 percent passing through the number-200 standard sieve.- Particle size indices of Layer E are summa-rized on Table 2.g-5.
The dry densigies range from approximately 1600 to lj20 kg/m (1g0 to 120 lb/ft ), and average approximately 1760 kg/m -(110 lb/ft ).
All of the index properties of Layer E are summarized in Table 2.5-4.
A summary of triaxial compression test strength data is presented on Table 2.5-8.
The strength parameters selected for the bearing capacity analyses of Section 2.5.4.10.3 were based on the peak strengths which occurred at low strains.
Field standard penetration test resistance generally exceeds 100 blows
~
per foot.
The remaining underlying sedimentary soils consist of alternating' strata of very hard clays and very dense silts and sands of the Cretaceous age.
Standard penetration test resis-tances exceed 100 blows per foot in these strata.
In the vicinity of the powerplant structures, these soils extend to approximately elevation -92 m (-300 f t), where residual soils are encountered.
The Precambrian and/or Paleozoic weathered rock (saprolite) overlies the parent bedrock, and, in the powerplant area, generally ranges in thickness from 4.3 to 15.2 m (14 to 50 ft).
Bedrock was encountered in the powerplant area in Borings 105, 105A, 309, 310, 321, 322, 323, and 324 at elevations varying fron -98.8 to -106 m (-324 to -347 f t).
A detailed description of the weathered rock (saprolite) and the bedrock is provided in Section 2.5.1.4.2.
2.5.4.3 Exploration The Perryman Site was initially investigated through a two-phase program that was carried out in 1972 by Dames & Moore and the Bechtel Corporation.
Additional site studies were completed by Dames & Moore in 1976 in order to more completely define those geologic, hydrologic, and foundation engineering character-istics that determine the suitability of the Perryman Site as a location for a nuclear powerplant.
The 1976 studies were neces-sitated, in part, by the changes made in the plant design and
. layout from that proposed in 1972.
The 1972 investigations are referred to herein as Phases I and II, and the 1976 investigation is referred to as Phase III.
Phases I and II were not performed under a formally organized
]
quality assurance-program.
The Phase III investigation was completed under a quality assurance program that is consistent with the requirements of American National Standards Institute (ANSI) N45.2., Quality Assurance Criteria for Nuclear Power
(
1 2.5-75
)
Plants.
The three field programs are described in detail in the pOragraphs which follow.
Additional details with respect.to-Phase III are provided in Appendix 2.5.G.
-2.5.4.3.1 Phase I Subsurface Investigation k.
.The 21 borings (100-series numbering) of the Phase I field program were performed, from January through March in 1972, by W0rren George, Inc. of Jersey City, New Jersey under the direction of. Dames & Moore.
Continuous technical supervision of the drilling and sampling operations was provided by Dames & Moore cngineers and geologists.
These personnel were present at all times to observe and' record all field operations and to provide review, inspection,-and direction of the boring program.
The primary purpose of these borings was geologic investigation.
As indicated in the Site Plan, Figure 2.5-36, most of the borings were located around the periphery of the site and in the Bush River.
The land-based borings varied in depth from 46 to 137 m (150 to 448 f t), while those located in Bush River extended from 8 to 46 m (25 to 151 f t) below the water surface.
The borings were advanced by the use of rotary drilling methods, drilling mud, and in some instances, casing.
Soil camples were obtained using the standard split-spoon sampler and the Dames & Moore sampler type U.
The standard split-spoon sampler was 35-mm (1.4-in) interior diameter (ID) and 51-mm (2.0-in) outside diameter (OD) and was driven a distance of 46 cm (18 in) into the soil with a 63-kg (140-lb) hammer dropping a distance of 76 cm (30 in).
The number of blews required to drive the sampler the last 30 cm (12 in) is the Standard Penetra-tion Resistance.
The Dames & Moore type U soil sampler was cdvanced with a 136-kg (300-1b) hammer falling a distance of 76 cm (30 in).
The number of blows required to drive the sampler the last 30 cm (21 in) was recorded as the blow count, although the values were not used for correlative.
In four of the 21 borings of Phase I, bedrock was sampled using a Christenson diamond-tipped, double-tube, core barrel that measured 75.7-mm (2.98-in) OD and 54. 7-mm (2.16-in) ID.
For each core run a Dames & Moore geologist determined the percent recovery and provided a description based on visual oxamination.
The Logs of Borings are presented in Appendix 2.5.G.
After the completion of all drilling and sampling, the borings (except 105A, 106, 118, 119, and 120) were gamma ray logged with a Wideo Porta-Logger.
The Widco Porta-Logger is a geophysical device.that utilizes a number of wire line probes in conjunction with an electronic module and recording unit.
D$pending on the nature of the probe used, a graphical printout 2.5-76
of geophysical properties versus hole depth is produced.
The gamma ray log provides a prcfile of the naturally occurring radiation emitted from geologic formations, and is expressed in terms of counts per second.
The source of this radioactivity is principally the natural decay of uranium, thorium,'and a potassium isotope of atomic weight 40.
Clayey formations usually contain a higher proportion of these elements than do sands and, therefore, show a relatively higher level of gamma radiation.
Gamma ray logging may be performed in cased or uncased borings, and is unaffected by borehole fluid.
The results of the electric logging are presented on the appropriate Log of Borings figures in Appendix 2.5.G.
All borings that were not used for piezometers were grouted with a sand and cement mixture after ground water level measure-ments had been taken.
Permanent piezometers were installed in five selected borings.
The piezometers were made of perforated plastic poly-vinyl chloride (PVC) pipe, with a surrounding gravel pack.
The remaining portion of the hole above and below the gravel-packed zone was filled with grout.
Five geophysical explorations were conducted at the site during the Phase I investigation.
1.
A seismic refraction survey was conducted to define the bedrock topography and evaluate the compressional wave velocities of the materials overlying bedrock.
The results of this survey are presented in Appendix 2.5.G.
The survey was conducted at the site along seven seismic lines with a total length of approximately j
397 m (13,500 ft).
Seismic energy was produced by the detonation of a small explosive charge in both drilled and hand-dug holes.
The holes ranged in depth from 0.9 to 4.6 m (3 to 15 ft).
The energy released by the explosives was picked up by vertically oriented geo-phones fitted with a spike for coupling with the underlying soil.
The compressional wave velocities and the depths to the various subsurface layers under the site were evaluated by plotting the first arrival times of the seismic energy at each geophone against the distance of each geophone from the source of the seismic energy.
2.
A seismic refraction line using long offset shots was used to determine characteristic types of surface waves and to study the shear wave ve' loci-ties of near-surface materials.
The results of this survey are presented in Appendix 2.5.G.
2.5-77
f A surface wave and shear wave velocity survey was conducted along a section of seismic refraction Line C.
Surface and shear wave velocities were computed from the recording of two three-component, Sprengnether Engineering seismograph geophones that were used in conjunction with.a seismic amplifier and a recording oscillograph.
Ir 'ormation from eight one-component geophones placed at 30-m (100-f t) intervals was recorded at the same time.
The Sprengnether geophones were laid out and explosions were detonated at distances that varied from 214 to 610 m (700 to 2000 f t).
The surface waves generated by small explosions at this site were of relatively small amplitude.
The velocities raeasured provided some data on shear wave velocities of the subsurface materials.
Shear wave velocitics measured in this manner confirmed the shear wave velocities measured by the down-hole technique.
3.
An up-hole velocity survey was conducted in Boring 105 to confirm the compressionel wave
{
velocities that were measured during the seismic refraction survey.
The results of this survey
{
are presented in Appendix 2.5.G.
Tha boring was cased to 2 m (6 ft) below the ground surface with steel casing.
Small explosive charges J
were buried at depths of from 60 to 120 cm (2 to 4 ft) nnd at distances of from 4.6 to 7.6 m (15 to 25 ft) from the boring.
The seismic response to the explosive charges was detected in the boring with a 12-trace l
geophone cable (velocity cable), and recorded on a
/
seismograph.
4.
A down-hoic, chear wave survey was c.onducted to evaluate shear wave velocities of the materials overlying the bedrock and, if possible, the shear wave velocity of the bedrock.
The down-hole, shear wave survey was performed using Borings 105 and 105A.
A three-component, low-frequency geophone was lowered into each boring.
Both geophones were maintained at the same elevation in each boring.
Explosive charges were fired at distances of from 183 to 366 m (600 to 1200 ft) away from Boring 105.
The resultant seismic energy was recorded on a seismic amplifier and recording oscillograph.
Recordings were made of the seismic energy at successive 15-m (50-ft) intervals in each boring.
2.5-78
5.
Ambient ground vibration studies were conducted to measure.the predominant frequencies of back-ground ground motions at the site.
Measurements of the ambient background motion of the site and its response to natural motion generators, such as wind and tides, are indicative of the dynamic properties of.the materials underlying the site.
These measurements were made at four locations on the site, shown on Figure 2.5-36.
The measurements at locations 1, 2, 3, and 4 were made during relatively quiet periods of ground activity, such,as during lull periods of ordinance testing at Aberdeen Proving Ground.
A second measurement at location No. 4 was made during the passage of a passenger train approxi-mately 760 m (2500 ft) northeast of the measurement location.
Three components (radial, vertical, and transverse) of ground motion were measured which yielded characteristic frequencies of 100, 5, and 8 hertz, respectively.
Location No. 3 appears to be the quietest location, while location No. 4 appears to be the least quiet location.
Location No. 4 is close to the transmission lines and railroad tracks on the northern boundary of the site.
2.5.4.3.2 Phase II Subsurface Investigation The foundation soil test boring program was developed by the Bechtel Corporation and the borings were made by Maryland Foundation Testing Company of Timonium, Maryland, a subsidiary of Green Associates, Inc.
Continuous technical supervision of the drilling and sampling operations'was provided by Maryland Foundation Testing Company's inspectors and was directed by their Manager of Operations.
A Bechtel Corporation soils engineer was at the site at all times to observe and record all field operations and to provide review, inspection, and direction of the boring program.
The boring program (200-series numbering) included 45 standard penetration test borings for a total of 2050 m (6720 ft) of drilling.
The boring locations are shown in Figure 2.5-36.
The Logs of Borings are presented in Appendix 2.5.G.
The borings were advanced by the use of rotary drilling methods, drilling mud, and casing.
The standard split-spoon sampler was used for disturbed soil sampling.
The penetration testing and split-spoon sampling were done in accordance with ASTM Standard D1586-70.
All borings were grouted with a sand and cement mixture after several days of ground water level measurements.
2.5-79
i I
Twenty-five undisturbed sample borings wara made cdjacent to the standard penetration test borings.
Thin-walled tube ermples, 76-mm (3-in) OD and 73-mm (2.9-in) ID, were obtained I
where it was possible to push the tube into the soil.
The undisturbed sampling of soils by tnin-walled tube was done in 4
cccordance with ASTM Standard D1587-67.
Where the soil was too hard to push the thin-walled tube, a Denison sampler was used to j
obtain undisturbed samples by rotary coring means.
A total of 169 undisturbed samples of the site soils were obtained for lcboratory testing.
Bulk soil samples were obtained to determine the properties of excavated materials.
A total of 63 bag samples, each weighing from 18 to 22 kg (40 to 50 lb) were obtained from 21 auger holes, nine of which were made parallel to the standard penetra-tion test borings.
The locations of 12 separate auger holes (AH-1 through AH-12) are shown in Figure 2.5-36.
For sandy gravels below the natural water teble, disturbed bulk samples ware obtained by driving a 76-mm (3-in) OD split-spoon sampler with basket retainer.
Bulk samples were obtained for use in dynamic triaxial compression a, compaction, and static soil strength tests.
All split-spoon, undisturbed, and bulk soil samples were examined by a soils engineer and visually classified according to the Unifiec Soil Classification System.
These classifications are indicated on the Logs of Borings.
Representative clay I
split-spoon samples were placed in wax-sealed jars and transported to the lal.cratory for testing.
Diluto hydrochloric acid was used on the soil samples to investigate the presence of any calcareous materials.
All acid test results were negative, showing that no calcareous materials exist in the soils at the site.
Split-spoon samples and undisturbed samples that were selected for testing were shipped to the Green Associates, Inc.
soils laboratory in Towson, Maryland.
The laboratory testing was conducted in accordance with the program developed by the Bachtel Corporation.
Some bulk samples were shipped to Geo-l Tasting, Inc., San Rafael, California, for the dynamic triaxial compression testing of recompacted specimens.
After each test boring was completed, clear water was used to flush out the drilling mud so that the water level in the borehole could respond to the natural ground water table.
Twenty-four or more hours later, the depth of the water was mnasured.
In some cases, the borehole caved in near the ground water level.
In such cases, the depth of the cave-in was measured and recorded, but it was not used in the ground water evaluations.
" Results of dynamic triaxial compression tests on recompacted samples are not considered appropriate for submission with
)
this Early Site Review.
2.5-80
Six piezometers were installed as part of the Phase II investigation.
The purpose of these piezometers was to investigate whether differential, excess, hydrostatic pressure existed in the various sand layers, or whether these various sand layers were hydraulically connected.
The two piezometer groups were located near Borings 220 and 241.
The locations of all piezometers are shown in Figure 2.4-65.
All piezometers consisted of Sl-mm (2-in) ID PVC pipe with a 2-m (7-ft) slotted section at the tip.
The slotted portion was surrounded with clean sand, which was separated from the soil backfill above by an impervious layer fMbentonite.
In each case, the hole was drilled using Revert
, which performs as a drilling mud in preserving a stable open hole.
Revert breaks down chemically within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />, so it does not form a barrier that is impervious to water.
A 60-cm (2-ft) thick bentonite seal was placed at each clay stratum, and at a point approximately 1 m (3 f t) below the ground surface to prevent hydraulic connection between adjacent piezometers and to prevent the entrance of surface water into the upper aquifer.
Each piezemeter was tested several days after installation and checked for proper response to changes in water level.
At five boring locations, field permeability tests were performed according to the U.S.
Bureau of Reclamation field test procedure E-18 (1974).
These tests were performed at various sand layer depths in borings 207, 220, 234, 237, and 240.
Two_well pump tests were conducted at the site:
one in the plant area (Test Well 1) and one near the Bush River (Test Well 2).
Each test setup consisted of a 23-cm (9-in) diameter, 24.4-m (80-ft) deep test well and three observation wells at known distances from the test well.
Test wells 1 and 2 were screened for tha bottom 12 and 15 m (40 and 50 ft), respectively.
Water levels in the test well and in all the observation wells were measured just before the test was begun.
The well pump was started and run at a constant pumping rate.
The water levels in the test well, the observation wells, and several piezometers were read at varying intervals of time for 23 hours2.662037e-4 days <br />0.00639 hours <br />3.80291e-5 weeks <br />8.7515e-6 months <br />.
Then, the pump was shut down and the rebound of the water levels was monitored.
The permeabilities of the subsurface materials were calculated based on the water level, the pumping rate data, and
)
the distances from the test well to the observation wells.
The i
locations of the test wells and the observation wells are shown in Figure 2.4-65.
)
)
As part of the Phase II field investigation, a cross-hole seismic survey was conducted by Weston Geophysical Engineers, Inc.
The purpose of the cross-hole seismic exploration was to measure both the P (compressional) wave and the S (shear) wave velocities of the foundation materials.
2.5-81 j
1 j
Data were obtcin;d uaing c 12-chtnnal, porttblo ceicmogrcph.
Surface measurements were made to obtain velocity values for the nner-surface materials (0 to 4.6 m (15 ft) depth) and to confirm j
tha data for the materials immediately below the near-surface materials that were obtained by the cross-hole measurements.
Vartically and horizontally oriented geophones were used in th se measurements.
i In the cross-hole procedure, three-component geophones were l
lowered into four boreholes, to equal elevations, and a small cxplosive charge was detonated in the fifth borehole at the same f
olcvation. Measurements of the seismic energy generated in the boreholes by the explosives were made at 3-m (10-ft) intervals.
j In addition, data were obtained with horizontally-oriented grophones on the surface when seismic energy was generated by cmnll explosive charges at the bottom of the boreholes.
The cptcing of 30 m (100 ft) between geophone detectors allowed for c total cable length of 335 m (1100 ft), which gave deep penetra-
)
tion (approximately 30 m (100 ft)) beneath the bottom of the boreholes.
Data from the cross-hole survey are presented in Tcbles 2.5-16 through 2.5-19.
2.5.4.3.3 Phase III Subsurface Investigation The Phase III subsurface investigation involved the drilling of 24 test borings (300-series numbering) at locations shown in Figure 2.5-36.
The test borings were performed, under the direction of Dames & Moore, to provide additional information
'i for foundation analyses, dynamic soil parameters, and liquefaction potential, and to further define general site geologic conditions.
The investigation is summarized in paragraphs which follow; cdditional information on such concepts as drilling, sampling, cnd piezometer installation are provided in Appendix 2.5.G.
Although many of the borings served multiple purposes, the 24 borings may be divided into three groups:
(1) foundation engineering; (2) hydrology; and (3) geology.
The test borings for foundation engineering testing were drilled at the locations of proposed powerplant structures.
Except for two borings (309 and 310), the depths of these borings rcnged from 13 to 58 m (42 to 191 ft).
Borings 309 and 310 were drilled to depths of 122 m (400 ft) and 134.5 m (441.3 ft),
rcspectively, at the centers of the two proposed Reactor Buildings.
Both borings penetrated the bedrock surface.
Borings 301 through 306, 315, and 320 provided soil samples for hydrologic testing co well as foundation testing.
A piezometer was installed in occh of these holes.
Borings 321 through 324 were drilled to more completely investigate the rock conditions encountered in Boring 310.
These borings penetrated the bedrock surface and rcnged in depth from 119 to 140 m (390 to 458 ft).
)
2.5-82
1 o
Subsurface materials encountered in all borings were continuously observed and logged in the field by an engineer or geologist.
The soils.were classified in accordance with the Unified Soil Classification System, described in Figure 2.5.G-3.
The Logs of Borings are presented in Figures 2.5.G-5 through 2.5.G-95.
1 1
Conventional truck-mounted, rotary-wash, drilling equipment j
advanced the borings.
The holes were approximately 15 cm (6 in) in diameter and were stabilized with drilling mud.
Casing was placed in the upper soils, when required, to prevent caving.
Several different types of soil samplers were employed during the field program.
In most of the borings, the standard split-spoon sampler provided disturbed samples at regular inter-vals for visual examination and index tests, as well as standard penetration test data.
The Dames & Moore type U sampler provided disturbed samples for hydrologic testing in six of the borings j
(301 through 306).
The device for undisturbed sampling of j
cohesionless soils was the Pitcher sampler, while the primary undisturbed sampling device in cohesive soils was the osterberg piston sampler.
In many cases, the cohesive soils were too hard to be penetrated by the Osterberg sampler, so the Pitcher sampler was employed.
The Denison sampler was used occasionally to obtain samples of very hard cohesive soils and very dense cohesion-l less soils.
Rock coring was performed with an NX-size, double-tube, core barrel, which obtains rock samples approximately 55 mm (2.2 in) in diameter.
Undisturbed soil sample tubes were sealed upon recovery.
These samples were carefully transported to the soils laboratory i
by Dames & Moore personnel.
A limited number of samples were subsequently transshipped via commercial carrier to other labora-tories for static consolidation testing.
These samples were shipped in sturdy containers that were lined with several inches of foam padding.
Rock core was p3 aced in strong, wooden boxes and carefully transported by Dames & Moore personnel.
Photographs of the rock core were taken prior to transport.
{
Several water tests for evaluating the approximate values of permeability of the individual strata penetrated by borings were performed (U.S. Bureau of Reclamation, 1974).
These test' measure the amount of water accepted by the soil through the open bottom of the pipe casing within a boring.
The test is I
begun by adding clear water through a metering system that maintains gravity flow at a constant head.
Measurements of the constant head, constant rate of flow into the hole, diameter of pipe casing, and elevations of top and bottom of casing were recorded.
The permeability values obtained from these tests are presented in Table 2.4.A-7.
2.5-83
Piezometers were installed in eight of the test borings to cerve as observation wells during test pumping and to monitor long-term water levels.
The piezometers were placed at various depths in order to monitor water levels within the aquifers of
)
Layers B and C.
The penetration of the piezometers ranged from cpproximately 13 to 55 m (42 to 180 ft).
The piezometers are made of 76-mm (3-in) diameter PVC pipe j
with.a 3-m (10-ft) slotted section capped at the bottom.
The i
portion of the hole around the slotted section was backfilled J
with sand, above which was placed an impervious bentonite barrier.
The portion of the hole from the bentonite barrier to the ground i
curface was backfilled with grout.
A sketch of a typical piezo-meter installation is presented in Figure 2.5.G-1.
Each piezo-meter was developed and cleaned by air-lift discharge.
After from 24 to 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br />, the piezometers were field checked by cdding clear water, equivalent to 4.6 to 6.1 m (15 to 20 ft) of head, and measuring the rate of water level decline in the pipe.
In all borings at the site, conventional, electric logging techniques were used to augment the data obtained from drilling cnd sampling.
Standard resistivity, self potential (SP), and gamma ray logs were cbtained by using a portable, field logging unit operated by a Dames & Moore geologist or engineer.
Data obtained through electric logging were used to correlate sub-curface stratigraphy, especially at the deeper depths where camples were more widely spaced.
The results of the resistivity, celf potential, and gamma ray logs are shown on the Logs of Borings.
)
After completion of electric logging, each bore hole was filled to the surface with a cement grout.
The grout was placed by either pumping through the drill rods or by pumping through a cmaller diameter tremie pipe.
The level of the grout in each hole was checked in the field at a later date.
Dry, cement was cdded near the surface in cases where the grout had subsided.
A high-resolution, seismic reflection survey was carried out at the site along lines as indicated on Figure 2.5-17.
A total of 5344 m (17,520 ft) of line was surveyed by Target Survey, Incorporated, of Houston, Texas, using a non-explosive, Varipulse energy source and surface-arrayed geophones.
Enhance-ment of signal quality in the field was accomplished through the use of 600% comm6n depth point shooting techniques and multiple-ehot stacking at each shot point.
Data were processed and final cections produced by Applied Research Concepts, of Houston, Texas, using computerized techniques for the application of geometric and velocity corrections to the field data.
The details of this survey are discussed in Appendix 2.5.F.
Ground magnetometer reconnaissance surveys were carried out along the lines indicated in Figure 2.5-17, in order 1) to investigate any magnetic features under the site that might be 2.5-84
t associated with a suspected fault in Boring 310; and 2) to determine the-general magnetic character of the~ basement under the site..The. reconnaissance profiles were-measured alo.'g roads and lines'that were-surveyed for.the seismic reflection investi-gations.
Readings were made along each profile at either 30-ft or 40-ft intervals.- Distances were measured by tape.-
Readings
'of magnetic intensity:were obtained by means of a Geo Metrics G816 portable magnetometer.
The profiles were tied to'a. local reference station which was occupied.during the surveys.approxi-mately once per hour, in order to maintain a base. control for
.the profiles.. Profiles' measured during the reconnaissance are presented in Figure 2.5-18.
2.5-85 4
r I
2.5.4.4 Geophysical Explorations The following geophysical explorations were conducted at the site:
i 1.
A seismic refraction survey to define-the bedrock topography, and to evaluate the compressional wave velocities of the materials overlying bedrock.
2.
A seismic refraction line using long offset shots, to determine characteristic types of surface waves, and to study shear wave velocities of near surface materials.
3.
An uphole velocity survey to further define compressional wave velocities.
4.
A downhole shear wave survey to evaluate shear velocities of the materials overlying the bedrock, and if possible to evaluate the shear wave velocity of the bedrock.
5.
Ambient noise studies to determine the predominant frequences of ground motion at the site due to background noise levels.
6.
Crosshole geophysical exploration work was conducted, in the areas of the proposed containment structures and the auxiliary building by Weston Geophysical
)
Engineers Incorporated.
7.
A seismic reflection survey, using high resolution equipment, to evaluate the subsur-face stratigraphy over the entire site pro-perty, with emphasis on features encountered in Boring 310.,This program j
is discussed in detail in Appendix 2.5.F.
8.
A ground magnetometer reconnaissance survey along the above seismic lines and in the vicinity of Boring 310, to evaluate the magnetic character of Bedrock under the site.
The results of this reconnaissance are discussed in Section 2.5.1.4.
The locations of the seismic and magnetometer lines are shown on Figure 2.5-17.
A summary of the results of each phase of the gsophysical exploration is provided in the following paragraphs:
Seismic Refraction Survey This survey is described in Section 2.5.4.3.1. The time-distance data from each profile surveyed during this investigation are shown on Figures 2.5.G-96 through 2.5.G-102.
In addition, profiles on the various subsurface layers are shown directly below 2.5-86
)
each corresponding time-distance plot.
It should be j
noted that on Seismic Line D, there is evidence of the
{
probable existence of a layer having a compressional wave velocity of 7700 to 8000 ft/ sec.
Although this layer is shown on the subsurface profile to indicate its possible presence, data on the other seismic lines fail to confirm it.
The compressional wave velocity data as determined from the seismic refraction survey are summarized on Figure 2.5.G-103.
A bedrock contour map is shown on Figure 2.5-17.
This map is based partly on data obtained from the seismic refraction survey as well as from the seismic reflection survey and the holes that were drilled to bedrock. The accuracy of the calculated depths to bedrock are considered to be +10 percent for the complete survey.
Surface Wave and Shear Wave velocity Survey This survey is described in Section 2.5.4.3.1. The surface waves generated at this site by small explosions are relatively small in amplitude.
Three surface waves were observed in this study.
The characteristics of these waves are given in Table 2.5.4.16.
Surface waves two and three do not have the charac-teristics of any of the classic surface waves, and are apparently the results of the site geometry.
A strong transverse motion refracted wave train occurs just after the normal compressional refraction wave train.
This tranverse-motion wave train has an apparent velocity across the surface of about 7000-8000 ft/sec which indicates that this energy is trapp,ed above layer three at the site.
All the surface waves gen-erated at the site are apparently associated with this transverse energy.
The site has a characteristic frequency range between 7.0 and 12.5 hertz.
Significant amplification of seismic energy will probably occur only within this f
frequency range.
The velocities measured in the surface wave survey provided some data on shear wave velocities of the subsurface materials.
Shear wave velocities measured in this manner confirm the shear wave velocities measured by the down-hole technique.
i Uphole Velocity Survey
{
Purpose and procedures of this survey as described in Section 2.5.4.3.1.
The results of the uphole velocity survey are presented on Figure 2.5.G-104. It can be 2.5-87 l
\\
l
~
s 3.
4 I
O
' assn'that thsfcompreccions1"w2va valocities mansured from1thisLaurvey differ slightly from theLeompressional
!waveLvelocities? measured:in the seismic refractions L
- surveys.
The seismic refraction survey. measures the E
compressional; wave. velocities over:a distance,-whereas the.uphole velocityksurvey measures the compressional wave velocitiesiat an: isolated. point (Boring 105).
Downhole Shear Wave! Survey The? purpose and procedures of this survey are. described
~
~
in Section 2.5.4.3.1.
The:results'of thefsurvey are
' presented.on' Figure;2.5.G-103. These. data are referenced.
to subsurface-conditions found.at the. location of' Borings;105 and 105A.
' Ambient Vibration Measurements
- The purpost of
- this survey is described in Section
- 12. 5'.'4. 3. l.. : Ambient vibration measurements were made at four locations on.the site, shown on Figure 2.5-36.
The measurements at locations 1, 2, 3, and 4 were'made during relatively quiet periods of no noise or. ground activityi(such'as ordinance testing at Aberdeen Proving Ground). A'second measurement at location No. 4 was mad'e during passage of.a passenger train approximately 2,500 feet. northeast of the measurement location.
A three component direct-writing Sprengnether Engineering i
Seismograph, Model VS-1200,'was used for recording ambient ground motion. -The seismograph has gain' characteristics in the. velocity mode of 20, the:accelera-tion mode of 12, and the. displacement mode of 200.
A VS-1100D amplifier with'a: gain characteristic of 100 was used..in all' recordings.
The resultan,t maximum gain level.for velocity is 2000, acceleration 1200 and for' displacement 20,000.
The.three components of ground motion measured were radial, vertical and transverse.. The observed characteristic frequencies of the site are 100 and:5 to-8 hertz.
Location No. 3 appears to be the quietest location while location No. 4 appears to be the least quiet location.. This-last location is closed to transmission lines and railroad tracks on the northern boundary of thefsite.
Results'of the ambient ground motion measure-ments are presented on Table 2.5-17.
Crosshole Seismic Survey The purpose'and procedures of this survey are described in Section 2.5.4.3.1.
Figure 2.5-17 shows the location 2.5-88 i
r of the boreholes used in these measurements.
Boreholes A, B,C, 1, and 2 were used as follows:
Shot Hole Recording Holes A
1, B, 2, C B
A, 1,2,C C
2, 1, A, B Table 2.5-18 shows the compilation of the "P" and "S" wave velocity data down to 61.9 m (200 f t) depth (elevation 54.3 m (178 f t) ).
Table '.5.A-19 gives the summary of the compilation of velocity data, a generalized stratigraphic correlation, and the elastic moduli values resulting from the summary.
In addition, data were obtained with horizontally oriented geophones of the surface when seismic energy was generated by small explosive charges at the bottom of the boreholes.
The spacing of 30.5 m (100 ft) between geophone detectors allowed for a total cable length of 335.5 m (1100 ft), giving deep penetration, that is approximately 30.5 m (100 ft) beneath the bottom of the boreholes.
The "S" wave velocity recorded for the deeper materials was (2400 to 2500 ft/sec).
Seismic Reflection Survey The purpose and procedures of this survey are described generally in Section 2.5.4.3. and in detail in Appendix 2.5.F and Section 2.5.1.4. Results and interpretations
{
are disccused in Appendix 2.5.F.
Ground Magnetometer Reconnaissance The purpose and procedures of this survey are described i
in Section 2.5.4.3.1.
Corrected field data were l
plotted as profiles as shown in Figure 2.5-18, and the profiles compared with other subsurface data at the site.
Correlation of the magnetic data with interpreted basement topography and drill-hole informa-tion was very good.
These results and their signifi-cance are discussed in Section 2.5.1.4.
2.5-89
l 1
2.5.4.5 Excavations and Backfill 2.5.4.5.1 General i
Major excavations are planned for the construction of the proposed mat foundations of the Category I structures.
Existing ground surface; elevations in the area of proposed Units 1 and 2 i
.v2ry from approximate elevation +4 to +11 m (+13 to +35 ft).
l Tha reactor mats will be generally founded at elevation -0.3 m
(-1. 0 f t) on compacted fill that will in turn extend to elevation t
-9. 8 m (-32 f t).
The detailed procedures to be used for founda-ti0n excavation, construction, and backfilling should not be a principal factor in determining the suitability of the Perryman Site as a location for a nuclear powerplant, except, perhaps, for the excavation-dewatering system, which is discussed sepa-rntely.
Therefore, such construction details as the following will be presented at a later time.
1.
Stability and/or design of temporary excavation slopes; 2.
Plans for geologic mapping of excavations; 3.
Plans for monitoring systems for the measurement of heave and settlement; 4.
Criteria for selection of fill materials; 5.
Procedures for placement, compaction, and quality
)
control of proposed fills; 6.
Erosion control measures.
Thnse items of concern will be addressed in information submitted with the application for a construction permit.
Discussion of the approximate extent of the Category I excavation is provided in Section 2.5.4.5.2.
Because portions of Layers A and B may be used as fill, some physical properties of laboratory compacted specimens from these layers were measured.
These test results are discussed in Section 2.5.4.5.4.
The final selection of the type or sources of fill has not yet been d3termined.
Nonethelesa, the Category I fill will be one of three principal types:
(1) well-graded sand and gravel; (2) crushed stone; or (3) lean concrete.
2.5.4.5.2 Extent of Category I Excavations and Fills All excavation for Category I structures, including the E2sential Service Water (ESW) cooling towers, will be performed after the dewatering of the subsurface soils.
Although analyses of potential safe construction slopes have not yet been performed, 2.5-90
slopes of 1.5:1 or 2:1 (horizontal: vertical) will likely be adequate, given the relative soundness of Layers A, B, C, and C' (Section 2.5.4.2.3., Description of Principal Soil Layers), in which such slopes may conceivably be constructed.
With side slopes of 1.5:1 or 2:1, the excavation for foundations of Category I structures will have a maximum width on the order of 320 m (1000 ft) along a line through the ESW cooling towers at each unit.
In other directions, the excavation may extend approxi-mately 60 m (200 f t) beyond the building limits that are shown in Figures 2.5-37a and 2.5-37b.
The category I fill will extend from the bottom of the foundation mats, elevation -0. 3 m (-1.0 f t), down to the bearing level, elevation -9. 8 m (-32 f t), except when local soft pockets are encountered causing slightly deeper extension of the fill.
The final selection of the fill material will be dependent upon the anticipated compatibility of the alternate soils, as well as the outcome of additional strength and liquefaction tests on representative compacted samples.
The quantity of Category I 3
fill required will be gn the order of from 250,000 to 300,000 m (330,000 to 390,000 yd ).
Regardless of whether the sources of fill material are onsite excavations, offsite fill, or crushed stone, the material will have a maximum size of 15 cm (6 in) and contain no more than 15 percent of material passing through the number-200 standard sieve.
All material will be compacted to an in-place relative density of at least 80 percent, as determined by testing performed in accordance with the provisions of ASTM specification D-2049, Relative Density of Cohesionless Soils.
The approximate areal extent of the surface fill in the vicinity of the Category I structures and Turbine Generator Buildings is shown in Figures 2.5-37a and 2.5-37b.
After stripping the existing topsoil, compacted fill will be added to raise the general grade to elevation +10.7 m (+35.0 ft).
This fill will eventually support roads, parking areas, and some lightly loaded nonsafety-related structures.
Although the final selactions of material type and source have not yet been made, the areal fill may be composed of soils from Layers A and/or B.
Because the compacted fill layer will be relatively thin (maximum thickness approximately 6 m (19 ft)), the surcharge effects of the fill on the anticipated settlement of the Category I and Turbine Generator Building foundations will be small.
This effect will be manifested in the form of incrementally larger settlements around the edge of the foundation mats than would be the case were the fill not present.
The effect of the surcharge on settlement under the center of the mat will be negligible.
Thus, the net effect of the surface fill will be a slight tendency to make the edge settlements more compatible with the settlements under the interior portion of the mats.
This effect is discussed further in Section 2.5.4.10.2, Settlement: Category I Structures and Turbine Buildings.
2.5-91
2.5.4.5.3 Dewatering System Description of Dewatering System The ground water conditions that affect foundation design cnd/or construction have been previously discussed in Section 2.4.13.
The proposed dewatering system is conceptually discussed in Section 2.5.4.6, and will consist of a system of deep wells end/or well points, working in conjunction with a second system that is made up of deep wells into the lower aquifer (below cpproximate elevation -43 m (-140 ft)).
The second deep-well l
I cystem may be required to reduce the piezometric head in order ta guard against hydrostatic uplift and related problems.
The d; watering system will be designed after the powerplant design h;c been finalized and the construction plans developed.
Effect of Dewatering on Settlement The effect of a temporary lowering of the ground water icvel from an. approximate elevation of +2.4 m (+8.0 f t) to an approximate elevation of -11 m (-35 f t) will be an increase in tha effective stress that is imposed by existing overburden on tho foundation layers that will eventually support the structures.
This increase in stress would also be a temporary condition b cause excavation would proceed relatively soon after dewatering.
In view of the fact that the foundation soils are all highly ovsrconsolidated, temporary changes in effective stress, such as ths increase due to dewatering and the subsequent decrease due to excavation, produce relatively small effects on the final i
foundation performance.
Thus, it is anticipated that the proposed dcwatering system will not contribute significantly to foundation cattlement.
2.5.4.5.4 Description of Fill Properties The requirements for compacted fill are not completely cddressed in this report.
There are, however, three types of fill planned:
a Category I fill underneath the major structures cnd two non-Category I fills, a foundation excavation backfill cnd an areal fill to raise the general site grade.
Although final decisions on the. source of these fills have not yet been mnde, some tentative sources have been identified.
Because the coils of Layers A and B (Section 2.5.4.2.2, Description of
~G:neralized Profile) have been judged as unsuitable for foundation cupport of major powerplant structures, these soils will be excavated and partially replaced by controlled compacted fill.
Tha extent of this foundation fill is conceptually shown on the cross sections provided in Figures 2.5-38a through 2.5-41b.
It is anticipated that portions of the soils of Layers A and B will ba suitable for reuse as fill for one or more of the fill types.
For this reason, representative recompacted samples of Layers A and B were subjected to static and dynamic laboratory tests.
2.5-92 4
r The compaction characteristics of selected portions of Layers A and B were evaluated by performing laboratory compaction tests according to ASTM Standard D-698-71C and ASTM Standard D-1557-70C.
Figure 2.5.H-3 presents the individual compaction curves, and Table 2.5-6 provides a summary of the maximum dry densities and optimum moisture contents.
Unconsolidated-undrained (UU), consolidated-undrained with pore pressure measurement (CU/PP), and consolidated-drained (CD) triaxial compression tests were performed to evaluate the static compressive strength of samples that were recompacted to approxi-mately 95 percent of their maximum dry densities.
The results of the triaxial compression tests are summarized on Table 2.5-8.
The strength parameters, angle of internal friction (4),
and cohesion (c) were evaluated, and Mohr's circle stress diagrams j
were plotted for data that were selected from Table 2.5-8.
Yield, peak, ultimate, and residual strengths are provided in an j
effort to permit selection of strength parameters that are 1
compatible with whatever engineering problem is under considera-tion.
Since shear stresses in laboratory test samples vary with strain level, it follows that the strength parameters that are assumed from those tests should also vary with strain.
The soil parameters actually used in the bearing capacity analyses are provided as part of the discussion of that topic (Section 2.5.4.10.3 and Appendix 2.5.I).
After a decision regarding the selection of backfill material is made, an adequate number of samples will be selected, reconsti-tuted to specified densities, and tested to define the variation of shear modulus and damping ratio with strain and confining pressure.
Strain-controlled, cyclic triaxial tests and resonant column tests will be performed to define the dynamic properties.
The dynamic properties that are thus defined will form the input for the soil-structure interaction analyses that will be performed at a later s tage.
The material that is eventually chosen for backfill will be specified to possess particle size, gradation, and compaction characteristics such that the material can be considered nonliquefiable under the Safe Shutdown Earthquake.
With regard to the compressibility of Layer B soils that may be used as Category I fill, the initial tangent moduli were evaluated from stress-strain curves of triaxial compression tests on recompacted samples of Layer B.
The actual selection of strength parameters for any one type of analysis presented in this report is explained within the discussion of that analysis.
2.5.4.6 Ground Water Conditions The ground water conditions at the site are described in detail in Section 2.4.13.
The records of field and laboratory permeability tests are presented in Section 2.4.13.2.2. and 2.5-93
r.
\\
s
. ' Appendix.2.4.A.. Thio; history of. grounc; water fluctuations and
'information relatedLtoithe_ periodic. monitoring.of' local wells end piezometers are presented.in Sections. 2.4.13.2.2 and 2.4.13.2.3; Ground wateriflow directions,Jgradients, and velocities are discussed in~ Sections 2.4.13.2.3'and.2.4.13.3.
The following discussioniaugments thefinformation presented in-these sections.
The critical.caseiofl subsurface ~ hydrostatic loading'is
' discussed in-Section 2.4.13.5. -As presented'therein, the..
dssign' basis maximum ground' water levelfis' controlled by the combined {effect of'an-extreme hurricane ~ surge and associated
'hcavy rainfall, coupled'with'the break of1a large-diameter, high-capacity water pipe. : Rigorous' analysis of'the' effects of these; events upon ground; water levels at the site would require plant design'detailsLthat are not'available at this' time.
LTherefore,';the~ design basis maximum; ground water level is con-1
'ocrvatively selected'tolbe not greater-than elevation +10.7 mL
(+35. 0 f t),_ plant? grade..
Dewatering of the main excavation will be required _during Econstruction.- The~ main' excavation will be made-within the-upper aquifer,Lwhich will probably be_dewatered by a system of deep walls, drainage trenches, and/or well points that are peripheral to'and within the excavation. 'The. dewatering system will be "dssigned,to safely control'the. location of the potentiometric surface within'the upper aquiferLin' order to provide for required I
slope: stability, a suitably. dry working surface at the base of excavation, and reduction'in-hydrostatic uplift in the upper l aquifer.- Inladdition to the dewatering. system, a system of deep
)
twells'that arelsealed into:the: lower aquifer will be. employed, as-required, to reducelthe piezometric surface in the= lower equifer'.under the excavation to an elevation below the base of the excavation.
This is done to guardLagainst hydrostatic uplif t, popouts, and. quick conditions..
The systems will be designed to minimize. impact upon offsite ground water _ users, and may include the construction ofiinfiltration basins and ditches or injection walls:near property boundaries. 1 The dewatering and recharge isystems. types and designsLwill be determined'after' plant designs
- end construction plans have been developed in detail.
The-ground water levels will'not be controlled during plant operation.
2 5.4.7 JRespo~nse,of Soils to Dynamic Loading A seismic responsefanalysis was_ performed to estimate the
~ stresses, strains, and-accelerations at different depths within
.the soil profile, resulting from the Safe Shutdown Earthquake loading atLthe Perryman. Site.
This section presents the features
- of the. response analysis.
2.5-94 1
2.5.4.7.1 Soil'Model Used in the Response Analysis Based upon a review of the data from the subsurface investi-
~
gation at the Perryman Site', a representat.ve, idealized soil profile was established for the one-dimensional wave propagation analysis.
This idealized soil profile corresponds to an avtrage surf ce elevation of +6.1 m (+20 ft).
Figure 2.5-43 presents the idealized soil profile and the soil properties that were used in the response analysis.
The soil description from a typical boring (Log of Boring 309, Figure 2.5.G-13a) is also presented in this figure for comparison with the idealized soil profile used in this analysis.
The upper 113 m (370 f t) of the soil deposit was divided into 19 sublayers.
Detailed descriptions of the soils encountered at the Perryman Site are presented in Sections 2.5.4.2.2 and 2.5.4.2.3.
2.5.4.7.2 Soil Properties Used in the Response Analysis The soil properties that are required for the wave propaga-tion analysis are: (1) unit weight; (2) shear modulus; (3) damping ratio; and (4) coefficient of earth pressure at rest.
l A brief discussion of each of these properties follows.
Unit Weights The details and the results of laboratory tests that were I
performed for determining the unit weights are presented in Section 2.5.4.2.1.2.
The average values (based on test data) of unit weights of soils that were used in the response analysis l
are presented in Figure 2.5-43.
Shear Modulus 1
In general, the shear modulus of a soil is influenced by several variables, including effective cor3 fining pressure, void j
ratio, stress history, degree of saturation, soil structure,
{
amplitude of strain, and frequency of vibration (Hardin and l
Drnevich, 1972).
In situ shear modulus can be estimated by I
I reviewing data from the geophysical survey.
This value of_ghear modulus corresponds to low strain levels (approximately 10 percent).
Shear moduli corresponding to other strain levels can be determined by performing strain-controlled, cyclic triaxial tests and resonant column tests.
The extensive field and labora-tory investigations on different soils that were conducted by independent researchers have generally established shear modulus l
versus strain relationships of soils (Seed and Idriss, 1970).
I The shear modulus versus strain relationships of sands and clays j
at the Perryman Site were developed duly considering the low j
strain data that were obtained from the geophysical survey and generalized trends from the published data at other strain j
levels.
1 i
2.5-95
)
, Shear Modulus'of Sands Based on.the findings of Seed and Idriss (1970),'the shear modulus, at.lowLstrain levels'of coarse grained soils, can be cxpressed by theequat.icn
'G = (1000) (K I I m}
2 where G is the, shear modulus (lbs/ft )
2 3,is'the-effective mean confining pressure (lbs/ft )
.K is a constant for'a.given compactness of soil 2
The measured values of shear wave velocities and the shear modulus values corresponding to these-velocities are presented
.G2 functions of depth in Figures 2.5-43 and 2.5-44.
The values of K were computed from the equation 2
G K2=
(1000) (8,)
where G is the low strain shear modulus (lbs/ft ) from the geophysical survey 3,
is the effective mean confining pressure (lbs/ft )
at the depth of interest The' values of K are presented in Figure 2.5-43.
The shear i
2 modulus ~ varies nonlinearly with Ltrain level.
This variation was assumed to follow the' pattern of average data on the J
coarse-grained soils presented by Seed and Idriss (1970).
The
{
nonlinear strain. dependence of shear modulus that was used in this analysis is presented in Figure 2.5-45 and summarized on Table 2.5-10.
q Shear. Modulus of Clays Based on the findings of Seed and Idriss (1970), shear moduli of clays can be considered a function of strain level and undrained shear strength.
The average values of shear modulus, which are normalized with respect to the undrained shear strength (S ) of saturated clays, are available in literature (Seed and IdEiss, 1970).
The low strain shear moduli of clays at the
'Parryman Site were obtained by reviewing the data from the i
geophysical survey and the undrained shear strengths measured in
{
the laboratory.
The variation of the shear modulus with the.
)
ctrain level was assumed to follow the pattern of average data l
that'was provided by Seed and Idriss (1970).
Strain dependence
{
of the shear modulus of clays is presented in Figure 2.5-45 4
and summarized.on Table 2.5-10.
1 2.5-96
p
~
Damping Ratio Most of the parameters discussed in-relation to shear modulus have an opposite-effect on the damping value.
The damping value increases with increasing strain amplitude, decreases slightly with increasing! ambient stress, and decreases with increasing void ta;io.
Strain-controlled, cyclic triaxial tests and resonant cod;w.n tests on undisturbed samples are necessary to experimentally define the variation of the damping ratio with strain level.
However, for the purposes of Early Site Review, it was considered satisfactory to assume that the damping ratio of the soils at the Perryman Site, both in magnitude and in its variation with strain level, were identical to the average results presented by Seed and Idriss (1970).
These values are the average values obtained from the experimental investigation performed by several independent researchers on typical sands and saturated clays.
The strain-dependent values of the damping ratios for typical sands and clays, which were used in the response analysis, are presented in Figure 2.5-46 and summarized on Table 2.5-10.
Coefficient of Earth Pressure at Rest Based upon a review of laboratory test data on the angle of internal friction, a value of 0.4 was assigned for the coefficient of earth pressure at rest for all the granular soils.
2.5.4.7.3 Design Earthquake Used in the Response Analysis The horizontal component of a digitized acceleration-time history (Section 2.5.4.9) was used as the input motion at the surface of the soil deposit.
The corresponding accelerogram is presented in Figure 2.5-47.
The duration of the design earthquake was assumed to be 15 seconds, and a maximum ground surface acceleration of 15 percent j
of gravity was used, based on the findings of seismicity studies l
1 of the Perryman Site (Section 2.5.2).
2.5.4.7.4 One-Dimensional Wave Propagation Analysis s
A mathematical model was used to evaluate the response of the soil deposit at Perryman Site that was subjected to the Safe Shutdown Earthquake loading.
This model is based on one-dimensional, strain-compatible, shear wave propagation through a layered system.
Each layer in the system is assumed to be isotropic, homogeneous, and of viscoelastic behavior (Schnabel and others, 1972).
A_ computer program developed by Schnabel, and others (1972) was modified by Dames & Moore to include additional input and output.
The nonlinearity of the shear modulus and damping ratio 2.5-97
10 cecounted for, in thio program,_by tha use of equivalant linear properties.
This' computer. program (Dames & Moore, 1975b) was verified for various practical problems, certified in l
.cccordance with quality assurance requirements, and used to parform the analysis for the soil deposit at Perryman Site.
2.5.4.7.5 Results of the Response Analysis The objective'of the response analysis was to estimate the resulting cyclic shear stresses, strains, and accelerations due to ground motion during the Safe Shutdown Earthquake.
The' variation of maximum shear stresses and strains with d3pth and the corresponding strain-compatible soil properties cre presented in Figures 2.5-48 and 2.5-49, respectively.
The variation of the maximum acceleration with depth is shown in Figure 2.5-50, 2.5.4.8 Liquefaction Potential Liquefaction occurs when a soil undergoes continued deforma-r tion at a constant, low-residual stress,'or has no residual resistance, due to the buildup and maintenance of high pore-water pressures, which reduce the offective confining pressure to a very low value.
Pore pressure buildup that leads to true liquefaction may be due to either static or cyclic stress applica-tions (Seed, 1976).
The liquefaction potential due to cyclic otress applications was evaluated for the free-field conditions at the Perryman Site.
The details of this evaluation and the conclusions drawn from them are presented in this section.
2.5.4.8.1 Factors Influencing the Cyclic Liquefaction Character-istics of Soils The phenomenon of cyclic liquefaction is governed by various factors, such as the particle size characteristics, relative d nsity, ambient stress, intensity and duration of ground motion, cnd lateral earth pressure coefficient.
Empirical criteria have buen established to determine the influence of these factors on the cyclic liquefaction potential.
These criteria are based on the performance of soil deposits at various sites during past certhquckes.
Ohsaki (1969) and Kishida (1969) have presented criteria for particle size characteristics of potentially liquefiable soils.
Figure 2.5-51 shows the' range of particle size distribu-tion curves for typical soil. samples in the upper 21 m (70 ft) eieveopeningpermitting10percentbhgrainsizes of soil at the Perryman Site.
The D (size of the material, by weight, to pass) vary from 0.3 mm to less than 0.08 mm.
Coarse-grained coils having D
's greater than 0.074 mm are considered potentially liquefiable.
hSeD f r the typical soils at the Perryman Site 60 2.5-98
varies between 0.090 mm and 2.1 mm, and the D varies between 5
0.075 mm and 1.5 mm (Figure 2.5-51).
Typicalhaluesofthe uniformity coefficient lie between 1 and 8.
According to empirical j
criteria developed by Ohsaki (1969), Kishida (1969), and others',
i some of the granular deposits at the Perryman Site could be
{
considered potentially liquefiable.
j t
Ohsaki (1969) and Kishida (1969) further consider that, for liquefaction to occur, the ground water level should be near the surface, the thickness of the liquefiable stratum should be less i
than 7.6 m (25 f t), and the ratio of the thickness of nonliquefi-able soil strata to the liquefiable soil strata should be less than unity.
These criteria indicate that the coaditions for liquefaction to occur are present at the Perryman Site, and an in-depth study is necessary to make definitive cone.usions regarding the liquefaction potential of the granular soils at the Perryman Site.
2.5.4.8.2 Evaluation of Liquefaction Potential:
General There are two basic approaches for evaluating the liquefac-tion potential of a deposit of saturated sand that is subjected to earthquake loading.
The first approach utilizes the informa-tion available on the performance of various sand deposits in previous earthquakes.
This approach is essentially empirical, and the response of soil to dynamic loading is not evaluated by any direct means.
Simplified methods of analysis, with known limitations, have been proposed by various investigators.
- Also, a large number of factors that significantly affect the liquefac-tion characteristics of a given sand have been recognized, and may be studied in detail to confirm the conclusions of the analysis.
In the second approach, the evaluation of stress conditions in the field is done by using an analytical technig.ue, such as the one described in Section 2.5.4.7.
These stress conditions are compared with the results of extensive laboratory investi-gations to determine the cyclic stresses causing liquefaction at various depths.
At a given depth, a factor of safety against j
liquefaction can be evaluated by computing the ratio of the cyclic shear stress ratio required to cause liquefaction, or an acceptable limit of cyclic strain in representative samples in the laboratory, and the cyclic stress ratio that is induced during the design earthquake.
Methods that were based on both approaches were utilized for assessing the liquefaction potential of the granular soils i
at the Perryman Site.
(
2.5-99 1
7 L
2[5.4.8.3 Evaluation of Liqu3fcction Pot;ntiial Approach 1 L
^
In the first. approach, the procedure recommended by Seed (1976)_was,v. sed for: estimating _the. cyclic shear stress. ratio rcquired_to cause. liquefaction and the cyclic shear stress ratio
' induced during. shaking.:.The_ basic steps involved in this pro-ccdure are as.follows:
1.
Convert the N; values from the standard penetration tests to tho'N values.
Ny isfthe penetration resis-3 tance, cogect8d to an effective overburden pressure ofl96:kN/m (1.0 tons /ft ) using the relationship
=
(N)
N{ = CN i
1-1.25logjc, where C
=:
N
- 1 i
' Effective overburden pressure (tons /ft )
=
c 2
Constant which is equal'to 1.0 ton /ft E
=
y 2.
Compute the' cyclic stress ratio at any' depth in the ground that is-induced by the design earthquake using the relationship V
0.65 yd
=
"c c
Effective overburden pressure on sand where o
=
C layer under consideration a,,x Maximum acceleration at the ground surface
=
Total overburden pressure on sand layer o
=
under consideration yd A stress reduction factor varying from a
=
value of 1.0 at the ground surface to a value of 0.9 at a depth of 9 m (30 ft)
T,y Average cyclic shear stress
=
Acceleration due to gravity g
=
3.
Based on a collection of data from actual field per-formance and a few additional site studies, the lower bounds for the cyclic stress ratios that cause liquefac-tion in the field and which correspond to different Np values.and magnitudes of earthquakes, have been established (Seed, 1976).
The lower bound, cyclic 2.5-100 t
shear strength values that are obtained from such empirical charts can then be compared with the average cyclic shear stresses obtained in Step 2, and the liquefaction potential at various depths can be evaluated.
The range of N values that were obtained from standard penetration tests performed at the site was converted to a range of N values, and the corresponding cyclic shear strength values y
were plotted against depth (Figure 2.5-52).
The lower bound for stress ratios that cause liquefaction was obtained from Figure 2.5-53 (reproduced from Seed, 1976) for an earthquake of magnitude 5.6 on the Richter scale.
Knowing the vertical overburden pressure and other parameters in Step 2, the induced shear stresses were computed and plotted in Figure 2.5-52.
The plot shows that the lower bound of the strength curve is above the average induced shear stress curve, with a clear margin and a minimum factor of safety greater than unity.
These stresses and strengths, and their corresponding minimum factors of safety are summarized on Table 2.5-11.
2.5.4.8.4 Evaluation of Liquefaction Potential: Approach 2 Cyclic Shear Stress In the second approach, the computation of induced cyclic shear stresses was done by using the mathematical model that is described in Section 2.5.4.7.
Stress histories at various depths in the design soil profile, which result from the specified input motion at the surface, were obtained.
The maximum shear stress levels in these stress histories are presented in Figure 2.5-48, and discussed in Section 2.5.4.7.
All of the stress computations were done for two cases of ground water conditions.
The first case simulates the existing ground water conditions, which were reported at 3 m (10 f t) below the average ground surface elevation.
In the second case, the ground water is assumed to be at the ground sur. face, to represent the worst condition during the project hurricane.
It was found that this variation in the ground water level does not change the results significantly, except that the maximum shear stresses in the latter case are slightly higher.
Cyclic Shear Strength The next important step in this approach is to determine the cyclic shear strength of undisturbed samples obtained from various potentially liquefiable layers.
Sixteen samples, repre-senting different layers in the design soil profile, were chosen for' stress-controlled, cyclic triaxial testing.
Figure 2.5-51 shows the envelope of particle size curves for these samples.
Stress-controlled, cyclic triaxial tests were performed according i
i 2.5-101
gyy.,.
to the procedures described;in Section-2.5.4.2.1.4, Dyntmic T: sting.
The'results ofLthese tests are summarized on Table 2,5-12.
These test results were plotted on a semi-logarithmic plot to produce a single curve, presented-in Figure 2.5-54, which rcpresents the relation between the number of. cycles required to rcach failure and the corresponding cyclic shear stress ratio.
The curve.shown in Figure 2.5-54 was produced by a least-square, hyperbolic approximation of the test data.
The failure criterion uced for the purpose of preparing this curve was initial liquefac-tion,_which denotes the condition of equal confining and pore pressures.
Conversion of Irregular Stress History into Equivalent Uniform Cyclic Stress Series In approach 2, the stresses induced in the ground are compared directly with those determined to cause the liquefaction of representative soil samples.
Therefore, it is necessary to convert the irregular stress history that is actually developed into an equivalent, uniform, cyclic stress series.
This conver-cion is'necessary because it is usually.more convenient to parform laboratory tests using uniform cyclic strass applications than to attempt to reproduce the actual, field stress history.
-Three basic methods exist by which this convwrsion can be accom-plished.
However, it has been shown that different procedures uced in this step of the analysis have little offect on the final analysis (Seed, 1976).
Based on the results of the statis-
)
tical study of the representative numbers c2 cycles for a nuft.ber of different earthquake motions, a convenient basis for selecting en equivalent, uniform, cyclic stress series for earthquakes of different magnitudes has been presented by Seed (1976).
According is 5 corresponding to Seed, the number of equivalent cycles, Ne5,percen,t of the to an average cyclic shear stress, T of 6 maximum shear stresses for earthquakEy,agnitudes of from 5 to 6.
m Therefore, the maximum cyclic shear stresses that were obtained in Section 2.5.4.7 were multiplied by 0.65 to obtain the average cyclic shear stress at any point.
The cyclic shear stress ratio required to cause liquefaction was obtained from Figure 2.5-54, cnd corresponds to five cycles.
Correction Factor, Cr The cyclic triaxial test does not directly simulate the field sample shear conditions.
Also, the effect of multi-directional shaking is not included in this testing.
As a rosult, the stress ratio obtained in the cyclic triaxial test is higher, and a. correction factor, C, is applied to modify these r
0.4), a value of
. values.
For normally consolidated sands (K
=
0.57 is considered appropriate for C (Seed 1976), and the r
atress ratio causing liquefaction in the laboratory was reduced cccordingly to account for the field conditions.
2.5-102 l
l Factor of Safety' Computation TheLcyclic shear' strength at a particular depth is found by multiplying =the cyclic shear stress ratio,'obtained from Figure 2.5-54, by the: confining pressure at that depth.
The variation
~
of.the cyclic shear strength, the induced average shear stress (obtained.by the one-dimensional wave _ propagation analysis), and their ratio.(that is, therfactor of' safety against liquefaction) with depth'is shown in-Figure 2.5-55?for two different ground
. water conditions.
These results are also summarized on Table 2.5-13..
For existing ground water conditions,.the minimum-factor: of safety is found to' be 1.50 at a depth of approximately 9 m. (3 0 f t)~. _ In the other case, assuming;the ground water level to be at the ground surface has the effect of reducing the effective overburden pressure and the cyclic shear strength,
)
which results in lower factors of safety against liquefaction.
1 Even with this very' conservative assumption,-the factor of safety exceeds unity at all depths.
2.5.4.8.5 Summary and Conclusions a
Thefliquefaction potential of the granular materials at the Perryman^ Site was evaluated using two. approaches.
In the first
. approach, the. cyclic. shear strength was estimated by correlating the. blow counts from standard penetration. tests with the cyclic.
shear stresses. required.to cause liquefaction during past earth-quakes; and, the stresses were computed using the well-established, simplified procedures presented by Seed and Idriss (1971).
In the second approach, the cyclic shear strengths were estimated by laboratory testing of undisturbed samples, and the cyclic
- shear stresses were computed by performing a one-dimensional wave propagation analysis.
These studies indicate that during the Safe Shutdown Earthquake, the cohesionless soils at the Perryman Site are not susceptible to liquefaction under free-
- field conditions.
2.5.4.9 Earthquake Design Basis
, The~thme history of motion that envelopes the Safe Shutdown
~ Earthquake response spectra for damping ratio values of 0.005, 0.01, 0.05, 0.07,'and 0.10 will be used as the input motion for all dynamic. analysis.
The structures and the foundation soil will be analyzed-to find the maximum response values, such as i
stress and displacement, that will be used in design.
2.5.4.10 Static Foundation-Analyses 2.5.4'.10.1. General From a foundations standpoint, this Early Site Review is primarily concerned with the stability and anticipated settlement of. Category I, safety-related structures.
It is the purpose of i
i 2.5-103 7
1 I
i, this report section to show that a nuclear powerplant, such as cna of the two types proposed, can be safely supported on a rainforced concrete mat foundation founded on Category I compacted fill under static loading conditions.
The analyses of settlement cnd bearing capacity that are provided in Sections 2.5.4.10.2 cnd 2.5.4.10.3 are suitably conservative, and demonstrate that tha estimated foundation settlement will be of manageable propor-tien and that an adequate factor of safety exists with respect to potential bearing capacity failure.
The type of foundation to be used for the Turbine Generator Building has not yet been selected.
At this time, two general options exist:
(1) a large, relatively rigid, concrete mat foundation at shallow depth, or (2) a deep, friction /end bearing pile, or caisson, foundation.
It is believed that a nearby concrete mat founded at a shallow depth would offer a greater contribution to the load stresses imposed on the soils beneath tha Category I_ facilities than if the Turbine Generator Building wac founded on a nearby deep foundation.
Thus, for the foundation cnolyses of Category I structures presented herein, a shallow concrete mat foundation has been assumed in order to make these cnnlyses represent a consideration of the most conservative site conditions that are likely to occur.
The bearing capacity and cattlement analyses of the assumed Turbine Generator Building m2t have been included in this Early Site Review as an extension of similar studies that were carried out for the adjoining Category I structures and not out of concern for the effect that Turbine Generator Building foundation performance may have on ths general question of site suitability for a nuclear facility.
Several pipelines and electrical duct banks are classified cs Category I facilities.
The sizes, materials, and routes of many of these conduits have not been finalized.
However, prior to application for a construction permit, all Category I buried conduits will be designed to resist the estimated static earth-qunke loads.
Established engineering practices will be followed in the construction.
Controlled compacted bedding beneath, and b ckfill around, the buried pipes will be provided.
All Category I buried pipelines will be aseismically designed to prevent failure dua to ground motions caused by the Safe Shutdown Earthquake of 15 percent of g, maximum ground acceleration.
The two large, natural-draft cooling towers located approxi-mately 150 m (500 ft) from the Category I facilities are not clcssified as Category I, safety-related structures.
Thus, the foundations of these towers should not be a principal factor in determining overall site suitability.
The foundation conditions Ct the tower sites are represented in subsurface cross section E-E',
Figure 2.5-42.
These conditions are consistent with the f
gnneralized soil profile described in Section 2.5.4.2.2, at j
lonst with respect to Layers A, B, D, and E.
As to sublayers C l
cnd C',
the relative dominance of the clay fraction (sublayer l
C') that was revealed beneath the northeast portion of Unit 2 l
l l
2.S-104 t
(subsurface cross sections B-B' and C-C', Figures 2.5-39a through 2.5-40b) reappears at the tower sites.
Owing to the typically very high unit loads imposed'by natural-draft cooling towers and_their relative sensitivity to differential settlement, deep foundations are planned for support of these structures.
The type, size, and capacity of alternative deep foundations have not yet been determined.
It.is probable that whatever deep foundation is eventually selected, that system will extend to at least the top of sublayer C or C' (the bearing strata for Category I structures), which extends from elevation -6 to elevation -12 m
-(-20 to -40,ft).
The final foundation design for the natural-draft cooling towers will be provided with supportive analyses at the time of application for a construction permit.
2.5.4.10.2 Settlement: Category I Structures and Turbine Generator Buildings 2.5.4.10.2.1 General The results of the settlement analysis of the Category I structural mats and the Turbine Generator Building mats are presented herein.
Analyses with regard to settlement of other non-Category I structures are not included in this Early Site Review, but will be provided at the time of application for a construction permit.
The results presented in this section verify that the differential settlements and tilts anticipated are,.in general, of manageable proportion.
The locations at which differential settlements and tilts seem critical, primarily because of a high degree of conservatism introduced into the analysis, are delineated and discussed with respect to their effect on the feasibility of the Perryman Site to support the static foundation loads.
The prediction of settlement of the variable, multilayered, anisotropic soil common to the Perryman Site, when. subjected to asymmetric structural loads such as those imposed by the proposed facilities, is a very difficult and complex problem.
The total settlement experienced by the soil due to the application of loads consists of three components:
(1) initial (elastic) settlement; (2) primary consolidation (recompression and/or virgin compression); and (3) secondary compression.
These three components, though custonc _ly separated into three distinct phases, do not occur independently.
The division of the componente into three distinct phases is a simplification that is essential for obtaining engineering solutions.
The rate at which the primary and secondary compression takes place is also important in understanding the impact of settlements on the various structures.
Various methodologies and techniques are presently available for obtaining solutions of the magnitude and time-rate of settle-ment.
As a result of the degree of complexity of the foundation loads and subsurface conditions at the Perryman Site, a single 2.5-105
)
(cource solutien to.tha sstticm2nt'prcbicm wIo not:pocsible.
A combination of.three methods of analysis was used to estimate icettlements:for this report.
A detailed. discussion of the I-
.cpplication of each analytical method that was used is presented Jinithe paragraphs which follow. :Because of the limited extent of. design parameters available at.the time, several simplifying,
~but conservative, assumptions.were made.. Therefore, it is-believed that,' based'on. presently available' data,'the results prssented'herein: represent.an estimate ofLthe maximum possible esttlements that are likely.to occur.
A detailed discussion of
~
th3 simplifications,and assumptions introduced;into this. analysis 10 presented further.on in this section and also in Appendix 2.5.I.
2.5.4.10.2.2 Design Considerations.
Of the two-alternative types of. powerplants under considera-tion for use at the Perryman Site, the Boil'er Water Reactor
.(BWR) plant provides the greatest' foundation loads.and represents the most conservative load scheme to. analyze with respect to the
-cottlement of Category I structures and. Turbine Generator Build-ings.
Category I' structures, including the Reactor Building, Control and Administration Building, Rad-Waste Building, Fuel-H ndling Building, and the Auxiliary Building, will be supported
.on a common'. rigid, reinforced concrete mat.
This cluster of buildings has.been assumed to be monolithically connected.
For purposes of discussion, this group of buildings will be collec-tively referred to as the " nuclear. island."
The'two proposed Category-I Essential Service Water (ESW) cooling towers and the
)
non-Category I. Turbine Generator Buildings are detached from the
-nuclear island, and are.also founded on rigid, reinforced concrete mats.
Other non-Category I structures were considered in the analysis, but only to the extent that these loads may contribute to the settlements of the Category I structures and the Turbine Gsnerator Building.
In addition'to loads from non, Category.I structures, the weight of the areal fill required to raise the ground elevation to the proposed plant grade of +10.7 m (+35 ft) has also been considered.
The magnitudes of individual foundation lords L(dead plus live) as -well as : the.ldentification of the extent-of loaded areas for each type of powr.rplant, are shown in Figures 2.5-56a'and 2.5-56b.
The extent of the areal fill is shown in' Figures-2.5-37a and 2.5-37b.
Construction schedules for each of the two powerplant units have not been determined; therefore, the impact of the construc-tion of one: unit on the other cannot be completely assessed.
Thn.results'of preliminary settlement analyses indicate that, regardless~of the construction. phasing, contributions to the v
cattlement'of' Unit 1 due to'the foundation loads of Unit 2 will
- be relatively insignificant even with the relatively close prox '
Rimity of.two-corners.of the nuclear islands.
Therefore, the
-finalfsettlement calculations'for any one unit consider only 2.5-106
fcundation loads from that unit (with appurtenant structures) and neglect the small load contribution imposed by the other unit.
If it were considered, this contribution to settlement would tend to reduce long-term differential settlement and tilt by causing settlements'under the edge of the foundation mat to increase and become more compatible with settlements under the interior portion of the mat.
The construction schedule (the rate at which excavation, foundation construction, and static load application. progress) was determined from a typical nuclear powerplant project milestone chart.
The. family of load-history curves shown in Figure 2.5-57 represents-the general variation of estimated static loads (at foundation level), with time, during the construction period.
As indicated in this figure,-the construction of all structures within a given generating unit is assumed to take place simultaneously.
The installation of the Nuclear Steam Supply System (NSSS) is considered to be a critical construction stage.
Beyond this point, corrections for tilting and differen-tial settlements can no longer be made without remobilizing the heavy rigging equipment used to adjust the alignment of the reactor vessel.
Accident conditions resulting in higher static foundation loads than the loads presented in Figures 2.5-56a and 2.5-56b were not incorporated in the analysis due to the temporary nature-of such loads.
The foundation response in these conditions reflects the elastic compression of subsoils rather than the long-term consolidation settlement.
The magnitude of elastic compression is expected to be'small because the accident load, although substantial, reflects only a relatively small increase in effective stress in supporting soils.
2.5.4.10.2.3 Subsurface Conditions 1
The generalized subsurface profiles used in the settlement i
analysis have been developed from subsurface cross sections A-A',
B-B',
C-C',
and D-D', presented in Figures 2.5-38a through 2.5-41b, respectively.
Three major, generalized subsurface profiles were deemed necessary to adequately represent the varied soil stratification underlying Units 1 and 2.
Each profile consists of basically the same principal layers found in
)
the cross sections, al* hough the thickness and lateral extent of these layers may differ.
These modified profiles, which are believed to reflect the most adverse conditions with respect to settlement, are presented in Figure 2.5-58.
A detailed discussion of these principal layers is presented in Section 2.5.4.2.3.
Layers A and B found in the cross sections have been omitted from the generalized subsurface profiles for settlement because these layers will be excavated.
The interbedded sands, silts, and clays of Cretaceous age encountered in the exploratory borings below Layer E have been divided into two principal 2.5-107
lcyers (Layers F and G)'in this discussion..The soil profile i
lcxtends;to'the top of;the weathered saprolite, which is referred i
to as Layer-H.
The areal extent for which the three' profiles, i
orfcombinations of the profiles, are' applicable is delineated in the: form;of generalized soil maps in: Figures 2.5-56a and 2.5-56b.
~
The present ground surface elevation in the area of. thel
. proposed Category I structures and Turbine. Generator' Building.
Tveries.from approximate elevation +5.5 m (+18 ft)Lto elevation
+11 m (+36 - f t).
The following ground surface elevations, with respect to the mean sea level datum, havre been assumed in the analysis"for the computation of the initial vertical effective
- ctressfimposed by the existing overburden.
Elt"; : ion Facility.
(m)
(ft)
Category I: Structures
+ 6.7 (+22)
Turbine Generator Building.
+ 5.5 (+18)
' Unit 2' Category I Structures
+ 9.2 (+30)
Turbine Generator Building
+11.0 (+36) s
'The static water. level elevation assumed for this analysis was +1. 5 m (+5 f t).
The1short-term reduction of this water 1
~
level elevation duelto pumping, as in the case of dewatering for excavation'and construction, is neglected in'the settlement
')
computations._. Subsidence-due to the temporary lowering of the water leve]'is believed to be insignificant with respect to the total anticipated settlements.
This~was previously discussed in 1
.Saction 2.5.4.5.3, Dewatering System.
]
The material properties _of the layers comprising the general-ized' subsurface profile were based on a review of laboratory tost.results from all three phases of investigation for the Parryman Site and,1in part, from typical soil properties of coils cited in the_ literature (Shannon and Wilson, 1972).
The following set of properties was established for each layer included in the settlement' analysis: _ total unit weight of soil (y ), drained modulus of elasticity (E), Poisson's ratio (v ),
of consolidation (c ),-coefficient of vertical perEEa)bility rs ompression ratio (RR), maximum past pressure (o coefficient (k ), ' and coef ficie t of _ secondary compression (C A summary of the testing. procedures utilized to obtain thesE) properties is y
presented'in Appendix 2.5.H.
It is believed that highly conserva-
- tive soil 1 parameters were incorporated in the analysis for magnitude and. time-rate of settlement.
Soil' parameters will be Leonfirmed'and/or refined through additional testing prior to the application for a construction permit.
The values of soil l parameters _actually used in this analysis are presented in tcbular format'in Figure 2.5-58.
2.5-108
2.5.4.10.2.4 Analytical Approach General The analytical approach used to obtain magnitude and time I
rate of settlement employs three different computer solutions.
j The programa are described in detail in Appendix 2.5.I.
This combination of three programs enables one to incorporate the various aspects of the complicated analysis without imposing severe limitations on the numerical model used to represent the physical problem.
As a result of this approach, the effects on the estimated settlement of rigid mat foundations, multilayered anisotropic soils, and finite areal loads of varying intensities were all considered in the analysis.
The effects of structure I
embedment on settlement were conservatively neglected because, I
with all other conditions being equal, settlements of embedded structures are generally less than settlements for structures l
founded at the ground surface.
Stress Distribution Figure 2.5-59 presents a comparison of the vertical, effective stress distribution resulting from the application of identical loads on both a flexible and a rigid foundation overlying a multilayered soil system.
The applied loads indicated in the figure are typical, net static loads of the BWR plant for Unit 1.
The noil profile used represents a hypothetical profile with layers of differing rigidities.
The hypothetical profile extends to 49 m (160 f t) below the bearing stratum.
The computation of stresses due to imposed loads was made using computer programs EP10 (Dames & Moore, 1974a) and EP91 (Dames & Moore, 1975a).
Computer program EP10, Settlement Analysis Due to Areal Loads, utilizes the Boussinesq stress distribution theory, which is applicable to a homogeneous, semi-infinite, elastic half-space that is subjected to flexible loads.
Terzaghi's on.e-dimensional consolidation theory, incorporating the effects of settlement at a point from surrounding finite areal loads, forms the basis of this solution.
Computer program EP91 (CONSOL), Two-Dimensional Consolidation by the Finite Element Method, utilizes a numerical approach that is based on the theory of finite elements to model the physical problem.
The soil profile is considered to be an elastic medium subdivided into a systematic set of rectangular elements.
The rigidities of surface loads and soil layers may be considered.
The plane strain condition incorporated in this analysis assumes all loads to be strip loads of infinite extent.
The undulating stress diagram obtained from computer program EP10 (Figure 2.5-59) is characteristic of the stresses induced at a depth of approximately 3 m (10 ft) below a flexible ma.t foundation.
As a result of modeling a rigid mat foundation with computer program EP91, the local undulations in stress at the same depth are eliminated due to the more equal distribution of 2.5-109
rpplicd lo2d] through tha rigid mat.
Tha r culta of computar program EP91 better approximate the actual conditions with rc:pect to mat rigidities than do those of computer program EP10.
Because the design of the Category I foundation mat has not been finalized, a simplified mathematical model of the mat waa adopted in this analysis.
In this model, the mat was assumed t3 consist of 7.0 m (23 ft) of unreinforced concrete.
It should be noted that at approximately 46 m (150 f t) below foundation icvel, the distribution of stresses on a horizontal plane, as computed by the two programs, becomes similar.
The magnitudes of stress vary as a result of the different numerical techniques cnd load configurations that were employed.
As expected, edge atresses (reference points A and C in Figure 2.5-59) beneath the foundation mat resulting from the computer program EP91 rigid mat analysis are higher than those computed by computer program EP10.
In turn, stresses directly beneath the center (point B in Figure 2.5-59) of the foundation mat are less for the computer pr gram EP91 analysis than for the computer program EP10 analysis dua to the redistribution of stresses by the rigid mat.
S7ttlement Computation Settlement profiles were developed along two perpendicular CCctions through each of the two powerplant units.
Settlements dua to net static loads from the nuclear island, Turbine Generator Building and the areal fill were computed.
Net static loads rofer to foundation loads in excess of the existing weight of overburden at a particular depth in the soil profile.
1 It is recognized that relatively short-term changes in stress will occur within supporting strata prior to the start of f
m2t foundation construction resulting from (1) construction j
dnwatering, (2) excavation, and (3) placement of the Category I i
fill and concrete.
While any one of these construction operations may produce significant stress changes (either positive or j
ncgative), these changes tend to be partially self-compensating.
During the period of construction dewatering, stresses in bearing i
etrata increase because of the loss of the buoyant effects of subsurface water.
However, foundation excavation occurring chortly after dewatering would, on the other hand, tend to cause a decrease in effective stress in bearing soils.
When-the dewatering program has produced its maximum drawdown end foundation excavation has attained its maximum depth, the not stress change in the bearing strata from that which existed before construction operations, will be negative.
However, soon after this stage, construction of the Category I fill and segmental construction of the concrete mat will begin which will have the l
offect of balancing the net negative change in stress attributable to dewatering and excavation.
Upon completion of the Category I mat foundation, the net negative change in effect tho bearing surface will be approximately 53 kN/m{ve stress at2).
i (1100 lb/ft i
2.5-110
r i
Subsequently, the mat foundation will experience (1) some deflec-tion due to recompression of bearing strata up to a state of j
stress wherein foundation loads equal the weight of original overburden, and (2) foundation settlement as a result of net static loads.
Owing to the relatively small magnitude of the recompression load imposed by the rigid mat foundation, the effect of recompression on the ultimate settlement profile was qualitatively assessed to be of minor proportion.
Hence, the settlements estimated in this report are settlements attributable j
to net static loads only.
Settlement was estimated along the two perpendicular sections of the BWR powerplant since that type of plant would provide the greatest foundation loads.
Initially, the numerical model (Figures 2.5-60 and 2.5-61) and plane strain analysis of computer program EP91 were utilized.
The soil profile was divided into two meshes to facilitate the analysis.
Vertical stresses at the base of the upper mesh served as loads for the lower mesh.
The i
results of both meshes were combined based on the principal of superposition.
Because the assumption of plane strain is overly conservative when applied to nonuniformly loaded areas of finite extent, the results obtained from the EP91 computer program were reduced to take this consideration into effect.
Reduction factors were developed by using computer program EP10 to obtain a ratio of the settlement due to strip loads (plane strain) to the settlement due to areal loads of finite dimension.
This ratio approximates the applicability of plane strain for a given set of conditions.
As this ratio approaches unity, the assumption of plane strain becomes increasingly more valid.
Reduction factors were developed for each point along the sections analyzed with the EP91 computer program.
Plane strain settlements were reduced by as much as 13 percent beneath the nuclear island, and by as much as 23 percent beneath the Turbine Generator Building, after apply.ing these factors.
These results indicate that the assumption of plane:
strain is indeed much more concervative for long, narrow leads when settlements for these loadr. are cr.lculated along the longi-tudinal axis of the load.
The actual magnitudes and distribution of these settlements are presented in Section 2.5.4.10.2.5, Results of Settlement Analysis.
An estimate of the heave resulting from the excavations required for construction was obtained for the center of the nuclear island and Turbine Generator Building excavations.
The procedure followed was similar to that described earlier for settlements due to net static load.
The plane strain limitation of computer program EP91 did not permit consideration of the contribution to settlement from adjacent areal loads not in line with the settlement profiles.
Computer program EP10 was used to establish the effect that the 2.5-111
ESW cooling towers and non-Category I building loads have on cattlement along the settlement profiles.
These contributions cra included in the final results for ultimate settlements due to net static loads.
Settlements at the corners and center of each ESW cooling tower were obtained using computer program EP10.
These results crs also highly conservative, based on the discussion of vertical etresses presented earlier.
Secondary compression effects were estimated and shown to bn negligible with respect to the ultimate net settlements.
H2nd calculations, which incorporated a range of coefficients of c:condary compression estimated from laboratory tests, were performed.
A hypothetical soil profile, consisting of 61 m (200 ft) of homogeneous clay, was used for this calculation.
Time-Rate Analysis An insight into the time-rate of settlement was obtained through the use of computer program EP82, One-Dimensional Consolidation of a Layered Soil System by a Crank-Nicholson Finite Difference Method (Dames & Moore, 1974b).
The one-dimensional consolidation theory normally provides a conservative Gpproximation of time-rate of settlement.
Settlements in the field should actually occur at a faster rate than the rate computed from computer program EP82, because pore water pressures in the field are being dissipated in three dimensions.
- However, the one-dimensional consolidation theory offers a good approxi-
)
mation of actual field conditions in cases where the foundation width is large compared to the depth of material undergoing consolidation, as is the situation beneath the large mat founda-tions here.
The stresses computed by the two-dimensional finite element program, EP91, were utilized to compute the influence factors at locations where time-rate computations were to be performed.
These factors served as input to the computer program, EP82, used to compute the time-rate (progress) of settlement in order to better approximate the actual stress distribution beneath the rigid mat foundation.
i
)
2.5.4.10.2.5 Results of Settlement Analyses The results of the static settlement analysis are presented i
graphically and in tabular form in Figure 2.5-62.
As noted l
previously, a time occurs during construction beyond which it is
)
not practical to make corrections for foundation settlements that have occurred.
This construction stage corresponds to the time of installation of the NSSS equipment, which is projected to take place about 3.2 years after the start of construction.
The data presented in Figure 2.5-62 include settlements calculated to occur at the critical construction stage as well as ultimate settlements.
As presented in Figure 2.5-62, the corrections 2.5-112
that will be made at 3.2 years are believed to be of manageable proportion and are not uncommon in practice.
The settlements remaining after this stage in construction will again impose some tilting across the main components of the plant.
The magnitude of these movements is presented on Table 2.5-14.
At the Unit 1 location, it is estimated that all settlement will be completed within 27 years of the start of construction, while settlement at the Unit 2 site will take an additional three i
years.
These estimates for 100 percent consolidation, obtained from the one-dimensional consolidation theory, should be considered i
approximate, because the load schedule is very generalized and subsurface drainage conditions are extremely complex.
The settlements occurring after the installation of NSSS j
equipment appear to be within the range of normally accepted j
values, except for settlements along a portion of the longitudinal I
section between the nuclear island and the Turbine Generator l
Building.
The relatively sharp cusp in the settlement profiles (Figure 2.5-62) is developed there as a result of the discontinuity between the nuclear island and Turbine Generator Building mats.
This discontinuity does not allow for a transfer of stress from one mat to the next, and therefore, subjects the foundation soils in this area to the cumulative effect of the high edge stresses developed under both mats.
In practice, structural design changes can be instituted, along with the application of some special construction techniques, to reduce these estimated edge settlements.
Ultimate settlements of the ESW cooling towers due to the net static loads and surrounding areal fill are presented in tabular form in Figure 2.5-62.
These settlements are believed to be even more conservative than settlements computed for the nuclear islands and Turbine Generator Buildings.
Estimated differential settlements and tilts are generally within the acceptable range for this type of structure.
Margi.nally accept-able cases, such as those for the north tower of Unit 2, will be reevaluated prior to application for a construction permit.
The maximum expected heave at the center of the excavation for the nuclear island is estimated to be approximately 7.6 cm (3.0 in) for Unit 1, and approximately 11.4 cm (4.5 in) for Unit 2.
The anticipated heave at the center of the excavation for the Turbine Generator Building (Generator Area) is approximately 6.4 cm (2.5 in) for Unit 1, and approximately 10.2 cm (4.0 in) for Unit 2.
These values will be approximately equal for both types of plants (BWR or PWR).
In light of the conservatism incorporated in this analysis, the subsurface soils at the Perryman Site appear to be capable of adequately supporting all of the proposed foundation loads imparted by the rigid mats.
2.5-113
2.5.4.10.3 Bearing Capacity: Category I Structures and Turbine Generator Buildings 2.5.4.10.3.1 General The results of the bearing capacity analyses of the Category I structural mats and the Turbine Generator Building mats are presented herein.
Analyses with regard to the bearing capacity of other non-Category I structures are considered unnecessary for Early Site Review, and will be provided at the time of application for a construction permit.
The analyses presented in this report demonstrate that, for the most unfavorable possible combination o'f subsurface conditions and foundation loading at the Perryman Site, an adequate factor of safety against bearing c pacity failure can be shown to exist.
The classical bearing capacity theory.for a foundation on coil has been developed over the years by Prandtl (1921), Terzaghi (1943), Meyerhof (1948), Caquot and Kerisel (1953), Vesic (1973),
and others.
This theory involves failure in three principal modes:
a general shear failure, a local shear failure, and a punching shear failure.
The failure pattern consists of a wedge and slip surfaces, which start at the edges of the footing and end somewhere in the soil mass.
Vertical compression under the
)
footing is significant, with a visible tendency toward soil bulging along the sides.
The mode of failure that can be expected depends on a number of factors that are not,in general, clearly understood.
The failure mode for large mat foundations in particular is not well understood.
Vesic (1973) postulated that I
a large mat foundation may fail in punching shear and not in general shear, even on a dense soil.
Nonetheless, the conventional approach to bearing capacity has been through various bearing capacity formulas.
The results of such an analysis are included in this report.
A comparison of the classical bearing capacity failure pattern with a typical circular failure surface suggests that the bearing capacity problem can be satisfactorily handled as a general stability problem.
Current computer-oriented solutions that are normally used for slope stability analyses are available for such problems.
The slope stability solutions and the bearing capacity solutions both consider the plane strain case (continuous footing).
By considering the foundation to be an embankment with vertical sides, the slope stability solutions can be used to estimate the factor of safety against a bearing capacity failure.
The factor of safety for a given trial surface is obtained by comparing the overturning moment caused by the foundation stress with the potential resisting moment generated by the shear strength mobilized along the trial surface.
The critical failure surface should provide the lowest factor of safety.
The results of such moment equilibrium analyses are provided in this report as a conservative alternate approach to bearing capacity calculation.
2.5-114
p 2.5.4.10.3.2 Design Considerations of the two alternate types of reactors under consideration for use.at the Perryman Site, the BWR plant represents the most conservative load scheme to analyze with respect to the bearing capacity of Category I structures.
The Reactor mat-includes loads provided by the Reactor Building, as well as those of the Rad-Waste,. Auxiliary, Fuel-Handling, and Control and Administration Buildings.
The approximate static foundation loads (dead plus live loads) for the BWR plant are as follows:
Total Stgtic Pregsure Facility (kN/m ) (lb/f t )
Control /Adminis'tration 390 8100 Auxiliary 200 4200 Fuel-Handling 200 4200 Rad-Waste 220 4500 Reactor 460 9600 ESW Cooling Towers 240 5000 j
These structures (except the ESW cooling towers) will be founded on a common rigid mat, which measures approximately 80 by 110 m (270 by 350 f t) in plan dimensions, at approximately elevation zero.
Each of the two ESW cooling towers will be founded on a smaller rigid mat, which measures approximately 30 by 35 n. (100 by 120 ft), at approximately elevation zero.
The mat foundations will be supported on controlled, compacted fill.
In the case of.the Turbine Generator Buildings, the Pressure Water Reactor (PWR) plant layout provides the most critical foundation plan of the two powerplant alternates, because its mat is founded at a higher elevation (approximately +8 m (+28 ft)).
Turbine Generator Building foundation loads are about the sam 9
,for each pignt, with the generator area contributing 2250 kN/m (5300 lb/ft ) and the service bay providing 160 kN/m (3400 lb/ft2).
The Turbine Generator Building will be supported by a mat founda-tion that will measure approximately 40 by 120 m (130 by 400 ft).
This mat will also be supported by controlled, compacted fill.
When the plant design has been finalized and a limit of tolerable settlements established, it may become necessary to i
consider some type of deep foundation for support of the Turbine Generator Buildings.
In such an instance, a detailed analysis of the bearing capacity for alternative deep foundations will be undertaken.
The rigidity of the concrete foundations was not taken into account-in terms of the effect that it may have on the elimination of sharp stress-discontinuities immediately beneath the mats.
In the moment equilibrium analysis, however, potential failure arcs, such as those generated by the computer study, that extended up through the rigid mat were discounted.
These failure arcs 2.5-115
r w;re the result of inputting the loads to tha probicm rather thrn the arcs which represent viable failure modes.
During accident conditions, buildup of temperature and pr ssures may indyce dynamic strgsses equivalent to load increases of up to 960 kN/m (20,000 lb/ft ).
To account for this condition 2
in the bearing capacity analyses, an additional 960 kN/m load was assumed to occur over a 30-m (100-ft) diameter area on the Recctor mat.
During an earthquake, transient loads that are imposed on tha foundation are both eccentric and inclined.
These transient lords would have the effect of decreasing the ultimate bearing capacity.
Accurate determination of the magnitude, eccentricity, cnd angle of inclination of the resultant load would require a d3 tailed dynamic analysis of the soil-structure system.
Typically, this analysis involves the input of earthquake-generated ground motions to a two-or three-dimensional finite element model for the purpose of establishing the effects of soil-structure inter-cction.
Because a final decision as to the type of powerplant to be constructed at the Perryman Site has not been made, the rcquired analysis is not possible at this time, and has not been undertaken for this Early Site Review.
Prior to the time of cpplication for a construction permit, when the final plant damign has been established, a suitable analysis of soil-structure interaction and a subsequent evaluation of bearing capacity will ba completed.
2.5.4.10.3.3 Subsurface Conditions
)
As indicated in Section 2.5.4.10.2, Settlement: Category I Structures and Turbine Generator Buildings, three subsurface profiles have been selected to conservatively represent soil etratification underlying these facilities because actual condi-tions are somewhat variable.
For bearing capacity. calculations, coil profile 2A was assumed because it presents the least favor-able conditions with regard to foundation stability.
The soil profile is presented with respect to the proposed foundations in Figures 2.5.I-4 through 2.5.I-6.
Among the assumptions made with regard to subsurface condi-tions are the following:
1.
The ground water level exists at the foundation level, elevation -1 m (-3 f t).
A preliminary analysis performed with an assumed ground water level of +6.8 m
(+22.3 ft) yielded no significant change in the factor of safety of the nuclear island foundation mat as computed from moment equilibrium analysis.
2.
Total stress (undrained) parameters at low strains were chosen for foundation clays, which implies that the total building loads are applied instantaneously.
2.5-116
c 3.:
,The shear. strength of the soils above the foundation level has been ignored.
2.5.4.10.3.4 Analysis.by the General Bearing Capacity Equation The bearing capacity. equation utilized in this analysis was the classical.Terzaghi equation modified by Vesic (1973).
The equation-appears,in Appendix 2.5.I.. The solution of the equation applies only to. uniformly' loaded circular, rectangular, or strip l
footings resting on a homogeneous soil.
Some modifications to the procedures for~ applying the bearing capacity equation have been made for a two-layer clay system, but these modifications i
have only' limited applicability; for granular soils, most do not apply.at all. tin addition to layering effects, problems of geometry effects and boundary conditions become of increasing concern in evaluating wide (i.e.,. 80-m (260-f t)) foundations j
underlain by a comparatively thin (i.e.,120-m (390-f t)) layer
-of soil, which is in turn underlain by bedrock.
Some additional modifications in the form _of a rigidity index have been applied to analysis by conventional formulas to account for soil compres-sibility.
Hence, it can be concluded that the application of the classical bearing capacity equation to Category I and Turbine Generator Building foundations is very limited.
However, the
-very conservative.results of this conventional analysis are presented in Table.2.5-15, along with the factors of safety from the moment equilibrium studies (also conservative), for purposes of comparison.
The values in this table were developed by assuming that the foundation materials consist of a homggeneous clay with sgrength parameters of 4 = 0 and c = 192 kN/m (4000 lb/ft ).
2.5.4.10.3.5 Analysis by. Moment Equilibrium The moment equilibrium analysis of bearing capacity was performed through the use of a Dames & Moore computer program, GENSAM (1976), that employs the Spencer-Wright procedure for general slope stability analysis.
The program exists as a modification of a program, initially coded and documented by S.G., Wright in.1974, which is capable of analyzing a slope, including horizontal and/or vertical slopes for any given shape of potential failure surface.
However, only circular failure surfaces were considered in this application.
The analysis is performed by a method of slices in which the potential failure mass is divided into a number of vertical slices and the equilib-rium of each slice is considered.
The Spencer-Wright procedure can be termed an accurate method of analysis in that, unlike many older methods of slices, all conditions of equilibrium are satisfied.
The program assumes that all interslice forces are parallel and, for each slice, the weight, the normal force on the. base of the slice, and the resultant of the two resultant
-side. forces are coincident at the midpoint of the base of the slice.
2.5-117 L
E LTh3 Cell prop;rtiO3 rGquirCd CD input in th3 GENSAM computer program are the total. unit weight, the angle of internal friction, 4, the cohesion intercept, c, and a phreatic surface (pore water pressures'may not be specified for a total strength analysis).
.The approach to the stability analysis of each of the three basic foundation mats (Reactor, ESW cooling tower, and Turbine Generator Building) is illustrated in Figures 2.5.I-4 through 2.5.I-6.
A summary of the factors of safety developed from each annlysis, along with the results of the Terzaghi equation calculations, are provided on Table 2.5-15.
Both methods of enalysis imply that, for those major foundations evaluated, an cdequate. factor of safety exists with respect to a static bearing
'cepacity failure.
Details of both methods of bearing capacity computation are provided in Appendix 2.5.I.
With regard to fcundation stability under1 earthquake loading conditions, the b:aring capacity of all Category I structures will be reevaluated ot=a time'when plant design has been finalized, taking into consideration the ef fects of soil-st ructure interaction, prior to application for a construction permit.
2.5.5 Stability of Slopes The stability of earth slopes is considered qualitatively in~this Early Site Review.
There are no natural slopes that will affect the safety of the proposed powerplant structures.
Detailed analyses of temporary excavation and compacted fill clopes will be presented at the time of application for a construction permit.
These later analyses will demonstrate the dynamic and static stability,of all slopes, the failure of which
.could adversely affect the safety-related structures of the nuclear plant, or pose a hazard to the public.
This section of the Early Site Review report demonstrates that no adverse subsurface conditions exist that could prohibit the design and construction of safe slopes.
2.5.5.1 Naturel Slopes No natural slopes exist that will affect plant or public cafety.
The Bush River shoreline is approximately 670 m (2200 ft) from the nearest Category I structure, and thus need not be considered for plant safety.
The proposed location of the non-Cctegory I Auxiliary Make-up Water Pond is approximately 122 m (400 ft) from the Bush River shoreline.
The failure of shoreline
.clopes also will not affect the performance of the Auxiliary MOke-up Water Pond dikes.
At the present time, the Bush River choreline at the site consists of nesrly vertical bluffs that vcry in height from 3.to 6 m-(10 to 20 ft).
These bluffs will b3 cut back to a more suitable cross section prior to the
.etartup of plant operation.
2.5-118 o
7 2.5.5.2 Manmade slopes Manmade slopes of compacted earth fill will be constructed in conjunction with. (1) the raising of the plant grade from approximate elevation +6 ' m (+20 f t) to elevation +10.7 m (+35.0 ft), and ~ (2) the construction of the Auxiliary Make-up Water Pond.
Onsite materials may be used, to some extent, to build up the site in the vicinity.of the two generating facilities.
Raising the plant grade will yield a maximum fill height of approximately. 6 m (20 f t), with the average fill height being approximately 3 m.(10 ft).
One source of fill may be the surficial silts (Layer A) stripped during the excavation for foundation construction.
Test results indicate that these soils can be recompacted to original density and strength (Table 2.5-8).
A check of static slope stability of a typical 2-on-1 slope with a height of 6 m (20 f t) yields a factor of safety on the order of 2.0.
The check was performed utilizing Taylor's Stability Chart (Taylor, 1937), which assumes a circular failure surface-in a homogeneous embankment.
This check cannot be considered a rigorous examination of fill slope stability nor proof of the adequacy of a 2-on-1 slope.
Hcwever, it does indicate that the safety of these slopes will likely not be an area of major concern in assessing overall plant safety.
The location of the Auxiliary Make-up Water Pond is shown in Figure 2.5-36.
The pond will be approximately 4 hectares (ha) (10 acres) in area and will contain approximately a 24-hour supply-of make-up water.
It will be classified'as a non-Category I structure.
As implied by boring results from that area, subsurface conditions at the proposed pond location are generally consistent j
with the profile discussed in Section 2.5.4.2.2, Description of i
Generalized Profile.
The uppermost soil stratum (Layer A) consists of from 1.5 to 4.5 m (5 to 15 f t) of stiff.to very stiff clayey silt, which is underlain by medium dense to dense sands and. gravels (Layer B) that extend to approximate elevation
-8 m (-26 ft).
These sands and gravels are in turn underlain by very dense sands and hard clays.
The design of the pond has not been completed at this time; thus, the questions of dike stability, seepage, and dewatering cannot be quantitatively discussed.
Because the subsurface conditions described earlier do not suggest any site character-istics that might require an unusual design or unique construction technique, dike foundation stability at the proposed pond site is not expected to present any significant difficulty.
Seepage considerations will depend on the proposed elevation of the pond basin.
If the pond basin in founded within the Layer A silts and clays, it may be adequate to seal the soil surface by compac-tion with conventional earth-rolling equipment.
If the basin is located within the Layer B sands and gravels, the problems of 2.5-119
dawataring of ths cita during excavation and coeptga from the pond during operation may be the principal concerns for design.
An impermeable barrier, in the form of either a compacted clay layer or perhaps a synthetic pond liner, will probably be necessary if the pond is to be founded in the sands and gravels.
Based on information presently available, the construction cnd operation of the proposed non-Category I Auxiliary Make-up Wnter Pond will not prove to be a hazard to either safety-related powerplant structures or the public.
2.5.6 Embankments and Dams The present plant design includes retention dikes for an Auxiliary Make-up Water Pond and an embankment of compacted fill reculting from the raising of the ground surface elevation in ths vicinity of the Reactor and Turbine Buildings.
The location of the pond and the extent of the site fill are shown in Figure 2.5-36.
The specific exploration, soil testing, and engineering Enslyses necessary for the design of these dikes and embankment ero not included in this Early Site Review.
The Auxiliary Make-up Water Pond retains a standby supply of water, which would be nrcessary to replace evaporative losses in the turbine cycle cooling towers should loss of the primary supply of make-up water from the Susquehanna River occur.
The proposed plant grade of elevation +10.7 m (+35.0 ft) will place the plant well above the probable maximum surge level of elevation +6.1 m
(+22.1 f t) (Section 2.4.5).
Thus, the fill embankment will be functional in terms of plant flood protection; therefore, these fill slopes must be designed to withstand the effects of the mnximum surge without affecti'ng powerplant operation.
A discussion of the stability of fill slopes is provided in Section 2.5.5 of this report.
The proposed pond will be designed and constructed such that it will perform properly during the operation'of the nuclear powerplant.
With application for a construction permit, information concerning the investigation, engineering design, propose? construction, and performance of the pond dikes will be providuv..
2.5-120
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{
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4
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