ML20148J113
| ML20148J113 | |
| Person / Time | |
|---|---|
| Site: | Black Fox |
| Issue date: | 11/02/1978 |
| From: | PUBLIC SERVICE CO. OF OKLAHOMA |
| To: | |
| Shared Package | |
| ML20148J110 | List: |
| References | |
| NUDOCS 7811150136 | |
| Download: ML20148J113 (37) | |
Text
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,/ M S UNITED STATES
- NUCLEAR REGULATORY COMMISSION
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MDIORANDUM FOR: TERA Corp.
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'B & V Project 6212 ' November 2, 1978 SWi~ Job W-3405 'Page 1 of 6
/3
.A7 INTERIM REPORT GEOLOGIC INVESTIGATIONS'OF THE BLACK FOX STATION !
. UNIT ONE EXCAVATION f l
PURPOSE AND SCOPE l I
o Geologic mapping of the.excavawion for the proposed Elack Fox Station ~ Unit One has identified anomalous structures in the Pennsylvanian bedrock. underlying the site. The purpose of this-report 'is to discuss the current status of the geologic investi-
.gations of these1 features, and to present our findings and conclusions on their origin-and their significance to the safety l 1
of the proposed. reactor. A fina'l report will be prepared after-the excavation to final grade has been completed,and the walls and floor of the excavation have been mapped and documented.
O FIELD METHODS Geologic mapping of the trenches and the excavation walls were performed in accordance with Secticn 2.5.4 of the PSAR. The exca-I vation walls have been mapped at a scale of 1 inch = 10 feet, utilizing survey stations at intervals of 20 feet at the top and bottom of the,1:1 slopes. Elevations and coordinates of these stations'were established to the nearest 0.1 foot. The trenches were mapped at'a scale of 1 inch ='5 feet, except in areas where a scale of 1-inch = 2-feet was required to more accurately depict the' geology. Survey stations were' located every 10 feet (+ 0.1. foot) at the top and bottom of the1 trench walls, and datum horizons were !
surveyed along the face.of each trench to aid in mapping. The geologic' logs of the trenches and excavation walls were prepared by taped measurements (to the nearest 0.1 foot) from surveyed reference O
17sI(Icrtala;6, c -
B & V Project 6212 November 2, 1978 I l
SWI Job W-3405-01 Page 2 of 6 f
v) points and datums. All mapping was performed by Shannon & Wilson, Inc.: geologists.
Detailed color photographs were taken to document all the mapped excavation walls and trenches. These photographs include vertical scales, and are indexed to the field geologic logs. Panoramic color photographs were taken to provide an.overall view of the geologic features; large-scale photographs were taken of the important smaller features.
GEOLOGIC INVESTIGATIONS The excavation and trenching program was designed to expose any geologic features that might underlie the proposed Unit One. The location of all trenches is shown in Figure 1. The geologic logs of the trenches are presented in Figures 2 through 15, and selected
[} photographs of the anomalies are included as Plates 1 through 14. :
When the excavation reached 562 ft. elevation, two north-south and two east-west trenches were excavated through the Drywood coal to depths of 10 to 12 feet. These trenches (T-1 through T-4 ) exposed anomalies in the Pennsylvanian strata, including a depression in the coal that had been identified previously in subsurface inves- l l
tigations for the PSAR. Eight additional east-west trenches (T-5 - I through T-12) were then excavated to further investigate these I anomalies.
1 1
The trenches expose three main anomalous structures (Anomaly A l through C) and several lesser features in the excavation. Anomaly l A is a depression in the coal in the eastern half of the excavation; l Anomaly B, an offset along the west flank of Anomaly A; and Anomaly j l
C, an offset in the northwestern part of the excavation. These l l
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- B ' & H V: Proj e'ct ' 6 212. November 2, 1978
- SWI Job'W-3405 >Page 3 of 6
- - features are labeled 'cn1 , the geologic logs-and are shown in plan view on'a' Structure Contour Map on Top of the Drywood Coal (Figure
! 16).- These three anomalous structures are described in detail and
- the1' evidence for their origins discussed below.
. Anomaly A - Depression in the Coal. This north-trending anomaly
, was first identified during subsurface investigations for the Black j
Fox Station.PSAR. Borehole stratigraphic correlations of the-coal and a sandstone bed approximately 80 feet below the coal indicated that this. anomaly is a depression in the coal which is not reflected !
in the deeper strata. On the basis of the boring data, the anomalous depression was' interpreted to have formed by deposition of the coal in an erosional channel cut in the underlying Savanna Shale. This evidence is. discussed in Subsection 2.5.1 and Appendix 2B, Section 2B.5.5.2, and the anomaly is depicted in Figures 2B.5-14, 2B.5-15, and 2B.5-16 of the PSAR.
The geometry of the depression in the coal bed, as exposed in the
- trenches,is essentially as depicted in the PSAR (Figures 2, 4, 7, 12, 16,and Plates 1 and 2). I,t is a broad downwyrp that extends below the northern excavation wall and dies out la the southeastern l part of the excavation. The depression is not epntinuous at depth.
This is evident from the boring data and by a relatively flat-lying sequence of concretionary shales exposed in Trench T-3 and T-10 a few feet below the deformed coal bed (Figure 4 and 13, and Plate 2).- The depression'also is less pronounced in the Pennsylvanian strata overlying the coal. .
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The. stratigraphic record exposed in the trenches indicates that the depression formed in Pennsylvanian time as a result of differential f
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L i B & V Project:6212 November 2, 1978 SWI Job W-3405-01 Page 4 of 6 O compaction of a. soft gray.siltstone that directly underlies the coal.. This.is evidenced by approximately 6 to 7 feet of thinning of the siltstone between the coal and an underlying concretionary-shale below the trough of the depression (Figures 4 and 13) . Most e
of the deformation occurred after deposition of the coal, and prior to the deposition of Pennsylvanian marine shale' strata directly overlying the coal. This sequence af events is apparent from the unconformable contact between the coal and the overlying i strata, and from the basin-filling character of the marine shales within the depression (Figures 2 and 4, and Plates 1 and 2). Later downwarping in this basin was relatively minor (about 1.5 feet), and occurred only after.at least eight feet of marine shale had been
' deposited above the coal.
Anoidaly B - Off set Along West Flank of Anomaly A. This offset is exposed =in Trenches T-1,.T-3, T-3NB, T-5,.T-6, T-7, T-8, and T-12
() (Figures 2, 4 ', " 6 , 8, 9,'10, 11, and 15, respectively).
Figure 16 and Plate 1, it is a north-trending offset along the As shown in west flank'of the depression in the coal.. It has a low-angle, west-ward-dipping slippage zone with a normal sense of displacement. The horizontal separation of the coal bed across the offset ranges from 6.5 to 10 feet, and the vertical separation ranges from 1.5 to 2.5
- feet. All-of.the Pennsylvanian strata above the coal are cut by this offset, but there is no evidence of displacement either in the overl~ying Quaternary strata or in the erosional contact between the j Quaternary-and Pennsylvanian deposits (Figures 2, 9 and 15 and Plate'3).
I 1
In. Trenches T-l', T-5 and T 12,.the offset has a discrete slippage !
plane in-the-strata above the coal (Figures . 2, 8, and 15, and Plates 3 and 8)'. In. Trenches T-3~and T-3NB the offset is characterized L by pull-aparts, (Figure 6, Plates 9 and 10) and a series of rotational i slumps H(Figure T 4,1and Pla tes 11 and 12').. Exposures in Trenches T-3 l
()' and T-3NB ral so indic' ate that the soft gray siltstone underlying the )
l
B & V Project 6212 N(.vember 2, 1978 SWI Job W-3405-01 Page 5 of 6 O coal was squeezed upwards into'the ;c ' as the displacement occurred (Plates 7 and 13).
The offset cannot be traced into the underlying siltstone, nor can it be identified in the concretionary shales underlying the siltstone. These shales are fractured below the anomaly (Figures 4 and 13,and Plates 11 and 14), but there is no evidence to suggest they have had more than a few inches of displacement. Their style of deformation is also considerably different from the slumps and pull-aparts in the overlying coal bed.
Thus, the offset is apparently confined to the siltstone, coal, and overlying strata, and resulted primarily from differential compaction of the siltstone. This is a similar situation to the development of the depression in the coal immediately to the east, although the offset formed somewhat later than the depression, based on the stratigraphic record preserved in the trenches.
(])
Anomaly C - Offset in Northwestern Part of Excavation. This offset is exposed in Trenches T-1, T-2, T-3NA, and T-ll (Figures 2, 3, 5, 8 and 14, respectively), and has a north to northeasterly trend, as shown on Figure 16. It dips northwestward along a curvilinear slippage surface,and has a normal sense of displacement. The offset has a horizontal ~ separation ranging from less than an inch to as much as approximately 4.5 feet and a vertical separation ranging from a few inches to approximately 2 feet. In Trenches T-1, T-2, and T-5 (Figures 2, 3, and 8), the offset cuts the coal and all overlying Pennsylvanian strata, but it cannot be traced into the underlying siltstone. In Trench T 3NA, however, the offset does not cut the ' coal. Instead, it displaces the strata above the coal progressively less with depth until it reaches the top of the coal,
.where it dies out or is confined to a slight bedding plane slippage (Figure 3). A similar minor displacement immediately east of the
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5
B.& V Project 6212 November 2, 1978 SWI. Job W-3405-01 Page 6 of 6 O(%
offset in Trench T-1 also cuts only the strata overlying the coal, but it does not extend to the top of the coal (Figure 2).
The offset is capped in Trench T-11 by the youngest Pennsylvanian strata exposed in the excavation (Figure 14) . This thin capping sequence of shale and ironstone is found only along the north and west excavation walls and in parts of Trenches T-11 and T-12 (Figures 14 and 15) .
1 CONCLUSIONS Detailed geologic mapping and documentation of the exploration trenches in the excavation for the proposed Black Fox Station Unit One have been completed. Additional geologic mapping will be conducted as the excavation ~is taken to final grade.
A)
(, The geologic investigations to date have revealed three main anomalous structures in the excavation. The evidence disclosed in the trench exposures and from the subsurface investigations for the PSAR indicates that: 1) these structures occur within a restricted part of the Pennsylvanian bedrock, and 2) they resulted from peneco c.emporaneous deformation. They appear to have formed in Pennsylvanian time (280-320 m.y. ago), either shortly after, or during deposition of the sediments, as a result of stress from depositional loading. There is no indication that these features are tectonic in origin. Therefore, they are not considered faults, as defined in 10 CFR Part 100, Appendix A, Seismic and Geologic Siting Criteria, paragraph III (e) ; and hence, they have no impact on the safety of the proposed Black Fox Station.
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W-3405-01 Black Fox Station GENERAL DESCRIPTION OF LITHOLOGIC UNITS N
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3 / stiff, brown to gray CLAY; iron-stained; (gray SHALE; severely weathered) stiff, gray to brown CLAY (gray SHALE; severely weathered) l soft to medium soft,. gray to black, carbonaceous SHALE
. stiff, brown CLAY (gray SHALE;' severely weathered)
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,$i;tQ L--- perpendicular'to bedding soft, gray SILTSTONE;. predominately massive; upper .5 f medium stiff to stiff grey CLAY; moist to wet 1 soft,qgray SHALE; calcareous concretions
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PUBLIC SERYlCE C0ttPANY OF DELAHOMA BLACK FOX STAT 10N O
PLATE 2 2 NOVEMBER 1978 W-3 4 05-01 SHAhhCN 1 IILSCN,INC.
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See Plate 4 for close-up view of the offset.
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PUBLIC SERYlCE C0tlPANY OF OELAHDMA BLACK FOX STATION 3
PLATE 2 NOVEMBER 1978 W-34 05-01 ShANNON L llL30H,INC.
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l PUBLIC SERYlCE COUPANY Of OELAHOMA BLACK FOX STATIG!i O PLATE 4 l W-34 05-01 2 NOVEHBER 1978
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Trench T-5 showing low-angle westward-dipping slippage plane. See Plate 7 for close-up view of the offset at the base of the coal.
j PUBLIC SEF.YlCE COMPANY OF 0F.LAH0HA BLACK F01 STAT!0N O PLATE 6 2 NOVEUSER 1978 W-3 4 05-01
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! gray siltstone squeezed upward into the !
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PUBLIC SERYlCE C0tlPANY OF CM AH0t!A i
BLACK FOX stall 0N l
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2 NOVEtiBER 1978 W-3405-01 SHANNON 1 1ILSON,INC.
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. l PUBLIC SERYlCE C0!1PANY OF Or,LAH0tiA BLACT, FOX STATION O PLATE 8 ,
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O l View to the south of Trench T-3NB showing pull-apart of the coal in Anomaly B and upward squeezing of the underlying gray siltstone.
l See Plate 10 for close-up view.
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PUBLIC SERYlCE C0tlPANY OF OKLAH0tiA l
BLACK FOX STATION l
PLATE 9 2 NOVEttBER 1978 W-34 05-01 l
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PUBtlC SERYlCE C01.lPANY OF OKLAH0HA l BLACK FOX STATION PLATE 10 2 NOYEUSER 1978 E-34 05-01 SHANNON 1 flL50h,INO.
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View the south of Anomaly B offset in l Trenc). T-3 showing rotational slumping in ;
the u il and overlying Pennsylvania strata.
l See Plate 12 for close-up view of slippage plane.
PUBLIC SERYlCE COLtPANY OF Of4AHOL(A ELACK FOX STATION O
PLATE 11 2 H0YE!!BER 1978 F-3405-01 SHANNON L t it10N, INO, GIC1(CNMICAL ConsvLinats
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I Close-up view to the south of Anomaly B offset in Trench T-3 showing rotational !
i slumps in coal and overlying strata. The f offset cannot be traced into the under- l
]ying gray siltstone. ;
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l PUBLIC SERYlCE C0tjPANY OF OKLAH0HA BLACK FOX STATION O ptire 12 2 NOVE!1BER 1978 W-3 4 05-01 SHANNON & IlLSON,INC.
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View to the south of minor offsets immediately east of Anomaly B in Trench T-3 showing slump features and squee* zing of the soft gray siltstone upwards into slippage planes in the )
coal.
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PUBLIC SERitCE CONFANY OF OKLAHOMA BLACK FOX STATION O PLATE 13 2 NOVEMBER 1978 F-3405-01
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PUBLIC SERYlCE COMPANY OF OKLAHOMA BLACK FOX STATION i
Q PLATE 14 l
2 NOVEMBER 1978 (-3405-31 l
SNAhhCN & flLSch,INO.
stortchnical consvttaats
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