ML20141N572

Preliminary Technical Evaluation Rept for Proposed Remedial Action at Lakeview Tailings Site,Lakeview,Or

ML20141N572
Person / Time
Issue date:	02/20/1986
From:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
To:
References
REF-WM-64 NUDOCS 8603170151
Download: ML20141N572 (32)

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'86 FEB 20 N1:09 Preliminary Technical Evaluation Report For The Proposed Remedial Action At The Lakeview Tailings Site Lakeview, Oregon Prepared by Uranium Recovery Field Office U.S. Nuclear Regulatory Commission WM Record File WM Project-Docket No.

PDR V 0603170151 860220 LPDR E

PDR WASTE PDet Distribu lon: _

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Table of Contents Section Pag 1.0 Introduction................................................ 1 2.0 Geology / Seismology.......................................... 2 2.1 Geologic Site Characterization......................... 2 2.2 Seismotectonic Site Characterization................... 2 2.3 Geothermal Conditions..................................

2.4 Seismic Design.............................

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........... 4 2.5 Conclusion................................. ........... 4 3.0 Water Resources............................................. 5 3.1 Surface Water - Processing Site........................ 5 3.2 Ground Water - Proces s i ng Si te. . . . . . . . . . . . . . . . . . . . . . . . . 6 3.3 Surface Water - Disposal Site.......................... 10 s.4 G round Wa te r - D i spo s a l S i te. . . . . . . . . . . . . . . . . . . . . . . . . . . 10 3.5 Conclusion............................................. 12 4.0 Surface Water Hydrology and Erosion Protection. . . . . . . . . . . . . . 12 4.1 Hydrologic Description................................. 12 4.2 Geomorphic Considerations.............................. 12 4.3 Flooding Determinations................................ 12 4.4 Upstream Das 4.5 Design of Erosion Failures.................................. 14 Protection........................... 14 4.6 Conclusion............................................. 16 5.0 Geotechnical Stability...................................... 17 5.1 Geotechnical Site Characterization..................... 17 5.2 Soil Properties........................................ 17 5.3 Slope Stability........................................ 18 5.4 5.5 Settlement............................................. 19 Liquefaction........................................... 20 5.6 Construction Criteria.................................. 20 5.7 Conclusion............................................. 21 6.0 Radon Attenuation and Site C1eanup.......................... 21 6.1 Characterization of Tailings and Cover Material........ 21

6. 2 Radon Attenuation...................................... 21 6.3 Site C1eanup........................................... 24 6.4 Conclusion............................................. 24 7.0 Summary..................................................... 24 References....................................................... 26 Appendix - Tables and Figures

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1.0 INTRODUCTION

4 The Lakeview tailings site is located in south-central Oregon,

.approximately 1 mile northwest of the town of Lakeview, Oregon and 16 miles northwest of the California-Oregon border. The location is shown on Figure 1. The site consists of a main tailings pile of approximately 30 acres and a series of evaporation ponds covering approximately 69 acres. The site is shown on Figure 2.

The Lakeview site was designated as one of 24 sites to be reclaimed by the Department of Energy (00E) under the Uranium Mill Tailings Radiation Control Act (UMTRCA) of 1978. UMTRCA requires that the Nuclear Regulatory Commission (NRC) concur in the selection and performance of remedial actions at the 24 sites. The purpose of this report is to document the NRC staff review of DOE's proposed remedial action for the Lakeview site.

The remedial action proposed by DOE consists of relocation of approximately 204,000 cubic yards of off pile contaminated material and 424,000 cubic yards of tailings pile materials to the Collias Ranch site located about seven miles northwest of Lakeview, Oregon (Figure 1). The contaminated material will be placed behind an embankment and covered with a soil layer to attenuate radon and a rock layer to protect against erosion. Drainage ditches will be provided to direct runoff water away from the site.

The proposed remedial action must comply with criteria established by the Environmental Protection Agency (EPA). These criteria are as specified below:

(a) The reclamation plan is to be effective for 1000 years, to the extent practicable, but in any case for a minimum of 200 years.

(b) The radon flux from the contaminated materials must be reduced to less than 20 picocuries/ square meter /second, averaged over 100 square meters.

4 (c) Radium-226 concentrations in soil must be reduced to 5 picocuries/ gram above background in the top 15 centimeters of soil and to 15 picocuries/ gram above background in any subsequent 15-centimeter layer.

Specific ground-water standards for the remedial actions will be established by EPA in the near future. Final decisions regarding the need for ground-water restoration activities at the processing site will be made following promulgation of the standard. i The staff review of the proposed remedial action included reviews of the l following documents:  !

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(a) Remedial Action Plan (RAP) - draft dated March,1985, and final dated September, 1985.

(b) Environmental Assessment dated April, 1985.

(c) Disposal Site Characterization Report (DSCR) dated October,1985.

(d) Processing Site Characterization Report (PSCR) dated October, 1985.

(e) 00E responses dated August 20, 1985, to previous NRC comments.

(f) Preliminary design documents transmitted by letter dated October 22, 1985.

The staff review of the proposed remedial action is based on a Standard Review Plan (Reference 15) developed by the NRC's Division of Waste Management.

2.0 GEOLOGY / SEISMOLOGY 2.1 Geologic Site Characterization The Lakeview processing site and the Collins Ranch disposal site are both located in the basin and range (BAR) physiographic province.

The regional topography is characterized by alternating north to northwest trending ridges (horsts) and valleys (graben) caused by normal faulting. During the Pleistocene these valleys (grabens) often contained lakes which filled the valleys with sediments to depths greater than 5000 feet. The processing and disposal sites are located in the Goose Lake Graben. The Goose Lake Graben sediments range from silts and clays to conglomerates and are underlain by Miocene and Pliocene volcanic deposits. Specifically, the sediments underlying the processing site are interbedded silts, sands, and clays of lacustrine and alluvial origins, while the disposal site is located on a remnant terrace deposit consisting of interfingered layers of silty sands, sandy silts and surficial lenses of high plasticity clays.

2. 2 Seismotectonic Site Characterization Regionally, the Lakeview processing site and the Collins Ranch disposal site are located in the extreme northwest portion of the BAR, bounded on the west by the Cascade Mountain Province and on the north by the Columbia Plateau Province. The boundary between the

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BAR and the Columbia Plateau is delineated by a series of right lateral strike slip faults. These northwest trending faults are the result of crustal extension which created westward transport of the BAR with respect to the Columbia Plateau to the north. The faults j bound blocks which were subjected to internal extension on a set of conjugate normal faults trending about N20*E and N40*W. The sites 2

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are located in one of these blocks'. Present day regional stress in I this northwestern portion of the 8AR is approximately N70*W to l 570*E, and as a result would cause rotation of the blocks and extension on the northwest and northeast conjugate faults. Previous

' fault displacements within this system have the typical BAR structure. . Displacement on the major normal faults has been '

estimated to be at least 5000 feet based on well logs.'

Historically, southeastern Oregon is an area characterized by low to moderate seismicity. The region is characterized by moderate-sized  :

' earthquakes within seismic zones associated with the right lateral j shears and low to moderate seismicity on normal faults within the i horst graben blocks. Earthquakes with a Modified Mercalli Intensity j of VII have been recorded in the region. '

The Lakeview site lies within the Goose Lake Graben, a BAR graben  :

bounded on the west by the Fremont Mountains and on the east by the '

Warner mountains. Large displacement normal faults of Pliocene to j Holocene age bound the graben and probably additional fracturing and '

faulting exist in the down dropped block underlying the graben. The Lakeview site is located 0.5 miles west of the fault which separates the graben and the Warner Mountains. The DOE analysis of the hazards due to' active (Holocene) faulting indicates that significant

- hazards exist due to the following faults or fault zones: the Goose Lake graben fault, the Warner Valley fault, the Summer Lake fault, the Surprize Valley fault zone, the frontal fault on the east flank  !

of the Fremont Mountains, and unmapped faults in Goose Lake Valley.  !

The RAP and the DSCR do not provide a site specific discussion of the proposed disposal site and its relationship to the regional tectonics. Considering the active nature of the region, additional '

information to demonstrate that faulting will not adversely affect the site must be provided prior to approval of the RAP.

2.3. Geothermal Conditions ,

The Lakeview Processing site is located in a Known Geothermal Resource Area (KGRA). The BAR is a province of high heat flow

- generally attributed to the existence of a thin, extending crust.

The pattern of known geothermal anomalies in the BAR appears to follow the major north-south normal faults which mark the boundary between the mountain front and basins. In Oregon, there are five

-major areas, including the Lakeview KGRA.

The Lakeview KGRA is on the east side of the Goose Lake Valley and contains three hot springs and over 40 geothermal wells from 3 to j . 529 meters in depth. Both north and south of the KGRA and west along the western border of the Goose Lake graben additional hot

springs and geothermal wells are located. Many of these wells and springs are located within 1.5 miles of the processing site.

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F closest, Hunters Hot Springs, lies about 250 feet north of the northernmost evaporation pond and 0.4 miles northwest of the tailings pile. Evidence of geothermal activity at the Lakeview site

" itself consists of water temperatures in the two monitor _ wells l

.immediately north of the evaporation ponds which register 60* and 41* C, respectively, as well as a four-inch blowhole which opened {

through the snow in the south evaporation pond in January, 1984.

Since the mill tailings are to be removed from the processing site to the Collins' Ranch disposal site during remedial action, the geothermal activity noted has no impact on the proposed remedial action. No ir.fonmation was provided in the DSCR to evaluate the

' impact of geothereal activity on the Collins Ranch site. This  !

information must be provided prior to approval of the RAP. '

2.4 Seismic Desion The PSCR provided a detailed and conservative determination of seismic design parameters based on a detailed evaluation of the '

regional and site specific active faulting and regional and site i

. specific seismicity for the Lakeview processing site. However, since the proposed remedial action is to move the tailings to the l

Collins Ranch site from the Lakeview site, the site specific  :

seismotectonics for the Lakeview site is not relevant to the disposal site. With regards to the Collins Ranch site, the OSCR provides no site specific discussion of the seismotectonics and, ,

therefore, no evaluation of the impacts or the adequacy of the seismic design can be made. Additional information in this regard has been requested.

2.5 Conclusion In order to develop a remedial action plan for stabilization at the Collins Ranch alternative site that adequately addresses long-ters  ;

stability, additional geologic, seismic and geothermal information ,

must be provided. While the DSCR provided a very thorough analysis of the site specific and regional geologic, seismologic and geothermal conditions at the Lakeview site, only the regional  ;

portion of this study has any bearing on the Collins Ranch site. i The DSCR does not discuss the Collins Ranch alternative site and its  ;

location with respect to site' specific faulting, the determination '

of the design acceleration, or the site's relationship to the KGRA. .

Therefore, the RAP should provide a detailed discussion of the site f t

specific geology, seismology and geothermal activity for the Collins Ranch site which inc. ides, but is not Ifmited to, the following: l The relationship between the regional tectonics and the site

specific structural geology.

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The relationship'between the regional and site specific seismicity and the determination of the HCE and the resulting horizontal ground acceleration.

. 3. 0 WATER RESOURCES 3.1 Surface Water - Processing Site l

3.1.1 Surface Water Characterization The Lakeview Processing Site is situated within the Thomas  !

Creek Drainage Basin. Hammersley Creek flows from the '

northeast across the site and exits in a southwesterly direction, at which point it feeds into the East Branch of Thomas Creek. Hunters Hot Springs Creek (Hunters Creek) originates at the geothermal Hunters Hot Springs and runs in a southwesterly direction where it enters Warner Creek, which. i flows just north of the processing site evaporation ponds (Figure 2). ,

3.1.2 Surface Water Quality Water samples were taken and analyzed by the DOE from selected locations along these creeks. The testing program enabled the DOE to identify two chemical types from the surface waters of the area. The East Branch of Thomas Creek exhibits a sodium l and bicarbonate ion trend, with TDS concentrations of 220 to 260 milligrams per liter (ag/1). Samples taken from Hunters l i

Creek exhibit a sodium and sulfate trend, with TOS- t concentrations of 800 to 850 mg/1. Hunters Creek was also  !

shown to have elevated arsenic values when compared to the East  !

Branch of Thomas Creek.

The 00E has interpreted the difference in chemical type to be  !

associated with Hunters Hot Springs, which is located directly upstream from sampling sites on Hunters Creek. Hunters Hot i Springs is an active geyser area that contributes higher than  !

normal concentrations of sodium, sulfate and chloride to the  ;

surface waters. The PSCR also indicates that the Hunters Hot '

Springs area is a source of higher concentrations of TDS and arsenic. I The surface water profile shows that all parameter  :

concentrations are within EPA established limits for drinkinq  !

water, excluding the elevated arsenic concentrations found in  :

Hunters Crcek. A recent :urvey indicates that surface water resources in the area are mainly used for purposes of l t

irrigation of cropland and livestock watering.  !

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j 3.1. 3 Surface Water' Impacts and Restoration The' staff review of information presented in the RAP and PSCR i indicates that Hammersley and Warner Creeks flow only during periods of increased precipitation and otherwise act as '

intermittent streams. Also, surface water quality data presented in the RAP for monitoring stations upstream and downstream of the processing site show little or no chemical i quality variability occurring in surface waters in the vicinity ,

of the mill site. This would indicate that the tailings have  !

not had an impact on the quality of surface water at the processing site.  ;

The RAP states that_ steps will be taken to minimize surface water degradation during performance of the remedial action.

These steps will include synthetically lined catch basins where

. water contaminated during the construction activities will be treated to meet applicable Federal and State standarrk prior-to discharge. Runoff from unaffected areas will be diverted  !

around the site by diversion ditches. In addition, water quality monitoring of the intermittent streams will continue  :

during the remedial action.

i Based upon submitted information, the staff has concluded that degradation of surface waters in the vicinity of the alli site has been and will continue to be negligible.

3.2 Ground Water - Processing Site 3.2.1 Ground-Water Characterization Information on subsurface lithology existing at the processing site was obtained from 32 borings and accompanying borehole

-logs. The borehole logs indicate that the subsurface stratigraphy is complex and consists of alterrating sequences of silty sands and gravels interspersed with lenses of clays and silty clays. This type of stratigraphy is characteristic of lacustrine and fluvial sediments of the region.

To get an understanding of the ground-water regime existing beneath the processing site and surrounding area, monitoring wells were installed as shown on Figure 3. Six of the monitoring wells were screened at zones from 9 to 25 feet beneath the ground surface, and 26 monitoring wells were paired and screened at depths of 20 to 25 feet and 70 to 75 feet beneath the ground surface. These two zones were determined to '

be water transmitting strata based on analysis of borehole logs and visual interpretation conducted during drilling.

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Water level measurements taken from wells screened in the shallow zone indicate that ground-water flow is from northeast to southwest beneath the processing site and surrounding area. The data also indicated anomalous water temperature readings at one well pair. The water temperature readings for wells 523 and 524 were 41*C and 61*C, respectively. This occurrence is interpreted by the. DOE to be caused by upward moving geothermal water and is localized at only this particular well pair. The staff agrees with the DOE interpretation.

Parameters such as hydraulic conductivity, storativity and porosity were obtained through a series o' pump and slug tests conducted at the processing site. A 24-huur pump test with a 24-hour recovery analysis was conducted in August,1984, for both shallow and deep zones. A pumping rate of 12.4 gpm was used during the test of the deep zone and 0.6 gpa was used for the shallow zone. ,

TransmissivitieswerecalculatedusingtheHantus$-bacobmethod and the Jacob-Cooper approximation. Both methods are widely used by grour.d-water professionals as tools for exploration and analysis of water resources and are acceptable to the staff.

The values for vertical hydraulic conductivity of aquitards were calculated with the Hantush-Jacob method. The saturated thicknesses for all calculations with regard to mcnitoring wells is stated to be the difference between initial water level elevation and the elevation at the bottom of the screened interval.

Results of pumping tests conducted give average transmissivity values of 33.7 ft2/ day for the shallow zone and 103.4 ft2/ day for the deeper zone. These averages are based on six pumping wells and six observation wells. Averages are also given for storativity and vertical hydraulic conductivity values as well, and are presented in Table 5.4 of the PSCR. However, there is some uncertainty associated with these values because they are calculated from a very small population of pump tests. The DOE has been directed to address this problem and submit values more reflective of conditions found in the field.

Pump test data has shown that a hydraulic connection exists between the shallow and deeper zone. Indications are that the entire sequence of strata between the two zones acts as a multiple aquifer system. The entire layered sequence of sands, 7

gravels, and clays existing beneath the processing site tends to give credence to this interpretation.

The DOE also conducted slug tests to measure local variability in hydraulic conductivities in saturated strata beneath the processing site. The Skibitzke method, the Bouer-Rice method, and the Hvorslev esthod were used to analyze the test data.

All three methods are widely used by ground-water professionals to determine hydraulic conductivity; however, the Bouer-Rice method is most applicable to the hydrogeological environment at the processing site since it meets more of the assumptions necessary for field application than the other methods. The slug tests analyzed for hydraulic conductivities by the Skibitze method averaged 1.02 ft/ day as compared to the Bouer-Rice method of 1.28 to 0.86 f t/ day, and the Hvorslev method of 0.76 ft/ day. These average values correlate fairly well.

Seepage velocities for both the shallow aquifer zone and deep aquifer zone were calculated using hydrogeologic parameters acquired from pump test analyses. The shallow and deeper aquifer zone seepage velocities were calculated to be 0.23 ft/ day (84 ft/ year), and 0.96 ft/ day (170 ft/ year),

respectively. These values represent a range over the entire sequence of strata acting as an aquifer zone.

3.2.2 Ground-Water Quality The DOE conducted an extensive ground-water sampling program at the processing site to attempt to characterize ground-water quality and determine the extent of impact of the tailings.

All samples of water and soil solids were collected and analyzed using established procedures and methods prescribed by USGS, EPA, ASTM, and other accepted professional, institutional and industrial standards.

Geochemical analysis of the samples show that the ground water is characterized by four different facies: a) evaporation pond seepage, b) tailings pile seepage, c) low temperature background water, and d) high temperature upward moving geothermal water.

Sampling and analysis indicates that seepage from the evaporation ponds and tailings pile results in leachate that enters the shallow aquifer zone beneath the -

processing site. This leachate movement is identified by two plumes that intersect at a point just west of the tailings pile area.

Background, low temperature ground-water samples taken at the processing site and surrounding area exceed State or Federal 8

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. standards for zinc, manganese'and iron. Background samples taken where geothermal mixing takes place exceed State or Federal . standards for arsenic, boron, and fluoride. Samples taken where geothermal mixing occurs also show TDS measurements in the range from 368 *.o 690 mg/1, compared to values of approximately 200 mg/i for low temperature background water samples.

3.2.3 Ground-Water Impacts and Restoration Based upon ground-water samples taken from the shallow aquifer zone downgradient of the evaporation ponds and tallings pile, The DOE has identified six constituents that exceed state or federal standards. These constituents are sulfate, antimony, chromium, iron, cadmium, and manganese.

Ground-water samples extracted from monitoring wells that ta,7 the deeper aquifer zone did not exceed state or federal standards for chromium, cadmium, or antimony, and show a much lower sulfate concentration level. However, monitoring wells situated in the deeper aquifer zone downgradient from the evaporation pond and tailings pile do exhibit a trend toward increasing sulfate concentrations with distance. This can be attributable to shallow aquifer zone water moving downward into the deeper aquifer zone due to an increase in permeable strata in a southwesterly direction away from the processing site.

Another contribution to the increase in sulfate concentration with depth is the introduction of geothermal mixing of background water with geothermal sources that occur in the area.

The DOE's preliminary position is that ground-water restoration with regard to the processing site is not warranted.

This position is based on the following items:

(1) The contaminant species originating at the site are non-toxic with the exception of arsenic, and that arsenic levels in the geothermal water are higher than in the contaminant plume.

(2) Ground-water quality data indicates that contamination is limited to a distance of approximately 800 feet in the downgradient direction from the processing site and to a depth of approximately 25 feet (shallow aquifer zone,).

(3) There are no known ground-water users within the influence of the contaminant plume.

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(4) 'There will be no future contaminant source once the mill tailings and site materials are relocated to the disposal site.

At the present time, EPA is in the process of promulgating ground-water quality standards pertinent to Uranium Mill

. Tailings Remedial Action Projects. Until such time as EPA completes this task, no final decistuns regarding the need for ground-water restoration can be made.

3.3 Surface Water - Disposal Site 3.3.1 Surface Water Characterization The fromdisposal site is situated within a small drainage emanating Auger Hill. Runoff in the drainage flows from the northeast to southwest across the disposal site. The runoff which occurs in this area is dependent on precipitation and is not frequently observed. This is due to the fact that basin and range areas similar to that of the disposal site receive minimal precipitation as a result of elevation and topographic location. The nearest flowing water course is located at a distance of over 0.5 miles in a westerly direction from the disposal site.

3.3.2 Surface Water Impacts Surface water impacts will be minimized by measures identical to those proposed for the Lakeview site. Water contaminated during the performance of the remedial action will be contained in a synthetically lined catch basin. The water will be treated to meet applicable Federal and State standards prior to discharge. Runoff from unaffected areas will be diverted around the site by diversion ditches.

The staff concludes that the measures proposed to minimize impact to surface waters at the Collins Ranch site are adequate.

3.4 Ground Water - Disposal Site 3.4.1 Ground-Water Characterization To obtain information on subsurface lithology at the disposal site, 17 boreholes were drilled. These borings show that lithology at the disposal site consists of alternating layers of silty sands, sandy silts and lenses of plastic clays. These materials were encountered to a depth of 250 feet and are interpreted to be outwash deposits with a total depth of approximately 1000 feet.

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i Of the 17 boreholes drilled, ten were completed as monitoring wells. However, only five encountered ground water. Four of l the wells are located west of the site and one well is et the south boundary.

These five wells were used to measure water t levels in the water tab'io or shallow zone. These measurements l show that. ground water moves from northwest to southeast in the vicinity of the disposal site.  ;

i Slug tests were conducted to determine hydraulic conductivity  !

and transmissivity. .The' data was analyzed using the Skibitzke method, Bouer-Rice method, and Hvorslev method. All methods  !

t are widely used by ground-water professionals for exploration I and analytical purposes and are acceptable to the staff. The hydraulic conductivities ranged from 0.12 ft/ day to 1.5 ft/ day '

and averaged 0.64 ft/ day. The average transmissivity was calculated to 2.5 fta/ day.-

3.4.2 Ground-Water Quality i

Ground water samples-from monitoring wells at the disposal site '

were analyzed for various parameters. The results of the  ;

analysis show that the grou9d water in the shallow zone is low in TDS, high in pH, and high in silica. This chemistry is i indicative of volcanic complexes. This supports the contention l that the shallow ground water zone is recharged by the Fremont  !

Mountains, which are volcanic in origin.

3.4.3 Ground-Water Impacts i The proposed design includes placement of a low permeability '

cover over the tailings and recompaction of existing foundation i soils to serve as a low permeability liner under the tailings. '

During the construction phase, including the relocation of tailings, the ground water will not be affected because the t water levels are approximately 20 feet below the surface. {

Design calculations indicate that minimal infiltration will  ;

take place due to the low permeability cover. This will  ;

greatly reduce the potential for water to move down through the  !

tallings, which minimizes the possibility of contaminants leaching into the subsurface. It is expected that some  !

contaminant movement will take place, but calculations show '

that an equilibrium would be established whereby most chemical species will be attenuated within the recompacted foundation '

soil laye..

The staff review of design plans and submitted information indicates that minimal infiltration and leaching will take place at the disposal site. Any leaching that does take place ,

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i. .t will result in minimal contaminant migration due to attenuation properties'of clay soils existing at the disposal site. i Supplemental monitoring wells will be installed downgradient of i the disposal site as a means of evaluating design j effectiveness.

3.5 Conclusion '

The staff concludes that impacts to surface water at both the processing and disposal sites have been and will continue to be minimal. In addition, the remedial action plan includes measures which should assure that impacts to ground water at the disposal site will also be minimal. The need for ground water restoration at

'the processing site, however, cannot be adequately addressed until EPA promulgates appitcable standards.-

4.0 SURFACE WATER HYDROLOGY AND EROSION PROTECTION '

4.1 Hydrologic Description The Collins Ranch site is situated in a relatively steep area  !

against the southwest slope of Mt. Augur. Flood runoff in drainage channels .is produced by rainfall on very small drainage areas at the site. l i

i The DOE proposes to stabilize the tailings and contaminated materials behind an engineered embankment to protect them from {

flooding and erosion. The tailings will be consolidated into a  !

single pile, which will be protected by soil and rock covers. The  !

. covers will have maximum slopes of 35 on the top and 20E on the i sides. Disposal will be partially below grade, and the 1

irregularly-shaped pile will be surrounded by drainage channels and I access roads. Design criteria utilized by the DOE included the l Probable Maximum Precipitation (PMP) and the Probable Maximum Flood l

(PMF) events, both of which are considered to have very low i

probabilities of occurrence during the 1000 year stabilization period. i 4.2 Geomorphic Considerations 1 l

The geomorphic setting at the site is relatively stable. The slopes in the area are generally well protected by a natural gravel and )

cobble armoring. There are no nearby water bodies which have a potential to affect the site by meandering or erosion.

4.3 Floodine Determinations In order to determine site impacts from flooding, the DOE analyzed flooding in various on-site drainage channels to determine peak 12 J

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flows and velocities and to evaluate tte need for erosion protection measures. The DOE estimated the PMF peaks in the channels resulting from an occurrence of the PMP over the limited areas draining into the channels. These design events meet the criteria outlir.ed in the Standard Review Plan (Reference 15) and are, therefore, acceptable.

However, our review of the preliminary design indicates that several aspects of the PMP and PMF determinations were not appropriately applied. The details of the flood computations were analyzed by the NRC staff as discussed below.

A. Probable Maximum Precipitation (PMP)

A PMP rainfall was developed by the DOE using Hydrometeorological Report (HMR) 43 (Reference 9). Based upon independent calculations, the staff concludes that the PMP from HMR 43 was acceptably derived for this site. However, the rainfall was not extrapolated to the proper duration (See C, below). In addition, the location of the site is such that HMR 49 (Reference 14) could be just as appitcable as HMR 43, because even though the site is located in the region covered by HMR 43, it is only about twenty miles from the region covered by HMR 49. Therefore, a comparison should be made and the most conservative estimate should be used, if there is a significant difference. This information has been requested from the DOE.

B. JnfiltrationLosses The DOE estimated no infiltration losses to occur. Based on a review of the computations, the staff concludes that this is a very conservative assumption.

C. Time of Concentration Various times of concentration (tc) for the ditches and embankments were estimated by the DOE using procedures discussed in Reference 3. In general, the method used for computing tc may not be appropriate or conservative.

Specifically, sheet flow and channel flow will occur at fairly high velocities, and the DOE's computed times of concentration may be overestimated. The DOE should use methods which are representative of the small, steep drainage areas present at the site. The NRC staff concludes that the stream hydraulics method (Reference 3) would likely be more appropriate for this site, and should be used, particularly for flow in the ditches.

The DOE has been requested to re-estimate tc using the stream hydraulics method and submit this information for review and approval.

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D~ D. P M Rainfall Distributions The 00E derived rainfall distributions and intensities from M R 43, which is acceptable. However, in the determination of peak flood flows in ditches, the minimum time of concentration and rainfall duration that was adopted was 5 minutes, even though the actual times of concentration are much shorter than 5 minutes in many case's. The staff conclude that rainfall intensities should be extrapolated to the appropriate time of concentration or to a minimum of 2.5 minutes. Additionally, the rainfall intensities should be compared _with those t- extrapolated from HMR 49, and the more conservative 1

distribution applied if there is a significant difference between the two. The staff has requested that the DOE re evaluate rainfall intensities as discussed above.

E. Computation of PMF i.

00E utilized the Rational Formula (Reference 3) to compute the peak PMF flows in the ditches, given the input parameters discus:ed above. Based on review of the calculations presented, the staff conclude that this method of computation is acceptable, but the peak PMF flows have not been acceptably derived. This is principally due to improper application of

-times of concentration-(See 3C, above) and rainfall distribution (See 30, above).

4.4 upstreme Dem Failures There are no dans whose failure could affect the site. The site is not located near any surface water impoundments.

4.5 Desion of Erosion Protection A. Perimeter Ditches The 00E proposes that the erosion protection in the perimeter drainai)e ditches will be designed for an occurrence of a local PMP. "his design basis meets the criteria outlined in the SRP i

and is, therefore, acceptable. However, there are se:veral aspects regarding the design and laycut of the ditches which are not acceptable and will require additional changes. These aspects are as follows:

a. At those locations where the proposed diversion ditches transition into existing channels and gullies, the riprep protection should be keyed into bedrock or designed so that erosive velocities at the outlets are not produced.

In the proposed design, it appears that the termination i areas of the riprap have not been sufficiently protected.

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b. At those locations where the ditches merge and discharge flows over the access road, the riprap protection in the ditches should be increased to account for turbulence.

-hydraulic jumps, and energy dissipation. Additionally, the access road in these areas should be designed with riprap which is sufficient in size to resist expected velocities. Also, additional erosion protection should be provided on the IV:3.5H side slopes of the road and should be designed for the velocities and turbulence which will be produced.

c. Riprap sizes should be increased in those portions of the diversion ditches located at channel bends to account for increased velocities and shear stresses,

d. The possibility of one drainage ditch overtopping into an adjacent diversion ditch should be considered in the design,

e. The computations of rock sizes for the ditches appear to be very sensitive to selection of a Manning's "n" value.

Sensitivity analyses should be conducted for this parameter, with adjustments made accordingly. In addition, it is not clear why riprap sizes are larger for certain ditch segments where the computed velocities are actually lower than in other segments. It appears that one likely explanation is that "n" values (and resulting velocities) may not vary as widely as shown in the calculations. Another possible explanation is that too much flow is assumed to pass through the rock, and the resulting calculations are distorted,

f. The use of average ditch side slopes (if the slopes differ) for computation of erosion protection may not be appropriate. The most critical slope should be evaluated for design of the riprap.

This information has been requested from the DOE for staff review and approval.

B. Top and Sides of Piles The rock covers, which will be used to protect the soft cover from wind and water erosion, are designed to resist an occurrence of the local PMP. This design basis meets the criteria specified in the Standard Review Plan and is therefore acceptable. For the top of the pile (3% slopes), the DOE proposes to provide an 18-inch layer of rock with a median size (0-50) of about 5 inches. For the sides of the pile (20% slopes), the DOE proposes an 18-inch layer of rock 15 i

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with a D-50 of about 9 inches. Each of the rock layers will be placed on a gravel filter layer. The Safety Factor 5 Method (Reference 12) was used to determine required rock sizes.

Based on a review of the calculations provided, the staff conclude that the proposed rock for the top and sides of the pile has been conservatively designed.

C. Rock Durability For the rock to be placed in the ditches and on the pile, proposed gradation and rock durability criteria were presented.

However, our review indicates that the rock durability criteria and durability tests proposed may not be adequate to assure that rock of acceptable quality will be provided at this site.

As proposed, the rock will have difficulty meeting minimum U.S. Bureau of Reclamation (USBR) criteria for poor-quality rock. The staff conclude that one or more of the following additional measures be adopted:

a. modify the acceptance criteria so that USBR criteria for good quality rock is met, b.

find other sources of rock that meet USBR criteria for good quality rock, or

c. perform additional tests (such as petrographic examination and freeze-thaw tests) that will further document the acceptability of the rock.

The DOE has been requested to provide this information for review and approval.

D. Construction Considerations At the present time, construction specifications for many hydrologic protective features are not known. Such details include: 1) specifications for the monitoring and maintenance programs needed to ensure the integrity of the on-site slopes and erosion protection; 2) final specifications for riprap layer size, thickness, durability, placement, testing, and source; and 3) testing and quality assurance programs that will be used during construction. The staff requires that the above construction and monitoring programs be submitted for review and approval prior to their implementation.

l 4.6 Conclusion Based on a review of the information submitted by the DOE, the staff is unable to conclude that the site conceptual design will meet EPA i

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requirements as stated in 40 CFR 192 with regard to flood design 7 measures and erosion protection. Additional information, analyses, and redesign of erosion protection have begi requested from the DOE to satisfy the above concerns. '

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' 1 5.0 GE0 TECHNICAL STA8ILITY e

5.1 Geotechnical Site Characterization b e . s ,j The subsurface stratigraphy at the Collins Ranch site was determined #

by drilling 17 borings to depths ranging from 25 to 250 feet and digging eight test pits. Standard penetration tests were run on a / ^f e nearly continuous basis over the entire depth of each boring. 'Soth disturbed and undisturbed samples were obtained from the borings and test pits for further testing. .The, locations of the borings are shown on Figure 3. The boring logs'are provided in Appendix 8 to

'the OSCR.

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.I The boring logs and subsequent testing show the foundation soils to .a consist of a complex series of interfingered and discontinuous <[.

lenses of silts, clays, sands, and various combinations of these. '

The complexity of the stratigraphy prevents the development of meaningful cross sections. The material for the radon barrier will be obtained through selective stockpiling of foundation excavation material at the Collins Ranch site. /

r d.' i The complex stratigraphic picture described above is present at great depths underlying the site. The boring logs'indienta,that the near surface conditions extend to depths in excess of 250 feet. The .f results of the standard penetration tests show the, soils to be of a ~,

generally dense nature. ' ' ' -#

The staff concludes that the field exploration progias was conducted in accordance with standard engineering practice. Further, the r extent of the program was adequate to characterize the site. '

5.2 Soil Properties * <

Geotechnical properties of the foundation soils were determined by 4 ,

performing various laboratory tests. The tests included moisture  ?

content, gradation, Atterberg Limits, specific gravity,  ;

consolidation, triaxial shear, and dispersivity tests. The results of the testing program are discussed in detail in Sections 7, 8, and 9 of the DSCR. Blow counts obtained using the Standard Penetration Test (SPT) were also used to help determine geotechnical properties.

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The foundation soils generally classified as CL (clays), SM (sands),

or MH (silt) soils according to i;he Unified Soil Classification I ^

System. Of particular note are the MH soils due to a potential for ~ '

undesirable behavior. The MH soils exhibited high SPT blow count 17 l

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values and overconsolidation ratios ranging from 11 to 16. In addition, the results of three types of dispersivity tests show that the soil is non-dispersive. The test results indicate that the MH soils do not exhibit any characteristics which could eliminate the proposed site as a disposal alternative.

A similar laboratory testing progiam was conducted to characterize the tailings and evaporation pond materials to be transported to the disposal site. The tailings consist of sands (SP, SM) and slimes (ML,CH). The evaporation pond material consists of a low density, high moisture content silt (MH). The DCE documents often refer to this material as " ash."

All tests were conducted in accordance with applicable ASTM standards. The staff concludes that the extent of soils testing was adequate to characterize the soils and tailings and support the soil parameters used in the stability and settlement analyses performed.

5.3 Slope Stability The DOE performed slope stability analyses to evaluate the stability of the reclaimed pile. Static and dynamic loading conditions were evaluated using the computer program STABL, which utilizes the Janbu method, and infinite slope stability analyses.

A typical cross-section of the reclaimed pile is shown on Figure 4.

The cross-section consists of the following layers: rock erosion protection, radon barrier, contaminated materials, tailings, recompacted foundation soils, and natural foundation soils. The top

.of the pile will be graded to a slope of approximately 3%, while the embankment outslope will consist of a 5H:1V slope.

Parameters used as input in the stability analyses were determined during the field and laboratory testing programs described previously. Parameters for the period immediately following construction were obtained by performing unconsolidated-undrained triaxial tests, while long-term strengths were obtained from consolidated-drained tests. SPT blow count values were used to estimate soil strengths for the foundation soils. A summary of the strength values used is provided on Table B.1.7 of the RAP.

The results of the static stability analyses showed minimum factors of safety of 4.5 for the end of construction stage and 3.5 for the long-term stability. These values are well in excess of the minimum factors of safety of 1.3 and 1.5, respectively, recommended in Regulatory Guide 3.11 (Reference 16).

The psuedo-static stability analysis performed utilized a maximum ground acceleration of 0.35 g. The acceleration value was based on a postulated maximum credible earthquake (MCE) with a Richter 1 18

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magnitude of 6.9 and a'n epicenter four milec from the site. Using attenuation curves developed by Seed and Idriss (Reference 17), the maximum acceleration in bedrock was determined to.be 0.52 g. The maximum acceleration at the ground surface was based on a site

. stratigraphy consisting of deep, cohesionless soils ( 250 feet). s 5

This is acceptable, based on the information obtained from site borings. The psuedo-static analysis resulted in a factor of safety of 1.1. he value recommended in= Regulatory Guide 3.11 is 1.0.

The' stability analyses conductediby DOE. indicate'that the proposed

. design exceeds the minimum factors of' safety ' recommended in , "

Regulatory Guide 3.11. In addition, the staff conclude that the stability analyses performed by the DOE utilized methods which are widely used in engineering practice and are therefore acceptable.

However, additional information regarding the' seismic aspects of the disposal site is necessary before that portion of the staff' review can be completed. If the additional information results in an increase in the maximum surface acceleration associated with the MCE, a re evaluation of the psuedo-static stability of the proposed design will be necessary.

5.4 Settlement

.An analysis of the settlement expected during and following

, ' construction activities at the disposal site was performed to evaluate the potential for disruption of the radon barrier and erosion protection layers. The settlement analysis was based on estimated compression / consolidation parameters for the granular

' foundation soils and the foundation clays, and the results of consolidation' tests performed on remolded samples of evaporation pond materials and tailings. A 3 c '

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The compression values for the granular foundation soils were estimated based on the SPT testing performed during the" field exploration program. The consolidation parameters for the foundation clays were based on typical values from the engineering literature. The staff review indicates that the values used are conservative.

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The results of the analysis indicate that the total settlement for' \

the embankment and foundation soils is estimated to be approximately 2.25 feet, with 1,71 feet of the settlement expected to occur within the embankment itself. Since the materials comprising the embankment will be placed at water contents significantly less than saturation, the DOE estimates that about 90% of the total settlement wil1 occur prior to placement of the cover materials. Further, the DOE t concludes that the relatively small settlements occurring after

cover placement will result in very small differential settlement with little potential for disruption of the cover.

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The staff basically concurs with the analysis conducted by the DOE.

However, a review of material properties indicates that some of the evaporation pond soils are of very low density and high water content. It is not clear what percentage of the contaminated layer, which could be up to 20 feet thick depending on required excavation depths, consists of the low density material. It is also not clear what assumptions DOE made with regard to the amount of low density material in performing the settlement calculations. This

-information has been requested. Until the information is received and reviewed, the settlement analysis will remain an open item.

5.5 Liquefaction The boring logs for the site show the foundation soils to consist basically of fine grained, cohesionless soils. As these are the types of soils considered susceptible to liquefaction, an analysis of the potential for liquefaction was conducted by the DOE.

There are two factors considered necessary for liquefaction of fine grained, cohesionless soils: (1) saturation of the soils, and (2) a low relative density (soils with a relative density exceeding 70%

are generally not considered susceptible to liquefaction). A review of data generated during the field program ccnducted by the DOE indicates that the minimum depth at which saturated soils were encountered was 35 feet. Thus, the sofis above 35 feet do not have a potential for liquefaction. The SPT values for soils deeper than 35 feet indicate a relative density of at least 95%. These soils therefore do not exhibit a potential for liquefaction.

The staff therefore concludes that an acceptable analysis of liquefaction potential was conducted and that the site should not be subject to liquefaction.

5.6 Construction Criteria Some construction specifications were provided in the RAP. More detailed specifications will be included in the Remedial Action t Inspection Plan (RAIP) to be developed by the DOE. The RAIP will be reviewed by the staff and approved prior to initiation of construction.

The RAP states that the evaporation pond and tailings materials will be placed at a minimum of 90% of the maximum dry density as determined by the Standard Proctor test (ASTM D698) and at 0 to 2%

below the optimum moisture content. The radon barrier material will t

be placed at a minimum of 95% of the maximum dry density as determined by the Standard Proctor test (ASTM D698) and at a moisture content 2 to 3% above optimum moisture content. In addition, the RAP states that standard filter criteria will be used l

in designing rock layers which will be in contact with the radon 20 l

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barrier. This should assure the stability of the radon barrier layer.

The staff review of the construction criteria provided in the RAP

. indicates that the criteria are consistent with standard engineering practice and, therefore, acceptable. The staff does, however, have ,

reservations about the narrow range (2-3%) assigned for moisture l~

content for the radon barrier and the ability of a contractor to meet this requirement in the field. Additional construction specifications, including the quality control program to be implemented to assure that the construction specifications are met in the field, will be included in the RAIP.

S.7 Conclusion The staff generally concludes that the proposed remedial action should meet the EPA criteria with regard to geotechnical stability.

However, a re-evaluation of the psuedo-static stability and settlement analyses will be performed by the staff upon receipt of additional information requested from the DOE.

6.0- RADON ATTENUATION AND SITE CLEANUP 6.1 Characterization of Tallinas and Cover Material

'The review of the radon attenuation design encompassed independent evaluation of pertinent design parameters for both the tallings and radon barrier soils. The tallings properties evaluated for acceptability include: long-term moisture content, radon diffusion coefficient, radium content, radon emanation coefficient, material thickness, bulk density, specific gravity, and porosity. The cover material properties evaluated for acceptability include: long-term moisture content, radon diffusion coefficient, bulk density, specific gravity, and porosity. The tailings consist of two distinct layers: an upper tailings layer (off pile contaminated material) and a lower tailings layer (actual tallings).

Independent verification of the required cover thickness using acceptable values for the tailings and cover characterization  :

l properties as input parameters for the computer code RAdCOM .

(Reference 18) comprises the basis for staff concurrence on the l radon attenuation portion of the RAP.

6.2 Radon Attenuation Calculation of a cover thickness using DOE values for input parameters indicates that no barrier is required to reduce the radon flux to 20 pC1/m2 sec. However, a minimum cover thickness of 15 centimeters would be required to meet the surface radium standard; therefore, the DOE proposed a 1-foot thick cover. A 21

i discussion of the acceptability of the tailings and cover characterization properties, based on the Standard Review Plan (Reference 15), is presented below.

Review of Figure 4 indicates that the thickness of the two proposed tailings layers is based on the conceptual engineering design. The bulk densities of the tallings and cover material are averages of 28 and 20 sub-samples of three tailings and two cover material bulk samples, respe cively. The densities were based on standard Proctor tests at the Jesign Compaction of 90 percent and 95 percent for the tailings and cover, respectively. The tailings and cover porosities are calculated using the equation presented in NUREG/CR 3533 (Reference 18). The specific gravities of the various materials were either measured or estimated from the other geotechnical parameters.

The values for the thicknesses and bulk density of both tailings layers are acceptable based on the conceptual design and the Standard Review Plan. However, the cover material bulk density seems high compared to the bulk density based on samples from test

. pit LKV02-805, which is representative of the radon barrier soils.

Using this sample as an estimate of cover parameters yields a bulk density of about 0.98 g/cm3 and a porosity of 0.61. The bulk density and porosity values used by the DOE for the cover are 1.19 g/cm3 and 0.53, respectively. The values used by the DOE are based on many samples, some of which are not representative of the radon barrier soils.

The long-term moisture content of the mixed tailings material (sand, sand / slime mix, slime and evaporation pond " ash") is based on the average long-term moisture content of the first three materials (20.7 %) as determined by laboratory tests utilizing two-bar suction. This procedure should be conservative, as the ash material has a significantly higher water retention capacity than the other contaminated materials.

The long-term moisture content of the cover material is based on laboratory tests utilizing 15-bar suction. Specifically, the average 15-bar suction moisture content for radon barrier samples was 18.7%, as shown on Table 9.5 of the DSCR. The DOE used a value of 16 percent for the cover long-term moisture content.

The long-term moisture contents for the tailings and cover materials are realistically estimated. However, the thin cover layer, approximately 1-foot thick, will exhibit a higher potential to lose moisture than a thick layer and will also exhibit larger fluctuations in moisture content. Thus, a more conservative value such as 13%, based on the. equation in Reference 18 should be utilized in consideration of the potential long-term dessicating environmental effects.

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LAn average radon emanating ~ fraction of 0.27 was calculated based on

!. 42. tailings samples. This value was used in both the upper and

l. . lower tallings layer. 'The Ra-226 content of the tailings sample tested ranged from about 140 to 700 pC1/g.

Usage of the average tailings emanating fraction is acceptable for i-1 the lower tailings layer (main tailings pile material), since the measurements'were performed on this material. However, usage of the

. average tailings pile emanating fraction is not acceptable for the

' upper tailings layer. This is because the average Ra-226 concentration for the upper tailings layer is about 20 pCf/g, while the emanating fraction measured for the tailings at Ra-226 concentrations.of between 140 and 220 pC1/g averages 0.39. This

'value represents the samples with the lowest Ra-226 content which were tested. The emanating fraction was not measured for materials with lower Ra-226 concentrations which would more closely correspond to the upper tailings ~1ayer. Hence, the use of an average emanating fraction of 0.4 is recommended for preliminary design. Additional data should be collected to ensure that the emanating fraction is

' not underestimated for the lower activity material.

Radon diffusion coefficients for the tailings and cover were derived from a correlation curve as a function of moisture content as depicted in Figures B.1.11 and 8.1.12 of the RAP, respectively.

l This approach results in radon diffusion coefficients of 0.016 cm2/sec at 21 percent moisture for the tailings and 0.025 coa /sec at 16 percent moisture for the cover.

a Use of a diffusion coefficient of 0.016 ce /s and a moisture content of 21 percent is acceptable for the lower tailings layer based on References 15.and 18. However, the upper tailings layer is comprised partially of evaporation pond " ash" which has. a greater diffusion coefficient. Based on a moisture content of 21 percent, a diffusion coefficient of about 0.04 co a/s is obtained f rom the

. relationship in Reference 18. Therefore, the more conses vative value of 0.04 cm2/s should be utilized or additional testing should l- be performed to adequately characterize the upper tailings layer diffusion coefficient.

The cover diffusion coefficient is unacceptable since most radon barrier samples were tested at moisture contents significantly above the acceptable long-term moisture content of 13 percent. Therefore, either the value of 0.037 cm2/s should be used based on the relationship in Reference 18, or additional testing of the actual cover material at the acceptable long-term moisture content should be conducted.

The average radium content of the tallings pile based on 120 samples of the existing tallings pile and cover is 192 pCf/g for i

322,500 cubic yards (cy). Based on 60 samples of the sub-base, it 23 l

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was calculated that the average radium content is 59 pCi/g for 101,700 cy. Thus, the volume weighted average radium concentration for the tailings plie, existing cover and sub-base is 160 pC1/g.

The RAP estimates the Ra-226 concentration for the upper tallings layer at 14 pC1/g, based on Ra-226 ingrowth from Th-230.

The value chosen for the lower tailings layer,160 pCi/g Ra-226, is acceptable. However, the value of 14 pCf/g Ra-226 for the upper tailings layer is not acceptable. Staff calculations indicate that a value of 20 pCi/g, based on a volume-weighted average, more accurately describes the average Ra-226 concentration of the upper tailings layer.

6.3 Site Cleanup Review of pertinent information regarding depth of excavation at the various contaminated areas based on Ra-226 encompasses the basis for NRC concurrence on tne site cleanup portion of the RAP. The DOE proposes to base the excavation of contaminated soils underneath the main tailings plie on arsenic levels. The DOE states that excavation of the main tailings pile will be approximately 1 foot deeper than required to meet the Ra-226 standard, based on, arsenic contamination. The excavation of the evaporation ponds will be based on the Th-230 concentration.

The staff concludes that excavation based on these contaminants is acceptable as long as it is verified that the site meets the EPA Ra-226 standards.

6.4 Conclusion Table 1 presents a comparison of the tailings and cover material properties utilized by the DOE and the staff. Table 2 presents the results of a RAECOM run utilizing the staff values for input parameters. As shown in Table 2, a computation of the required cover thickness utilizing the staff values for input parameters indicates that about two feet of cover is required. The staff has requested that 00E provide tho results of additional testing to justify their choice of parameter values or revise the RAP to include placement of two feet of cover. In addition, the 00E must provide the quality assurance procedures for the control of excavation at both the main tailings pile and the evaporation ponds and a proposed testing program to verify that Ra-226 concentrations meet the EPA standard. This information will be submitted for staff review and approval.

7.0 St# MARY This Preliminary Technical Evaluation Report documents the NRC staff review of the proposed remedial action plan for the Lakeview tailings 24

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4 site. - Additional infonmation is needed before NRC can concur on the '

proposed plan. Specific items have been identified in the text and the infomation requested from DOE. The Final Technical Evaluation Report will incorporate the staff's review of the additional information received from 00E and will include the NRC position regarding concurrence on the proposed remedial action plan.

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i REFERENCES and BIBLIOGRAPHY

1. U.S. Army Corps of Engineers, Hydrologic Engineering Center," Flood Hydrograph Package, HEC-1," continuously updated and revised.

2. U.S. Nuclear Regulatory Commission, Regulatory Guide 1.59, " Design Basis Floods For Nuclear Power Plants," January,1983.

3. U.S. Bureau of Reclamation, U.S. Department of the Interior,

" Design of Small Dams," 1973.

4. Staff Technical Position WM-8201, " Hydrologic Design Criteria for Tailings Retention Systems," January, 1983.

S. U.S. Army Corps of Engineers, Hydrologic Engineering Center, " Water Surface Profiles HEC-2," continuously updated and revised.

6. Chow, V. T., "Open Channel Hydraulics," McGraw-Hill Book Company, New York, 1959.

7. U.S. Army Corps of Engineers, " Hydraulic Design of Flood Control Channels," EM 1110-2-1601, 1970.

8. U.S. Army Corps of Engineers, " Additional Guidance for Riprap Channel Protection," ETL 1110-2-120, May, 1971.

9. U.S. Department of Commerce, U.S. Army Corps of Engineers, Hydrometeorological Report No. 43, " Probable Maximum Precipatation Northwest States, " 1966.

10. U.S. Army Corps of Engineers, " Engineering and Design - Standard Project Flood Determinations," EM 1110-2-1411, 1965.

11. Crippen, J. R. and Bue, C. D., " Maximum Floodflows in the Conterminous United States," USGS Water Supply Paper 1887 (1977).

12. Simons, D. B., and Senturk, F., " Sediment Transport Technology,"

Fort Collins, Colorado, 1976,

13. Codell, R. B., " Design of Rock Armor for Uranium Mill Tailings Embankments," U.S. Nuclear Regulatory Commission, Unpublished Draft Report,' February, 1985.

14. U.S. Department of Commerce, U.S. Army Corps of Engineers, Hydrometeorological Report No. 49, " Probable Maximum Precipitation Estimates, Colorado River and Great Basin Drainages," 1977.

15. U.S. Nuclear Regulatory Commission, " Standard Review Plan for UMTRCA Title I Mill Tailings Remedial Action Plans," October, 1985.

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16. U.S. Nuclear Regulatory Commission, Regulatory Guide 3.11. " Design, Construction, and Inspection of Embankment Retention Systems for Uranium Mills," Rev. 2, December, 1977.

17. Seed and Idriss, 1982, " Ground Motions and Soil Liquefaction During Earthquakes," Earthquake Engineering Research Institute, Berkeley, California,

18. " Radon Attenuation Handbook for Uranium Mill Tailings Cover Design,"

NUREG/CR-3533, April, 1984.

6 27

7 . .

APPENDIX Tables and Figures

RAECOM Input Parameters Table 1 RAPA PTER**

Thickness (ca)

Layer 1 1220 1220 Layer 2 610 610 Layer 3 30 58 Diffusion Coefficient (cm2/s)

Layer 1 0.016 0.016 Layer 2 0.016 0.04 Layer 3 0.025 0.037 Porosity (fractional)

Layer 1 0.53 0.53 Layer 2 0.53 0.53 Layer 3 0.53 0.61 Radium-226 (pCi/g)

Layer 1 160 160 Layer 2 14 20 Layer 3 0 0 Moisture (%)

Layer 1 21 21 Layer 2 21 21 Layer 3 16 13 Density (g/cm2)

Layer 1 1.18 1.18 Layer 2 1.18 1.18 Layer 3 1.19 0.98 Emanating Coefficient (fractional)

Layer 1 0.27 0.27 Layer 2 0.27 0.4 Layer 3 0 0

• Remedial Action Plan (00E)

• • Preliminary Technical Evaluation Report (NRC)

(T .. - ~

kIo s RAECOM Cover Thickness Calculation Table 2

• • • • • • • • • • • • • • • I NPUT P A R A M E T E R S***************

Number of Layers: 3 Radon Flux into Layer 1: .000 pC1/m2/sec Surface. Radon Concentration: .600 pCi/ liter Layer 3 adjusted to meet JCRIT: 20.0 +/ .100E-02 pC1/m2/sec Bare Source Flux (J0) from Layer 1: 92.52- pCi/m2/sec LAYER THICKNESS DIFF COEFF POROSITY SOURCE MOISTURE (ce) _( cm2/sec) (pci/cm2/sec) (Dry Wt. Percent) 1 1220. 1.60000-02 .5300 2.00000-04 21.00 2 610. 4.00000-02 .5300 3.70000-05 21.00 3 30. 3.70000-02 .6100 .00000-00 13.00 RESULTS OF RADON DIFFUSION CALCULATION LAYER THICKNESS EXIT FLUX EXIT CONC. MIC (cm) (pCf/ma /sec) (pCf/ liter) 1 1220. 4.63870-01 4.74810-04 .6279 2 610. 2.19880-01 4.02790-03 .6279 3 58. 2.00180-01 5.00360-01 .8339

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