ML20012D621
| ML20012D621 | |
| Person / Time | |
|---|---|
| Issue date: | 03/22/1990 |
| From: | Lohaus P NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
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| Shared Package | |
| ML20012D613 | List: |
| References | |
| REF-WM-68 NUDOCS 9003280142 | |
| Download: ML20012D621 (72) | |
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FINAL TECHNICAL EVALVATION REPORT FOR THE PROPOSED REMEDIAL ACTION AT THE GREEN RIVER TAILINGS SITE GREEN RIVER, UTAH i
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U.S. Department of Energy Agreement No. DE-FC04 81AL16257 i
Appendix 8 (Remedial Action Plan) for Green River, Utah
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P SIGNATURE PAGE i
THE UNITED STATES OF AMERICA STATE OF TAH DEPARTMENT OF ENERGY.
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7 (f Mark L. Matthews Khn Alkema. Director Acting Project Manager Division of Environmental Uranium Mill Tailings Project Office Health Albuquerque Operations Office Utah Department of Health P.O. Box 5400 Albuquerque, New Mexico 87115 JAN 2 21990 JAN 2 2 1990 Date:
Date:
l CONCURRENCE NUCLEA EGULATO COMPh '0N By:
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l-Paul H. Lohaus, Chief l
Operations Branch L
Division of Low Level Waste Management & Decommissioning r
Date:
March 22, 1990 (See TER transmittal letter dated March 22, 1990, for conditions of concurrence)
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5 CONTRIBUTORS Sandra Wastler Project Manager Ted Johnson Surface Water lydrologist Ban 6a Jagannath Geotechnical Engineer Joel _ Grinn <
-Geologist 1
Michael Weber Hydrologist Freo Ross Hydrologist L.
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TABLE OF CONTEh1 Section PigLg 1.0 lhTRODUCT10N.....................................................
6 1.1 EPA Standards...............................................
6 1.2 Site and Proposed Act1on....................................
6 1.3 Review Process..............................................
7 1.4 T E R O r g a n i z a t i o n...........................................
10 1.5 Summary of Open Issues and Confirmatory Items..............
11 2.0 G E 0 L OG I C S T AB I L I T Y..............................................
12 2.1 Introductiont...............................................
12 2.2 Location.................................................... }2 2.3 G e o 1 c gy....................................................
1 2 2.3.1 Stratigraphic Se tting...............................
12 2.3.2 S t ru c tu ra l S e tti ng..................................
13 2.3.3 Geomorphic Setting..................................
13 2.3.4 S e i s m i c i ty..........................................
15 2.4 G e o l og i c S t a b i l i ty.........................................
16 2.4.1 B ed roc k S u i ta b i l i ty.................................
16 2.4.2 Geomor phi c Stab ili ty................................
16 2.4.3 Sei smotectoni c Stabili ty............................
18 2.5 C o n c l u s i o n s................................................
19 3.0 GE0 TECHNICAL STABILITY..........................................
21 3.1 I n tr o d u c t i o n...............................................
21 3.2 Site Char 6cterization......................................
21 3.2.1 Site Description....................................
21 3.2.2 Site Investigation..................................
22 3.2.3 Site Stratigraphy...................................
22
- 3. 2. 4 T e s t i ng P rog ram.....................................
2 3 3.3 Geotechnical Engineering Evaluation........................
24 3.3.1 Stabili ty Ev auat1on.................................
24 3.3.2 Liquifaction........................................
25 3.3.3 S e t t l eme n t..........................................
2 5 3.3.4 Cover Design........................................
26 3.4 Geotechnical Construction Criteria.........................
29 3.5 Conclusion.c................................................
31 4.0 SURFACE WATER HYDROLOGY AND EROSION PROTECT 10N..................
32 4.1 Hydrologic Description and Conceptual Design...............
32 4.2 Flooding Determination.....................................
32 4.2.1 Probable Maximum Precipitation......................
34 4.2.2 I nf i ltr ati on Lo s s...................................
34 4.2.3 Tine of Concentratio n...............................
34 4.2.4 PMP Rainfall Distribution...........................
35 4.2.5 C ompu ta tio n o f PMF..................................
3 5 4.2.5.1 On-site Drainage.............................
35 4.2.5.2 G r ee n R i v e r..................................
3 5 4.2.5.3 Brown's Wash.................................
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,. l 4.3 Water Surface Profiles and Channel Velocities............
36 4.3.1 On-site Drainage..................................
36 4.3.2 Green River.......................................
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4.3.3 B ro w n ' s W a s h...................................... 3 6 4.4 E ros io n P rotectio n.......................................
36 4.4.1 Green River.......................................
36 4.4.2 O n-s i te D ra i na g e..................................
3 7 4.4.3 To p a nd Si de s o f P 11e............................. 3 7 4.4.4 Rock Durab111ty.......:............................
37 4.5 U ps treata Da m Fa i l u r e.....................................
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4.6 C o n c l u s i on s..............................................
3 9 5.0 WATER RESOURCES PROTECT 10N....................................
40 5.1 Introduction.............................................
40 5.2 Hydrogeologi c Characteri zati on........................... 40 5.3 Conceptural Design Fe6tures to Protect W6ter Resources... 43 i
5.4 Disposal and Control of Residual Radioactive Material....
44 5.4.1 Grounawater Protection Standards f or Disposal..... 44 5.4.1.1 Haz ardou s Constituents..................... 44 5.4.1.2 Concentration Limits.......................
46 5.4.1.3 Point of Coinp11hnce........................
48 5.4.2 Performance Assessment............................
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5.4.3 C losu re Perf ormance Asses snent....................
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5.4.4 Grounowater Monitoring and Corrective l
Action Program.................................
54 5.5 Cleanup and Control of Exising Contamination.............
55 5.6 C o n c l u s i o n...............................................
56 6.0 RADON ATTENUAT ION AND SITE C LEAN-UP...........................
57 6.1 I n t ro du c t i o n............................................. 5 7 6.2 R aco n Atten u a ti on........................................
57 6.2.1 Evaluation of Paraneters..........................
57 6.2.2 Evaluation of Radon Barrier.......................
59 6.3 Site C1eanup.............................................
60 6.4 C o n c l u s i o n...............................................
61 7.0 S UMM A R Y.......................................................
6 2 8.0 RE FEkENC ES/ DI BL IOG RAP HY.......................................
63 APPENDIX A.........................................................
68 L
APPENDIX B.........................................................
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L LIST OF FIGURES Figure g
1.1 G reen River S ite Area Map................................... 8 1.2 Present Conditions, Green River Tailings Site...............
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2.1 Cross-section Through the Green River Tailings P ile and P roposed Di s posal Area..........................
14 5.1 Diagrammatic Cross-section of the Green River Disposal Unit............................................
45 5.2 Location of Point of Compliance for the Green R i ve r D i s pos a l Uni t......................................
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i LIST OF TABLES Table M
2.1 Primary and Secondary Geologic Hazarcs Associated With the Green River Project Site and Their Proposed Remed i al Ac ti on.......................................... 20 5.1 Hazardous Constituents and Concentration Limits for Disposal at the Green River UMTRAP Site..............
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1.0 INTRODUCTION
The Green kiver site was oesignated as one of 24 abandoned uranium mill tailings piles to be renediated by the U.S. Departuent of Energy (DOE) under the Uranium Mill Tailings Radiation Control Act of 1978 (UMTRCA). UNTRCA requires, in part, that NRC concur with DOE's selection of remedial action.
l U.S. Envirotsental Protection Agency ;propriate standards promulgated by the such that the remedial action meets ap EPA). This final Technical Evaluation Report (TER) docunents the NRC staff's review of the DOE final design and remedial action plan.
i 1.1 EPA Standards As required by UMTRCA, remedial action at the Green River site must comply with regulations established by the EPA in 40 CFR Part 192, scLparts A-C.
These regulations may be sunmarized as f ollows:
1.
The disposal site shall be designed to control the tailings and other residual radioactive naterials for 1000 years to the extent reasonably achievable ano, in any case, for at least 200 years
[10CFR192.02(b)]
i 2.
The disposal site design shall prevent radon-222 fluxes f rom residual radioactive materials to the atmosphere from exceeding 20 picocuries/ square meter /second or from increasing the annual 1
average concentration of radon-222 in air by more than 0.5 picocuries/
j liter [40 CFR 192.02(b)].
3.
The remedial action shall ensure that radium-226 concentrations in land that is not part of the disposal site averaged over any area of i
I 100 square noters do not exceed the background level by more than 5 picocuries/ gram averaged over the first 15 centimeters of soil below the surface and 15 centimeters below the land surface
[40CFR192.12(a)].
l On September 3,1985, the U.S. Tenth Circuit Court of Appeals remanded the groundwater standards (40 CFR Part 192.2(a)(2)-(3)) and stipulated that EPA promulgate new grounowater standards.
EPA proposed these standards in the form of revisions to Subparts A-C of 40 CFR Part 192 in September,1987.
The t
proposed standards consist of two parts; a first part governing the control of l
any future groundwater contamination that nay occur from tailings piles after renadial action, and a second part that applies to the clean up of I
contamination that occurred befcre the remedial action of the tailings.
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accordance with UMTRCA Section 108(a)(3), the remedial action shall comply with the EPA proposed standard until such time as the final standards are promulgated. At that time DOE has committed to re-evaluate its groundwater protection plan and uncertake such action as necessary to ensure that the i
I final EPA standaros are net.
1 1.2 Site and proposed Action The Green River uranium mill site is located in Grand County, Utah, approximately one mile southwest of the city of Green River (see Figure 1.1).
The 48 acre site consists of the tailings pile (8 acres), the mill yaro and
-7 ore storage oven (23 acres), four n41n building, a water tower and severa1 snell tuildings. Windblown and waterborne contamination covers a spinic.ately 30 acres. The uranium mill tailings on the designateo site ano tie windblown contaminated materials total approxim.tely 382,000 cubic yards (cys).
Figure 1.2 depicts the general features of the Green River tailings site prior to initiation of remedial action.
The remedial action proposed by DOE consists of the following major activities:
1.
Movement of all contaminated materials (uranium mill tailings
)
winoblown and waterborne contaminants and cenclition debris from the mill building addition, office building addition, ar.o rooster building) to a disposal embankment on a terrace locatcd above Brown's i
Wash.
2.
Stabilization of contaminatec material in the errbankment which is to be constructed primarily below the existing ground surface. 16111ngs and winablown contaminated naterini will be placed and compacted on j
top of a six f eet thick buf ft.r layer of select soil till.
3.
Coverage of the embanksent with a three foot thick infiltration / radon barrier of compacted silty clay, amendec with a six percent by weight sodium bentonite; an erosion protection layer consisting of bedding material; and Type A and Type B riprap to ensure long-term stabilicy, reduce radon emissions and protect ground and surface water.
Atter completion of remedial action, the disposal site will be fencea and pested with appropriate warning signs to discourage human intrusion.
In addition, the site will be surveyed and nchitorea periccically by a custodial agency under a NRC 11 cense.
1.3 Review. Process The NPC staff review was performed in accordance with the Standard Review Flan for UMTRCA Title 1 Mill Tailings Remecial Action Plans (Ref 5) and consisted of comprehensive assessnents of DOE's final oesign and remeoiel action plan. The remedial action information assessed by the NRC staff during this review was provicea primarily in the following cocuments:
1.
Remedial Action Plan and Final Design for Stabilization of the inactive Uranium Mill Tailings at Green River, Utah, Final, Volunes 1,llA, and 111, December,1989, UMTPA-DOE /AL 05010.GRNO. (Ref.8) 2.
Calculations and Data to Support the Renedial Action Plan and Final Design for Stabilization of Inactive Mill Tailings, Green River; December,1989(Ref46) 3.
Uranium Mill Tailings Remedial Action Project (UMTRAP), Green River, Utah, Design Calculations, Volumes 1,11 ano 111, November,1987 (Ref. 10)
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Uranium Mill Tailings Remedial Action Plan (UMTRAP), Green River; Design Calculations, Addendum 1, February,1988. (Ref.11) t 6.
Supplemental Geotechnical Data in support of the Remedial Action Plan, Letter f rom J. Arthur, DOE to ). Lohaus, NRC, March 11, 1988, i
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Environnental Assessment of Remecial Action, Green River Urantum M111 Tailings Site, Green River, Utah, December,1987. (Ref.29)
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Responses to NRC corunents by DOE dated September,1907 ard December, 1987.(Ref.30) 9.
Uranium Mill Tailings Remedial Action Plan UMTRAP), Green River, Design Calcult.tions, Acdendum 2, January,1989. (Ref.35)
- 10. Trip Report for UMTPA Cover Design Data Review, Hen.orandum from M. Weber to R.J. Starmer, NRC, March 3,1989. (Ref.36)
Meeting) Minutes from the April 5,1959 NRC/ DOE Green River Meeting.
11.
(Ref.44
- 12. Contaminated Material, Moisture Content, Density and Compaction Data, i
Green River; Morrison and Knudsen Engineers; November,1989 (Ref.47)
- 13. Transmittal of January 12, 1990 from M. Matthews, DOE to P. Lchaus.
NRC(Ref.48)
- 14. Letter of July 3,1989 to M. Matthews, DOE from P. Lohaus, NRC (Ref.49)
- 15. Letter of February 23, 1990 f rom M. Matthews, DOE to P. Lohaus, NRC 1.4 TER Organization The purpose of this final Technical Evaluation Report is to document the NRC staff review of DOE's final remedial action plan f or the Green River Site and to discuss any open issues or confirmatery items that remain as conditions to the NRC's concurrence in the remedial action plan.
The sections of this report have been organizec by technical discipline relative to the EPA standards in 40 CFR Part 102, Subparts A-C.
Sections 2, 3, and 4 provice the technical l
basis for the NRC staff's conclusions with respect to the long-term stability l
stancard in 192.02(a). Section 5, Water Resources Protection, summarizes the NRC staff's conclusions and with regards to the adequacy ot DOE's compliance demonstration with EPA's groundwater protection requirements in 40 CFR Part 192.
I Section 6, Radon Attenuation and Site Cleanup, provices the basis for the staff conclusions with respect to the radon control standards in 192.02(b).
I While DCE is legally obligated to obtain the NRC's concurrence in their proposed remedial action, they are not constrained from implenenting, at their own risk,
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j i the renedial action plan prior to NRC's concurrence.
In this case, DOE has chosen to complete renedial action at the Green River site prior to NRC's concurrence. Therefore, unlike sown TER's, much of the laboratory data j
evaluated by NRC is supported by actual field sensurenents.
1.5 Sunnary of Open issues and Confirmatory Items 1988 the NRC issued a draft TER for the Green River UMTRAP site On A>ril 20,fieo thirteen o>en issues resulting from a review of the whic) identi i
preliminary final RAP.
On February 3,1989 DOE issued the RAP for NRC 3
review and concurrence.
in this document DOE revised their technical approach i
to certain aspects of the design and the hydrologic assessment which closed sone issues identified in the craf t TER anc made several of the cpen issues irrelevant. Appendix A lists the 13 draf t TER issues and provides the status of each issue as a result of the staff review.
In addition, the NRC staff review of the February 3,1989 final Renedial Action Plan and its ancillary documents i
resulted in aco1tional open issues.
NRC and DOE net on April 5,1989 to discuss these remaining issues. As a result of this neeting L0E comitted, by I
their signature, to fulfill specific agreements which woulo resolve the j
renaining open issues and assure NRC that the EPA standards would be met (Ref.
44). Once the agreements were net, the NRC agreed to conditionally concur on the renedial action plan. These agreements are listed in Appendix B.
j As a result, however, of DOE's unsatisfactory fulfillment of two of their connittnents, the NRC notified DOE that the NRC's connittment to concur un the renecial action was being withdrawn and that all on-going work at the Green River site would be conducted at their own risk (Ref.48).
DOE completed the remedial action at Green River and submitted a revised final Renedial Action Plan, which addressed the: April 5,1989 agreenents, for hRC concurrence on January 3,1990.
As a result of our review of the revised final Remedial Action Plan, the NRC has concluded that only one of the twelve agreements listed in Appendix B remains open and will be a condition to concurrence. This open issue relates to DOE's deferral of grounawater cleanup until promulation of the EPA's final groundwater protection standards. While the NRC staff considers DOE's deferral to be acceptable for conditional concurrence, the issue must be andressea before NRC will-provide final concurrence on the remedial action 6t this site.
The remaining agreements have either been nrt or DOE has provided detailed information and justification f or an alternative approach that assures compliance with the EPA standard. The resolution of these agreements is discussed in the following text.
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. j 2.0 GEOLOGIC STABILITY 2.1 Introduction i
This-section of the TER cocuments the staff's review of geological information i
for proposed reredial action at the Green River uranium mill tailings disposal site. Background geologic information for this TER is derived f rom DOE's Renedial Action Plan (Ref.8), Final Design for Review (Ref.9.10, ano 11),
supplementary information provided during the review process, staff site visits, i
and indepencent sources, as cited.
2.2 Location The site is located along Browns Wash, a tributary of Green River in the northern Coloraoo Plateau, Utah. Brown's Wash drains a basin from the Cook Cliffs and Grand Valley to the northeast. This project requireo site characterization for two adjacent locations: (1) the Brown's Wash flood plain underlying alluvium and bedrock, and an abandoned mill tailings pile, and (2),
an higher terrace, its deposits, and the underlying Cretaceous bedrock, which will provide the stabilized tailings foundation.
In addition, the occurrence of a number of f aults in the region influenced the investigation of seisruic stability of the site.
2.3 Geoloqy EPA standaPJs listed in 40 CFR 192 do not include generic or site-specific requirements for the characterization of geological conoitions at UMTRA Project sites. Rather, 40 CFR 192.02(a) requires that control shall be designed to be ef f ective for up to 1,000 years, to the extent achie.vable, and in ar.) case for at.least 200 years. NRC staff have interpreted this stancaro to nean that certain geological conoitions must be met in oroer to have reasonable assurtnce that the long-term performance objective will t,e achieved. Guiaance with regard to these conoitions is specified in the Stanoord Review Plan (SRP)(Ref.5).
2.3.1 Stratigraphic Setting DOE characterizec stratigraphy by refering to published reports and conducting original field investigations as reconsnended in SRP section 2.2.2.1 (Ref.
5). The Green River site consists of two principal areas of focus: (1) the abandoned tailings pile, and (2) the inactive mill and proposed tailings disposal area.
The abandoned mill tailings lie on the Browns Wash flood plain atop 12 to 20 feet of sandy and gravelly alluvium. The mill buildings and proposed disposal area occur on a terrace or pedinent about 50 feet higher than the flood plain (Figure 2.1). Deposits beneath the terrace consist of sandy alluvium with uncifferentiated amounts of mud and gravel.
The alluvium is up to 20 feet thick.
Both areas of interest are underlain by Cretaceous strata in excess of 200 feet thickness (Fig. 2.1). Bedrock is exposed along the scarp formed by Browns Wash, as well as in numerous gully exposures and roao cuts throughout the site.
Strata beneath the area include Mancos Shale, Dakota Sandstone, anc Cedar
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The Dakota Sanostone occurs below the Mancos, cropping out along the tailings pile at the base of the scarp. Grey to yellow sandstone and conglonerate of the Dakota also crop out along Browns Wash's flood plain, along Brown Wash's banks west of the site, and in gullies across the mill yard and proposed disposal area. The Dakota's northward cip causes it to subcrop south of the mill yard where it is burieo by Quaternary deposits.
The exact utent and continuity of the Dakota has not been established by remedial action investigations. However, it appears to be discontinuous beneath the terrace due to erosion or original stratigraphic thinning. South of the terrace and near Interstate 70, it rises again to the surf ace and is exposed in ro6ccuts.
The Cedar Mountain Forn.ation, which lies unconfom:bley beneathe the Dakota sandstone, forms the region's basal Cretaceous untt. The Cedar Mountain consists of varigateo bentonitic and calcareous mudstone ano shale with abuncont interbeds of sandstone, siliceous limestone ncdules, ano a distinctive basal conglomerate (Ref. 7). The Cedar MountairJs detailed stratigr 9hy is consplex. DOE relied most on well log to characterize the Cedar I wntain.
Thus, illustrations of the unit's stratigraphy are highly interpretive.
00E further assertea that the Cedar Mountain s geochemical environn.ent was reducing, owing to observations of pyrite mineralization. hkC staff and consultants reviewed these data in detail, ano challenged the conclusion that contaminants l
migrating through the rock in ground water wculd be attenuated and precipitated, See section 5.0 of this report.
1 I
i Cretaceous strata are underlain by Jurassic and older strata which are not of significance to the remedial action.
2.3.2 Structural Setting i
DOE characterized the region's structural setting by referring to published l
regional geologic maps, and conducting aerial reconnaissance, field observation, and mapping of features critical to assuring the long-term stability of the remedial action. These sitiit i were recou,enced in SRP section 2.2.2.3 (Ref. 5). The Green River site is~ situated on the axis of an open anticline plunging approximately 31 degrees northward (Ref.s 4 and 6). A series of broad arcuate normal faults are found in t% area. The Little Grand Wash fault cuts across the anticline 21 miles south " ihe site.
Faults associated with the Salt Wash Graben lie 7 miles south of Oe site. Two normel faults associated with extension ano collapse along the anticline's axial plane are found between the Little Grand Wash Fault and Salt Wash Graben between 3 and 6 miles southeast of the site.
Each of these faults trends directly toward the site but appear to end ncrthward at Little Grand Wash fault, i
2.3.3 Geon. orphic Setting ls DOE characterized the region's physiography by referring to published literature and topographic n.aps, as recommenced in SRP section 2.2.2.2 (Ref. 5). Site geomorphic conditions were characterizeo by aerial photographic interpretation and field observations. Green River is located in the Canyonlands Section of the north central Colorado Plateau physiographic province (Ref. 33). The Book Cliffs, a few miles to the north, form the northern boundary of the Canyonland's Section ano the southern ease of the Vinta basin. The Colorado and Green rivers form Grano Valley, occurring along the strike of the Mancos Shale.
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too 200 300 aco 500 VE=5x M Terrace Alluvium Km Mancos Shele Kd Dakota Sandstone Figure 2.1:
Cross-section through the Green River tallings pile and proposed disposal area. Topographic profile is derived from DGE site map. Geological data are derived primarily from DOE we;i-log data, supplemented by staff observations, and geological reference materials. Actual dip of bedrock strata is approximately 31' to the north.
Cross-section does not indicate water table levels or pervasive joints or fractures in the bedrock.
n
, Browns W5h orains 83 square miles and has approxistely 3,000 feet relief.
The tailings pile, containing approxim6tely 205,000 cubic yards of contaminated material, occupies eight acres of the Brown's Wash flood plain (Ref.46).
Tailings are up to 10 feet thick and occur less than 10 feet above the unconfined alluvial aquifer as measured in October,1987. The pile has minimal erosion protection consisting of a thin cover derived from Mancos Shale and a low berm along a portion of the wash.
Floods in Browns Wash eroded an estimated 14,000 tons of teilings during 1959 and 1968.
The mill yaro and proposed disposal area occur on a fluvial terrace 50-60 feet above the flood plain (Fig. 2.1).
The terrace is eroded on Mancos, Oakota, ano Cedar Mountain bedrock and is covered by up to 20 feet of alluvium. The terrace is dissected by several gullies exposing bedrock. The terrace surface has also been extensively disturbed by construction, and borrow and fill activity. Drainage across the terrace consists of only about 110 acres (0.45 hr).
Runoff probably occurs riostly as sheetflow into a number of gullies, all of which drain north or northwestward to Browns Wash.
Interstata 70 presently provides a orainage divide above the site.
2.3.4 Seismicity DOE characterizea regional seismicity by. obtaining earthquake data bases provided by the National Oceanographic and Atmospheric Administration (NOAA),
by applying accepted techniques to determine earthquake magnitudes, and by employing methods suggested in SRP section 2.2.2.3 (Ref. 5) for calculating peak horizontal ground acceleration generated by a design-basis
(
event.
Green River is located in a relatively stable interior area of the Colorado l
Plateau.- Historical and instrumental seistric events have been concentrated i
I l
along the margins of the Plateau, where it neets the Basin and Range province, (Ref. 8)g the intermountain seismic belt 100 miles west of Green River includin l
Most of the major structural and tectonic f hatures of the site region date to Laramice time and are considered inactive in the present seismotectonic regime.
A majority of tvents whose epicenters occur in the site region are known to be generated by controlled blasting, rockbursts and coal bumps (accidental mine-gas explosions) in the Book Cliffs coal mining area Reference 8). These evcnts have generated Richter magnitudes up to 4.2.
DOE's analysis of potential earthquake magnitude for the interior Colorado Plateau included determination of both the Maximum Earthquake (ME) ano Floating Earthquake (FE) for the region. Sparse seismic records for the Colorado Plateau suggests the ME value could be between 6.2 and 6.8 (Ref. 8). The average, 6.5, is the value adopted by previous authors (Ref. 32) and appears very conservative considering that events of magnitude 5.0 or greater have been scarce on the plateau and its border zones.
An FE magnitude, resulting from an earthquake unassociated with known tectonic structures, is generally less than an ME magnitude for a given seismotectonic province. DOE suggests a range of 5.5 to 5.8 may represent reasonable values of FE magnitude, based on the historical record for the Colorado Plateau.
' Because the range of'ME magnitudes are higner 00E adopted 6.2 as a conservative design event. Because no eapable fault was ident1tico, an FE event of magnitude 0.2 occurring 15 k2 f rom the site was chosen as the design earthquake. This event would result in horizontal ground acceleration of 0.21g (Ref. 8) based upon Campbell (Ref.1).
(See Seiuotectonic Stability
~
Section).
2.4 Geologic Stability Geologic conditions and processes are ch6racterized to determine the site's ability to meet 40 CFR 192.02(a).
In general, site lithologic, stratigraphic, 3
i and structural conditions are considered for their suitability as a disposal foundation and their potential interaction with tailings leachate and ground water. Geonorphic processes ate considered 1or their potential impact upon long-term tailings stabilization and isolation. Potential geologic bazards, including seisniic shaking, liquefaction, on-site f ault rupture, ground collapse, and volcanism are identified for the purpose of assuring the long-term stability of the disposal cell and success of the renedial action design.
2.4.1 Bedrock Suitability Even though surficial deposits and bedrock units beneath the teilings pile and proposec disposal site appear suitable for meeting EPA standards iur longterm l
stability, adequate characterization of the site presented a major concern e
early in NRC's review pro uss.
Precise characterization of site stratigraphy was hampered because the area's Cretaceous rocks exhibit considerable thinning and pinching out in the area.
The units also vary considerably in their lithology and grain size, and each exhibits gradational contacts or interbedding with adjacent units.
Bedrock expcsures are pour ano data collection relied on well-bore methods. Stratigraphic and lithologic complexities made it difficult to characterize connections between adjacent units or isolation of certain units from others.
Finally, design changes and l
inconsistencies in portrayal of site geology-resulted in uncertainty which geologic units would form the disposal foundation.
Careful reviews of the Ren.edial Action Plan, reference to independent geologic literature, requests for additional inforration, additional orilling by DOE, and staff site visits resulted in a better understanding of the site stratigraphy and structure. Precise details regarding the exact extent of the i
Dakota 56ndstone and its contact with the underlying Cedar Mountain remain unclear at this tine. It is the staff's opinion, however, that DCE's level of l
characterization effort was suitea to the information required and methods L
available.
In addition, DOE modified the design so the tailings excavation I
will completely remove the Dakota Sandstone, and the foundation will consist L
wholly of Cedar Mountain shales. Therefore, the relationships between the two l
formations does not present a concern. Small-scale complexities of the site's L
underlying bedrock probably cannot be better characterized by well-bore methods. The staff has reasonable assurance the drilling program adequately i
l characterized underlying lithologies.
l 2.4. 2 Geomorphic Stability l
DOE concluaed that attempts to stabilize the tailings in place could be l
i a,*
,, acconplished only by drastic seasures and with uncertain 6ssurance of achieving long-tern, stability. Proposed removal of Green River's tailings from Browns i
Wash flood plain to the site's fluvial terrace will result in elimination of the site's major geomorphic hazard: erosion of tailings during 6 c6tastrcphic
. flood event in the Browns Wash drainage basin. 00E analyses show that the disposal site elevation of 4,130 f t is above the PMF elevation of 4,092 f t (Ref.8). See section 4.4 of this TER for reviews of flooding potent 161 i
and elevations.
DOE considers that all other geomorphic hazards at the site occur with frequency or extent such that remedial actions can be designed to minimize their effects and neet long-term stability stancards. However, even the
)
alternate disposal site is subject to long-term geomorphic changes 6s site gullies continue to etcde, and as the banks of Browns Wash rccede. DOE proposes to protect the site f rom continued gully growth, heaccutting, and j
downcutting by (1) contouring the proposed pile ano environs to minimize runofT l
concentrations into existing gullies and minimize formation of new gullies, (2) creating a riprap 6 pron at the topographic base of the pile to halt future gully encroachment, and (3) keying the base of erosion-resist 6nt covers and I
aprons to beorock so a resistant foundation is n.aintained.
No critical structures are planned to be founded upon surficial deposits or Mancos Shale (Ref.8).
i To achieve the above site-stability criteri6, the following oesign features were adopted:
(1) DOE designed a tailings embankment totalling 6 acres with top 4? opes of 5% and side slopes of 20%, each covered by erosion-resistant riprap. Runoff is to be directed in fcur separate directions leaving the en.bankment and crossing the recontoured environs under sheet-flow conditions (00E,1987; calculation 10-555-01-00). The embankment's environs will h6ve its gullies filled in and will be recontoured to slopes approximately 5% to 8%
and extending 100 to 400 feet outward from the embankment. These design elements should eliminate gully formation atcp the tailings and minimize potential continued gully enlargement inaeciately surrounding the disposal.
(2) DOE's design provides ripr6p toe protection consisting of an apren 20 feet wide around the embankment. This feature is designed to protect the tailings embankment from encroachment of re16tively shallow gullies which develop ouring the performance period.
(3) Riprap forming an apron will descend to bedrock on the three sides of the embankment, northeast northwest and southwest, which will be subjectedtopotenti6lgullyheadcuttinganddeepeningduringthe performance period. The riprap wall will preserve the emb6nkment cover in the event that all surficial deposits 6nd fill are eroded during the site's performance period. Stability will be attained because the riprap, descenoing and keyed to bedrock, cannot be undercut by gullies deepening and headcutting through the surficial materials, Prin.ary and secondary geomorphic hazards identified by DOE and the intenced remedial actions are summerizeo in Table 2.1.
The steff has
s
, 4 reason bit assurance that gecnorphic conditions of the site have been adequately characterizeo and that the remedial actions listed above will mitigate the effects of long-term gecmnrphic changes.
For a discussion of rock-size requirea.ents, rock gradations, quantities, curability and other aspects of erosion protection design details, see section 4.4 of this TER, 2.4.3 Seisnotectonic Stability Studies by DOE to analyze seismic harcrds incluoed searching for a design-basis fault, selecting of a design earthquake, calculating estimated peak horizontal ground acceleration, recognizing potential on-site f ault rupture, anc recognizing potential earthquake-induced geologic f ailures at the site.
Delineating f aults with recent rovement in the site region consisted of low-sun angle aerial reconnairsance, interpreting aerial photocraphs in black-ano-white, color, f alse-color infreeo, and LAhDSAT iretery, and fielo reconnaissance mapping of f aults within 60 km of the site.
in accition, the DOE obtained ano analyzed NOAA's. list of instruidntally and historically recorced ecrthquake data for the Coloraco Plateau ano e area of 200 km radius around Green River.
Epicenter locations within a 65 km radius of the site were plotted on an fcult and seismicity base m6p (Ref. 8; plate labeled D.4.1).
Supplementary information (Ref. 3) provided at NRC's request included:
(a) NOAA earthquake epicenter data files, and (b) Notes and discussion of observations made during aerial reconnaissance, field work, and photogeologic interpretation.
DOE did not discover any unknown f aults. Therefore, examining regional faults for design purposes concentrated upon faults already mappeo ano cited in the geologic literature. Staff site visits incluced inspection of three fault groups nearest the site, groups 1, 2, and 5 (Ref. 34).
1,11 three faults exhibit topographic scarps where differing 11thologies occur in each fault block.
Such scarps can be attributea to differing resistance to erosion.
1 Where similar lithologies are juxtaposed in each block of a fault no topographic displacement was observeo.
At the observation points, the faults do not display signs of recent t.ovenent or truncation of Quaternary aeposits.
Based on these observations, DOE concludes the potential design faults are not capable (Ref.8).
Given a lack of capable faults within 65 km of the site, DOE based its evaluation of site seismic hazards on a general appraisal of Colorado Plateau seismotectonics and the available earthquake records. Because an earthquake of magnitude 6.2 can be expected to occur in the Colorado Plateau (see Section 2.3.4), and because a capable design-basis fault is not identified in the site's region, 00E adopted a Floating Earthquake of magnitude 6.2 occurring 15 bn from the site es the design earthquake. NRC staff consider this a justified value because:
(a) Table 1 of Algemissen and others (Ref. 44) inoicates that the maximum magnitude earthquake for the Colorado Plateau (Algermissen's source zone no.16) is 6.1.
Algermissen's relationship for magnitude as a function of intensity, M = 1.3 + 0.6(1), shows a magnitude 6.1 would be the equivalent of Modifiec Mercalli Intensity of I This value is near or slightly above the maximum intensity ever
p e..,.
.- observed in the Colorado Plateau.
It is not overly conservative to assume a somewhat higher magnituce value since the perico 01 performance is signiticantly longer than the historical period.
(b)
In its assessment of seismic hazards at potential sites for high-level radioactive waste repositories in the Paradox Basin, DOE (1984) identified structures capable of generating carthquakes with magnituoes as high as 6.5.
The presence of such structures within I.
the plateau, and evidence that f ault-scarp expression can be reduced by only a few cecades or centuries of erosion, indicates that such an earthquake may have occurred despite a lack of any existing surficial deformations. Despite sur.h structures, the staff consider thet this p
tragnitude is unjustifiably conservative for a oesign evant at Green l
- River, i.
(c) D0E's calculations of the Maximum Credible Earthquake fcr other UMTRA L
Project sites in the Colorado Plateau are given as 6.2.
l l
NRC staff concur th6t peak horizontal acceleration at Green River resultirg
)
from a 6.2 magnituoe earthquake at a distance of 15 km, using Campbell I
(Ref. 1) 84th percentile values, is 0.219 Staff find data inputs and these results to be reasonable and conservative for DOE's calculation of the t
seismic coefficient for the site.
See section 3.3 of this TER f or calculations and applications of the seismic coef ficient and the geotechnical stability of l
the remedial action design.
2.5 CONCLUSION
Based upon review of the Final Euredial Action Plan, Final Design for Review, and DOE s resrense to NRC concents on drafts of these documents, Nkt stef f has reasonable assurance that regional and site geologic conditions have been characterited adequately to meet 40 CFR Part 192. Conditions hindering long-term stability of the site have been identified and either avoicea by alternative site selection or mitigatto by features in the rernedial action utsign.
I
s -. TABLE 2.1 PRIMARY AND SECONDARY GEOMORPHIC HAZARDS ASSOCIATED WITH THE GREEN RIVER UMTRA PROJECT SITE AND THEIR PROPOSED REMEDIAL ACTION
. P&rdazards Proposed R6aecial Action Catastrophic flooding in Removal of tailings above flood plain Browns Wash PMF runoff from embankment, Erosion-resistant riprap covcr erosion of tailings Gully headcutting into Riprap tot protection (apron) embanknent Gully deepening 6nd under-Buried riprap wall descending and cutting of enhanknent keyed to competent bedrock Secondary Hazaros Proposed Remedial Action Rain splash erosion, sheet-Riprap erosion protection
/
wash, and eclian erosion of
(
tailings Chemical weathering of erosion-Use of durable, noncalcareous resistant materials lithologies for riprap Shrink-swell of bentonitic Elimination of Mancos Shale as a lithologies foundation for the embankment Frost heave and solufluttien Burial of racon attenuation layers of enbanknent covers below f rost zone and it.hibition of surface-water infiltration i
. 3.0 GE0 TECHNICAL STABILITY-i 3.1 Introduction The NRC staff review of the geotechnical engineering aspects of the remedial actions at the Green River site is presented in this section. The review consisted primarily of evaluations of the site characterization and stability j
aspects of the stabilized tailings embanknent (disposal cell), and cover design. The object of the review was to determine whether the proposed.
reneci41 actions would result in the stabilizea disposal cell complying with the long-term stability requirements of the EPA Standards in 40 CFR Part 192.02
-(a) Subpart A, from a geotechnical engineering perspective of slope stability, liquefaction, and settlement. The staff review of related geological aspects such as geologic, geomorphic, ar.c seismic characterization of thc site is presented in Section 2 of this report. The staff review of the groundwatet conditions at this site is presented in Secticn 5 of this report.
At the Green River Uranium Mill site (presently an inactive site), the ore concentrate was shipped to a processing plant in Rifle, Colorado, and thus the tailings left at this site were precominantly sancy tailings with no sline.
The remedial action of stabilization-on-site consisted of placing all the contaminated material at the site (approxinetely 362,000 cyds) into a single pile, which is called the disposal cell. The location of this oisposal cell is approxinately 500 feet south and about 50 feet higher in elevation than the existing tailings pile location. The disposal cell bottom (elevation 4098 feet) is approximately 42 feet below the existing ground surface (elevation 4140 feet), and the top of the disposal cell (elevation 4181 feet) is about 41 feet above the adjoining ground surface.
The construction of the portion of disposal cell below the ground surface required excavation of approxiniattly 16 feet of overburden material and 26 feet of beorock. The portion of the disposal cell above the existing ground surface rises to the crown of the cell (elevation 4181 feet) at a gentle slope of 5 horizontal to 1 vertical (5H:IV).
The disposal cell cesign provided for placiae a six-feet-thick layer of select material as a buffer zone at the bottom of de cell between the bedrock and the I
contaminated materials. The disposal cell is been covered, in the ascending croer, with (1) a three-feet-thick infiltration /racon barrier, (2)(ariprap).
six-inch-thick gravel bedding, and (3) a 12-inch-thick rock layer The cover was designed to ensure the following: (1) long-term stabilit embanknent and reduced radon emissions;)(2) reduced l
(4 protection against animal i-trusion; p(rotection of surface water quality;(6) prevention of inadvertent hu.an v
- 5) minimized plant root intrusion; l
intrusion; and (7) prevention of material dispersion (Ref 8).
This section I
presents the geotechnical engineering evaluation of the long-term stability l
aspects of the proposed remedial actions.
3.2 Site Characterization 3.2.1 Site Description Section 1 of this report presents a description of the Green River project site.
. 3.2.2 Lite Investigations i
Subsurface explorations at the site were performed by the following investigators:
(1) Bendix Field Engineering Corporation outermineo the extent of contamination. The investigations resulted in data from 105 bore-holes,184 in situ Ra-226 neasurements, and 139 soil samples.
Addendum DI to Appenoix D in reference 8 presents detailed information on this investigation. The results of this investigation were used in establishing the volume of contaminated material to be removed from its present location to comply with the EPA Standards.
This removed contaminated naterial was placco in the disposal cell.
(2) Jacobs Engineering Group, Inc. (1986, 1987,)1986) and Morrison-Knudson Engineers, Inc. (1966-1907. The scope of the geotechnical investigations included (1))bcrings from which soiltest pits from which samples and rock ceres were obtaineo, (2 samples were obtained, and (3) installation of monitoring wells.
These investigations were performed to determine geotechnical characteristics of the site and to obtain san.ples of the soil at.d rock materials for laboratory determination 01 their properties.
Information to Didders, Volunes 1, II, and 111 of Reference 9, and Volume IIA Appendix 0 of the draf t final HAP dated January 1989 (Ref.
- 8) present detailed information on site conditions and logs of these
=
field investigations and laboratory test results.
k 3.2.3 Site Stratigraphy The elevation of the Green River project site varies from about 4050 to 4200 feet above nean sea level. Borings were drilled using standard geotechnical drilling and sampling techniques. These methods incluced dr1111ns with hollow stem augers, and sampling at near continuous intervals with Standard Penetration Tests (SPT). On occasion, a 2.5-inch inside-diaceter, ring-lineo split-barrel sampler was used to sample the materials. The SPT tests were conducted according to ASTM 0 1586 procedures.
Figure 3.7 of the RAP (Refs. 8 and 46) shows locations of the borings ano test pits.
Section 2 of this report presents an evaluation of the geologic, geomorphic, and seismic characteristics of the site.
The overburden materials at the site consist of an alluvium deposit uncerlain by a thin layer of gravel which in turn overlies the bedrock. The alluvium deposit consists of silty to clayey sand, with dense sand and gravel occurring at the bottom of this denosit. The alluvium deposit is in a. loose to dense condition, with the Studcrd Penetration Test resistance values ranging from 3 to 43 and averaging 18 cNws/ foot. The sedimentary bedrock units at the site consist of a shale cenber of the Mancos shale, the Dakota sandstone, and the Cedar Mountain Formation. The upper portion of the bedrock is weathered and f ractu red. Section 2 of this report presents a detailed evaluation of the bedrock conditions at the site.
At the existing tailings pile area, the site Stratigraphy consists of sand ta111ngs overlying the alluvium deposit (silty sand-clayey sand) which in turn
., overlies the bedrock. Tailings and underlying contaminated alluvium materials were excavated from their present location and pieced in the disposal cell.
The overburden soil at the disposal cell location consists of from 5 to 16 feet j
of loose to dense alluvium (silty sand - clayey sand). Thick lenses of clay are contained within this layer. Dense to very cense sand and gravel occur at the bottom of this alluvium deposit. Since the disposal cell-was founded on the bedrock, the overburden material was excavated. This alluvium material was j
selectively useo as Select fill Type-A material, for the six-feet-thick buffer 1
zone placed at the bottom of the cell between the bedrock and the tailings.
The disposal cell excavation extended to a depth of approximately 26 feet into the bedrock. This excavation resulted in removing the entire Mancos stale anc DeFota sandstone stratum, and part of the Cedar Mountain Fornation shale /mudstone down to an elevation of 4098 feet.
The groundwater table at the disposal cell location is estimated to be 4083-4085 feet in elevation, approximately 55 feet below the grouno surfece and 13 feet below the bottom (elevation 4098 feet) of the disposal cell. Section 5 of this report presents a detailed evaluation of the groundwater conoitions at
'l the site.
Soil for the radon barrier cover and gravel for the bedding layer were taken from Borrow Site 1.
Figures 3.15 through 3.24 of the RAP (Refs. 9 and 46) show the location and stratigraphy of the borrow area. A total of 24 test pits i
were dug to investigate the availab111ty and suitability of the soils for the intended use. The stratigraphy at the borrow site consists of an alluvial deposit with a Jurficial layer of silty-clayey sand, underlain by low-plasticity clay.
The clay layer is underlain by a alluvial sand and gravel stratum.
The test pits were terminateo in the sand-gravel stratum. The low-plasticity clay was used for the infiltration / radon barrier cover and the alluvial sand-gravel material was processed to obtain the gravel needed for the i
bedding layer.
The staff has reviewed the details of the borings and test pits as well as the scope of the overall geotechnical exploration program. The staff ccncludes that the geotechnical investigations conducted at the Green River site have adequately established the stratigraphy and soil conaitions to support an L
assessment of the geotechnical stability of the stabilized tailings and l
contaminated material in the disposal cell.
Further, the geotechnical explorations are in general conformance with applicable provisions of Chapter 2 l
of the NRC Standard Review Plan (SRP) for UMTRCA Title I Mill Teilings Remedial l
ActionPlans(Ref.5).
l 3.E.4 Testing Program L
The staff has reviewea the geotechnical engineering testing program for the Green River site. The testing program included physical properties tests, compaction tests, triaxial shear strength tests, pern.eability tests, and dispersion tests on samples of tallings and borrow materials intended f or use in the disposal cell.
However, the DOE had not sutmitted all the test data (for exampic, capillary-moisture relationship, adequate nunber of hyoraulic conductivity 1
1
. tests) for the infiltration /racon barrier material in the craft final RAP (Ref. 8). As a result of an NRC/ DOE meel.ing to ciscuss the staff evaluation of the oreft final rap, the DOE committed to provide the following cata to support the design in the RAP (Ref 44).
Hydraulic conductivity test results for field-compacted samples of l
infiltration / radon barrier material.
Density ano moisture content of tailings and contaminated materials as.placed in the disposal cell.
The staff has reviewoo the above test cata submitted by the DOE along with the final RAP (Ref. 46), and conclude that the DOE has net the couaitments in tern.s of providing the data to support their design. Details of the relevance of this dt.ta to the design is aodressed in the staf f evaluation of the cover properties ano geotechnical stability of the disposal cell.
The staf f finas that the testing program employed to aefine the material properties was appropriate for the sup? ort of necessary engineering analyses I
J.
described in the following sections.
urther, the scope of the testing program r
and the utilization of the resulting cata to define the n.aterial properties are in general agreement with applicable provisions of the SRP (Ref. b).
i 3.3 GeotechMcOJn,gineeringEvaluation 3.3.1 Stability Evaluation The evaluation of the geotechnical stability of the slopes of the oisposal cell containing stabilizec thilings and other contaminateo soils is presented in j
this section. The staff has reviewed the exploration data, test results, slope characteristics and methods of analyses pertinent to the slope stability aspects of the ren.edial action plan (Ref s.10 & 11). The analyzed cross section with a 5 horizontal to 1 vertical slope has been compared with the exploratory records and design cetails. The staff finds that the characteristics of the slope have been properly representeo ano that 1.he nost critical slope section has been considered for st6b111ty analysis.
Soil parameters for various meterials in the disposal cell slope have been adequately established by appropriate testing of representative materials.
Values of soil paraneters have been assigned to other layers (riprap, gravel i
bedding, bedrock etc.) on the basis of data obtained from geotechnical explorations at the site and data publishea in the literature. The staff finds that the determination of these parameters for slope stability evaluation follow conventional geotechnical engineering practice, and are also in compliance with the applicable provisions of Chapter 2 of the SRP. The staff also finos that an appropriate method of stability analysis (Bishop methoo) has been employed and has addressed the likely adverse conditions to which the slope might be subjected. Factors of safety against failure of the slope for i
seismic loading conditions have been determined for both short-term (end-of-construction) state and long-term state. Factors of safety for ttc static loading conditions were not determined because the seismic loading condition is more critical and results in lower factors of safety than those for the static loading condition. The seismic stability of the slope was
l investigated by the pseudo-stetic nethod of analysis using horizontal seismic coef ficients of 0.1 for end-of-censtruction case ano 0.14 for the long-term i
case. The values of the seismic coefficients were calculated as per guidance in-the SRP and are acceptable to the staff. The staff finos the pseudo-static j
sethoo'of analysis to be acceptable considering the degree of conservatism in the soil parameter values and the flatness of the slopes (5H:1V).
The minimum factors of safety against failure of the slopes were 2.3 and 1.67 for the end-of-construction seismic and long-term seismic conditions, ccmparea to a required minimum of 1.1 for both seismic conditions.
The above analysis was perforned for the slopes of the disposal cell that was proposed in the draft final RAP. However, during the actual construction more winoblown neterial was encountereo and disposing it in the disposal cell-resulted in increasing the height of the oisposal cell.
In response to a steff request, the DOE submitteo a conservative analysis (infinite slope analysis) to support their assertion on the stability of the final slope of the disposal cell. The resulting f actors of safety are 2.44 and 1.42 respectively for long-term static and long-term seismic loaoing condittens. These factors of saf ety are higher than the requirec minimum of 1.5 and 1.1 respectively. The staf f has reviewed the DOE's analysis ano agrees with the results from this i
analysis af ter (1) reviewing the conservatism in the properties of materials in the potential tailure zone determined in the rigorous analysis performed during the final draft RAP stage, (2) considering the flatness of the slope (5H:1V),
and (3) assessing the margins in the computed factors of safety compared to the required minimum values.
The staff concludes that the slopes of the cisposal cell will be stable under both short-term and long-term conoitions from a geotechnical engineering slope perspective ano this as ct of the design will comply with the EPA stability (40 CFR Part 192.02(a)) f or long-term stability.
i Standard I
3.3.2 Liquefaction l
Based on review of results of the geotechnical investigaticos, including boring logs test data, soil prof 11es, and disposal cell design, the hRC staff concludesthattheDOEhasadequatelyassessedthepotentialforliquefaction l
at the Green River site. Because the compacted dry density of the tailings ano other contaminated materials in the disposal cell are a mininon, of 90 percent of the maximum cry density by the ASTM D-698 test, and by design these materials are in an unsaturated cor.dition, these materials are not susceptible l
to liquefaction. The disposal cell is founded on bedrock, which is also not susceptible to liquefaction. The grounc ater table at the site is estinated to be approximately 13 feet below the foundation of the disposal cell.
Considering the placement density and absence of free moisture in the disposal L
cell, the materials in the disposal cell are judgea to be not susceptible to liquefaction.
3.3.3 Settlenent Long-term settlement of materials in the disposal cell, which could result in either local depressions on top of the cover or cracks in the cover, has been adequately aooressed in the RAP. If depressions in the cover were to form they
a w
could initiate erosion gully pathways followed by a potential exposure of the tailings u terials. A crack in the cover might open up a pathway for surf ace water to infiltrate into or through the tailicts materials.
Since the tailings and contaniinated materials in the disposal cell are sancy naterials compacted to.a mintamm of 90 percent of Standard Proctor density at 4 acisture content of 3 or more percent below the opttamm scisture content, a major portion of the settlement will be instantaneous and will take place during construction. Any potentially adverse effects of the instantaneous settlement of these sandy uterials was rectified before completion of the construction anc therefore, will not adversely af fect the long-term perforunce of the disposal cell. Time dependent or delayed settlement is expected to be miniul cr insignificant and is not expected to result in any cifferential settlement crecks in the cover.
1he staff concludes that the long-term settlements of the sancy uterials in the disposal cell will be mininal and will not have any adverse impact on the performance of the disposal cell cover. Therefore, f rom a long-term settlement perspective, there is reasonable assurance that there will be no aoverse effects on the ability of the disposal cell to met the EPA Stendards.
3.3.4 Cover Design The cover for the disposal cell consisted of the following, in descending croer from the top: (1) an erosion protection feature composeo of a one-foot-thick, Type-A riprap; (2) a 6-in.-thick gravel bedoing layer; and (3) an l
infiltration / radon barrier coniposed of a three-foot-thick layer silty-clay j
anendedwithBentonite(Refs.8and46).
The staff's evaluation of the cover design considered the design adequacy with regard to erosion protection, radon ettenuation, frost penetration and '
infiltration. The riprap and its bedding layer is designed to prctect the racon/ infiltration barrier in the long-term. The staff's evaluation of the erosion protection layer and its ability to conply with the long-term stability aspects of the EPA Standards is presented in Section 4 of this repert. The staff evaluation of the adequacy of the infiltration barrier, as part of the DOE's design to comply with the EPA Groundwater Standards, is addressed in Section 5 of this report. The staff's evaluation of the adequacy of the l
thickness of the adon barrier to attenuate the release of radon to comply with the EPA standards is addressed in Section 6 of this report.
The DOE has performed an evaluation of the freezing conditions at the Green River project site and has concluded that the maximum freezing aepth at the site is 39 inches. The DOE has used 200-year weather data for the Green River site and a com) uter code developed by U.S Aruly Cold Regions Research and Engineering La> oratory for the modified Bergren Solution to calculate the depth of frost penetration. As part of the design, the DOE has performed a sensitivity analysis to arrive at the recommended frost penetration cepth of 39 inches. Tho staff has reviewed the values of the input parameters and the range of paranaters investigated in the sensitivity analyses and concurs with the DOE's analyses and reconsnendations. As an independent verification, the depth of frost penetration indicated in Figure 7.1-42 of Reference 42, prepared by the U.S. Arnty Corps of Engineers, is 36 inches for the project site region.
Therefore, the staff agrees with the DOE's estimation of the frost penetration l
l t
l_
. depth of 39 inches at the site. A 39-inch frost penetration will result in the freezing of the opper 39 inches of the 54-inch thick cover, while the lower 15 inches of radon / infiltration barrier layer will te in the unfrozen or intact condition. Therefore, the DOE's design of the radon barrier for freezing / frost condition is satisfactory. The adequacy of this lower 15 inches of redon/ infiltration barrier to control the infiltration into tLa disposal tell and to reduce the radon emanation from the disposal cell to comply with the EPA Standards is addressed in Sections 5.0 and 6.2, respectively, of this report.
The radon / infiltration barrier design assunes that the Bentonite amenden silty clay material, used for the radon barrier, can be compacted to result in a material whose saturated hydraulic conductivity does not exceed 2x10-8 cm/sec.
Further, the design against infiltration assunts that the long-term moisture saturation condition of the radon bar rier will be unsatureted, and therefore, magnituce lower (ydraulic conducL1vity will be approximately an order ofi.e.,1x10 the unsaturated h conductivity. This permanent unsaturated condition will result in an infiltration rate or flux of 1x10-9 cm3/cm2.sec or less through the cover.
This inf11tration rate value is the critical parameter in the design of the disposal cell cover to comply with the EPA Groundwater Standaros for UMTRCA projects. Section 5 of this report presents details on the evaluation of the disposal cell cover to satisfy the EPA Grounowater Stancards.
The laboratory test data (Table 0.4.4 of draft final RAP, Ref. 9) presented in l
support of the saturated hydraulic conductivity consists of three tests on silty clay anended with 3 percent of Bentonite resulting in saturated hydraulic conductivities of 2x10-8,1.5x10-8, and 3.4x10E-8 cm/sec with an average value of 2.3x10-8 cm/sec.
However, the data presented in Table D.4.4 for the redon barrier material only (without Bentonite) show the hydraulic conouctivity parameter to range f rom a low of 2.4x10-8 to a high of 8.5x10-5 cm/sec. The l
staff notes that in the cata presented in Table 0.4.4 there were two tests on soil amendeo with 6 percent of Bentonite, and both yielded hyoraulic conductivity in the range of 1x10-8 cm/sec. Considering the range of the hyoraulic conductivity values presented in Table D.4.4, 6nd the sensitivity of this parameter to compaction density, Bentonite content, moisture, and percent fines in the soll, the staff believed that in the draf t final RAP document the DOE had not adequately established with reasonable assurance that the silty clay amended with 3% Bentonite (for radon barrier) would have a saturated 1
hydraulic conductivity of 2x10-8 cm/sec.
In addition, mixing silty clay with three percent by weight of Bentonite in the f1 eld to achieve a uniform mixture coulo >= difficult to accomplish, and could result in a nonhomogeneous or i
heterogeneous soil-Bentonite mixture, which in turn may not have the desired l
average hydraulic conductivity as determined from tests on laboratory compacted samples.
Increasing the Bentonite content to 6 percent resulted in the soil-Bentonite mixture being relatively uniform. This mixture, when compacted to 100% Standard Proctor density, achieved the desired average hydraulic conductivity; viz., in the range of the values determined from laboratory testing. Data in Table D.4.4 shows that s11ty clay material, with 55 to 60 percent fines passing No. 200 steve and anended with 6% of Bentonite and compacted to 100% Standard Proctor density, had a saturated hyoraulic conductivity in the range of 1x10-8 cm/sec. Also, silty clay with 70% fines passing No. 100 sieve and amended with 3% of Bentonite and compacted to 100%
Standard Proctor density had an average saturated hycraulic conductivity of l
2.3x10-8 cm/sec. Therefore, the silty clay material mixed with 6% by weight of l
i
, Bentonite and complying with the above gracation and compacted to 100t Stancard Proctor density at a moisture content of 0 to 2f higher than the optimum is j
expected to result in a saturated hydraulic conductivity not exceeding Ex10-8 cm/sec.
As a result of a NRC/ DOE neeting on the results of staff evaluation of the i
draft final FAP, the DOE committed to three changes in the RAP (Ref 44). The i
final RAP (Ref. 46) presents the information to support that the DOE has made the changes and developeo the requirec accitional information to support the oesign. The following is 6 listing of the DOE comitments and NRC's evaluation of the DOE's fulfilnent of the comitments.
1.
The DOE corraitted to constiucting the first lif t of the infiltration / radon barrier with material that has greater than 70 percent of the material passing the No. 200 sieve and material for the other liits having 50 percent passing the No. 200 sieve.
The basis for this requirenent was that the radon barrier materiai should be sini114 to that tested in the laboratory, 6nd the soil san.ples used in hydraulic conouctivity tests performed in the laboratory hac an average fines (passing No. 200 sieve) content of 70 percent. Although the infiltration /racon barrier is three feet thick, the lower 12-inch
- ortion of the cover is acequate to fulfill its function, and therefore, t11s requirenent was imposed oit the first lift.
The DOE has changed the subcontract specifications to include this condition (Section 02200 PART 2-B.3, pg.02200 - 9 Appendix T of Ref.
46), and proper implenentation of this specification will satisfy the comitnent.
2.
The DOE connitted to mix no less than six percent by weight of Bentonite into the radon barrier material.
The basis for this requirement was that the hydraulic conductivity test results presented in the diaft final RAP scattered over a w.de range, ano only samples with six percent Bentonite consistently met the hydraulic conductivity requirenent of 2x10-8 cnis/sec., Because the hydraulic conductivity of the radon / infiltration barrier was a critical paraneter in the design of the cover to comply with the EPA Grcundwater Standards, a conservative approach was taken in requiring six percent by weight Bentonite in the radon barrier soil.
The DOE has changed the subcontract specifications to include this requirement (Section 02200 FART 3 - Section 3.5. C.2. pg 02200 -22, Appendix F of itet. 46), and proper implenentation of this specification will satisfy the commitment.
3.
The DOE comitteo to perform noisture content anc hyoraulic conductivity testing of the radcn barrier to oemonstrate that the as-built saturatto hydraulic conductivity does not exceed 2x10-8 cms /sec. The testing to be I
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e 4 at a frequency of at least one test per 2,000 cubic yarcs of radon / infiltration barrier material.
The design of the cover to satisfy the EPA Grounawater Sttodards was not finalized at.the time of the draf t final RAP review. and based on a siele analysis it was determined that a saturated hydraulic conductivity of l
2x10-8 cms /sec. for the radon / Infiltration barrier would result in a cover that would racet the desired groundwater travel tine through the disposal cell; (details of this cspect of the design are addressed in Section 5 of thisreport). Therefore, the above requirenent of saturated hycraulic conductivity of the as-constructed radon / infiltration barrier was in. posed.
The hydraulic conductivity was to be dunonstrated by laboratory tests pelformed on as-compacted block serrples of the radon /ir filtration bstrier layer taken from the fielo.
The DOE has completed the placement of the radon / infiltration barrier layer and has submitted the results of hyoraulic conductivity tests l
pertoimed on as-built or field compacted bic.ck samples of radon barrier L
layer taken during construct:en. The f.eiu-cornpacted samples wert. testeo l
in the laboratory, and the saturated hydraulic conductivity of 14 sarnples l
r6ngeo f tom a low of 0.17x10-8 cms /sec to a high of 1.5x10-8 cms /see with l
cn average of 0.61x10-8 cms /sec. The hydraulic conductivity average value compared favorably with the required value of less than 2x10-8 cms /sec.
All the samples had been compacted to a dry density of 100 percent Proctor l
density and a moisture content of 0 to 3 peretnt higher than the optimum, as per the s)ecifications (Section 02200 PART 3, Section 3.8, pg 02200 -28 of Append.x of Ref. 46). The DOE has demonstrated compliance with the consnitment on the hydraulic conductivity of the radon barrier.
Full cerap11ance by the LOE with the above cenmitments is an adequate basis for the staff to reach a conclusion that there is a reasonable assurance that the radon barrier has been constructed to ensure that the as-built saturated hyoraulic conductivity not exceed 2x10-8 cm/sec.
The design of the cover, from a perspective of providing protection against freezing of the racon/intiltration barrier is satisfactory. The staff j
concludes with reasonkble assurance that the racon barrier has been constructed J
to have a saturated hycraulic conductivity of 2x10-8 cm/sec or lower. The evaluation of the disposal cell and cover regarding ccinpliance with the EPA Grounawater Standards is addressed in Section 5 of this report.
3.4 Geotechnical Construction Criteria The DOE's strategy to meet the EPA Groundwater Standards includes ensuring that L
the tailings and other contaminated iraterials in the disposal cell are at their equilibrium or steady state moisture content, i.e. at unsaturated condition.
This unsaturated condition will slowdewn the migration of any inoisture towards the bottom of the disposal cell. The specifications state that these materials content determined by ASTM D 698 test (Standard Proctor test)ptimum moisture should be compacted at a minimum of 3 percent less than the o The in situ meisture contents range from a low of 1.2 percent to a high of 15.5 percent (Table D.5.22 of Ref. 8) f or tailings and approxitautely 6 to 9 percent for ll
i
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t buffer zone matei ial (overburden maten616t the cisposal site). The optimum misture content for these mate:1als range from 10 to 16 percent for tallings and i to 13 percent for buffet zone material, and 11 percent for the winoblown material. The flux calculations, using the SUTRA code to calcul6te the groundwater travel time through the disposal cell, indicate that tt; required percent in Table E-3-5 of Reference 8) percent of values presented as volume steedy state moisture contents (weight are approximately 9% f or buffer zone material, 6% to 9% for winablown material, and 3% to 9% for tallings material.
Placing the buffer zone material at the an situ moisture content would result in the material being placed close to its ste603 state moisture. The proposed placenent moisture content for the windblown material was close to the desired state of approximately 3 percent drier than its optimum moisture content.
Placing the tallings at its in situ moisture content resulteo in the placement moisture content close to the steady state mo4ture content (3% to 9%)
indicated in the analysis.
It 1s reiterateo that the moisture centents mentioned above are all weight percent moisture contuits useo by geotechnical engineers at:d not volumetric moisture contents used by hydrogeolvgists. 510ce the design objective was to place all the materials in the disposal cell at as low a roisture content xs possible, and all the materials placed in the disposal cell were granular material, ther e was potential of not being able to compact the relatively cry granular material to the desireu censity.
The specifications piovice for the first 1,000 c,yos of the fill material to be placed under controlled conditions to develop compaction proce & as that would ensure 'tne specified density.
The staff indicated that this trial compaction should be extended to at le.ast four lif ts and that the desire 0 density shoulo be achieved for the full depth of compaction 1.e. f our lif ts. Since compacting 7
at such dry state was not originally contemplateo in the draft KAP oesign, the staff asked the DOC to cemonstrate that these materials con be placed in tne disposal cell at the censities and moisture contents assonied in the final design.
As a result of a NPC/D0E meeting on the results of staff evaluation of the draft final RAP, the DOE committed to the following (Ref. 44):
The DOE committea to placing and maintaining contaminated traterials in the disposal cell at the specifleo densities and at average troisture contents that 4re less than their avtrage steady-state moisture contents and, in any case, less than 5% by volume (3% by weight) for the ta11 hgs aua less than 10.6% by volume (5.5% by we'ght) f or the windblown and other vicinity property contaminated materials. The DOE conmiitted to place and test at least f our lifts of conta..unated motet 1als curing the trial compaction (first 1,000 cyd of material), which was intenced to develop procedures to ensure compaction of the raaterials in accordance with material specifications. The DOE also connitted to submit physical prcperties ano r
compaction data on winablown materials and any other data to support compliance with the condition that contaranated materials will be placed ano maintained at the specified censities and moisture contents.
The basis for this requit ement was that LOE should demonstrate that the densities and low moisture condition assumed in the design can be achieved in the field.
'e, 4
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c In response to this comitment,-the DOE has submittea results and analyses of field tests periormed to deterniine the actual placement density and moisture content. Because of difficuhy in com))ying with the dust control requirements, the DOE could not place tie materials at the desired incisture contents. Some water had to be added tu control the dust and this resulted in the placement moisture content being slightly higher than the oesired values. All the materials were compacted to the specified densities. The average percent compaction for the materials placed in the disposal cell is 95.6, 94.67 and 97.38 percent Proctor compaction for tallirgs, contaminated materials ano buffer zone materials respectively, whereas the specifications required a minimum of 90 percent Proctor compaction. Therefore, the materials in the disposal cell have been placed to comply with the density specifications. The placement moisture content is slightly higher than the values comittto to by the DOE, i
l' because of adding water to control the cust. The placement moisture l
content was 7.2 % percent and 10.2 percent by volume 1or tallings and windblown and other y scinity property-contaminated material, respectively.
l~
The corresponding nioisture contents by weight ere 4.6 and 5.5 percent, I
respectively, for tailings and windblown and other vicinity property-L contaniinated material. The 00E.comitted placement moisture contents are 5 and 10.6 percent by volume for tailings and windblown and other vicinity property-contaminated materials, resoectively. The effect of slightly higher moisture content of the contaminated waterials placed in disposal cell on the remedial action at the site (disposal cell)t.he complying with the EPA Groundwater Standards for t!MTRCA projects as addressed ir, Section 5 of this re) ort. From a perspective of geotechnical stability of
(
l the disposal cell, tie contaminated inaterials have been placed at specified density and the as-placed morsture content of the contaminatea materials in the disposal cell has no adverse impact on the gectechnical stability of the dis;iosal cell.
3.5 Conclusion J
Based on a review of the design for the Green River site as presented in the remedial action plan (Refs.'8, 9, 10, 44, and 46), the NRC staff concludes that f rom a geotechnical engineering perspective the remedial action will comply w(a)h the long-term stability aspects of the EPA standards (40 CFR Part it 192-02
).
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- . 7., e 4.0 SURFACE WATER HYDROLOGY AND EROSION PROTECTION 4.1. Hydrologic Description and Site Conceptual Design The Green River site is located near Green River, Utah and is situated on a plateau. approximately 50 feet above the Green River channel.
The Green River has.a drainage area of approximately 40,590 square miles and is located approximately 2000 feet east of the site.
L Brown's Wash is located inneciately north of the site and has a drainage area of approx *ately 85 square miles. Overland flows north of the site are
' oivertea f rom Biown's Wash by a ra alroad enibankn.ent;. surface flows south of the site are diverted by a highway embankt;,ent. Significant floocing has occurred in Brown's Wash, and tailings have been eroced in the past.
Iri order to coinply with EPA standards, which require stability of the tailings for a 1,000-yehr period, DOE prcposes to stabilize the tailings sno contar.dnated materials in an engineereo embankment to protect them f rom flooding and erosion. The existing tailings will be moved from their present location in the floodplain of Brown's Wash to a locatic.1 on a plateau about 40 j
feet above the maximum level of flooding in Brown's Wash.
o The tailings will' he consolidated into a single pile, which will be protected by soil ano rock covers. The covers will have maximum slopes of 5% on the top and 20% on the-sides. The square-shaped pile will be surrounded by aprons which will shfely convey flood runoff away from the tailings and prevent gully erosion into the stabilized pile.
'4.2 Floo g d tg rminations
- The con;putation of peak flood desigri discharges for various design features at the site was perforned by DOE in several steps. These steps included (1) selectionofadesignrainfallevent,(2)determinationofinfiltrationlosses, l_
(3) determination of Iwas of concentration, and-(4) cetermination of-appropriate rainfall.cistributions, corresponding to the computed times of l
concentration.
Input parameters are den ved from each of these steps to
,j l
determine the peak flood discharges v.o be used in water surface prof 1le and velocity modelling and in the final determination of rock size for erosion
~
o protection.
1.
"alection of Design Rainfall Event. DOE has determined that one of the most disr0ptiv~e~pEeiionsinffecting long-term stability is water erosion and L
has recognized that it f s ve'ry important to select an appropriately conservative rainfall event on which to bue the flood protection designs. DOE L
has conciuoed (Ref. 53) and the NRC staff concurs (Ref. 52) that the selection k
of a oesign flood event should not be based on the extrapolation of limited l
historical flood data, due to the unknown level of accuracy associated with l
such extrapolatiora. Rat.her, DOE utilized the Probable Maximum Precipitation l
h l
p L
L b
a.
(PMP),1which is-computed by deterministic methods (rather than statistical methods), ana is based on site-specific hyorometeorological characteristics.
Tne ItlP has been define 6 as the most severe reasonably possible rainfall event i
that could occur as a result of a combination of the most severe meteorological conditions occurring over a watershed. No recurrence interval is normally assigned to the PMP; however, DOE and the NRC staff have concluded that the probability of such an event being equalled or~ exceeded during the 1000-year stability period is extremely small. Therefore, the PMP is considered by the
- NRC staf f to. provide an acceptable design basis.
Prior to determining the runoff from the drainage basin the flooding analysis requiresthedeterminationofPMPamountsforthespecificsitelocation.
. Techniques for determining the PHP have been developed for the entire United States primarily by-the National Oceanographic and Atmospheric Administration (NOAA) in the form of hydrometeoiolcgical reports for specif1c regions. These techniques are widely used and provide straightfornia proceoures with minimal var iability. The staff, therefore, concludes that use of these reports to derive PMP estimates is acceptable.
2.
Infiltrati,on Losses.
Detemination of the peak runoff rate is dependent on the amount of precipitation that infiltrates into the ground during the occurrence of the rainfall.
If the ground is saturated from previous rains, very little of the L
rainfall will infiltrate and.most of it will become surface runoff. The loss rate is highly variable, depending on the vegetation and soil characteristics of the watershed.
Typically, a11' runoff models incorporate a variable runoff coefficient or
-vartable runoff rates. Concionly-used models such as the Rational Formula (Ref.
-14) incorporate a runoff coefficient (C); a value of 1 represents 100% runoff ano no infiltration. Other mooels such as HEC-1 (Ref.12) separately compute infiltration losses within a certain period of time to arrive a runoff: amount during that time period. For this site, DOE used the rational formula and the Santa Barbara Method (Ref. 54) which uses Green-Ampt (Ref. 55) infiltration parameters. DOE's use of these methods generally results in conservative r
L infiltration est1; nates and are therefore considered to be acceptable.
L 3..
Time,of_ Concentration.
The time of concentration is the amount of time required for runoff to reach the outlet of a drainage basin from the most remote point in that basin. The peak runoff for a given drainage basin is inversely proportional to the time of-concentration of that basin.
If the time of concentration is computed to be small, the peak discharge will be conservatively large. Times of concentration and/or lag times are typically computed using empirical relationships such as those developed by Federal agencies (Ref. 14). Velocity-based approaches are also used when accurate estimates ate neeoed. Such approaches rely on
- 34'-
1 estimates of channel velocities (since most runoff becones rapidly channelized)
L
-to cetermine the time of concentration of a drainage basin.
Staff. review of the methods used by DOE indicate that the methods are L
appropriate for the small crainage basins at UMTRA sites. The methods 6re
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' velocity-based and produce conservatively low estimates of the time of concentration, and are, therefore, acceptable.
e 4.
Rainfall Distributions.
. After the PMP-is determinea, it is necessary to determine the rainfall
' intensities corresponcing to shorter tir.es of concentiation. A typical PPP l-value is derived for periods of about one hour.
If the time of concentration-1s'less than one hour, it is necessary to extrapolate the data presented in the l
various hydrometeorological reports to shorter time periods.
DOE utilized a L
procedure recommended by i;0AA and endorsed by the NRC staff. This procedure l
involves the determination of rainfall ancunts as a percentage of tie che-hour PMP,-and computes rainfall intensities for a very short periods of time.
DOE and the NRC staff have concluoed that this procedure conservatively computes rainfall amounts for such short cime periods.
4.2.1-ProbableMaximumPrecipitation(PMP)
'A PMP rainfall depth of approximately 8.5 inches in one hour was used by DOE to compute the PMF for the small crainage areas at the site. This rainfall estimate was developed by DOE using Hydrometeorolog1 cal Report (HMR) 49 (Ref.
25). The staff performed an independent check of the PMP value, based on a review of HMR 49. Based on this. check of the rainfall computations, the staff concludes that the FMP was acceptably cerived for this site.
P 4.2.2 Infiltration Losses y
In computing the peak flow rate for the design of the rock erosion protectior.,-
DOE used the rational formula.
In this formula, the runoff coefficient (C) was I
assumeo by DOE to be unity;.that is, DOE assuned that no inf11tration losses would occur. Based on a review of the computations, the staff concludes that this is a very conservative assumption when using the iational formula and is therefore acceptable.
4.2.3 T'.me of Concentration Within a computer 12eo design procedure (Ref. 56) that estimates riprap sizes, the-times of concentration for the pile top and stoes were estimated by computing the actual flow velocity over and through the riprap and dividing the L
length of the design segment by that velocity. Such a-velocity-based method is L
considered by the staff to be appropriate ano very precise for estimating times of concentration. Baseo on the precision and conservatism associated with such a method, the staff concludes that the tc's have been acceptobly derived.
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Tismsof. concentration (tc)fortheapeonsandembankmentswereestimattoby DOE usin l
b d methocs. The Kirpich Method and the Brant-Obern.an Method-(g ve ocity-aseRef. 56) are also used for somewhat larger drainage areas.
The staff-concluces that the procedures used for computing tc are representative of the sus 11 steep drainage areas present at the site.
For very small crainage areas with very short times of concentration, DOE utilized tc's as low as 2.5 minutes; the staff considers such tc's to be conservative.
4.2.4 PMP Rainfall Distributions Using the one-hour PMP estimate as discussed above, DOE derived rainfall
' distributions arid intensities using preceoures recorm. ended by the NRC staff.
In the determination of-peak flood flows in ditches ano aprons, rainfall intensities for ourations as shott as 2.5 minutes were used. The staff checked the rainfall amounts for the short time. periods associated with small crainage-basins. ' Based on a review of this aspect of the flooding determination, the staff concludes that the. computed peak rainf all intensity of about 56 inches / hour (corresponding to a tc of 2.5 minutes) is conservative, and therefore, acceptable.
4.2.5 Computar.1on of PMF Follo <ng the determination of the various input parameters, as discussed above, DOE used these parameters to derive peak discharge estimates for (1)-
onsite drainage, which includes the inanediate encapsulated area and the erosion rotection for the top, sides, and aprons of the pile; (2)theGreenRiver;and p(3) Brown' swash.
4.2.5.1 Onsite Drairiage The peak runoff rate for the top and sides was estimateo within a computerized design procedure for riprap sizing (Ref. 56), which iteratively cortputes the riprap size requited. The rational formula (Ref.14) forrrs the basis for computing the peak sheet flows cown the slopes and flows on the aprons. Based
-on,our review of the calculations presented, the staff concludes that the peak rates of runoff have been conservatively derived.
4.2.5.2 Green River The PMF for the Green. River was not estimated by D0E. However, the Green River is located well below the lowest site elevation, and by inspection,_it can be seen that flooding on the Green River will not affect the site.
4.2.5.3 Brown's Wash The PNF for Brown's Wash was estimated by DOE using HEC-1 (Ref.12), which is a standard computational method for estinating peak flood discharges. DOE provided copies of the computer output, and our review of the computations indicates that DOE has used conservative and/or reasonable methods for
- 4 t., 3.
estimating input parameters such as lag times, infiltration losses, and
- rainfall distributions within this complicated model. Based on that review and on a comparison with other peak flood discharge data such as that given by Crippen and Bue (Ref. 22), we. conclude that the estimated peak PNF discharge of 100,000 cfs is acceptable.
. 4.3 Water Surface Profiles and Channel Velocities following computation of the peak discharges, as discussed in 4.2.5, above, DOE determineo the water surface profiles, velocities, and shear stresses needed to design.the erosion. protection for the plie.
Such coniputations were performed as discussed below for the (1) onsite drainage, (2) Green River, and (3) 7 Brown's Wash.
4.3.1 Onstte Drainage Within a computeriz(d oesign procedure, DOE determinea the parameters r,ecessary for sizing the erosion protection. The staff checked the computer output-l:
provided by DOE to' determine the accuracy of the computations.- Based on this check, the staff concludes that the estimates are appropriate.
. 4.3.2 Green River i
Water surface profiles for the Green River were not developec by DOE.
- However, the elevation of Green River below the site is such that flooding will not pose a threat to the encapsulated cell.
4.3.3 Brown's Wash Water surface profiles in Brown s Wash were oeveloped by DOE using HEC-2 (Ref.
16), a standard computational procedure used nationwide. The NRC staff checked the results of several computations to determine the adequacy of the stream profiles. We reviewed the cross-section data, loss coefficients, Manning's 'n' values, and the-overall profile analysis.
Based on this review, we agree with DOE that the computed maximum PMF water level in Brown's Wash will be approximately 40' feet below the stab 111zec pile. We therefore concluce that Brown's Wash poses no flooding threat to the stabilized site.
4.4 Erosion Protection 00E proposes to provide rock riprap erosion protection to assure site stability. The r1prap will be providea on the top and side slopes of the pile and will'also be provided for a rock apron which will surround the pile ana
-prevent gully intrusion.
4.4.1.
Green River The elevation and location of the site are such that flooding on the Green River poses no threat tn the integrity of the tailings pile. Therefore, no m
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f erosion protection is necessary to pievent erosion due to floocing in the Green j
' River.
4.4.2
' Onsite Drainage and Aprons i
The erosion protection design includes riprap toe protection consisting of an apron 20 feet wide surrounding the embankment. This measure is designed to u
L protect the tailings from headward advancement of onsite gullies.- The riprap l-forming the apron will penetrate into bedrock and will be subjected to L
potential headcutting and deepening. The ripra) will protect the tailings and p
the cover in the event of surface erosion.
Sta)ility will be sssured because I-the riprap,l keyed into bedrock, cannot be uncercut by gullies deepening eno heaccutting through the surficial mater 161s.
The rock to be placed in the apron areas was designec using the Safety Factors Method. The riprap will have an minimum averagt. size of approxin.6tely 18 j
i inches and will be placed on a bedding layer.f. Bused on our review of the calculations of the rock size and thickness, we concluoe that the proposed riprap for-the apron areas is acceptable. Based on its review, the staff finds these designs acceptable, since they have been conservatively developed in accordance with' documented, referenceo methods. Such methods include those recommen6ed by ihe U. S. Army Corps of Engineers (Ref. 18) to determire rock I'
thickness, depth, and general sh6pe of the rock mass in the toe area.
4.4.3 Top and Sides of P11es The rock covers, which will be used to protect the soil cover from winc and water erosion, are designed for an occurrence of the local PMP. For the top of the pile-(maximum 5% slopes) and for the sides of the pile (20% slopes) DOE proposes a 12-inch layer of rock with a minimum average rock size (D50),cf about 3-3) inches. The sock layers wall be placed on bedding layers. A computerized design procedure utiliz1ng T.he Shfety Fhetors Method was used to
' determine required rock. sizes for the top slopes of the pile. The computerized procedure used the Stephenson Method for the steeper side slopes.
~
E 4.4.4 Rock Durability The EPA standards require that control of residual radioactive naterials be effective for up to 1000 years, to the extent reasonably achievable, and, in any case, for at least 200 years. The prevtous sections of this teport examined the ability of the erosion protection to withstand flooding events reasonably expected to occur in 1000 years.
In this section, rock durability is considered to determine if there is reasonable assurance thht the rock itself will survive and remain effective for 1000 years.
H Rock durability is defined as the ability of a material to withstand the forces of weatherin.. Factors that' affect rock durability are (1) chemical reactions with water,( 2) saturation time, (3) temperature of the water, (4) scout by sediments,
) w'indblown scour, and (6) wetting and drying.
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DOE conducted investigations to identify acceptable sources of rock witnin a reasonable distance of the site. The suitab.ility of the rock as a protective cover was the.n assessed by laboratory tests to determine the physical characteristics. The results of these tests were used to classify the rock's t -
quality and to assess the expected long-term performance of the rock. The tests included:
~ 1...PetrographicExamination(ASTMC295).
Petrographic examination of rock is
- used to determine the physical ano chemical properties of the material in question. The examination establishes if the sock contains chemically unstable minerals or volumetric. ally unstable materials.
2.
Bulk Specific Gravity (ASTM C127). The specific gravity of rock is an 1tidicator of its stiength or durability; the higher the specific gravity, the better the quality of the rock.
3.
Absorption (ASTM C127). A low absorption is a desirabic property and indicates slow disintegration of the rock by salt action ar.d mineral hydration.
4.
Sulfate Soundness (ASTM C88).
In locations subject to freezing or exposure to salt water, a low percentage loss is desirable.
5.
Freeze-Thaw (AASHTO 103).- A low percentage loss is inoicative of resistance to weathering resulting from the crystallization. process.
6.
Schmidt' Rebound Hamirer. This test measures the hardness of a ock and can be used in either the field or tlA laboratory.
7.
Los Angeles Abraston (ASTM C131 or C535). This test is a measure of-rock's resistance to abrasion.
8.
Tensile Strength ( ASTM 03967). This test is an indirect test of a rock's tensile strength.
All : samples for testing were taken in accordance with Standaro Practices fcr Sampling Aggregate (ASTM 075). 00E used a si.ep-by-step procedure for rock durability, in accordance with procedures recoriunded by the evaluating (NRC,1990),asfollows:
NRC staff Step 1~. Test results from representative samples were scored on a scale of 0 to 10..Results of 8 to 10 are considered " good"; results of 5 to 8 are considered " fair"; and results of 0 to 5 are considered " poor".
Step 2.
The score was multiplied by a weighting factor. The effect of the weighting factor is to focus the scoring on those tests that are the most applicable for the particular rock type being tested.
Step 3.
The weighted scores were totaled, divided by the maximum possible score, and multiplied by 100 to determine the rating.
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7 Step 4..The r.
c,uality scores were then con. pared to the criteria which determines i m
' tabs 11ty, as defined in the NRC scoring procedures (Ref.
52).
For the roc'
' pl6ce'd-.in the ditches and on the pile, gradation and rock ourability criteria were piesented. DOE identified a quarry at Frenwnt.
. Junction w ere rock of acceptable quality was found. Rock samples from that h
' quarry were tested, dnd scores were determined as follows:
L Overall, the rock quality rating was found to vary from sample to sample, but k
inost samples had. average scores above 80, based on use'of the scoring procedure. We conclude that the rock source at Fremont Junction provideo rock of very good qualny, b6 sed on a comparison of the test results with the recoumended rock quality scores g iven.1n NRC pr ocedures. We, therefore, conclude that the rock is of adequate quality to assure long-term stability in x
accordance with the iequ1rements of 40 CFR Part 192.
i
[
4h SP.siream_ Dam. Failures h-,
There are no impoundments on the Greeti River whose failure could potentially affect the site.
m 4.6 Conclusions l
i Based on its review of the information submitted by D0E. the staff concludes that the site design will meet EPA requirements as st6ted in 40 CFR 192 with regard to flood design measures and erosion protection. An adequate hydraulic design has been provided to reason 6bly assure stability of the cont 6minated
~
material at Green River for a period of up to 1,000 years.
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e 5.0 WATER RESOURCES PROTECTION 5.1 Introduction The NRC staff has reviewed the Remedial Action Plan (Ref;B) and ancillary documents for the Green River, Utah VMTRA Proiect site for compliance with EPA's proposed groundwater protection standards in 40 CFR Part 192, Subparts A-C(52FR36000). NRC staff petformed the review in accordance with NRC's Draf t Technical Position on Information Needs to Demonstrate Compliance with EPA's Groundwater Protection Standards (Ref.37) anc relevant portions of the NRC staff's Standard Review Plan for UMTRCA Title 1 Mill Tailings Remedial-Action Plans (Ref.5). Consistent with EPA's standards, che NRC staff L
distinguished between groundwater protection aspects of the disposal of residual radioactive materials at the disposal site and the cleanup of existing groundwater contamination at the processing site.
1 00E has conclucea that the proposed remedici action complies with the-EPA standoids be.cause concentrations of. hazardous conststuents in groundwater i
downgradient from the disposal unit will.not exceed relevant concentration limits as a result of releases ftom-the unit for at least 1000 years.
Daseo ori the design of the disposal' unit and favorable site characteristics, DOE also concluded that the materials comprising the disposal-unit will remain i
unsaturated.. DOE's compliance conclusion is based on estimates of the L
groundwater travel time that exceea 1000 years from the base of the residual l-radioactive material'in the disposal unit to the water table.
Based on NRC staff's review of information presented by DOE and independent NRC assessments, the NRC staff concludes that DOE's proposed remedial acticn L
complies with the groundwner prctection standards in Subparts A and C cf 40 L
CFR Part 192 for the disposal of residual radioactive material.
The NRC staff has identified one condition to our concurrence which relates to DOE's proposed deferral of groundwater cleanup.until prcniulgation of EPA final groundwater standards. While NRC considers DOE's deferral to be acceptable for conditional concurrence, the issue inust be addressed before NRC will provide final concurrence on the remedial action at this site.
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5.2 RydrogeolofcCharacterization i
NRC staff-concludes that 00E, except for the limited data base for background l
water quality (see TER Section5.4.1.2)..has adequately characterized the hydrogeology of the Green River site to derr.onstrate compliance with EPA's groundwater protection standards for disposal. DOE employed acce) table techniques, methods, and approaches to assess the hydrogeologic claracteristics of the two uppermost hydrogeologic units at the site: (1) Quaternary alluvium alang Brown's Wash, and (2) calcareous shales, s11tstones, and sandstones of the tretaceous Cedar Mountain Formation. As seen in Figure 2.1, the existing tailings pile is underlain by, in descending order, the alluylum, Dakota Sandstone, and Cedar Mountain Formation. The sides of the new disposal unit will contact Quaternary terrace alluviurn and the Cretaceous Dakota Sandstone.
However, both of these units ete unsaturated at the disposal site. The disposal unit is underlain by the Cedar Mountain Formation. The stratigraphy and geology of the disposal site ate described in Section 2.3.1 of this TER.
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- Under epa's proposed standards an 40 CFR Part 1s2, the site-specific
- Groundwater Protection Standato is tailored for the uppernost aquifer.
cProtection of the uppermost aquifer will provide for protection of other aquifers that are hydraulically connected to the uppernost aquifer'within the
' boundaries of the disposal site. Based on lithologic logs and observations.of surface exposures, the uppermost aquifer at the Green River disposal site consists of the interbedded calcareous shales, siltstones, and sandstones of the Cedar Mountain Formation. DOE distinguishes between the clayey and calcareous portions of the Cedar Mountain Formation (Upper Middle Hycrostratigraphic Unit - Kcmu) and the sandy portions of the Formation (Low Middle Hydrostratigraphic Unit - Kcml). However, the Fydraulic properties of the two units are sim11ar beneath the disposal unit ano, therefore, are treated as tne sent unit throughout this TER. The basal unit of the Ceoar Mountain
- Formation is the Buckhoin Conglomerate (Bottom Hyorostratigraphic Unit - Kwb).
Tne Cedai Mountain Forn,ation is approximately 150 feet thick beneath the disposal site.
The Cedar Mountain Formation at the sito is recharged primarily by groundwater flow through the Formation from the south.. Although the recharge area for 1.he Geoar Mountain Formation has not been establisheo, the Formation is probably iecharged by infiltration of incident precipitation where it is exposed at the land surface south of the site. The unit may also be recharged at the site by upward groundwater flow from the underlying Not rison Formation and by limited
-infiltration through surface units. The Cedar Mountain Formation discharges into the Dakota Sandstone ~and alluvium beneath Brown's Wash, as evidenceo by the~ strong upward hydraulic gradient beneath the Wash; several nonitoring wells completed in the Cedar Mountain Formation beneath the tailings pile.
alluvium, and Dakota Formation flow at the land surfcca.
In adoition, the Formation probably discharges to the Green River ne th and west of the site.
Groundwater flow in the Cedar Mountain Formation is complicated by small-scale stratigraphic variation, structural cip, and pervasive fracturing. The upper
- portions of the Formation are unconfined. The water table elevation within the j
upper portion of the Formation is approximately 4087 feet above mean sea level at the disposal site, which is approximately 60 feet below the existing 1and
~
surface ano about 10 feet below the base elevation of the disaosal unit. The 1
-maximum water level fiuctuation observed at the site was on tie order of 1 feet in the Buckhorn Member of the Cedar Mountain Formation W. ween Septenter 1986 and October 1987 in monitoring well 587 south of &
- m ul site. Water levels in most of the monitoring wells in 1.he Cedar Moura; e ormatiori vary seasonally on the order of several f eet.
Lateral gradients ithin the Cedar
-Mountain Formation _ trend to the North-Northwest, although gradients to the Northeast and East may also be inferred from the water level data. The magnitude of.the lateral gradient varies considerably from 0.002 to 0.075; this variation may be an artifact of the limited number, spacing, and construction of monitoring wells. Based on water levels measured in nonitoring wells completed throughout-the Cedar Nountain Formation, the vertical hycraulic
- gradien1. appears to be upward beneath the site. and beneath Brown's Wash.
However, calculated vertical gradients also vary spatially f rom 0.04 upward to 1.0 downward.
-A2-.
" DOE estimated the hydraulic conducuv aty of the Cedar Mountain Formation based on the results of slug and pumping tests. Hydraulic conductivities average R
i about 6 feet / day. Spatial variability of hydtaulic conductivity within the Formation.1s caused by stratigraphic variation and fracture characteristics.
u
- Groundwater in the Cedct Nountain Formation is primarily a sodium-sulfate type L
water with: elevated concentrations of total dissolved solids ranging from 2000 to more than 11000 mg/1. DOE characterized the quality of groundwater by
_ sampling monitoring wells upogradient and downgradient from the existing tailings pile and-the proposed disposal site.
The saniples were collected and analyzed using standard methods and techniques.
u es of groundwater 56niples, DOE determined that concentrations of Based on ana s
L' various contaminants, including unanium, selenium, nitrate, molybcenum, and I
chromium, are elevated in samples that DOE consider representative of background groundwate quality.
Background wells for the Cedar Mountair. cormation, excluding the Buckhor n Member, include monitoring wells 561, 5d2, 813, 806, ano L
816. Large variations in water quality were detected in samples f rom a1fferent L
background wells completed in the sane unit.
For example, the concentration of l
- nf trate was consistently less than 1 mg/l in well 561, whereas concentrations I
as high as-173 mg/l were observed in samples from well 562. The cause of such large variations in background g oundwater quality between wells has not been L
established.
It is 1:kely that the elevated background concentrations of uranium. selenium, and molybdenum have been caused by natural leaching of these L
constituents as groundwater flowed through the uraniferous Cedar Mountain and Morrison Formations upgradient from the disposal site (see Ref.7).
Tailings pore water samples from lysimeter 714 indicated that Mo ano Se concentrations were comparable with levels observed in background groundwater l-quali ty. Thus, it is unlikely that the tailings were a significant scurce of Mo and Se contamination in gioundwater at an appreciable distance upgrecient from the tallings pile. As discussed in TER Section 5.4,1.2, the flRC staff considers the background water quality data used by DOE to be hmited and DOE-has conantted to continue monitoring f or background data.
l.
The Green River mill produced a unanium concentrate from acio leaching of asphaltic sandstone cres from mines at Temple Mountain, Utah. The concentrate L
incluced both the pregnant uranium solution and slimes. Thus, the tailings at l
' Green River comprise only the sand fraction of the crushed uranium ore, whteh was slurried into the tailings pile along Brown's Wash.
Based on analysis of two pore water samples from lysimeter 714, the tallings represent a potential source of aluminum, annonium, chromium, cobalt, copper, iron, manganese nickel, nitrate, uranium, vanadium zinc, and major cations and anions (e.g.,
chloride, sulfate, sodium, calcium).
Based on water quality sampling, petrographic analyses, and field observations (e.g., sulfide staining on a monitoring well casing), DOE concluded that reducing conditions' ex)st in groundwater in the Cedar Mountain Formation dowrigradient of the existing tailings pile.
In contr ast, conditions are oxidizing in groundwater beneath and irrsediately downgradient f rom the proposed disposal site. DOE observed that the redox front between oxidizing and 1.________,____._
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. reducing conditions coincided with large decreases in the concentrations of uranium and nitrate, which have been releaseo fiom the tailings pile. Based on NRC staff r eview' of the information provided by DOE, it appears that i
geochemical conditions in the Cedar Mountain Fortr.ation downgradient f rom the existing tallings pile may be effective in attenuating hazardous constituents that may be releaseo f rom the disposal. unit. The magnitude of such-
~~
attenuat1on, however, has not yet been determined.
LBecause DOE has. deferred cleanup of existing contamination until after EPA promulgates final standards, the hRC staf f defers conclusions on the extent and rate of transport of existing contamination in groundwater and the. extent of
- contaminated sediments at the Green River site.
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5.3 Conceptual Design Features To Protect Water Rescuicts DOE' proposes to stabilize 382,000 cubic yaros of residual radioactive material in an eight-acre oisposal unit that will be partially below grade on a gently sloped area 500. feet south of the existing tailings pile. The disposal unit
. design is cepicted in Figure 5.1.
The base of the oisposal unit has been excavated down to an elevation of 4098 feet above mean sea level.
00E will place a 6-foot thick buffer layer of poorly sorteo silt ano sand on top of the fractured Cedar Mountain Formation beneath the unit. Contunnated materials will be placed in two main layers: 25 feet of contaminated vicinity property and windblown mater ials and 25 feet of tallings. The tapings will be covered by'a 3-foot thick racon barrier consisting of compacteo clay amenced witn 6%
sodium bentonite by weight. DOE estimates that the saturated hydraulic conduccivity of the radon barrier will be less than or equal to EE-8 cm/s. The l'adon barrier, in turn, Will be overlain by a 6-inch filter layer consisting of course sand and giavel with a satulated conouct1vity in excess of 0.1 cm/s.
The covei will be surfaced with rock riprap to protect.the disposal unit from surface water and wind erosion dunng its 1000-year design life.
DOE planned to implement leasonable measures to minimize the anount of water added ouring construction, while assur ing long-term stability of the disposal
. unit and mininnzation of airborne releases of contaminated cust.
DOE measured L
'in-situ moisture contents of the tailings, which ranged from 1 to 15% and averaged less than 5% by weight (see Table 0.5.EE in the' RAP, Refeience 8).
These noisture contents may approximate the long-term steady-state -conditions of.the tailings in their present configuration. They are also consistent with E
the noisture contents estin.ated by DOE in the steady-state analysis of the
?
_ disposal unit (see Table E.3.5, Ref.8). DOE estimated that steady-state moisture contents of the windblown and vicinity property material will average t
between 11 and 17%.
If the tailings and other contaminated materials are placed at moisture contents in excess of the steady-state moisture contents, releases of hazardous constituents from the unit may exceed the amount required to comply with the Groundwater Protection Standard as a result of gravity drainage of the excess water (see Section 5.4.2).
Therefore, in the April 5 1969 meeting an agreement n s reacned where DOE committed to place the tailings and oi.her residual radicactive mater ials at average moistut e contents less than their ave.' age s6eady-state moisture contents and, in any case, less than 5% (by volume) for the tailings and 10.6% by volume for the windblown ano-vicinity property contaminated materials to minimize releases of hazardous constitue nts due to addition of water during construction of the disposal unit.
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Upon completion of the disposal cell, the average emplacement volumetric moisture contents measured for the tailings and other resicual radioactive saterials was actually 7.1% and 10.6% for the windblown anc vicinity property
- ontaminated materials. The moisture content for tailings materials exceeded the emplacenent value comitted to by DOE in the Apr il 5,1989 agreements.
DOE indicated that 1n complying with the Ue h Department of Health requirements
~
for dust control, water was spu ingly-sprer J on construction areas during reewdia tion. Although the moitture content for the tailings was exceeded, DOE
.provided data in the final RAP supporting their conclusion that the additional
' water has no effect on modeled performance. The NRC staff has concluded based on independent review of-the results of DOE's moceling of the increased moisture content on the cover perfoimance and DOE's demonstration of the as-built cover's saturated hydrualic conductivity that the slight-increast in moisture content coes not adversely effect the performance of the cover.
5.4: Disposal And Control Of Residual Radioactive Material EPA's proposed standards in Subparts A and C of 40 CFR Part 192 tequire DOE to demonstrate that the cisposal of residual Notoactive material complies with descri)ed in the NRC-staff's Technical Position (performance standards as site-specific groundwater prctection and closure Ref.37). This section of the TER cescribes the staff findings with respect to the adequacy of DOE's
> denenstration of compliance with.the groundwater protection and closure performance standards in four areas: Standard for Disposal (Subsection 5.4.1), Performance Assessment-(Subsection 5.4.2), Closure Performance Standaro L
(Subsection 5.4.3), and Groundwater Monitoring and Corrective Action Program L
(Subsection 5.4.4).
4 5.4.1. Ground-Water Protection Standard for Disposal The site-specific Grour.dwater Protection Standard for Disposal consists of E
three elements:
(1)-a list of hazardous constituents, (2) a corresponding list of concentration limits for the constituents,-and (3) a Point of Compliance.
L
.SN.1.1 Hazardous Constituents Based on DOE's cheraccerization of the tailings and pore fluids at the Green L
- River site, DOE initially proposed the following list of hazardous constituents:
L caomium, chromium, cobalt, copper, molybdenum,- nickel, nitrate, selenium, L
uranium, vanadtum, zinc, radium-226/228, anc gross-alpha activity. NRC staff has revtewed DOE's assessments of the hazardous constituents using the following three criteria to select hazardous constituents: (1) whether the constituents are reasonably expected to be or oerived from the tailings, (2) whether they are listed in Appendix VIII of 40 CFR Part 261, and (3) whether they were
.detecteo in the tailings or groundwater at the site (Ref.37). Based on
- NRC staff analysis, hazardous constituents at the Green River site. are as l
follows: arsenic, cadmium, chromium, lead, methylene chloride, molybdenum, nickel, reaium-226/228, selenium, uranium-234/238, vanadium pentoxide, and gross-alpha activity.
The NRC staff reviewed DOE's list of hazardous constituents and concluded that l
arsenic anu lead should be included as hazaidous constituents, because they were detected.in pore water samples collectea from lysineter 714 in the 1
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FEET u*
20 0 20 80 HORIZONTAL SCALE IN FEET L
LEGEND Ot TERRACE SEDIMENTS
- s SAND AND SILT OR SILTSTONE AND SANDSTONE l
Kd DAKOTA SANDSTONE
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$ LIMESTONE
,3 LOWER-MIDDLE UNIT FRACTURES h CONGLOMERATE
_p POTENTIOMETRIC SURFACE Figure 5-1.
Diagrammatic cross section of the Green River Disposal *Jnit (Reference 8).
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' Green River tailings and they meet the other two criteria-listed above.
In addition, the list should also incluce the organic constituent methylene F
~
chloride because it satisfies the aformentioned criteria for selecting hazardous
- constituents.- DOE asserted that the methylene chloride observed in samples was introduccc by laboratory contaminacion because it was detected in a trip blank sample. Nevertheless, concentrations in the trip blank were significantly lower than concentrations observed in groundwater samples from monitoring wells 562, 583, and 705.
In accordance with the NRC/ DOE agteements of April 5, 1989, DOE has fulfilled their cormnittment and has incluced these constituents in their list of hazardous constituents.
1 Beryllium may also be a hazardous constituent based on sampling performed by NRC at active uraniuin mills (Ref.39). DOE did not analyze for berylliun.,
bul. 1nstead asserted that,ls.if present, it would not be released from the tallings at elevated leve Ahhough DGE's assessment of the mcbility of beryllium aay be accurate, beryllium also satisfies the selection criteria f or hazardous constituents (Ref.37). Therefore, in accordance with thr.
ngreement of April 5, 1989, DOE sampled the-tailings to determane it beryllium was present in the residual radioactive material during the
. construction of the disposal unit. Batch tests conducted by DOE on tailing and wincblown contaminated materials dio not detect beryllium. - As a result cf these tests, the NRC staff agiees that beryllium need to be incluoed in DOE's a
L list of hazardous constituents.
00E also proposed to monitor several constituents that are not listed in L
. Appendix VIII to 40 CFR Part 261, including cobalt, copper, and zinc. These-L constituents are not hazardous constituents because they are not listed in
- Appencix: VIII. DOE's voluntary compliance with concentraticn limits for these constituents indicates a gooo faith effort on the part of DOE to protect the groundwater.at the Green River site.
5.4.1.2 Concentration Limits DOE initially proposed to nieet Max) mum Contaminant Levels for Radium-226/228 L
ana Cadmium and site-specific background 13mits for the other proposed L
hazardous constituents in groundwater at the Point of Compliance, as shown in l
Table 5.1.
Based on a r eview of DOE's proposed. concentration 11nnts and analyses of gioundwater samples representative of background groundwater quality, the hRC 56aff was unable to agree that the DOE proposed limits -
appropriately repiesented background values. Therefore, the NRC staff
- established the interim concentration limits listed in Table 5.1 for hazarcous constituents for the disposal: action at the Green River site. The interim background concentration limits established by NRC foi-hazardous-constituents consist of either (1) Maximum Contaminant Levels (MCLs) based on Table 1 of 40 CFR ParL 264, Subpart f, as amended by Subpart A of 40 CFR Part 192, and (2)~ hvels based on-the h)gher of the mean concentrations.cetermined from analysis of groundwater samples from wells 806 ano 816 in the argillaceous and' calcareous units of the Cedar Mountain Fornation and from wells 561, 562, and 813 in the sandstones of the Cedai Mountain Formation:(excluding the
- BuckhornMember).
In the agreements of April 5, 1989, DOE-committed to and in the final RAP (Ref.iO did hoopt the NRC interim concentration limits for hazarcous constituents as listec in Table 5.1 for the disposal action.
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Table 5.1 Hazardous Constituents and Concentration Limits for Disposal at the Green River UMTRAP Site (units in mg/1, unless noted otherwise)
Constituent DOE Proposed Initial NRC Interim-
~TTEHs~~
Proposea~Cfihits CoRcesi. ration
~
Limits 0.05 MCL 0.
.L Arsenic-Cadmium 0.01 (MCL) 0.01 MCL 0.01 MCL Chromium 0.09(Ekg) 0.05 MCL 0.09 Bkg 0.05(MCL 0.05(MCL).
Lead 0.005(Bk) 0.005 (Bk )
Methylene Chloridi.
Molybdenum 0.24 Bkg 0.1 (MCL 0.24(Bkg Nickel 0.09 Bkg 0.06 (CLg 0.09 (Bkg 60 180 (Ekg 0.66((Skg/
2.50 (Bkg Netrate 180 Bkg Selenium 2.50 BKg Bkg)
Ur an ium-234/238 0.146 (Bkg) 0.044 (MCL) 0.146(Bkg 0.38 (Bkg)(MCL)0.09 (i3kg)(MCL) 0.38(Bkg',(MCL)
Vanadium Pencoxice 5.0 pCi/1 5.0 pCi/l 5.0 pCi/1 L
Radium-226/228 p
Gross-Alpha (exclucing U and Rn)-
195 pCi/1 (Backgiound) 24.5 pCi/1 (Background)
However, in the final RAP (Ref.8)l variation in background water qublity and DOE argued that NRC's interim concentiations did not adequately reflect natura that natural variability must be considered when cefining excursion *. Upon further consicerations of the available grounowater data, DOE's argument, and hRC experience in in. situ uranium f acility licensing, the staff agress G6t background water quality should be evaluated on a statistical basis L
(statistical maximum or maximum observed) and concentration limits established at levels that' incorporate natural variation. Therefore, except for arsenic, lead,- and methylene chloride. for which NRC interim limits still apply, the.
staff accepts DOE's proposed concentration limits, as shown in Table 5.1.
Even though the NRC has accepceo DOE's pioposed concentration limits, the NRC staff stall'conssoers.the amount of water quaiity data presently available as 1imited. As a result, the NRC scaff considers DOE's proposed background
~
concentration limits as interim values. Sampling from the monitoring wells, the POC wells and the upgradient wells may significantly change the statistical characteristics of the background data set used by DOE to develop their concentration limits. This conclusion originally resulted from the NRC review of the draft final RAP and was reflected in the April 5,1989 agreements in which DOE comitted to analyze groundwater samples quarterly from disposal site wells 807, 812, 813,'818, and 823 during remedial action.
In addition, DOE also conmicted to collect and analyze representative groundwater samples quarterly from wells 807, 812, 813, 818, and 823; the new wells to be instclir.d ut the P0C; and upgradient wells for 2 years from the completion of remedial acticn.
The. purpose of collecting this data was to oeveloped a larger data base to-be used to recalculate background concentration limits for the hazardous constituents listed above.
In the revised portions of the RAP submitted on February 23, 1990, DOE interpreted NRC's acceptance of DOE's concentration limits as final rar.her than interim concentration limits. As a result, 00E eliminated the post-remedial action
. groundwater sampling comitted to in the Apr 11 5, 1989 agreements (Ref.50).
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?he NRC staff still considers the DOE concentration limits to b6
-Int;; q Mues. As a result, DOE has modified the final RAP to comit to
- the post remedial sampling of of the existing well 813, the six new POC wils and-the four new upgradient monitoring wells for a two year post-remedial period (Ref.51).
DOE wiil continue to sample'these wells quarterly for two years and will utilize this data to recalculate background concentration limits.
Unlike the original agreement of April 5,1989, DOE will monitor only one of the existing monitoring wells, because the others are dry or are not located in the~ uppermost aquifer and, as e result, will be properly sealed and abandoned.
When DOE originally accepted using NRC's interim concentration limits they proposed that an " excursion" not be considered until two years of n.onitoring isd been completed and suff tcient background samples collecteo to recalcul6te final background concentration limits. The hRC staff considered this postponement of excursson monitoring as acceptable. This f act has not changed
.with NRC's acceptance of DOE proposed concentration limits. The procecures for excursion monitoring, evaluating the si.atistical significance of such excoedances and for implementing appropriate corrective actions, if any, will be established in the Surveillance and Maintenance Plan, t
5.4.1.3 Point of Compliance EPA standards require that the concentration limits for hazardous constituents in groundwater not be exceeded at or beyond the Point of Compliance.(POC).
DOE proposed in the draft final RAP that the POC be considered as a monitoring zone extending along the northwest coge of the disposal unit and along the noithernmost portion of the northeast edge of the unit. Given the variability in lateral hydraulic gradients within the Cedar Mountain Formation, the NRC staff concluded that the Point of Compliance needs to extend along the entire downgradient edge of the disposal unit as shown in Figure 5.2.
DOE comitteo in the April 5, 1989 agreements to accept the POC as defined by NRC and in the final RAP (Ref. 8) complied with this comittment.
'In the. April 5,1989 agreement DOE-also comitted to demonstrate that the POC wells could not be located closer to the disposal unit. For example, the draft final RAP did not make it apparent why the wells could not be drilled through the Select fill B material within 30 feet from the eoge of the residual l
radioactive material. The NRC staff reviewed the infornation provided in the final RAP and found that DOE dio not adequately demonstrated why-the
. compliance point monitoring wells could not be located closer to the dispovi unit. Subsequent modtfication to the final RAP by DOE provided adequate justification for the proposed location of the P0C wells and their rationale for not moving these wells closer to the disposal cell. Specifically, DOE sited the damage to the cover f rom the drilling operation and the inability of the monitoring wells placed in the cover to function properly in the rip rap (Ref.51).
5.4.2 Petfoimance Assessment DOE attempleo to demonstra n compliance with the aforementioned Groundwater Protection Standard by estimating r.he grounowater travel time from the top of the buffer layer u: the oisposal unit to the water table beneath the site. DOE stated that hazardous constituent concentrations in groundwater at and beyono the Point of Compliance will not increase above the prescribed concentration limits as a result of releases from the disposal unit fcr at least 1000 years Lafter completion of the remedial action for disposal. DOE concluded that igroundwater travel time will be at least 1500 years from the base of the
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E res'idual radioactive material to the water table beneath the disposal unit L"
(seeTableE.3.5ofRef.8). These estimates were based on neasured saturated hydraulic conductivities, estimated moisture characteristic and relative conductivity curves based on laboratory measuresents and nodeled steady-state moisture contents an assymed unit hydraulic gradient, and an 2
assuned upper boundary flux of IE-9 cm /cm -s.
DOE dio not estimate I
concentrations of hazardous constituents in groundwater in the uppermost aquifer at the Point of Compliance.
NRC staff reviewed DOE's performance assessment, including supporting site characterization information and modeling assessments using the SUTRA computer code (Refs.36, 40, and 41). The staff's review was also based in part on the NRC staff's observations and conclusions f rom the NRC-DOE Data Review Workshop l~
on Water Flux through the Radon Barrier at Shiprock, March 7-9,1989(Ref.36).
Based on its review, the NRC staff concluded that the protecteo, compacted radon berrier was expected to remain unsaturated over the 1000-year design lif e of the disposal unit and a unit-hyoraulic gradient may be assumed for estimating water flux downward through the iadon barrier at the Green River j
site. However, hRC staff also concluded that DOE had not demonstrated that the downward flux of' water tgrougg the indon barrier and disposal unit would be less
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than or equal to IE-9 cm /cm -s.
This conclusion was based p3 mapily on DOE's 1
l
' inability to defend the assuited upper boundary flux of IE-9 cm /cm -s.
In addition, DOE had not sufficiently characterized the noisture characteristic curve, saturated hydraulic conductivity, anc relative conductivity curve (hydraulic conductivity as a function of tension or moisture content) of the radon barrier at representative placement conditions (i.e.,100% standard
-Proctor compaction at 0 to +3% Optimum Moisture Content with 6% sodium L
bentonite admendment by weight).
Because DOE redeled the disposal unit under steady-state hydraulic conditions and the water flux thrcugh the radon barrier I
sign 1ficantly determines the groundwater travel time through the uncerlying i
units, NRC staff concluded thet DOE had not demonstrated that minimum i
groundwater travel times will exceed 1500 year s between the residual radioactive material ano the water table-bcneath the site.
Based on separate assessment, however, the staff concluded with reasonable assurance that the disposal unit at the. Green River site complied with EPA's proposed groundwater protection standards in 40 CFR Part 192.02(a)(3).
The staff arrived at this finding through a series of independent qualitative and quantitative assessments that collectively ptovided reasonable assurance that groundwater travel times from contaminated material to the water table are expected to exceed 200 years coupled with the determination that the propoteo design is the best reasonably achievable.
~.As an initial attempt to determine whether the disposal unit provided a sufficient groundwater travel time, the NRC staff conservatively assumed that thg stgady-state flux through the radon barrier would be equal to 2E-8 cm /cm -s, which is the pioduct of a unit hydraulic gradient and the average
-saturated hydraulic conouctivity of the radon barrier (compacted to 100%
Standard Proctor density at 0 to +3% of Optimum Moisture Content with a 3%
amendment of sodium bentonite by weight -- see Table D.4.4 of Ref.8).
The staff estimated the travel time by assuming steady-state, continuum flow through each: layer and using an effective porosity term equivalent to the average moisture contents modeled by DOE in its one-dimensional SUTRA model of the disposal unit. The calculations also used an average moisture content for the unsatut ateo iock beneath the disposal unit based on moisture content measureirknts performed on rock core.
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The flux of-2E-8 cm jg,2-s results in a groundwater travel tine through the 3
buffer layer ana unsaturatea rock beneath the urit on the order of 90 years.
The staff considered that the 90-year estimate of the gloundwater travel tine -
through the buffer layer and unsaturated rock as conservative for a nunber of reasons.- These reasons include:
(1) The steady-stgte yater flux through the disposal unit would probably be less than 2E-8 cm /cm -s because che iadon barrier is likely to remain unsaturated during the design life of the disposal unit.
The average unsaturated hydraulic conductivity of the radon barrier may be signficantly less than the saturated conductivity of 2E-8 cm/s because unsatus ated hydraulic conducciv sty decreases logarithmically as saturation decreases. ~ However, DOE had not established the dependence of hydraullc conductivity on satus ation f or the Green River radon barrier materials thiough representative testing.
In addition, DOE had not determined the long-term satuiation of radon barricr.
Thus, at that tine the effectue hydraulic conductivity of the radon barrier for the stenay-state conditicr.
had not been aetermined.
(2) The average moisture contents usea in the travel tine calculation might be lower than expected because DOE estimated the mo3stuge contents in the buffer layer at the lower boundary flux of IE-9 cm /cm'-s and moisture contents woula be greater at the higher value of flux assuned in the staff's cs 'culations. DOE, however, hac not determined the average moisture contents that woula be regresentative of the buffer layer at the higher flux density of 2E-8 cm*/cm -s.
(3) The calculations assuned steady-state hydraulic conditions, whereas groundwater travel time through the disposal unit may be furthei increased by the Line required for the new hydraulic system to equilibrate.
.Provided that-contaminated materials ano the buffer ar e placed in the disposal unit at moisture contents below their estimatea steady-state values and reasonable neasures are taken to minimize-accition of water during consttuction of the d sposal unit, significant discharge of water through the basal buffer layu may not occur for tens to huncreds of years L
until the steady-state moisture profile is establishec.
1 Although. the magnnude of the conserva6 ism in che staff's calculations could not be quantifica, the decrease.n the unsaturated hydraulic conductivity of the radon barrier alone-could increase. steady-state travel times significantly.
For example, if the unsaturated concition of the radon barrier reasonably reduces the hydraulic conductivity of the radon barrier by an order of' magnitgoe, the steady-state flux through the adon barrier decreases to 2E-9 cm /cm -s and travel times through the buffer layer and unsaturatea rock increases to more than 900 years.
Because DOE had not assessed the unsaturatea characteristics of the radon barrier and was unable to predict the long-term saturation of the barrier, this recuction in effective hydraulic conductivity was not demonstrated. Tius, although 00E was not be able to demonstrate ~ extremely long groundwater travel tines with certaigty,2 actual steady-state fluxes through the cell might be less than IE-9 cm /cm -s and travel times might be significantly greater than the 90 years estimatea by the staff for a saturated radon barrier.
'In addition, the groundwater protection standards require compliance with concentration linnts for hazardous constituents in groundwater at the POC.
a.
. s2 The groundwater travel time a>proach indicates the taillest time that hazardous constituents could reach the 100, if the contaminarts travel at the sane velocity as the groundwater..This approach was conservative because it did not take credit for potential cilution, dispersion, sorption, and precipitation of hazardous constituents in groundwater between the contaminated -
materials and the POC. Dilution and dispersion would reduce the concentrations of all' constituents to some extent along the transport pathway.
In addition, sorption and precipitation would be effective in reducing the concentrations of
- most of the constituents.
As an alternate approach to assess compliance with the EPA standards, the staff assessed groundwater travel time between the tailings and the water table beneath the disposal unit. This ass 3sstr9nt assumed a steady-state flux cown through the radon berrier of 2E-8 cm /cm -s.
The total travel time between the tailings ano the water table was composed of con.ponent travel tiroes through 3 layers: (1) winobLvn ano vicinity property contaminatec material (128 years),
(2) buffer layer (46 years), and (3/ the unsaturated Cedar Mountain Formation beneath:thedisposalunit(46 years). The travel time estin. ate through the d1sposal unit included travel time through the 25-foot thick layet of contaminated windblown and. vicinity property material between the tailir4s and buffer. These materials were included in the definition of residual radioactive material and, therefore, representeo potential sources of hazardous constituents.
.The NRC staff expected that these materials, however, would not be a significant source of hazarcous constituents at the Green River site. lhis expectation was based on the following observations: (1) the average concentration of radium-226 in the windblown material was approximately one third of the average concentration in the tailings (Table 3.1, Ref.8); (2) disturbance of the v)cinity property and w endblown macerial probably removed res1cual pore fluids and soluble salts that were once contained in the ta111ngt; (3) the windb1cwr, and vicinity property materials had been diluteo by mixing with sojacent, uncontaminated materials; and (4) 6hese materials contained organic and other materials, which might have been effective in attenuating hazardous constituent transport within-the disposal unit. Therefore, it was reasonable to allow credit for groundwater tiavel tine through the bottom 25-foot thick layer of vicinity property and winoblown material, provioed that it could be shown that the materials were not significant souices of hazardous constituents.
As stated in the April 5,1989 agreeme.nts, DOE consnitted to demonstrate that the windblown and. vicinity property materials were not significant sources of hazardous constituents by leaching several representative sartples anc by showing that the leached concentrations of the constituents were not significantly gieater than concentracions leached from representative soils in the vicinity of the site.
As provided in the final RAP (Ref.8), batch leach and column extraction tests were conoucted on samples of contaminated windblown soil collected from representative stockpiles at_ the Green river site. Analytical results are reported in Table D.5.27.
ho samples of uncontaminated soils were tested.
Section D.5.2.8 of the final RAP reports that batch extract concentrations for all hazardous constituents identified at the Green River site, except for vanadium and uranium, are below interim concentration limits set by the NRC.
Vanadium concentrations exceed the NRC interlm concentration level, but are well below the range of maximunireported backgrouno values.
The average uranium concentration (0.170 n>g/1) is above che NRC interim concentration limit (set at NCL 0.044 mg/1) and slightly above i.he maxiumu observed background value (0.146 mg/1).
In addition, column feed experiments show that uranium is
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E greatly attenuated by the buffer material located at the bottom of the
~ disposal cell. Although comparison iesults from non-contaminated soils are not available, the NRC concluded that test results reported in the final RAP adequately desenstrate that the contaminated windblown materials are not significant sources of hazardous constituents to groundwater.
Existing DOE and NRC estimates of groundwater travel tine between the disposal unit and the water table beneath were based on assumptions of low saturated hyoraulic conductivities of the radon barrier. The proposed average value of u
2E-8 cm/s was relatively low compared with hydraulic conductivities typically.
-attained by engineered, field-compacted barriers composed of-earthen materials.
3 In addition, the unsaturated hydraulic characteristics of the barrier had not i
been demonstrated. Thus, in the April 5, 1989 agreements, DOE committea to
.l conduct representative testing.of 6he radon barrier materials to assess its unsatur ated characteristics (noisture characteristic and relative conductivity -
curves) and to ensure that its sai.uraced hydraulic conductivity did not exceed 2E-8 cm/s. Testing samples were to be taken so that they wt re representative of the in-place radon barrier (100% standard Proctor density with 6% soditm
. bentonite acmendments by weight). These samples were to be testea in the l
laboratory using standard methods to confirm that the saturated hydraulic J
conductivity of the as-built radon barrier would be less than or equal to L
2E-8 cm/s.
Additional-technical information and data was submitted in the final RAP for Green River that demonstrates that laboratory hydraulic conductivity tests on l> +
field samples of the radon barrier were conducted as agreed upon. The saturated hydraulic conductivities of all 14 samples were less than 2E-8 cm/s, and range from 1.5E-8 to 1.7E-9 cm/s with a mean of 6.1E-9, thereby confirming
.that the as-built radon barrier's hydraulic conductivity is less than or equal to 2E-8 cm/s.
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'The EPA standard in 40 CFR 192.02 (a)(1) requires that the disposal site be designed;to control the tailings and other residual radioactive mateilal for 1000 years to the extent reasonably achievable and, in any case, for at least 200 year.. For-those site where DOE is unable to clear ly derronstrate that control measures will be effective for 1,000 years, DOE mus1. demonstrate that l'
(1) control will be effective for some duration in excess of 200 years, and K
(2). that the design represents the best reasonably achievable design to control residual radioactive materials and listed constituents. As a result-of information provided in the final RAP, as discussed above, the NRC has concluded that DOE has adequately demonstrate that the groundwater travel time for the Green River disposal site would clearly be effective for a period greater than 200 year. However in order to fully comply with the above stated H.
- por tion of the si.andard, DOE, as ronnitted to in the April 5,1989 agreement, was requited to present a justification which demonstrateo that the design of
.the disposal unit represented the.best design reasonably achievable. This
,; justification, as presented in the RAP, discussed various technical considerations and alternatives of the proposed design such as alternate sites, disposal cell configurations, the buffer layer, the windblown materials, the moisture content, the radon barrier, the filter layer, source modifications, and contaminated mater ial testing. Based on this assessment DOE has concluded
.and NRC concurs that the Green River disposal unit design represents the best design that is reasonably achievable to comply with the EPA stancaia.
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5.4'.3 Closure Performance Assessment In accorJance with the closure performanco standard of 40 CFR Part 192.02(a)(4), DOE is required to demonstrate that the proposed disposal design:
(1) niinimizes the need for further maintenance, and (2) controls, minimizes, or eliminates releases of hazardous constituents to groundwater to the extent necessary to comply with the site-specific Groundwater Protection Standard and, thus, to protect the human he11th and the environment (Ret.37)
Based on NRC staff _ ieview, the staff concludes that DOE has demonstrated that the need for further mainteriance of the disposal unit has been minimized in accordance with-the long-teim stability stancards in 40 CFR Part 192.02(a), as described in Sections 2,_3, ano 4 of this TER. Groundwater protection components of the d:sposal unit are composed of earthen materials that'are likely to remain stable and maintain their integrity during the 1000-year design life of the disposal ur.it. Therefore, DOE has demonstratec that the design features neeaed to comply with the site-spec.fic Groundwater Protection
. Standard do not t ely on active maintenance to ensure satisfactory performance in accordance with the closure peiformance standard of 40 CFR Part 192.02(a)(4).
In addition, the staff concluces that DOE has demonstiated compliance with the site-specific Groundwater. Protection Standards as described in Sections 5.4.1 and 5.4.2 of this TER. Thus, DOE has demonstrated that the proposed disposal unit design contr01s and minimizes the release of hazardous constituents to groundwater to the extent necessary to protect human health and the e7vironment.
5.4.4 Groundwater Monitoring and Corrective Action Plan Pursuant to the proposed EPA groundwater protection standards in 40 CFR Part 192.02(b) and (c), DOE is requireo to implement a groundwater monnoring and corrective action program to be carried out during the post-disposal period (Ref.37). As stated in RAP Section E.3.4 (Ref.8), DOE has comm*.tted to implement a groundwater monitoring and corrective action program to assure that performance of the disposal unit complies with the gioundwater protection and closuie performance standards.
Basec.on NRC staff's review, the staff concludes that DOE's proposed monitoring program should be able to detect aberrant penformance of the disposal unit.
In addition, the staff concluces that reasonable alternative corrective actions exist for correcting unexpected abeirant performance of the disposal unit to comply with EPA's standards. The monitoring program will include monitoring of both groundwater quality and moisture centents. Monitoring wells will be installed adjacent to the disposal unit to provide access to groundwater in the uppermost aquifer upgradient from the unit foi background monitoring and immediately downgradient from the unit at the Point of Compliance for detection monitoring. DOE will periodically co11ec6 and analyze samples extracted from the monitoring wells to confirm compliance with the Groundwater Protection Standaro (see Section 5.4.1). DOE will also monitor moisture contents in the radon bartier, residual radioactive material, and buffer layers of the disposal unit'to estimate water tlux through the cell.
In addition, DOE has committed in Section E.3.5 of the RAP (Ref. 8) to a phased progyam of assessment and implerentation of corrective actions chat may be necessary to ccr rect aberrant performance of the disposal unit in Section E.3.5 of the RAP (Ref.8).
-,s
. ' Specific details and procedures for. the groundwater monitoring and corrective action program will be established in the Surveillance and Maintenance Plan for the Gteen River site.
Therefore, based on review of DOE's conceptual plans for groundwater monitoring and potentia 1' corrective actions, the NRC staff concludes that DOE shoulo be able to demonstrate compliance with EPA's proposed nonitoring and corrective l
actionstandardsin40CFRPart192.02(b)and(c). NRC will concur with DOE's monitoring program upon successful conipletion of NRC staff's review of the Surveillance and Maintenance Plan for the Green River site.
5.5 Cleanup And Control Of' Existing Contamination DOE needs to demonstrate conpliance with the EPA standards listed in 40 CFR Part 192,. Subparts B and C for cleanup and control of existing contaien6 tion (Ref. 37). The NRC staff consicers that groundwater cleanup aay be deferred provided that DOE cemonstrates that disposal may proceed inoependently of cleanup.
DOE piefers.to defer the compliance denonstration for cleanup of existing gioundwater contamination at the Green River site. Based on NRC staff's review of DOE's assessment, the staff concurs with the deferral of cleanup because disposal at the Green River sste may proceed independently of cleanup.
As a condition of NRC's concurrence w.th the disposal action, however, DOE needs to demonstrate compliance with IPA's final groundwater protection standards for cleanup after they have been promulgated. The NRC staff's concurrence is based on DOE's statement that the disposal action will not prejudice or preclude future actions to cleanup or control existing groundwater
-contamination and on the following observations:
(1)Contaminatedgroundwaterisnotpresentlybeingconsumedandisnot expected to be consumed by humans at the site within the next couple years. Contaminant concentrations in the groundwater represent chtonic hazards from long-term ingestion of groundwater rather than acute hazaros.
The contamination appears to be limited to a relatively small area alcng Brown's Wash, which will be controlled by the State of Utah and 00E during the remedial action period to prevent access to contaulnated groundwater.
(2) Movement of the contaminant plume is relatively slow; the plume is not expected to increase significantly in volume or concentiation over the next several years.
(3) Alternate sources of water supply are readily available and preferable compared with shallow groundwater in the vicinity of the Green River site.
(4) DOE will be able to distinguish between existing contamination and potential future contamination from the new disposal unit. DOE intends to stabilize the tailings hydraulically upgradient from the existing tailings pile. The minimum separation destance between the Point of Compliance for the new disposal unit and the core of existing contamination is greater than 600 feet.
(5) Withdrawal of contaminated groundwater downgradient from the existing
.n.
. tailings pile in wells or trenches is not expected to cause drawdewns or other hydraulic changes that could significantly perturb or conpronase the performance of the view disposal unit.
(6) DOE will remove' any contaminated sludges or other wastes produced during the cleanup of existing groundwater contamination from-the site or stabilize them appropriately on-site in compliance with the EPA standards.
Therefore, compliance with the proposed groundwater cleanup standaros in
-Subparts B and.C of 40 CFR Part 192 can be deferred until after EPA promulgates final groundwater protection standards.
r
5.6 CONCLUSION
S Based upon icview of the Final Remedial Action Plan and its ancillary documents, the NRC staff concludes that DOE's proposed remedial action at the Green River, Utah, UMTRA Project site complies with reasonable assurance with EPA's proposed groundwater piotection standatos for disposal in Subparts A and C of 40 CFR Past 192, provided that DOE socisfies the following condition:
- 1. Demonstrate compliance wsth EPA's final groundwater cleanup standaros in Subparts B aric C of 40 CFR Part 152 af ter EPA promulgates-the standards, i
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i' 6.0 RADON ATTENUATION AND S0lt CLEAhUP 6.1 Introduction This sectior, of'the TER documents the staff evaluation of the radon attenuation design and the radiation survey plan to assure conpliance with the EPA standard..
6.2 Radon Attenuation The review of the cover design for the' radon attenuation included evaluation of the pertinent design paraceters for both the tailings and the radon barrier soils, and the calculations of the radon burrier (earth cover) thickness (Ref s.
9, 10, and 38).
Thi cesign parameters for the taillogs and earth cover c.aterials evaluated for acceptability include the following: long-term moisture content, neteriul thickr,ess, bulk density, porosity, and radon diffusion coefficient.
In addition, radium content and radon emanation coefficient parameters were evaluated for the ta111ngs materials only. The computer-code RAECOM was used to calculate the radon barrier cover thickness, and the input included the above. parameters.
6.2.1 Evaluation of Parameters To meet the EPA standards for limiting release of Radon-222 from residual radioactive material to the atmosphere, the tallings pile was covered with an earthen cover (sacon barrier). The radon barrier reduces the eftluence of Ra-222 by reducing the diffusion rate to acceptable quantities. The required thickness of the~ radon barrier depends on the properties of the barrier i;
material and' tailings.
For the eai$ hen cover for racon attenuation, the DOE L
. used silty clay fiom a borrow site and mixed it with 6 percent by weight of L
Bentonite. The material properties and radiological paraneters used in the design of the ladon barrier for the stabilized tailings disposal cell at the Green River site have been reviewed.
1 L
The racon barrier material was compacted at a moisture content ot 0 to 3 percent above the optimum moisture content.
This resulted in an average placenent moisture content of approx.rautely 16 percent. The staff has calculated the long-term moisture content using Rawls' (Ref. 5) method (a very conservative method) to be 9 percent. The DOE calculation uses a long-term I
moisture content of 11.9 percent based on data from a capillary-noisture test.
l Considering the presence of a one-foot-thick rip rap and a 6-inch-thick gravel L
bed on top of the radon barrier, and that only the bottom 15 inches of' the three-feet thick radon barrier is designated for protection against radon emanation, the staff concludes that the lower portion of the radon barrier will retain most of its placement moisture in the long-term. The staff, therefore, concurs with the DOE's estimation of 11.9 percent long-term moisture content for the racon barrier naterial.
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specified density al, their in situ moisture contehts of. 3 to 5 percent. But
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the DOE has placed the tailings mates ial and oi.her contaminated materials in the disposal cell at average placement moisture content of 4.6 and 5.5 percent
. respectively. The average as-compacted moisture content for both the tailings m and other contaminated materials is 5 percent. However, the DOE has used a
.j long-term moisture content of 10 percent for tailings in the design calculation.-
The effect of this lower moisture content on the thickness of the radon barrier is discussed in Section 6.2.2.
The material thicknesses (layers) used in DOE's-analysis are based on the conceptual design of the remeolal action plan and data available from field
- investigations. However, the tallings and other contaminatea materials were placeo in the disposal cell without any layering or preferred placement of these materials within the disposal cell. The design assumes unifoim, everage
' properties for these materials. The material thickr.ess (44 feet for tallings and contaminatec materials) used in the analysis for the radon barriet thickness calculation is a reasonable representation of the field conditions.
The staff is aware that the propertles of materials below a depth of 10 to 15 feet beneath the radon barrier have very little or no impact on the calculateo thickness of the of radon barrier.
Material-properties such as bulk censity and specific gravity were determined by field and laboratory tests, and the corresponding porosity was calculated.
t i
The bulk density and porosity for the tailings material are 1.52 gm/c.c and 0.430, respectively. The corresponding properties for the radon barrier soil (virgin soil, not mixed with bentonite) were 1.87 gm/c.c and 0.306 respectively. Though the DOE has not provideo 1.hese parameters'for the amended
- soil,.they are not expected to be very different from the values for the virgin soil, and any minor variations of these parametet s are not expected to have any significant impact on the calculated thickness of the radon barrier. The staff has reviewed the geotechnical parameters used in the design computations ano concluces that the above values of the parameters are a reasonable l _
representation of the average site _ conditions, g
l Radon diffusion coefficients for the cover material and tailings were derived from a correlation curve of moisture satulation ver sus racon diffusion l-coefficients based on the estimated moistute for the long-term for the I
materials. This curve was developed using diffusion coefficient and moisture saturation data from both field and laboratory measurements of soil samples that are representative of the condition in the stabilized pile. The diffusion coefficient for the radon barrier material es 0.00247 cm'/sec for the estimateo long-term moisture content of 11.9 percent. The diffusion coefficient for the tailings _ material used in the design is 0.021 cm2/sec for che long-term moisture content of 10 percent. However, because of the DOE's approach of l
l compacting tailings at as dry a condition as possible, the staff estimates the Llong-term moisture content will be in the range of 5.0 percent, and the corresponding diffusion coefficient (Figure B.2.1 of Ref. 9) woulo be in the range of 0.028 cm2/sec. The staff has reviewed the information useo in
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t determining the diffusion coefficient value for the radon barrier material ar.d 1
. judges it to be seasonable. The staff does not agree with the value of the
' diffusion coefficient for the tailings material (.021 cm2/sec for a long-term moisture content of 10%, Reference 3) used in the DOE's design because it is higher. than the placement moisture content of close to 5 percent. Based on review of the field data and placement moisture content specified in the RAP, j
an approptiate value for this parameter for a long-term moisture content of 5%
is 0.028 cm2/sec. The required thickness of the radon barrier, calculated using the RAECOM code and higher diffusion coefficient'of 0.028 cm2/sec fcr the tailings material, is 12 cm. compared to the thickness of.11 cm. calculated by DOE for a diffusion coefficient of 0.0210 cm2/sec. This change in the required thsckness of radon barrier is not significant because the impact of the j
diffusion coefficient of material at depth of ten feet and below the cover 15 not very significant-on the required thickness of 6he radon barrier. Section 6.2.2 of this report discusses the relevance of this thickness change by comparing it to the as-designed thickness of the radon barrier.
The t aalum content (Ra-226) of several materials at the. site was n.easureo. The average radium content to be used in the analysis was oetermined by weighted averaging with depth ~in a measurement hole and then averaging over an area at any given cepth. The weighted average value of the radium content for the e
entire pile was calculated to be 74 pCi/gm. However, the average radium content was verified by field measurements on the stabilized tailings pile before placing the radon barrier earth cover, and the radon barrier design was reassessed at-that time to ensure that i.he radium content used in the design is L
a reasonable representation of actual measured values. The staff concurs with l
the methodology used by the DOE to measure the radium content and the average values used in the design.
The radon emanation coefficient was measured in the laboratory on samples representative of field conditions. An emanating coefficient of 0.28 was conservatively used in design for the tailings material. Based on the values of this parameter determined for similar materials at other UMTRAP sites, the staff considers this value to be reasonable and acceptable.
. The airbient air radon concentration was measured to be 2 pC1/1. The technique used to measure the radon concentration has been previously approved by NRC, and the result is acceptable to che NRC staff. This parameter is an input for the RAECOM modehng calculation used in designing the thickness of the radon i
barrier cover.
L l
6.2.2' Evaluation of Radon Barrier The radon barrier (earth cover) thickness necessary to comply with the radon -
efflux limit was calculated using the RAECOM computer cooe.
For a given assumed thickness of 1.he radon barrier, the RAECOM code calculates the radon gas release rate. The EPA standard requires that the release of radon-222 from residual radioactive material to the atmospheie not exceed an average release rate of 20 picocuiles per square meter per second. The current cover design
t
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- has a three-foot-thick racon barrier beneath the riprap and gravel bedding. As discussed in Section 3.3.4 of:this report the upper 39 inches of.the cover consisting of 12-inch-thick riprap, 6-inch-thick gravel bed, and top 21 inches of the radon barrier will provide protection against freezing.
In a worst case scenario, the top 21 inches of the radon barrler. will be subjected to freeze-thaw conditions that could alter its as-compacted condition in terms of possibly initiating minor openings or cracks. Therefore, the upper 21 inches of the radon barrier is not 9iven credit for contributing to the radon diffusion function of the radon barrier, ano only the lower 15 inches (38 cms) of the radon barrier is designated to be functional in reducing the radon release.
1 The DOE design-(Ref. 43) estimates that only 11 cm. (4.3 in.) thickness of radon barrier is required to reduce 6he radon release to a value in compliance with the EPA standards. However, the required radon barrier thickness using a
.lcwer long-(term nxusture content for the tailings is estuaated by NRC staff to be 12 cm. 4.7 in.) or about the same as DOE's estimate.
The racon barrier as l
designed is 36 inches thick, and the lower 15 inches of that, which will be below the frost depth, is designated to be functional as a radon barrier.
Considering the built in conservatism in the current design thickness of the radon barrier, the staff concludes that the DOE design is satisfactory ano that the disposal cell cover will comply with the radon release requirenents of EPA (40 CFR Part 192.02 (b), Subpart A).
6.3 Site Cleanup Site characterization surveys have been conducted at the site to identify the subsuiface boundary of the tailings plie, as well as, she depth and area of the former mill yaros, ore storage, and windblown contaminated areas. Radiometric surveys and-sampling were also conducted in i.he buildings at the site. The results of the site characterization survey are being used to plan the control monitoring for the excavation and the bulloing cecontamination, as well as the final radiological verification survey for the land and the buildings. 00E has comniitted to 6he clean-up of the processing site and mill buildings in accordance with the EPA standard (40 CFR 192 Subpart B).
In addition to the EPA standards for the buildings DOE proposes that removable surface alpha contamination shall not exceed 1000 dpm/100 cm, and the average over one square meter total non-removable alpha contamination shall not exceed 5000 dpm/100 cm. DOE proposes an absolute maximum limit for total alpha contamination of-15,000 dpm/100 cm. These limits are in compliance with NRC Regulatory Guide 8.30 " Health Physics Surveys in Uranium Mills".
As a result of DOE's compliance with the EPA standard and NRC Regulatory Guide 8.30 with regard to removable alpha contamination, the NRC is prepared to concur with the D0E's radiological survey plan. Although it should be pointed out that while NRC has no objection to DOE's utslization of the NRC proposec 9
a-'*
y
- 61.-
' limits for rsmovable alpha contalinnetion, the DOE should. comply with their own-l) more stringent standards as provided in the UMTRA Project Environrental Health ana4 Safvty Plan (UMTRA-DOE /AL-150224).
56.4 Conclusions..
With. r egard to. the site' clean-up, the DOE has committed to clean-up the processing site and mill buildisegs in accordance with the EPA stanaards and NRC l
Regulatoiy Guide._8.30. Therefor e, the NRC f inds the proposed 5ite clean-up to be acceptable, I
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.7.0 SUlHARY
]
>This Technical Evaluation Report (TER) sorsarizes the NRC scaff review of the-
)
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proposed renedial action for the Green River Tailings site. Based on the
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staff review cf DOE's' final Rened.a1 Actinn Pisn, the NRC concludes that the
~'
remedia1Loction Lat proposed for the Green River site-by DOE will neet the EPA standard, provided.6he following condition is satisfied by DOE in performing renedial action:-
i
)
1.
Demonstrate compliance w eth EPA's final groundwater cleanup stand 6rds j
in Subparts Band C of 40 CFR Par t 192 af ter EPA pronolgates the staridards j
l Therefore the NRC will conditionally concur on the Srsen R1ver Reredial Action Plan.
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1.
8.0 REFERENCES
/ BIBLIOGRAPHY 1.
Campball, K.W.,1981, Near-sour ce attenuation of peak horizontal ground acceleration: Bulletin of the Seismoiogical Society of America, v. 71, p.
2039-2070.
2.
DOE,1984, Draft Environmental Assessnent, Davis Canyon site, Utah: DOE Document Number DOE /RW-0010.
3.
DOE,1987b, Green River draft Remedial Action Plan and Site Conceptual Design; geology, seismicity, and geomorphology: supplenents subniitted as enclosures to letter J.R. Anderson, DOE, to D.E. Martin, NRC, 3/13/87.
4.
McKnight, E.T., 1940, Geology of area between Green and Colorado rivers, Grand and San Juan counties, Utah: U.S. Geological Sur vey Bulletin 908, 147 p.
5.
HRC, 1985, Standard Review Plan for UMTRCA Title I Mill Tailings Remedial l
Action Plans; U.S. NRC, Division of Waste Management, October, 1985.
6.
Williams, P.E. and Hackman, R.J., 1971, Geology of the Salina quadrangie, Utah: U.S. Ccological Survey Mtscellaneous Investigations Series Map I-591-A.
(
7.
Young, R.G., Million, I., and Hausen, D.M., 1960, Geology of the Green River mining 01:;trict, Emery and Grand counties, Utah: U.S. Atomic Energy Conan.ssion Report RME-98 -(rev ised), 89 p.
1 1
8.
00E,1989, Remedial Action Plan and Final Design for Stabilization of l
the Inactsve Uranium Mill Ta lings at Green River, Utah, Final, Vol. I,II and III, December 1969, UMTRA-00E/AL 050510.GRNO.
9.
DOE,1987a, Ur anium Mill Ta. lings Remedial Action Project (UMTRAP), Green River, Utah; Information to Bidders, Volumes I, II & III, December 1987.
f
River, Utah; Design Calculations, Volumes I,II & III dated Novenber 1987.
l
- 11. DOE,1988, Uranium Mill Tailings Remedial Action Project (UMTRAP), Green River, Utah; Design Calculations - Addendum 1, February 1988, 12.
U.S. Array Corps of Engineers, Hydrologic Engineering Center," Flooo Hydrograph Package, HEC-1, continuously updated and revised.
- 13. NRC,1983, Regulatory Guide 1.59, " Design Basis Floods for Nuclear Power Plants," January 1983.
14.
U.S. Bureau of Recl6mation, U.S. Department of the Interior, Design,of Sma ll,Da'ns, 1973.
- 15. NRC,1983, Technical Position WM-8201, "Hyorologic Design Criteria f or Tailings Retention Sy:Lems," January 1983.
16.
U.S. Aimy Corps of Engineers, Hydrologic Enginee ing Center, " Water Sui f ace Profiles, HEC-2," continuously updated and r evised.
+;..
- 17. Chow, V. T., "Open Channel Hydrauhcs," McGraw-Hill Book Company, New York, 1959.
18.-
U.S. Arny Corps of Engineers, " Hydraulic Design of Flood Control Channels," EM 1110-2-1601, 1970.
19.
U.S. Ainy Corps of Engineers, " Additional Guidance for Riprap Channel-Protection," EM 1110-2-1601, 1970.
20.
U.S. Department of Commerce, U.S. Arny Corps of Engineers, Hydrometeotv-logical Report No. 43, " Probable Maxinum Precipitation, Northwest States,"
l 1966.
21.
U.S. Arny Corps of Enginess, " Engineering and Design - Standaro Project Flood Determinations," EM 1110-2-1411, 1965.
- 22. Crippen, J. R. and Bue, C. D., " Maximum Floodflows in the Conterminous j
United States," USGS Water Supply Paper 1887(1977).
l
'23.
Simons, D. B., and Sentui k, F., Sediment Transport Technology, Fort Collins, Colorado, 1976.-
~'
- 24. Codell, R. B, " Design of Rock Armor for Uranium Mill Tailings Embanknents, U.S. Nuclear Regulat.ory Commission, Unpublished Draf t Report, February 1985.
25.
U.S. Department of Commerce, U.S. Arity Corps of Engineers, Hydrometeoro-logical Report No. 49, " Probable Maxinom Precipitation Estimates, Coloraco River and Great Basin Dratnages," 1977.
i
- 26. Stephenson, D., Rockfill Hydraulic Engineerin Developments in Geotechnical Engineering #277ETsevierlcierif.Ificlublishing Company, i
1979.
- 27. Nelson, J. D. et al., " Methodologies for Evaluating Long-Term Stabilization Designs of Uranium Mill Tallings impoundments,"
NUREG/CR-4620, June 1986.
- 28. Supplemental Geotechnical Data in Support of the Remedial Aci. ion Plan, Letter f rom J. Atthur, DOE to P. Lohaus, NRC, March 11, 1988.
- 29. Environmental Assessment of Remecial Action, Uranium Mill Tailings Site, I
Green River, Utah, December, 1987 i
L
'30.
DOE's Response to NRC Connents, Letters form J. Arthur, DOE to P. Lohaus, NRC, September and December, 1987 1
l'
- 31. Letter to J. Arthur, DOE from P. Lohaus, NRC, March 14, 198B 32.
Kiikham R. M. and W.P. Rogers, 1981, Earthquake Potential in Coloraco:
A Preliminary Evaluation; Colorado Geological Suivey Bulliten No. 43.
- 33. Hunt, C. B.,1974, Natural Regions of the United States and Caiiada; San Fransisco, W.H. Freeman and Co., 725 pg.
34 Tr ip Report, Memor dndum f rom J. Gr imm to R. J. Starmer, June 17, 1987
et 35; DOE,1989a', Urantum Mill Tailings Remedial Action Pr oject. (UMTRAP), Green R.ver, Utah; Design Calculations, Addenduin 2, January,1989. Trip Report for the UMTRA Cover Data Review, Memorandum from M. Weber to R.J. Starmer, March 13, 1989.
- 37. NRC, 1988, Technical Position, "Information Needs to Demonstrate Compliance w:th EPA's Proposed Groundwater Protection Standards in 40 CFR Part 192, Subparts A-C", June,1988
- 38..NRC, " Staff Technical Position on Testing and Inspection Plans During" Cons 6ruction of DOE's Remedial Action ac Inactive Mill Tailings Sites.
6
- 39. Memorandum from R. Dale Smith to R. Browning, February 9, 1987, " Sampling of Uranium M.11 Tailings Impoundnsents for Hazardous Constituents."
- 40. Jacobs Engineering Group, 1989, " Design Calculations: Green River Utah, UMTRA Project Site, " Nos. GRN-01-89-12-20-02-00 (2 sets) ano GRN-01-89-12-08-00.
- 41. Jacobs Engintering Group,1989, Computer Input and Output for the SUTRA Model of the Green River Site.
42.
U.S. Dt. par tment of_ Navy, Soil Mechanics, Design Manual 7.1,NAVFAC.DM7.1, Naval Facilities and Engineering Command, Alexandr ia VA, May 1982
- 43. Letter from W.J. Atthur, DOE to P. Lohaus NRC, August 19, 1988, In'ormation on Radon-Barrit.r Design of Green River
- 44. Memorandum'from P. Lohaus-to J. Greeves, April 6, 1989
'45.
Algermissen, S.T., Pei kins, D.M., -Thenhaus, P.C., Hanson, S.L., and Bender, B.L., 1982, Probabilistic Estimates of Maximum Acceleration and Velocity in Rock in i.he Contiguous United Statcs:
U.S. Geological Survey Open File Report 82-1033
-46.
Calculations and Daca to Support the Remedial Accion Plan and Final Design for Stabilization of Inactive Mill Taihngs, Green River; December, 1989
- 47. Contaminated Material, Moisture Content, Density and Compaction Data, Green River; Norrison and Knudsen Engineers; November,1989
- 48. Supplemental information to the final RAP, transmittal of January 12, 1990 from M. Ma6 thews, DOE to P. Lohaus, NRC
- 49. Letter of July ~ 3,1989 to M. Matthews, DOE from P. ! ohaus, NRC
- 50. Additional information to i.he final RAP, transmittal of Febiuaiy 23, 1990 from M. Matthews, DOE to P. Lohaus, NRC
- 51. Additional information to the final RAP, transmittal of March 19, 1990 f rom M. Matthews, DOE to P. Lohaus, NRC
'..tc.."
.52.
NRC, 1989,. Draft Ti.chnical Position " Design of Erosion Protection Ccvers-for Stabilization of Uranium Mill Tallings Sites, August,1989.
53.- DOE, 1989, Te.chnical Approach Document.
- 54. Stubchaer,'J.,1975, The Santa Barbara Urban Hydrograph Method, presented at the National Symposium on Urban Hydrologf~and Sedime6f' Control, Univet sity of Kentucky, Lexington, Kentucky.
j
- 55. Sabol,. G.V., and T. J. Ward,1985, " Santa Barbara Hydrograph with Green-Ampt Infiltration," Watershed Mariagenent in the Eighties, American Society of Civil Engineers, New York, New York.
- 56. M.K.Ferguson,1988, Uranium Mill Tail 1ngs Reinedial Action Design Procedures Manuc1, Revised.
L 1
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i
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- 67'-
~ APPENDIX A 4
SUMMARY
AND STATUS OF DRAFT TER OPEN' ITEMS Draft TER Open Issues Draft TER Resolution l
Subsection 1.-
DOE has not submitted all the test data' 3.4 SEE TABLE 1.2 for the amended soil used in the in-6.2.2 AGREEMENT 3
' filtration / radon barrier and the demon-i stration of achieving the hydraulic i
conductivity assunea -in the design.
2.
DOE has not established che geocheniscal 5.2.5 CLOSED-conditions beneath the-current or pro-IRRELEVANT posed disposal areas.
3.
DOE has not determined whether a tailings 5.3.3 CLOSED-amendment =is necessary.
IRRELEVANT 4.
. DOE has not determined whether a geo-5.3.4 CLOSED-chemicaltliner is necessdiy.
IRRELEVANT 5.
DOE has not determined the source of 5.4.1.1 SEE TABLE 1.2 the organics in the leachatt.
AGREEMENT 8 1
6.
' DOE has not specified or proposed con-5.4.1.2 SEE TABLE 1.2 centration limit for all const uui.sas AGREEMENT 9-found in groundwater aiid 7.he tailings under Subpart A.
7.
DOE has not specified a P0C.
5.4.1.3 SEE TABLE 1.2 AGREEPENT 11 8.
DOE has not estimated potential down-5.4.2 CLOSED-gradient concentrations for all IRRELEVANT listed constituents.
-9.
DOE has not proposed a_ groundwater 5.4.4 CLOSED
. performance monitoring program.
- 10. DOE'has not pioposed a corrective 5.4.5 CLOSED
+
action plan.
- 11. DOE has not specified or proposed con-5.5.1.2 SEE TABLE 1.2 centration limit for all constitue nts AGREEMENT 12 found in groundwater and the tailings under Subpart B.
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APPENDIX A CONTINUED o
Draf t TER Open' Issues Diaft TER Resolution Subsection
- 12. DOE has not included a restoration plan 5.5.2 SEE TABLE 1.2 to cleanup relict grouno-water contam-AGREEMENT 12 inaticn.
- 13. DOE has not proposed a ground-water 5.5.3 SEE TABLE 1 2 monitoring program to verify plunm AGREEMENT 12 niDVumen Ls.
1 1
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o w
s i < x(
=r 9.
- , APPENDIX B t
- g 7l
SUMMARY
OF.0 PEN 155UES/ AGREEMENTS w
.....r...........................................................e............
Open Issuts/ Agreements Final TER Subsection Status O
1.
Given that the groundwater travel 5.4.2 CLOSED.
= time through the buffer and unsatur ated tock beneath the disposal unit may be
'less than 1000 years but greater than 200 years,'and that 191s difficult, if not ur4cssible, to estimate the groundwater.
travel time with accuracy DOE commits to submitting to NRC within 30 days of this meeting an adequate written Justification that the present design of the disposal unit, as mooif ted by the conditions agreeo
-to herein, represents the best design to
- comply, to the extent reascnably achievabh, with EPA's proposed standards.in 40 CFR Part 192, Subpart A.
2.
DOE will asse:s whather the contaminated 5.4.2 CLOSED windblown and-vicinity property materials are significant sources of hazardous constituents to groundwater by leaching representative samples of the materials using EPA's EP Tox tcity Test Procedure (40CFRPart 261, Appendix IIf or comparable NRC-approvt.d proceduie and comparing
. hazardous constituent concentracions in the
~
leachate w:th concentrations in leachate from representative soil sar41es collected in the vicinity of the site.
'3.
00E will perform representatwe testing of 5.4.2 CLOSED the radon barrier to ensure that its as-built saturated hydraulic conductivity does not exceed 2E-8 cm/s and to assess its untoturated hydraulic characttristics (tension as a function of moisture content; hydraulic conductivity as a function of moisture content). Semples for hydraulic conductivity tests will be taken at a frequency offat'least one per 2000 cyd of as-compacted radon
. barrier material, which is estimated to be 28000
- c
. cy d.
Sample locations should be distributed evenly over the cover, provided that at least 50%-
of the samples are collected from the side slopes of the d uposal unit. At least 13 of the 14 samples
-(approximately. 90%) must exhibit saturated hydraulic concuctivities less than or equal to 2E-8 cm/s.
Standard geotechnical parameters, such as physical
. properties, will also be determined for the-samples.
1 m
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01 yg r-APPENDIX B-- CONTINUED
~0 pen. Issues /Agrcements Final TER Subsection Status 14.
DOE commits to placing and maintaining 3.4 CLOSED
-contaminated materials in the disposal unit.
z lat the specified densities ano at average moistute contents.that are less than their everagt steady-state moisture contents 7
presented in the RAP and, in' any case, it.s s than 5% by volume for the tallings and less than 10.6% by volume for the w.noblown and I-l other vicinity property-contaminated materials.
DOE will place and test at least four litts of. contaminated materials during the trtal compaction (first 1,000 cyd of material),
which is intendeo to develop procedures to U
ensure compaction of the materials in accordance with material specifications. As part of
'the submission required under Condition 1 of this agreement, DOE will submit physical properties and compaction data on winablown meterial and 'any other data to support 7
coupliance with the condition that contaminated materials will.be placed and maintained at tne specified censities and moisture contents.
- 5. '00E commits to mixing homogeneously no less 3.4 CLOSED thar. 6% by weight socium bentonite into the-radon barrier mates tal and compacting T.he racon barrier to 100% of standarc Proctor density ~within 0 to +3% of Optimum Moisture Content,
- 6. = DOE commits to using a minimum gradation 3.4 CLOSED
. specification for the racon barrier material
- of greater than 70% of the material passing the no. 200 seive for the f1rst lif t and 50%
of the' material passing the no. 200 selve for the remaining lifts.
7.
00E commits to evaluating whether beryllium 5.4.1.1 CLOSED.
L 1s-a hazardous constituent in the contaminated Li-materials at Green River by determining its concentration in representative samples of the tallings or pore fluia within the tallings.
If present at elevated concentrations in the contaminated materials, DOE will incluce lC beryllium.in the 1ist of hazardous constituents 4
for the Green River disposal site.
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pa.
$1 'i f M i
71L-APPENDIX B - CONTIhUED Open Issues / Agreements Final TER Subsection Sta tus
'ltad,.and methylene chloride in'the list of hazardous constituents for 'the disposal unit.
9.
DOE commits to the concentration 5.4.1.2 CLOSED' limits listed'in the enclosed table as the appropriate interim concentration
-liniits for hazardous constituents in
-groundwater in.the_ uppermost aquifer at the Point of Conipliance..NRC may revise these interim limits based'on new monitoring data to be collected during and following-construction of the disposal L
unit.
- 10. 00E connits to collecting and 5.4.1.3 CLOSED analyzing' representative samples of groundwater from monitoring wells 807, 812, 813, 818, and 823 on.a quarterly basis ourIng construction of the disposal unit;. DOE connits to collecting and analyzing iepresentative samples of groundwater from these monitoring wells and new wells at the Point of Compliance and bacLground locations on a quar Lerly basis for two ycars after completion of the disposal ~ unit. DOE will establish details of the monitoring program in the Surveillance and Maintenance Plan or l
another appioprlate document upon NRC concurrence with:the Plan or 06her docunwnt.
- 11. DOE. comnnts to a Point of Compliance 5.4.1.3 CLOSED that is as close as reasonable to the disposal unit and extends along the entire northwest and northeast edges of the unit.
- 12. DOE will demonstrate compliance with 5.5 CONCURRENCE EPA's' groundwater cleanup standa ds of CONDITION Subpart B and C of_40 CFR part 192 after EPA finalizes them.
a i'
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