Final Technical Evaluation Report for the Naturita ...SUBJECT: FINAL TECHNICAL EVALUATION REPORT FOR...

'I"I

P 4 UNITED STATES

NUCLEAR REGULATORY COMMISSIONM ) WASHINGTON. D.C. 20555--0001

May 21, 1999

Mr. George Rael, DirectorU.S. Department of EnergyEnvironmental Restoration DivisionAlbuquerque Operations OfficeERD/UMTRAP.O. Box 5400Albuquerque, NM 87185-5400

SUBJECT: FINAL TECHNICAL EVALUATION REPORT FOR THE NATURITA, COLORADO,

URANIUM MILL TAILINGS SITE

Dear Mr. Rael:

The U.S. Nuclear Regulatory Commission (NRC) staff has completed its review of the finalRemedial Action Plan and Site Design (RAP) and the Remedial Action Inspection Plan (RAIP),Revision 1, for the uranium mill tailings disposal site at Naturita, Colorado. The staffs review is

-documented in the enclosed final Technical Evaluation Report (TER).

Based on this review, the NRC staff concurs in the Naturita RAP and RAIP, and the signaturepages are Enclosure 2. In its review of the preliminary final RAP for the Naturita processing anddisposal sites, the NRC staff identified 26 open issues. Those issues have been satisfactorilyaddressed by the U.S. Department of Energy (DOE) in the final RAP, with the exception ofseveral groundwater issues that have been deferred until a later phase of the Uranium MillTailings Remedial Action (UMTRA) Project.

If you have any questions concerning this subject, please contact the NRC Project Manager,Robert Carlson, at (301) 415-8165.

Sincerely,

N.7ing Stablein, Acting ChiefUranium Recovery and

Low-Level Waste BranchDivision of Waste ManagementOffice of Nuclear Material Safety

and Safeguards

Enclosures: As stated

cc: W. Woodworth, DOE AIbF. Bosilievac, DOE AIbE. Artiglia, TAC-AIbR. Edge, DOE GRJ

Mr. George Rael, Director May 21, 1999U.S. Department of EnergyEnvironmental Restoration DivisionAlbuquerque Operations OfficeERD/UMTRAP.O. Box 5400Albuquerque, NM 87185-5400

SUBJECT: FINAL TECHNICAL EVALUATION REPORT FOR THE NATURITA, COLORADO,.URANIUM MILL TAILINGS SITE

Dear Mr. Rael:

The U.S. Nuclear Regulatory Commission (NRC) -staff has completed its review of the finalRemedial Action Plan and Site Design (RAP) and the Remedial Action Inspection Plan (RAIP),Revision 1, for the Uranium mill tailings disposal site at Naturita, Colorado...The staff's review isdocumented in the enclosed final Technical. EvaIuation Report (TER).

Based on this review, the NRC staff concurs in the Naturita RAP and RAIP,.-andthe signaturepages are Enclosure 2. In its review ofthe preliminary final RAP for the Naturita processing anddisposal sites, the NRC staff identified 26 open issues. Those issues have been satisfactorilyaddressed by the U.S. Department of Energy. (DOE) in the final RAP, with the exception ofseveral groundwater issues that have been deferred until a later phase of the Uranium MillTailings Remedial Action (UMTRA) Project.

If you have any questions concerning this subject, please contact the NRC Project'Manager,Robert Carlson, at (301) 415-8165.

Sincerely,

Original Signed ByN. King Stablein, Acting ChiefUranium Recovery and.


and Safeguards

Enclosures: As stated

cc: W. Woodworth, DOE AIbF. Bosvac, DOE AIbE. Artiglia, TAC AIbR. Edge, DOE GRJ

DISTRIBUTION w/Encl.: File Center NMSS r/f URLL r/f PUBLICACNW RCarlson

w/o Encl.: JHolonich RWeller

DOCUMENT NAME: S:\DWM\URLL\JSC\NATURITA\NEWTER\NATLTR.WPDand S:\DWM\U RLL\JSC\NATURITA\NATFTER.WPD

*Please see previous concurrence.

OFC URLL* . 1"1URLL UR IJ 11

NAME, PSobel:cc Abr _ ta' b " i n

DATE CECOR Sta eOL ~ ~ ~ ~ ~ L: /9591 9 i2iILOFFICIAL RECORD COPY

Mr. George Rael, DirectorU.S. Department of EnergyEnvi onmental Restoration DivisionAlbuq que Operations OfficeERD/UM AP.O. Box 54Albuquerque, 87185-5400

SUBJECT: FINAL ECHNICAL EVALUATION REPORT FOR THE NATURITA,COLOR 0, URANIUM MILL TAILINGS SITE

Dear Mr. Rael:

The U.S. Nuclear Regulatory Co mission (NRC) staff has completed its review of the finalRemedial Action Plan and Site Des' n (RAP) and the Remedial Action Inspection Plan (RAIP),Revision 1, for the uranium mill tailing (disposal site at Naturita, Colorado. The staff's review isdocumented in the enclosed final Techn- al Evaluation Report (TER).

Based on this review, the NRC staff concurs - the Naturita RAP and RAIP. In its review of thepreliminary final RAP for the Naturita processin and disposal sites, the NRC staff identified 26open issues. Those issues have been satisfacto addressed by the U.S. Department ofEnergy (DOE) in the final RAP, with the exception several groundwater issues that have,been deferred until a later phase of the Uranium Mill ilings Remedial Action (UMTRA)Project. As a result of the staff's concurrence, NRC is epared to sign the signature pages forthe Naturita RAP, following their submittal by DOE.

If you have any questions concerning this subject, please con ct the NRC Project Manager,Robert Carlson, at (301) 415-8165.

Sincerely,

N. King Stablein, Acting ChiUranium Recovery and


and Safeguards

Enclosure- As stated

cc: W. Woodworth, DOE AIbF. Bosilievac, DOE AIbE. Artiglia, TAC AIbR. Edge, DOE GRJ

DISTRIBUTION w/Encl.: File Center NMSS r/f URLL r/f PUBLICACNW "' @NWRA-RCarlson 9 6

w/o Encl.: p JHolonich k

DOCUMENT NAME: S:\DWM\URW\JSC\NATURITA\NEWTER\NATLTR.WPDand S:\DWM\UR6\JSC\NATURITA\NAT FTER.WPD.

OFC URLL URLL URLL "

NAME PSobel::c" CAbrams NStablein

DATE 04/L'ý/99 04/ /99 . _04/ /99_ _1_I

OFFICIAL RECORD COPY

W

TECHNICAL EVALUATION REPORTFOR THE PROPOSED REMEDIAL ACTION AT THE

NATURITA URANIUM MILL TAILINGS SITENATURITA, COLORADO

Enclosure

W -4V

ABSTRACT

This Technical Evaluation Report (TER) summarizes the U.S. Nuclear Regulatory Commission(NRC) staff's review of the proposed remedial action for the Naturita Uranium Mill TailingsDisposal Site (Naturita site). The sections of the TER are arranged by technical discipline tocorrespond to the Environmental Protection Agency's (EPA's) standards in Title 40 of the Codeof Federal Regulations (CFR), Part 192, Subparts A through C (EPA, 1995). The NRC staffreview of the U.S. Department of Energy final Remedial Action Plan (RAP; DOE, 1994), MKFerguson Remedial Action Inspection Plan (MK, 1998), final draft Remedial Action Plan and SiteDesign for the Upper Burbank Repository (RAP; DOE, 1995) and associated documentsidentified open issues in geologic stability, geotechnical stability, erosion protection,groundwater hydrology, and radon attenuation and site cleanup, as presented in Table 1 .1(Summary of Open Issues). The final Remedial Action Plan and Site Design for the UpperBurbank Repository (RAP: DOE, 1998) has been reviewed by NRC staff for finalization of thisTER. Previously open issues have been adequately addressed or deferred as noted in Table1.1 of this' final TER.

NATURITA TER APRIL 1999

let,- *..,~.

TABLE OF CONTENTS

Section Pagie

1.0 IN T R O D U C T IO N ........................... *. ..... ..................... 1-11.1 EPA Standards ............................................ ....... 1-11.2 Site and Proposed Action ............. ......................... 1-11.3 Review Process ..................... ....................... 1-21.4 TER Organization ...... .............................. ........ 1-31.5 Summary of Open Issues ............. .. ................ 1-3

2.0 GEOLOGIC STABILITY ............2.1 Introduction ...............2.2 Location ..................2.3 G eology ..................

2.3.1 Physiographic Setting ..2.3.2 Stratigraphic Setting ...2.3.3 Structural Setting ......2.3.4 Geomorphic Setting ...2.3.5 Seism icity ............2.3.6 Natural Resources .....

2.4 Geologic Suitability .........2.4.1 Bedrock Suitability .

2.4.2 Geomorphic Stability.2.4.3 Seismotectonic Stability.

2.5 Conclusions ...............

.2-1.2-12-12-1.2-1.2-2.2-4•2-5.2-5.2-7.2-7.2-7.2-8.2-92-9

3.0 GEOTECHNICAL STABILITY .............................. ............ 3-13 .1 In tro d u ctio n . . . . ... . . .... . . . . . . . . . . . . . . ... . . . . . . . . . . . . . . . . . . . . . . . . .3 -13.2 Site and M aterial Characterization ..... * ............................. 3-1

3.2.1 S ite D escriptions ........................................... 3-13.2.1.1 Processing Site ................................. 3-13.2.1.2 Disposal Site at Uravan ............................... 3-23.2.1.3 Borrow M aterials Site ................................ 3-2

3.2.2 Site Investigations .......... .. .3-23.2.3 Upper Burbank Disposal Site Stratigraphy ..................... 3-33.2.4 Testing P rogram ............................................. 3-3

3.3 Geotechnical Engineering Evaluation .................. 3-33.3.1 Slope Stability Evaluation .......... ......................... 3-33.3.2 Settlement and Cover Cracking•....... ................... ........ 3-43.3.3 Liquefaction ........................................... 3-53.3.4 C over D esign .............................................. 3-5

3.4 Geotechnical Construction Details ................................... 3-63.4.1 Construction Methods and Features ............................ 3-63.4.2 Testing and Inspection .................................... 3-6

3 .5 C o nclusio ns .................................................... 3-6

NATURITA TER APRIL 1999

OF

4.0 SURFACE WATER HYDROLOGY AND EROSION PROTECTION .............. 4-14.1 Hydrologic Description and Site Conceptual Design ..................... 4-14.2 Flooding Determ inations ......................... ................ 4-1

4.2.1 Selection of Design Rainfall Event .............................. 4-14.2.2 Infiltration Losses ...................................... 4-24.2.3 Times of Concentration ................4.2.4 Rainfall Distributions ....................4.2.5 Computation of PMF ....................

4.2.5.1 Top and Side Slopes .... .......4.2.5.2 Aprons ....................4.2.5.3 Diversion Channels .......... ..

4.3 Water Surface Profiles and Channel Velocities.4.3.1 Top and Side Slopes .............. ....4.3.2 Upstream Aprons ........................4.3.3 Diversion Channels .....................

4.4 Erosion Protection ...........................4.4.1 Sizing of Erosion Protection ..............

4.4. 1.1 Top and Side Slopes ............4.4.1.2 Upstream Aprons ................

... 4-2

... 4-3

. 1 .4-3... 4-3..4-4. 4-4

.. 4-4. .. 4-4• 4-4...4-4

... 4-5

... 4-5... 4-5... 4-6... 4-6... 4-6... 4-6

4.4.1.3 Diversion Channels.. ............4.4.1.3.1 Channel Side Slopes4.4.1.3.2 Channels (Main Section) ...... .............. 4-74.4.1.3.3 Channel Outlets ........................... 4-74.4.1.3.4 Sediment Considerations ..................... 4-7

4 .4 .2 R ock D urability .............................................. 4-84.4.3 Testing and Inspection of Erosion Protection ..................... 4-9

4.5 Upstream Dam Failures ......................................... 4-104 .6 C o nclusio ns ........................ : ............. : ........... 4-10

5.0 WATER RESOURCES PROTECTION ..................................... 5-1,5 .1 In tro d u ctio n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 -15.2 Hydrogeologic Characterization .................................... 5-1

5,2.1 Identification of Hydrogeologic Units ........................... 5-15.2.1 A Processing Site ................................ 5-15.2. 1 B D isposal S ite ................................. .5-2

5.2.2 Hydraulic and Transport Properties ............................ 5-25.2.2 A Processing Site .............................. 5-25.2.2 B Disposal Site ................. 5-3

5.2.3 Extent of Contam ination ..................................... 5-35.2.3 A Processing Site ............................. 5-35.2.3 B D isposal Site ................................. 5-3

5 .2.4 W ater U se ............................................... 5-45.2.4 A Processing Site ............................... 5-45.2.4 B Disposal Site ................................. 5-4

5.3 Conceptual Design Features to Protect Water Resources ............... 5-55.3 A Processing Site .. . ....................................... 5-5

NATURITA TER i i APRIL 1999

5 .3 B D isp o sa l S ite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . .5 -55.4 Disposal and Control of Residual Radioactive Materials ................. 5-5

5.4.1 Water Resources Protection Standards For the Disposal Site ....... 5-55.4.2 Performance Assessment for the Disposal Site .................. 5-65.4.3 Closure Performance Demonstration for the Disposal Site ......... 5-75.4.4 Groundwater Monitoring and Corrective Action Plan at the

D is p o sa l S ite . . . . . . . . . . . . . . .$. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 -75.5 Clean-up and Control of Existing Contamination at the Processing Site ..... 5-75.6 Conclusions .... .................... 5-8

6.0 RADON ATTENUATION AND SITE CLEANUP .............................. 6-16 .1 In tro d u ctio n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6 -16.2 R adon A ttenuation ............................................... 6-1

6.2.1 Evaluation of Param eter Values ............................... 6-16.2.1.1 Contam inated M aterials ................................ 6-26.2.1.2 R adon B arrier .............. ..... .................... 6-4

6.2.2 Evaluation of Radon Attenuation Model .......... .............. 6-56.2.3 Durability of the Radon Barrier .. ............................. 6-5

6 .3 S ite C le a n u p ... . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6 -66.3.1 Radiological Site Character ization ................................ 6-66.3.2 C leanup Standards ......................................... 6-66.3.3 Supplem ental Standards ....................................... 6-76 .3 .4 V e rifica tio n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6 -9

6 .4 C o n clu s io n s . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 -9

7.0 R EFER ENC ES ...................................................... 7-1

NATURITA TER i APRIL 1999

7

LIST OF FIGURES

Figure Page

FIGURE 1.1FIGURE 1.2FIGURE 1.3FIGURE 1.4FIGURE 1.5FIGURE 1.6FIGURE 2.1

Table

LOCATION MAP OF THE NATURITA SITE, COLORADO ................ 1-3MAP OF THE NATURITA PROCESSING SITE .......................... 1-4NATURITA PROCESSING SITE ...................................... 1-5LOCATION OF THE UPPER BURBANK DISPOSAL SITE ................ 1-6DIAGRAM OF THE UPPER BURBANK DISPOSAL CELL ................ 1-7CROSS SECTION VIEWS OF THE UPPER BURBANK DISPOSAL CELL ... 1-8STRATIGRAPHY OF THE UPPER BURBANK SITE ..................... 2-3

LIST OF TABLES

Page

TABLE 1.1 SUMMARY OF OPEN ISSUES ........... ........................ 1-9TABLE 5.1 HAZARDOUS CONSTITUENTS ANC CONCENTRATION LIMITS FOR

TH E D IS PO SA L S ITE .............................................. 5-9

NATURITA TER i v APRIL 1999

I

Acronym orAbbreviation

ALARA

CFR

COE

DOE

EPA

HMR

LTSP

MCL

NEPA

NOAA

NRC

PMF

PMP

POC

RAIP

RAP

SRP

TER

UMTRA

UMTRCA

LIST OF ACRONYMS AND ABBREVIATIONS

Definition

As Low As Reasonably Achtievable

Code of Federal Regulations

U.S. Army Corps of Engineers

U.S. Department of Energy

U.S. Environmental Protection Agency

Hydrometeorological Report

Long-Term Surveillance Plan

Maximum Concentration Limit, or Maximum Contaminant Level

National Environmental Policy Act

National Oceanographic and Atmospheric Administration

U.S. Nuclear Regulatory Commission

Probable Maximum Flood

Probable Maximum Precipitation

Point of Compliance

Remedial Action Inspection Plan

Remedial Action Plan

Standard Review Plan

Technical Evaluation Report

Uranium Mill Tailings Remedial Action

Uranium Mill Tailings Radiation Control Act of 1978

NATURITA TER V APRIL 16999

4

1.0: INTRODUCTION

The Naturita site was designated as one of 24 abandoned uranium mill tak'ings piles to receiveremedial action by the U.S. Department of Energy (DOE) under the Uranium Mill TailingsRadiation Control Act of 1978 (UMTRCA). UMTRCA requires, in part, that the U.S. NuclearRegulatory Commission (NRC) concur with DOE's selection of remedial action, such that theremedial action meets appropriate standards promulgated by the U.S. Environmental ProtectionAgency (EPA). This Technical Evaluation Report (TER) documents the NRC staffs review ofthe DOE Remedial Action Plan (RAP) (DOE, 1994, 1995, and 1998), Remedial ActionInspection Plan (RAIP) (MK, 1998) and all associated documentation pertinent to the proposedremedial action.

1.1 EPA Standards

As required by UMTRCA, remedial action at the Naturita site must comply with regulationsestablished by the EPA in 40 CFR Part 192, Subparts A through C (EPA, 1995). Theseregulations may be summarized as follows:

1. The disposal site shall be designed to control the tailings and other residualradioactive material for 1000 years to the extent reasonably achievable and, inany casefor at least 200 years [40 CFR 192.02(a)(1)].

2. The disposal site design shall provide reasonable assurance that releases ofradon-222 from residual radioactive materials (RRMs) to the atmosphere will notexceed 20 picocuries/square meter/second or increase the annual averageconcentration of radon-222 in air at any location outside of the disposal site bymore than 0.5 picocurie/liter [40 CFR 192.02(b)(1)and (2)J.

3. The remedial action shall ensure that radium-226 concentrations, in land that isnot part of thedisposal site, averaged over any area of 100 square meters, donot exceed the background level by more than 5 picocuries/gram (pCi/g)averaged over the first 15 centimeters of soil below the surface and 15 pCi/gaveraged over any15-centimeter-thick ;ayer of soil more than 15 centimetersbelow the land surface [40 CFR 192.12(a)].

On January 11, 1995, EPA published a final rule for groundwater standards for remedial actionsat inactive uranium processing sites (40 CFR 192, Subparts A through C). The standardsconsist of two parts; a first part, governing the control of any future groundwater contaminationthat may occur from tailings piles after remedial action; and a second part, governing the.cleanup of contamination that occurred before the remedial action of the tailings. In accordancewith UMTRCA Section 108(a)(3), the remedial action shall comply with the EPA standards.

1.2 Site and Proposed Action

The Naturita uranium mill processing site is located in Montrose County, Colorado,approximately two miles northwest of the town of Naturita along Colorado State Highway 141(Figure 1.1). The site encompasses approximately 53 acres and includes the former tailings

NATURITA TER 1-1 APRIL 1999

area, the mill facility and ore buying station, and the adjacent ore storage area (Figure 1.2). Notailings pile remains at the site due to the removal and transport of tailings to the Durita facility atVancorum, Colorado, for reprocessing by the Ranchers Exploration and DevelopmentCorporation. The approximately 547,000 cubic yards (yd 3) of contaminated material remainingat the Naturita processing site (Figure 1.3) includes 115,000 yd 3 from 14 acres of mill yard,12,000 yd 3 from 12 acres of former ore storage area, 295,000 yd 3 from 196 acres of windblownand/or other material (areas A through G)', 117,000 yd3 from 27 acres of former tailings area,and 8,000 yd 3 of demolition debris. Radium-226 concentration for the contaminated materialranges from 15 to 143 pCi/I.

The proposed remedial action for the disposal and stabilization of the contaminated materials isto relocate them to the Upper Burbank disposal site at Uravan, Colorado. The Upper Burbankdisposal site is located approximately 13 road miles (21 kilometers) northwest of the Naturitaprocessing site (Figure 1.1). The disposal cell will be configured as shown in Figures 1.4 and1.5.

1.3 Review Process

The NRC staff review was performed in accordance with the Standard Review Plan (SRP) forUMTRCA Title I Mill Tailings Remedial Action Plans (NRC, 1993) and consisted ofcomprehensive assessments of DOE's RAPs for the Naturita processing and disposal sites(DOE, 1994, 1995 and 1998)

The 1996 staff review of the RAPs submitted by DOE indicated that there were open issues aspresented in Section 1.5 and discussed in further detail in Chapters 2 through 6 of the draftTER. The NRC staff reviewed all revisions to the RAP submitted by DOE in this regard. All theopen issues (with the exception of several groundwater issues) were resolved, and the NRCstaff can now concur with the proposed remedial action. The NRC staff revised the TER intofinal form, presented here, to include evaluations and conclusions with respect to the additionalinformation submitted by DOE.

The remedial action information assessed by the NRC staff was provided primarily in thefollowing documents (DOE, 1994, 1995, and 1998; MK 1994 and 1998).

1. DOE, 1994, Remedial Action Plan and Site Design for Stabilization of the InactiveUranium Mill Tailings Site at Naturita, Colorado, Final, UMTRA-DOE/AL/62350-40PF,March 1994 (NAT-RAP), Remedial Action Selection Report, including Attachments 1, 3,and 4.

2. MK Ferguson Company, 1998, UMTRA Project, Naturita Remedial Action InspectionPlan, Rev. 1 (April 17, 1998).

3. DOE, 1995, Remedial Action Plan and Site Design for Stabilization of the Naturita Title IResidual Radioactive Materials at the Upper Burbank Repository, Uravan, Colorado, finaldraft, with Appendices A - G (November 1995).


4. .DOE, 1998, Remedial Action Plan and Site Design forStabilization of the Naturita Title IResidual Radioactive Materials at the Upper Burbank Repository, Uravan, Colorado,page changes (June, 1998).

5. DOE, 1998, Remedial Action Plan and Site Design for Stabilization of the Naturita Title IResidual Radioactive Materials at the Upper Burbank Repository, Uravan, Colorado, finaldraft, with Appendices A - G (1998).

6. MK Ferguson Company, 1994, Proposed supplemental standards areas for Naturitaprocessing site and surrounding vicinity properties, 3885-NAT-R-01-01232-00,January 10, 1994.

1.4 TER Organization

The purpose of this TER is to document the NRC staff review of DOE's RAPs and RAIP for theNaturita disposal and processing sites. The following sections of this report have beenorganized by technical discipline relative to the EPA standards in 40 CFR Part 192, Subparts A-C. Sections 2, 3, and 4 provide the technical basis for the NRC staffs conclusions with respectto the long-term stability standard in 192.02(a). Section 5, Water Resources Protection,summarizes the NRC staffs conclusions and remaining open issues regarding the adequacy ofDOE's compliance demonstration with respect to EPA's groundwater protection requirements in40 CFR Part 192. Section 6 provides the basis for the staff conclusions and identifies openissues with respect to the radon control standards in 192.02(b) and soil cleanup standards in192.12.

1.5 Summary of Open Issues

In its review of the preliminary final RAP for the Naturita processing and disposal sites, the NRCstaff identified 26 open issues. Those issues have been satisfactorily addressed by DOE in theFinal RAP with the exception of several groundwater issues that have been deferred until a later-phase of the Uranium Mill Tailings Remedial Action (UMTRA) Project.


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NATURITA TER 1-8 A•PRIL 1999

TABLE 1.1 SUMMARY OF OPEN ISSUES

OPEN ITEMS TERSubsection

STATUSFINAL TER

4 41

DOE needs to provide additional information todemonstrate that Fault 90 is a salt tectonic featureand capable of no more than a magnituae 3 event.The staff will consider this an open issue pendingreceipt of information relating to Fault 90 to showthat the maximum earthquake determined for thesite, magnitude 6.9 at 14.9 km, is a conservativeconclusion.DOE needs to provide information to justify thatthe mean value from the 1994 model of Campbelland Bozorgnia (1994) will be adequate for thedesign acceleration.

2.3.5 and2.4.3

CLOSED

2. Until DOE completes testing of Upper Club Mesa 3.2.4 CLOSEDsoils, those analyses remain an open issue.

3. The PHA value will impact the stability analysis. 3.3.1 CLOSEDFor a PHA higher than 0.3g, a dynamic ordeformation analysis will be required.Determination of a satisfactory PHA with respect toslope stability remains an open issue.

4. DOE needs to address the discrepancy between 3.4.1 CLOSEDspecified radon barrier compaction (100 percent ofmaximum dry density) versus calculated values(95 percent of maximum dry density).

5. The RAP and specification do not address the 3.4.2 CLOSEDproblems associated with compacting a Fat Clay(CH) soil at the 100 percent of Standard Proctormaximum dry density. Since the CH soil must.presumably be compacted wet of optimum, anddesiccation cannot be tolerated, additionaldiscussion is needed in the RAP.

6. The staff is unable to comment on the 3.4.2 and CLOSEDgeotechnical/earthworks aspects of the Remedial 4.4.3Action Inspection Plan (RAIP) or the testing andinspection quality control requirements for theerosion protection materials as an up-to-dateversion of the RAIP was not available during thisreview.


OPEN ITEMS TER STATUSSubsection FINAL TER

7. DOE has not adequately addressed the design of 4.2.5.2, CLOSEDthe upstream apron. DOE needs to: (1) redesign 4.3.2, andthe apron; (2) provide adequate riprap sizes; 4.4.1.2(3) compute peak Probable Maximum Flood flowrates for the upstream apron using concentratedflood flows; and (4) consider natural gullies in theanalysis of the flow rates.

8. The location of the diversion channel outlet near 4.4.1.3.3 CLOSEDthe Uravan Title II cell is not considered to beacceptable. Flows discharging from the diversionchannel could adversely affect the toe of the Title I1cell. DOE should either relocate the outlet of thechannel or provide a revised design to account forflows potentially impacting the Title II cell.

9. A considerable amount of sediment frOrr the 4.4.1.3.4 CLOSEDupland drainage areas can be expected to enterthe diversion channels. To document theacceptability of the channel design, DOE shoulddemonstrate that: (1) the channels will havesediment carrying capacity; (2) potential sedimentdeposition in the channel will not significantly affectthe flow capacity; (3) any blockage in the channelswill not have an adverse effect on the stability ofthe contaminated tailings; and (4) the riprap in thechannel provides adequate protection.

10. The RAP should be revised to provide conclusive 5.2.3 CLOSEDevidence as to whether or not the followingconstituents represent site-specific contaminantsin the alluvium at the processing site: lead, nitrate,and silver. These constituents were excluded fromthe statistical analysis for a variety of reasons.

11. The RAP should provide analyses of the San 5.2.3 CLOSEDMiguel River during low flow periods, in order tosubstantiate that the river has not beencontaminated from the processing site.



12. The RAP should provide specific information about 5.2.4 CLOSEDthe existing wells, including their locations andwater quality, in order to substantiate that existingwells and water uses have not been impacted bythe processing site.

13. A clear strategy and/or short-term measures for 5.0 DEFERREDgroundwater remediation at the processingsite,should be included in the RAP. Short-termmeasures are needed for protection of humanhealth and the environment until a compliancestrategy is developed and implemented. In theabsence of short-term measures, DOE shouldestablish, and include in the RAP, site-specificcompliance standards for the processing site asrequired by the regulations. In addition, DOEneeds to designate a point of compliance for theprocessing site, which will be used to demonstratecompliance with the site-specific standards asrequired by the regulations. If groundwaterremediation at the processing site is planned torely on natural flushing, the RAP needs tosubstantiate that the processing site conditionsjustify such reliance to achieve compliance withthe standards.

14. DOE needs to provide a satisfactory justification 5.4.1 and CLOSEDfor applying supplemental standards consistent Table 5-1with the regulations or apply the primarystandards, including establishment ofconcentration limits and a Point of Compliance(POC) in the uppermost aquifer as required by theregulations.

15. DOE needs to identify site-specific hazardous 5.4.1 and CLOSEDconstituents based on procedures outlined in the Table 5-1EPA standards. All constituents that have beenidentified in the residual radioactive material andthat are also included in Appendix I of 40 CFR Part192 must be included.



16. The Background Water Quality Section of the RAP 5.2.3 CLOSEDshould be revised to include all of the site-specificconstituents, including organic and otherconstituents or provide adequate justification fortheir exclusion. Also, justification should beprovided for the use of data from Well 768 toestablish background, or additional informationshould be provided to support the position that thiswell has not been contaminated by the existingtailings located at the site.

17. The RAP should be revised to include 5.4.4 CLOSEDperformance monitoring at the POC, or by indirectmethods, such as recommended in 40 CFR192.20(a)(4).

18. The R.,P should include a ccmmimrnent to 5.6 DEFERREDundertake corrective action within 18 months torestore system performance to the concentrationlimits originally established for the disposal site, inthe event that such limits are found or projected tobe exceeded.

18A DOE should explain how the concentration limits 5.4.1 CLOSEDfor strontium and tin at the Upper BurbankDisposal site were derived.

19. DOE should provide the additional Th-230 and U- 6.3.1 CLOSED238 data obtained with the cobbly soil study tosubstantiate that adequate characterization ofthese radionuclides has been performed.

20. DOE should provide more soil background Ra-226 6.3.1 CLOSEDdata and correct the soil Ra-226 data in Table 6.1.

21. DOE needs to address how partial remediation of 6.3.3 CLOSEDthe areas proposed for no remediation wouldcause "environmental harm that is clearlyexcessive compared to the health benefits topersons living on or near the site, now or in thefuture" as required by 40 CFR 192.21(b).

22. DOE should remove the former ore storage area 6.3.3 CLOSEDfrom consideration of supplemental standardsunder Part 192.21(c). 1


~K. ~.


23. DOE should discuss possible future uses of all the 6.3.3 CLOSEDsupplemental standard areas in the section onpotential health risks to persons that might occupythe areas.

24. DOE should provide guidance (possibly a 6.3.3 CLOSEDreminder on the extent of excavation) indicatingthat the remediation will come as close to meetingthe otherwise applicable standards as isreasonable under the circumstances.

25. DOE needs to reconsider how muich removal can 6.3.3 CLOSEDbe performed around the gas line withoutincreased unit cost. Also, DOE needs to discusswhat entity has the future responsibility for anycontaminated material excavated from along thegas line and show that the designated entity hasknowledge of its responsibility. In addition,* Ra-226

.data for the area along the gas line should beprovided.

26. As required by 40 CFR 192.22(c), DOE should 6.3.3 CLOSEDprovide copies of any comments from land ownersregarding the proposed application ofsupplemental standards to portions of theirproperty.


A

2.0 GEOLOGIC STABILITY

2.1 Introduction

This section of the TER documents the staffs review of geologic and seismologic information forthe Upper Burbank disposal cell, slated for disposal of the remaining Title I material from theNaturita site. The EPA standards listed in 40 CFR 192 do not irclude generic or site-specificrequirements for the characterization of geologic conditions at UMTRA Project sites. Rather, 40CFR 192.02(a) requires control shall be designed to be effective for up to 1000 years, to theextent achievable, and, in any case, for at least 200 years. NRC staff have interpreted thisstandard to mean that certain geologic conditions must be met in order to have reasonableassurance that this long-term performance objective will be achieved

This review follows the guidance in 40 CFR 192.02, as specified in NRC's SRP for Title IUMTRA sites (NRC, 1993). The review is based on information provided in the Naturita RAP forthe disposal site (DOE, 1998), references cited in the RAP, additional references available in thegeologic literature, and associated documentation pertinent to the proposed remedial action.

2.2 Location

The Upper Burbank cell is located on Club Mesa, an erosional remnant bounded by the SanMiguel and Dolores River valleys, as well as Hieroglyphic Canyon. The mesa lies immediatelywest of Uravan in western Colorado. TER Section 1.2 contains additional location information.

2.3 Geology

The RAP contains a description of the site geology, which is compiled from avariety of maps,books, and journal articles available in the open literature.

2.3.1 Physiographic Setting

The site lies in the eastern portion of the Colorado Plateau physiographic province, a regioncovering much of eastern Utah, northern Arizona, northwestern New Mexico, and westernColorado. The Plateau is characterized by semi-arid climate, elevations mostly over 1500meters, and, with the notable exception of the Paradox Basin, bedrock of generally flat-lyingsedimentary units. The site is in the Canyonlands section of the Plateau, an area characterizedby deeply incised drainages and isolated remnant mesas. The major land forms near the siteare the Uncompahgre Plateau to the northeast and the Paradox Basin to the southwest(Figure 2.1, Page A2-2; DOE, 1998). Club Mesa is one of several mesas between the SanMiguel and Dolores Rivers. Tributaries of these streams have incised the upland between themto define these mesas, which are characterized by bedrock dipping at low angles to thenortheast.

The Uncompahgre Plateau is a northwest-trending upland about 160 km long and 50 km wide.The southwest border is marked geomorphically by the San Miguel and Dolores River valleys,and the northeast border by the Gunnison and Uncompahgre River valleys. The Plateau wasuplifted during the Late Cretaceous-Early Cenozoic Laramide orogeny, presumably due to

,NATURITA TER 2-1 APRIL 1999

reactivation of high-angle faults in the Precambrian basement rocks (Ely and others, 1986). Asthe Precambrian basement was-uplifted, Mesozoic sediments were faulted and folded intomonoclinal structures that presently drape the margins of th P'a' P.au. The Upper Burbankdisposal site lies approximately 10 km southwest of the hinge line marking the base of the.southwest monocline.

The Paradox Basin is a northwest-trending, elliptically Thaped region of relatively low reliefwithin the Colorado Plateau. Its long axis extends over 200 km from near Green River, Utah, toCortez, Colorado. The Paradox Basin is a paleostratigraphic basin that accumulated evaporitedeposits 1-2 km thick in the Pennsylvanian Period. An overburden of clastic sediments shed ina southwesterly direction from the ancestral Uncompahgre uplift, in combination with basementfault blocks trending toward the northwest, caused the salt beds to deform into a series ofnorthwest-trending anticlines and synclines from the Pennsylvanian through Jurassic Periods.Overlying Mesozoic sediments were folded during this episode of salt diapirism. Subsequentdissolution of salt has caused some subsidence of the Mesozoic units, and deformation duringthe Laramide Orogeny may have further folded Paradox Basin sediments. The northeastern-most anticline of the Paradox Basin underlies the Paradox Valley, approximately 5 kmsouthwest of the site. Club Mesa lies between the Uncompahgre Plateau and Paradox Basin.

Based on a review of the RAP (DOE, 1998) and otfer references', the staff finds thephysiographic setting to be adequately characterized.

2.3.2 Stratigraphic Setting-.

The Upper Burbank site is underlain by a sequence of Mesozoic and Paleozoic marine andcontinental sedimentary rocks (Figure 2.1). A thin sequence of pre-Pennsylvanian limestonesand shales may overlie Precambrian basement at considerable depth, but these rocks are notexposed in the site area. The Pennsylvanian Hermosa Group comprises the evaporites thathave experienced ductile deformation throughout the Paradox Basin. This unit is interpreted tobe thin and deep beneath the site, although it thickens rapidly where it crops out at the core ofan anticline 6 km southwest in the Paradox Valley. The Permian Cutler Formation, a sequenceof continental clastics derived from the ancestral Uncompahgre highlands, is several kilometersthick beneath the site. The Triassic Moenkopi and Chinle Formations, both shallow waterclastics with minor limestone, are separated from the Cutler Formation, and from each other, byunconformities. The Moenkopi and overlying Chinle are relatively thin in the site area(approximately 30 and 60 m, respectively), and only the Chinle has minor exposure. TheTriassic Wingate Sandstone and Kayenta Formation (sandstone and siltstone) are conformableover the Chinle, are each about 60 m thick near Uravan, and likewise exposed only in deeplyincised channels. The water table is near the Wingate-Kayenta boundary beneath the UpperBurbank cell. The Jurassic Navajo Sandstone conformably overlies the Kayenta Formation.RAP Table 2.1 (Page A2-10; DOE, 1998) states that this formation is not found atthe site area,but is found in the western part of the site region. However, RAP Figure 3.2 (Site Area, GeologicMap; DOE, 1998), shows Navajo Sandstone exposed in the bottom of Hieroglyphic Canyon nearthe confluence with the San Miguel River, less than 2 km northeast of the Upper Burbankdisposal cell.


SandaWM ne sf VqtrrerMf. 0=0"-ronW, light grgy. yello W 0.if ooh .oeomw awrowl" uo wwriao~us vm an m or cowa.

Sanoan one cong0forlW'4 wrU. gry. man red. Poony sorted. o0i-oodeadaIS)a-ed24110in Ocsole' OoM44 tr=SV Of 0r0t¶ in MWLiW. fjMfL altO lentiCjiw WUWa: mnUagon.snm. origf: green. thin wumse c4 wnsmiemo. miru cvwn&aaotA WW".

Shao amt rymdowf. wnftI. Oslo tedan green. DCMWfimif thin bsd. cll'aMfed, wrvibooftawrit d"a ruum -Mc OdAr-0ed00 th~~leU.in bde" of nsaloan StV a low hUij1Iot layo.iW

Sandsmmwlon. otuv. Wl Me 0 VWa, ihot buff Wrd nrust-fed. &am. 00 M* ,ff-qrniii~ OVu-00aod,musive. 1#acuw. vntn safle ano rmjostoflO red, green, or light gray, oczaswwa leons.ormnesn.

*--Upper Burbank Repository

Shaje. rsd. SwXI, adry, Nfl-boWdd.d intlbedded vnlt iun-ý.dd so4wrimil.a&M n~jw~no.

Sardsow. quwau orange, buff, and wtum. Wag edia~m crossedmng.

sawdwm, quartnz, buf. an wtuw. Min libeddd, a%=g Pbedded

-. S~umm.mudemna. and swiuleftis red In bu". omsonely Ight grown

Suidsmno. quaiu. dark reddish brown to buff, gray, Urthindeld caowabofdedw rbam oood won dam moodsh beamilumno afd a~e.

Sw~amwn, red D ",A finesyawid. musive, qeeialn,.y riose*dedinq, dweset vwruh oný 0 a' amto.

Sims. orange U red. ~~edded wit' ina.gr~rwd. aamdaene. ehaj. and kneemne,

FIGURE 2.1. STRATIGRAPHY OF THE UPPER BURBANK SITE.


Approximately 40 m of Jurassic Entrada Sandstone unconformably overlies the NavajoSandstone. The Entrada forms steep slopes in the lower portions of Club Mesa. TheSum,, irville Formation, a marine shale with .siltstone, is conformable over the Entrada. Thisunit is about 30 m thick near the site, and it serves as an aquitard inhibiting vertical fluidtransport. The Jurassic Morrison Formation, which serves as the cap rock of Club Mesa,overlies the Summerville Formation. The lower Salt Wash Member of the Morrison Formation isthe host rock for the tailings cell. This highly competent, fluvial sandstone and siltstone unit ismore than 100 m thick at Club Mesa. Immediately up-slope of the cell (southwest) is the base ofthe Brushy Basin Member of the Morrison Formation. Over 100 m of variegated shale,mudstone and sandstone of the Brushy Basin are present on Club Mesa. A remnant of theCretaceous Burro Canyon Formation remains at the highest elevations of the mesa,approximately 1.5 km west of the Upper Burbank cell. This remnant consists of approximately50 m of fluvial sandstone overlain by shale-mudstone. Any Tertiary units that may have beenpresent in the site area have been removed by erosion.

NRC finds that DOE has sufficiently described the stratigraphy of the site area.

2.3.3 Structural Setting

The site lies within the eastern portion of the Colorado Plateau, a relatively stable,intracontinental subplate with greater crustal thickness than adjacent provinces. Two majorshear zones were established in Precambrian time, and these features appear to exert somecontrol on the Plateau features present today. The northwest-trending Olympic-WichitaLineament extends from Washington to Oklahoma; the Uncompahgre uplift and Paradox Basinlie within this trend. The northeast-trending Colorado Lineament extends from Arizona toMinnesota and may have some relation to localized northeast-trending areas of seismic activityin the Colorado Plateau (Bernreuter and others, 1995). These broad lineaments intersect withinthe site region. The Colorado Lineament apparently served as a preferred pathway for Tertiarymagmas as they intruded Mesozoic sediments. The Miocene laccolithic intrusions of the La SalMountains are in the junction zone of the Colorado and Olympic-Wichita lineaments.. In addition,Abajo Mountain, a similar intrusion, is within the Colorado Lineament farther to the southwest.Club Mesa exhibits two orthogonal fracture sets, northeast and northwest trending, but these areregional sets that are probably not related to the lineaments.

The site lies several kilometers northeast of the Paradox Valley anticline, which contains stratafaulted and folded from salt diapirism and, perhaps, Laramide deformation. Some northwest-trending faults are associated with this anticline. Several kilometers northeast of the site is theUncompahgre Plateau, which was uplifted along basement-rooted, steeply dipping, curvedreverse faults (Ely and others, 1986) during the Laramide Orogeny"(Late Cretaceous to Eocenetime). These faults may be associated with shallow-rooted normal faults that compensate forcurvature in the reverse faults as they plunge beneath the Precambrian core of the uplift. Somestructures bounding the Plateau remain seismically active today, though possibly fromreactivation as extensional structures. The bounding fault, labeled Fault 81 by Kirkham andRogers (1981), has no historical seismicity, but was determined to be capable. This fault isresponsible for the design earthquake of the Upper Burbank site (see TER Section 2.4.3).


Club Mesa lies on the southwest limb of the northwest-trending Nucla syncline. This broad,shallow syncline lies between the salt-cored Paradox Valley anticline, the northeastern-mostanticline of the Paradox Basin, and the faults and monoclinal folds marking the southwestmargin of the Uncompahgre Plateau. The strata of Club Mesa dip homoclinally to the northeastat 1 to 3 degrees.

The staff finds that the structural setting has been adequately described.

2.3.4 Geomorphic Setting

There is considerable topographic relief near the Upper Burbank site due to both tectonic upliftand erosional denudation processes. Between Uravan in the San Miguel Valley (about 1525 melevation) and the crest of the Uncompahgre Plateau 20 km northeast (3000 m), there is nearly1500 m of relief. The Upper Burbank cell is approximately 200 m above Uravan on the easternmargin of Club Mesa, in a quarry into the Salt Wash Member of the Morrison Formation. ClubMesa is bounded on the north by the San Miguel River valley, the east by Hieroglyphic Canyon,-and the west by the Dolores River valley. The southwest margin of the mesa is marked by atributary of the Dolores River. The mesa is approximately 4 km east to west and 5 km north tosouth. The mesa edges are generally steep, supported by the resistant Salt Wash Member andEntrada Sandstone. The site is drained by side drainages of Hieroglyphic Canyon.

Both the San Miguel and Dolores Rivers are undersized for their valleys, indicative of greaterrunoff during Pleistocene deglaciation. The braided channel patterns and wide valleys of theserivers contrast with the steep, narrow valleys of their tributaries and the dendritic drainages oftributary headwaters. Since Miocene time, the major geomorphic processes in the area havebeen incision and widening of major stream valleys. Valley widening occurs largely throughscarp retreat. Mesa cliffs consist of resistant sandstones, and retreat occurs primarily by masswasting of more erodible underlying units.

NRC considers that the RAP adequately describes the geomorphic setting.

2.3.5 Seismicity

The Naturita site lies within the interior of the Colorado Plateau physiographic province. The siteis subject to seismic events in the Colorado Plateau, the Plateau's more seismically activeborder zones, and the surrounding.tectonic provinces. The border zones are defined byKirkham and Rogers (1981) based on structural boundaries and trends in seismicity. The

Colorado Plateau is bounded on the south and west by the Basin and Range Province, the eastby the Western Mountains Province, and the north by the Uinta-Elkhead and Wyoming BasinProvinces.

There is some debate about the precise geographic boundaries of the provinces and Plateauborder zones, but there is little question that seismicity overall is greater around the marginsthan within in the Plateau (Kirkham and Rogers, 1981). The interior of the Colorado Plateau is aregion of relatively low seismicity. The closest areas of moderate seismicity are located at theboundaries of the Colorado Plateau With surrounding provinces. The largest historical event inthe Colorado Plateau west of the site was a 1988 magnitude 5.5 event near the Wasatch fault

NATURITA TER 2-5 APRIL. 1999

zone. At the northeast edge of the Colorado Plateau, the largest events were magnitude 5.3and 5.4 earthquakes in 1969 and 1973. At the southeast edge of the Colorado Plateau, thelargest events were two magnitude 5.1 earthquakes in 1966 and 1967, and at the southwestedge, the largest event was a 1959 magnitude 5-1/2 to 5-3/4 earthquake in northern Arizona.

Any characteristic seismic event in the Plateau boundaries or adjoining provinces would be toofar away (>50 km) to adversely impact the site. Historical seismic records show less than adozen earthquakes of magnitude 5 or greater within the Colorado Plateau, and all of these wereproximal to the margins. An 1882 earthquake with magnitude estimated at 6.5 or greater mayhave been centered on the northeast margin of the Plateau (McGuire and others, 1986),although more recent evidence places. the epicenter in the Colorado Front Range (Kirkham andRogers, 1986).

There are several regional structural features within the Colorado Plateau that contribute to thesite's seismic hazard: the Colorado Lineament, the Paradox Valley fault system, and theUncompahgre uplift. Many small seismic events have occurred along specific segments of theColorado Lineament in the past. However, these spatially limited earthquake swarms havediffering characteristics, and, overall, the lineament does not appear to be a major seismogenicstructure (Brill and Nuttli, 1983). Bernreuter and others (1995) believe that a 50 km longbasement fault beneath the Colorado River south of IMAoab, Utah, may be capable of an evenc aslarge as magnitude 7, but with very low probability. This section of the Colorado Lineament ismore than 100 km west of the site. The staff notes that Section 2.10.2 of the RAP (DOE, 1998)misinterprets Bernreuter and others, (1995) regarding the name of this seismic zone.Bernreuter and others (1995) do not label this northeast-trending zone the Moab fault. Thoseauthors recognize the Moab fault to be a northwest-trending structure most likely due to salttectonics.

Ten to fifteen kilometers southwest of the site, the northeastern limb of the Paradox Valleyanticline hosts several structures, one of which is a 62 km long fault labeled as Fault 90 byKirkham and Rogers (1981). The RAP states that this and parallel faults of Paradox Valley arealmost certainly underlain by structures related to evaporite flow or dissolution. Hunt (1969) andCater (1970) are cited as support for this interpretation. The RAP states that, because of thisrelationship, the normal fault length-magnitude relationships do not apply; therefore, Fault 90'isinterpreted to be capable of no more than a magnitude 3 event.

NRC requested additional information to demonstrate that Fault 90 is rooted in the saltstratigraphy, and, thus, is capable of no more than a magnitude 3 event and exempt fromstandard fault length-magnitude relationships. The 1998 update to the RAP (pages A4-5 toA4-7) provided additional information on faults associated with collapse of salt anticlines in theParadox Basin and similar faults in other parts of the Colorado Plateau. Thefaults related to saltanticlines are not associated with the underlying tectonic system and the ages of movement onfaults -related to.salt flow is pre-Quaternary. Thus, these faults are not capable. Similar faultsassociated with salt structures in the Paradox Basin were investigated for the Slick RockUMTRCA Title I site (NRC, 1996). In their review of the Slick Rock site, the NRC staff concludedthat these collapse-induced faults are considered non-tectonic since they result from down-dropping sedimentary rocks that overlie areas of salt removed by flow and dissolution. Theobserved seismicity associated with salt flowage is magnitude 3 or less and, thus, not significant


compared to the design earthquake at the Naturita site (magnitude 6.9 at a distance of 15 kmfrom the site). The tectonic character of Fault 90 is now a closed issue.

Steeply dipping faults associated with the Uncompahgre uplift approach the site as close as 15km, and at least one of these faults appears to be historically seismogenic. In 1985, an event ofmagnitude 2.9 centered 55 km north-northwest of the site may have occurred along the steeplynortheast-dipping Granite Creek fault (Ely and others, 1986). There is some question whethermovement of the Uncompahgre uplift is continuing to occur or whether this seismicity resultsfrom reactivation of reverse faults as extensional features. Cater (1966) states that the upliftcontinues today; however, Ely and others (1986) believe that the 1985 event was extensional.The Uncompahgre-related structure.that passes 15 km from the site is called Fault 81 byKirkham and Rogers (1981). Cater (1970) found.this fault to have Quaternary offset, so it isconsidered to be capable. With a length of 34 km and possibly capable of a magnitude 6.9event, this is the design fault for the site.

NRC concludes that DOE presents adequate information on the historical seismic events of theColorado Plateau and surrounding areas of interest.

2.3.6 Natural Resources

The site region contains natural resources of oil, natural gas, uranium, vanadium, coal, andpotash; the immediate area features abundant uranium and vanadium. Deposits of theseminerals are concentrated in the Salt Wash Member of the Morrison Formation, which is thedisposal cell host rock. However, boreholes surrounding the site indicate no economic depositsbeneath the tailings cell (Umetco and Peel, 1994). Economic deposits of oil or gas are veryunlikely, as the site lies near the axis of a low, broad syncline. No faults that may serve ashydrocarbon traps are close to the site. Large oil and gas deposits in the area are generallyassociated with the salt anticlines of the Paradox Basin to the southwest. Potash is mined fromthe Paradox Salt Member of the Pennsylvanian Hermosa Formation; although, the only currentproduction is more than 100 km from the site. Any deposits near the site are likely too deep tobe economically viable. The Dakota Sandstone.contains coal deposits in the region, but this unithas been eroded. from Club Mesa. Mining occurs in the San Juan Mountains to the southeast,but mining in that area is in igneous units that are not present in the site area. NRC finds theRAP adequately describes natural resources in the area.

2.4 Geologic Suitability

In an effort to provide reasonable assurance that radiological barriers will remain intact for atleast 200 years, and up to 1000 years to the extent achievable, the RAP provides information onthe bedrock, geomorphi~c, and seismic stability of the site.

2.4.1 Bedrock Stability

The Upper Burbank cell is an excavation entirely within the Salt Wash Member of the MorrisonFormation, a competent sandstone and siltstone unit. Thirty-five meters of the Salt Wash unitlies between the base of-the cell and the underlying Summerville Formation; no soil lies beneaththe cell. Rock durability studies (Umetco, 1995) suggest that portions of the Salt Wash Member

NATURITA TER 2-7 APRIL .1999

are the most erosionally resistant horizons in the local stratigraphic column, one indication ofstability. The Salt Wash is moderately fractured in vertical, orthogonal northeast- and northwest-trendig sets, with average spacing approximately 1 meter. The Summerville Formation is aneffective aquitard beneath the Salt Wash Member. Water 'o-riginally within the tailings cellsnortheast of the Upper Burbank cell has caused a zone of perched raffinate to form on top of theSummerville, but this is down-dip and down-gradient of the Upper Burbank cell. The low dip ofthe contact, the thickness of the overlying Salt Wash Member, and the coherent elastic strengthof layers and their interfaces indicate that slip along the Salt Wash-Summerville contact plane isvirtually impossible, even with the addition of a perched water table. The closest mapped faultsrelated to the salt anticline and collapse structures of the Paradox Valley are 4 km from the site.Therefore, the cell is not at risk of displacement due to fault offset.

The staff considers that the RAP adequately addresses -the topic of bedrock stability.

2.4.2 Geomorphic Stability

Given the location of the Upper Burbank cell on Club Mesa, the cell has potential fordestabilization by mesa scarp retreat. Scarps at the edge of Hieroglyphic Canyon and SanMiguel River valley will continue to retreat, but long-term erosion rates are low. The San MiguelRiver appears to be presently incising its channel from Jravan several miles downstream, and,at the same time, it is either aggrading or migrating across its flood plain upstream of Uravan.The channel incision is not-expected to exceed the maximum average rate of 0.4 m perthousand years (Hunt, 1956; Yeend, 1969; Larson and others, 1975) for the Colorado Riversystem in the Colorado Plateau. The San Miguel River tributaries, such as HieroglyphicCanyon, are also unlikely to exceed this rate. Canyon widening (scarp retreat) may occur at arate 3 times that of incision, or upto 1.2 m/1000 years. Mass wasting of large fracture-boundedblocks can lead to high rates of scarp retreat, but the absence of large block accumulations orconical colluvium mounds at scarp bases in the area, as well as the smoothness of canyonwalls, indicates that this is not a concern. Moreover, scarp retreat rates on the order of 1m/1000 years in the site area have been documented by dating packrat middens and applyingother geochronologic methods (Smith, 1980). NRC concludes that scarp retreat of-San Miguel,River valley and Hieroglyphic Canyon does not'pose a threat to the site during cell life.

Headward erosion by Hieroglyphic Canyon tributaries that drain the site will not affect the cell,because it will sit 230 m from the canyon rim. Runoff from the mesa surface, up-slope of the cellwill be redirected to avoid the cell. This is discussed further in TER Section 4.4.

The .site is not at risk from debris flows, soil creep, rock falls, or eolian processes. No largeeolian features, such as dunes or sand ramps, are apparent in the area; although, such featuresare not specifically addressed in the RAP. Subsidence from salt dissolution is not a hazard inthe immediate vicinity, as any evaporites that may underlie the site are interpreted to be 2-3 kmdeep and relatively thin. The area has extensive uranium and vanadium deposits, but boreholesindicate no economic deposits beneath the Upper Burbank site. None of the many .mine aditson Club Mesa pass beneath the cell. The site is subject to ash fall from very large volcaniceruptions in the Western United States, but the probability of such an event occurring.over thelifetime of the cell is negligible.

NATURITATER 2-8 APRIL 1999

The RAP presents sufficient evidence that Club Mesa and the tailings cell will be geomorphically.stable far beyond the 1000-year performance period.

2.4.3 Seismotectonic Stability

The Club Mesa site is subject to ground motion from seismicity on faults associated with theUncompahgre uplift, as well as floating earthquakes in the Colorado Plateau, and seismicitylocated within the Colorado Lineament. Seismicity along the southwest margin of theUncompahgre uplift appears to present the greatest hazard to the site.

The RAP identifies Fault 81 of Kirkham and Rogers (1981) along the Uncompahgre margin asthe controlling fault for seismic hazard at the Upper Burbank site. Although this fault shows nohistorical seismicity, it has Quaternary offset based on geomorphic relationships observed inUnaweep Canyon (Cater, 1970). The fault is 34 km long, passing within 14.9 km of the cell.The RAP states that this fault is capable of a magnitude 6.9 earthquake based on the faultlength-magnitude eelationship of Bonilla and others (1984). The precise dip is unknown, but thefault is suspected to be steeply dipping. Section 4.2.7 of the RAP states that a magnitude 6.9event from Fault 81 at 14.9 km would produce a peak horizontal ground acceleration (PHA) of0.28 g at the site using the attenuation relationship of Campbell and Bozorgnia (1994). DOEstated in the RAP that 0.28g is the median value from this 1994 attenuation model.

The SRP for Title I sites (NRC, 1993) states that the 84th percentile ground motion value fromthe Campbell (1981), model could be adopted as the design value. This level of ground motionwas chosen because of the limited number of accelerograms available at that time to developattenuation relationships. Since 1981, updated ground motion attenuation relationships havebeen published based on more accelerograms, thus, providing confidence that the 5 0 th

percentile (median) value of ground motion is acceptable. In addition, a recent staff analysis ofthe risk associated with uranium recovery facilities led the staff to conclude that because of therelatively low risk posed by tailings piles, the choice of ground motion level at the 84th percentileis too conservative. For these reasons, the recent draft SRP for Title II sites (NRC, 1999) foundthat an acceptable level of design for UMTRCA sites is the 50th percentile (median) value ofground motion. Thus, the RAP value of 0.28g is adequate for the design acceleration.

The RAP uses 6.2 as the maximum magnitude for a floating earthquake in the site area.Magnitude 6.2 has been used at other UMTRCA Title I sites within the Colorado Plateau, suchas Slick Rock and Mexican Hat. This maximum magnitude is conservative because it is largerthan the historical earthquakes associated with the Colorado Plateau province. PHAcalculations for a floating earthquake assume an epicentral distance of 15 km, so the siteground motions from the floating earthquake .PHA are below the design ground motion fromFault 81.

Seismic zones within the Colorado Lineament may be capable of generating events as large asmagnitude 7 with low probability (Bernreuter and others, 1995), but the distance of such zonesfrom the site exceed 100 km. Therefore, site ground motions resulting from.such events are alsowell below the design ground motion for the site.


The staff concludes that a magnitude 6.9 earthquake associated with Fault81 and at a distance

of 14.9 km from the site is a conservative maximum earthquake for the site.

2.5 Conclusions

Based on a review of the RAP (DOE, 1998) and additional material, NRC finds that the geologyand geologic stability of the Upper Burbank disposal cell have been adequately characterized.


3.0 GEOTECHNICAL STABILITY

3.1 Introduction

This section presents-the results of the NRC staff review of the geotechnical engineeringaspects of the proposed remedial actions at the Naturita, Colorado, UMTRA Project site, asdetailed in DOE's RAP (DOE, 1998a and 1998b) and Remedial Action Inspection Plan (RAIP,MK-F, 1998): The remedial action consists of the removal of all remaining contaminatedmaterials from the processing site to the Upper Burbank disposal cell 13 road miles northwest ofthe Naturita processing site.

The disposal cell will be below-grade and will provide for the segregation of the Title I materialfrom other radioactive material at Uravan. Contaminated material will be consolidated andencapsulated in the cell and will be covered by a 3-foot-thick compacted earth radon/infiltrationbarrier, a 5.5-foot-thick compacted earth frost barrier, a 0.5-foot-thick bedding layer, and a1-foot-thick rock riprap layer. The geotechnical engineering aspects reviewed include:(1) information related to the processing, disposal, and borrow sites; (2) materials associatedwith the remedial action, including the foundation and excavation materials, building debris, andother contaminated materials; and (3) design and construction details related to the disposalsite, disposal cell, and its cover. The staff review of related geologic aspects such asstratigraphic, structural, geomorphic, and seismic characterization of the site is presented inSection 2.0 of this report.

3.2 Site and Material Characterization

3.2.1 Site Descriptions

3.2.1.1 Processing Site

The processing site (Figure 1.2) is located in Montrose County, Colorado, on Highway 141, twomiles northeast of the town of Naturita. The Naturita processing site includes the following,features: (1) the abandoned Naturita mill yard; (2) the former tailings pile area that is located onthe floodplain of the San Miguel River between Highway 141 to the west and the San MiguelRiver to the east; and (3) the former ore storage area located to the west of Highway 141.

During 1976-77, the tailings at the Naturita processing site were transported for furtherprocessing to the Durita Facility heap leach plant. Although the Naturita processing site nolonger has a tailings pile, the site has 400,000+ cubic yards (cy) of residual contamination that isdistributed approximately as follows:

- Contaminated soil (389,000 cy)- Stockpiled demolition debris (8,300 cy)- Stockpiled vicinity property (VP) materials (3,000 cy)- Stockpiled drums (55 gal) containing processing waste petroleum products

(72 cy)- Stockpiled bags (approx 18 cu ft ea) with asbestos-containing materials (665 cy)


DOE reports that actual quantities could vary from those tabulated above.

3.2.1.2 Disposal Site at Uravari

The Upper Burbank disposal site at Uravan is about 13 road miles northwest of the Naturitaprocessing site (Figure 1.1). The embankment will be located slightly to the south of a drainagedivide, and it will be necessary to accommodate only minor amounts of offsite runon plus therunoff from the surface of the disposal cell. The disposal cell will cover approximately 10 acresand will be designed to contain from 500,000 to 800,000 cy of contaminated materials. Theactual cell size will depend on the extent of contaminated materials excavated duringconstruction. The top slopes of the embankment will range from 2 to 4 percent, and thesideslopes will be 5H:1V. The disposal cell configuration is shown in Figure 1.4 and crosssections through the cell are shown in Figure 1 .5.

The Upper Burbank Repository is located in the northwestern part of the Upper Burbank Quarry,and is entirely underlain by sandstone and shale of the Salt Wash Member of the MorrisonFormation. See Section 2.3.2 of this TER for a more detailed description of the stratigraphicsetting.

3.2.1.3 Borrow Materials Site

The borrow material for the radon barrier and frost protection layer will be obtained from theUpper Club Mesa borrow site, which is approximately 1500 feet northwest of the Upper Burbankdisposal site.

3.2.2 Site Investigations

Geotechnical investigation and site characterization programs were performed at the mill site,the disposal site, and the borrow site. Data obtained during the characterization programs werereported in Appendix D to the RAP (DOE, 1998b).

The scope of the geotechnical investigations included excavating test pits and drilling boreholes.Information from several monitor well installations was also utilized. Borings and test pits werelogged by a field engineer or geologist. The locations of test pits, boreholes, and monitor wellswere given in the RAPs. Subsurface investigations for material properties of the underlying soilat the processing site were carried out in conjunction with the investigation to define the limits ofcontamination. The resulting samples of site materials were tested and analyzed in thelaboratory to evaluate the engineering characteristics of the materials.

Test pits were excavated with a backhoe. Bulk soil samples were collected from the pits.Individual borehole logs provide detailed information about the drilling methods used. Generally,hollow-stem augers (6.5-inch) were used until refusal; thereafter, a rotary bit (4.0 inches) andcasing were used to bedrock. Three sampling methods were used: (1) the StandardPenetration test; (2) a 2.42-inch inside diameter, ring-lined, split-barrel sampler; and (3) a 3.0-inch diameter, thin-walled Shelby tube.


The available data obtained from the field investigations and laboratory tests were used toconstruct stratigraphic sections and to define the engineering parameters of the soils to beincorporated into the cell.

3.2.3 Upper Burbank Disposal Site Stratigraphy

The Upper Burbank disposal cell is on a bedrock bench approximately 600 feet above the SanMiguel River. The bedrock beneath the disposal cell consists of sandstone of the Salt WashMember. The bedrock at the site is reported to be stable, and the sandstones at the contactbetween the Salt Wash Member and the Summerville Formation are reported to be dry.Additional stratigraphic information and a column are found in Section 2.3.2 of the .TER.

The staff has reviewed the details of the test pits and borings, as well as the scope of the overallgeotechnical exploration program discussed in Section 3.2.2 above. The staff concludes thatthe geotechnical investigations conducted at the Naturita processing and Upper Burbankdisposal sites, and at the Upper Club Mesa borrow site, adequately establish the stratigraphyand the soil conditions, generally conform with applicable provisions of Chapter 2 of the SRP(NRC, 1993), and adequately support the assessment of geotechnical stability of the stabilizedcontaminated material in the disposal cell.

3.2.4 Testing Program

The materials at the three sites were classified according to the Unified Soil Classificationsystem (ASTM D-2487). Atterberg limits (ASTM D-4318) and gradation tests (ASTM D-422)were performed on selected samples to classify the soils. In addition, the following tests wereconducted: specific gravity (ASTM D-854), compaction (ASTM D-698), saturated andunsaturated hydraulic conductivity, consolidation (ASTM D-2435), shear strength (EM 1110-2-1906), radon barrier erodibility (Crumb test, STP 623; dispersion, ASTM D-4221; and pinhole,STP 623), capillary-moisture relations (ASTM D-3152), and erosion barrier durability. Theresults of the individual tests completed to date are included in the RAP.

The testing program for the processing, disposal, and borrow sites was consistent with theneeds of the proposed remedial action; representative samples of construction materials andsamples of geotechnical materials that may affect or be affected by the remedial action weretested. The number of samples tested is considered sufficient to support the necessarygeotechnical analyses described in subsequent sectiors. In particular, the testing approach isconsistent with the NRC SRP and the DOE Technical Approach Document (DOE, 1989).Samples were tested in accordance with standard procedures, and quality assurance andquality control were performed in accordance with standard UMTRA Project procedures.Therefore, Open Item No. 2, regarding testing of the Club Mesa soils, is closed.

3.3 Geotechnical Enginreering Evaluation

3.3.1 Slope Stability Evaluation

The staff has reviewed the exploration data, test results, critical slope characteristics, andmethods of analyses pertinent to the slope stability aspects of the remedial action plan for the


!-I

Naturita UMTRA Project disposal embankment. The analyzed cross-section with the longest 5horizontal to 1 vertical sideslope has been compared with the exploration records and thedesign details. The staff finds that the most critical slope sectic - has been considered for thestability analysis.

Soil parameters for the various materials in the stabilized embankment slope have beenadequately established by appropriate testing of representative material. Values of parametersfor other earthen materials have been assigned on the basis of data obtained from geotechnicalexplorations at the site and data published in the literature.

DOE has proposed applying a peak horizontal ground acceleration (PHA) of 0.28g as discussedin Section 2.4.3. For a PHA of less than 0.3g, staff finds that the DOE evaluation has employedthe appropriate methods of stability analysis (Bishop's Simplified Method, Ordinary FelleniusMethod, Janbu's Simplified Method, and Spencer's Method) and has addressed the likelyadverse conditions to which the slope may be subjected.

Factors of safety against failure of the slope for seismic loading conditions and static loadingconditions were evaluated conservatively for both -the short-term (end-of-construction) and long-term state on the basis of a PHA equal to 0.3g. The values of the seismic coefficients used inthe pseudo-static analysis are 0.20g for the long-term condition and 0.15g for the short-termcondition. The staff finds that the use of the pseudo-static method of analysis for seismicstability of the slopes is acceptable considering the flatness of the slopes and the conservatismin the soil parameter values, if the PHA is less than or equal to 0.3g. The minimum factors ofsafety against failure of the slope were 2.19 and 1.22 for the short-term static and pseudo-staticconditions, respectively, compared to required minimums of 1.3 and 1.0, respectively. Theminimum factors of safety against failure of the slope were 3.58 and 1.73 for the long-term staticand pseudo-static conditions, respectively, compared to accepted minimums of 1.5 and 1.0,respectively. The analyses appear to have been made in a manner consistent with Chapter 2 ofthe NRC SRP. Open issue No. 3 is closed with the satisfactory selection-of the design PHA.

3.3.2 Settlement and Cover Cracking

The staff has reviewed the analysis of total and differential settlement of the disposal cell andfoundation materials and the resulting potential for cracking of the radon barrier. Calculationsindicate that all settlement due to placement of the relocated contaminated materials, radonbarrier, frost protection layer, and erosion protection willinclude immediate (elastic) andsecondary (creep) components. The foundation is assumed to be incompressible, because itwill consist of competent bedrock.

Fifteen point locations on section A-A' and 13 point locations on section B-B' (Figures 1B and2B, Appendix D, DOE, 1995) were selected for settlement analysis for both 500,000 and800,000 cu yd cover options. The staff agrees that appropriate sections have been chosen toassess the most critical conditions for differential settlement. Calculated settlements along theprofiles varied from 3 inches to.9.5 inches (section A-A') and 7.5 inches to 10.5 inches (sectionB-B') for the 500,000 cy cover, with resulting maximum local slopes of 0.005 and 0.0075,respectively. Calculated settlements along the profiles varied from 4 inches to 21 inches


(section A-A') and 3 inches to 21 inches (section B-B') for the 800.000 cy cover, with resultingmaximum local slopes of 0.007 and 0.014, respectively.

The maximum tensile strain was determined to be 0.00054 (section A-A') and 0.00020 (sectionB-B') for the 500,000 6y cover option, and 0.000068 (section A-A') and 2.3 x 10.20 (section B-B')for the 800,000 cy cover option.' The calculated tensile failure strain for the proposed radonbarrier material (PI=30) was 0.14 percent.

DOE has concluded that total and differential settlement of the materials comprising theproposed disposal cell will not have an adverse effect on the ability of the cell to meet thestability standards. The staff agrees that settlement generally will be small due to thecompaction of the materials in the cell and the granular nature of much of the material. Inaddition, differential settlement should not cause ponding concerns due to the slopingconfiguration of the cell, and cracking of the cover due to settlement should not occur becausethe resulting maximum strain is well below the calculated tensile failure strain.

3.3.3 Liquefaction

The staff has reviewed the information presented on the potential for liquefaction at the sitebased on the results of geotechnical investigations, including boring and test pit logs, test data,soil profiles, and other information. The soils in the disposal cell will be compacted to aminimum of 90 percent of maximum Standard Proctor density (ASTM D-698) and will be in anunsaturated condition; therefore, the disposal cell is not considered susceptible to liquefaction.The groundwater table at the site is substantially below the base of the disposal embankment.The foundation beneath the disposal cell is stable bedrock and, thus, not susceptible toliquefaction. Because of the absence of water and liquefiable soil, there is no potential forliquefaction of material within or beneath the disposal cell and, therefore, applicable provisionsof Chapter 2 of the NRC SRP have been met.

3.3.4 Cover Design

The cover system will provide a total of 10 feet of protection over the contaminated material andcollectively is designed to limit infiltration of precipitation, protect the pile from erosion, andcontrol the release of radon from the cell. In addition to the discussion of the cover presented inthis section of the TER, details of the staff review of the cover's performance related to erosionprotection features are presented in Section 4.0 of this document; the review of the cover'sperformance related to limiting infiltration is presented in Section 5.0; and the review of theradon attenuation aspects of the cover is presented in Section 6.0.

The RAP (DOE, 1998a and 1998b) indicates that the radon/infiltration barrierwill consist ofcompacted, silty-to-clayey soil that will limit infiltration and inhibit radon emanation. Thegradation requirements call for a minimum of 50 percent by weight passing the No. 200 sieve.Testing has indicated that the borrow soil should generally meet the requirements, and thatinspection procedures will verify gradation. Test results indicate that radon/infiltration barriermaterial, when compacted to at least 95 percent of maximum dry density (ASTM D-698), willproduce a laboratory-saturated permeability on the order of 10-7 cm/sec.


The frost protection layer will consist of materials excavated from the Club Mesa borrow area.DOE has evaluated the frost depth using the BERGGREN.BAS computer code developed at theU.S. A, my Corps of Engineers (COE, 1968). This code has been used fc- cther UMTRA sites.The total worst-case 200-year frost penetration depth at the disposal site is calculated to be 44.1inches. The cover design provides for the appropriate depth by the total thickness of riprap (12inches), bedding (6 inches), and frost protection layer (60 inches) above the radon barrier. Thestaff has reviewed the input data used in determining the total frost penetration depth, andconcluded that these values are a reasonable representation of the extreme site conditions to beexpected in a period of 200 years. Because DOE's calculation was based on the 200-yearrather than the 1000-year frost depth, actual frost penetration is likely to be somewhat in excessof the stated values. NRC staff accepts this approach for the Naturita site because theadditional frost penetration, if it were to occur, would not adversely affect the stability of the cell.

The RAP indicates that the layer immediately above the frost protection layer is to be a 6-inch-thick bedding/drain layer, intended to draih water laterally off the cell and protect the radonbarrier from the riprap. Details of the review of the erosion protection design are found inSection 4.0 of this report.

The cover design has been evaluated by NRC staff for geotechnical long-term stability, and, forthese aspects, the design is acceptable.

3.4 Geotechnical Construction Details

3.4.1 Construction Methods and Features

The staff has reviewed and evaluated the'geotechnical construction criteria provided inAppendices D and G to the RAP (DOE, 1998b). Design calculations and constructionrequirements were based on achieving 95 percent of standard compaction for the radon barriersoils. The staff concludes that the plans and drawings clearly convey the proposed remedialaction design features. In addition, the excavation and placement methods and specificationsrepresent accepted standard practice. Therefore, the staff concludes that Open Issue No. 4 wassatisfactorily addressed in the final specifications.

3,4.2 Testing and Inspection

An up-to-date version of the RAIP and specifications were reviewed for consistency, and foundto be satisfactory; therefore, Open Issue No. 6 is closed. Potential problems in the compactionof Fat CLAY (CH) soils were also addressed in the specifications, thus, Open Issue No. 5 isclosed.

3.5 Conclusions

Based on the review of the design and the geotechnical engineering aspects of the proposedremedial action as presented in the Naturita preliminary final RAP and supporting documents,NRC staff has been provided with reasonable assurance that the long-term stability aspects ofthe EPA standards will be met.


4.0 SURFACE WATER HYDROLOGY AND EROSION PROTECTION

4.1 Hydrologic Description and Site Conceptual Design"

DOE proposes to move contaminated material from the Naturita, Colorado, processing site tothe Upper Burbank disposal area at the Uravan site. Small localized drainage areas existupland of the Upper Burbank site and will contribute flood flows that must bediverted around thedisposal cell. Several gullies exist in the immediate site area upstream and downstream of thesite.

In order to comply with EPA standards that require stability of the tailings for 1000'years to theextent reasonably achievable and, in any case, for at least 200 years, DOE proposes to stabilize*the contaminated materials in an engineered disposal cell.to protect them from flooding and-erosion. The design basis events for design of the erosion protection included the ProbableMaximum Precipitation (PMP) and-the Probable Maximum Flood (PMF) events, both of whichare considered to have low probabilities of occurrence during the 1000-year stabilization period.

As proposed by DOE, the tailings will be consolidated into a below-grade disposal cell that willbe protected by a rock cover. The rock cover will have a maximum slope of 2-4% on the topslopes and 20% on the side slopes. The disposal cel will be surrounded by channels that will,safely convey flood runoff away from the cell. In addition, an interceptor channel, north of thecell, will be constructed to divert flood flows from the upland drainage area away from thedisposal cell.

The upland drainage areas around the cell have short, steep slopes and scattered, steep gullies.

Some of these slopes have competent rock exposed on the surface. These slopes ýand gullieswill discharge fiows directly into the diversion channels surrounding the cell and will require theuse of upstream rock'aprons to protect against erosion.

4.2 Flooding Determinations

The computation of peak flood discharges for various design features at the site was performedby DOE in several steps. These steps included: (1) selection of a design rainfall event;(2) determination of infiltration losses; (3) determination of times of concentration; and(4) determination of appropriate rainfall distributions corresponding to the computed times ofconcentration. Input parameters were derived from each of these steps and were then used todetermine.the peakflood discharges to be -used in water surface profile modeling and in the finaldetermination of rock sizes for erosion protection.

4.2.1, Selection of Design Rainfall Event

One of the most disruptive phenomena affecting long-term stability is surface water erosion.DOE has .recognized that it is very important to select an appropriately conservative rainfallevent on which to base the flood protection designs. DOE has concluded and the NRC staffconcurs (NRC, 1990) that the selection of a design flood event should not be based ontheextrapolation of limited historical flood data, due to the unknown level of accuracy associatedwith such extrapolations. Rather, DOE utilized the PMP, which is computed by deterministic

NATURITA TER. 4-1 APRIL 1999

methods (rather than statistical methods), and is based on site-specific hydrometeorologicalcharacteristics. The PMP has been defined as the most severe reasonably possible rainfallevent that could occur as a result of a combination of the most severe meteorological conditionsoccurring over a watershed. No recurrence interval is normally assigned to the PMP; however,DOE and NRC staff have concluded that the probability of such an event being equaled orexceeded during the 1000-year stability period is small. Therefore,, the PMP. is considered byNRC staff to provide an acceptable design basis.

Prior to determining the runoff from the drainage basin, the flooding analysis requires thedetermination of PMP amounts for the specific site location: Techniques for determining thePMP have been developed for the entire United States primarily by the National Oceanic andAtmospheric Administration (NOAA) in the form of hydrometeorological reports for specific.regions. These techniques are widely used and provide straightforward procedures withminimal variability. The staff, therefore, concludes that use of these reports to derive PMPestimates is acceptable.

A PMP rainfall depth of approximately 8.2 inches in 1 hour was used by DOE to compute thePMF discharges for the small drainage areas at the disposal site. This rainfall estimate wasdeveloped by DOE using Hydrometeorological Report (HMR) 49 (NOAA, 1977); The staffperformed an independent check of the PMP value based on the procedures given in HMR 49.Based on this check of the rainfall computations, the staff concludes that the PMP wasacceptably derived for this site.

4.2.2 Infiltration Losses

Determination of the peak runoff rate is dependent on the amount of precipitation that infiltratesinto the ground during the occurrence of the rainfall. If the ground is saturated from previousrains, very little of the rainfall will infiltrate, and most of it will become surface runoff. The lossrate is highly variable, depending on the vegetation.and soil characteristics of the watershed.Typically, all runoff models incorporate a variable runoff coefficient or variable runoff rates.Commonly-used models, such as the U.S. Bureau of Reclamation Rational Formula (USBR,1977), incorporate a runoff coefficient (C), where a C value of 1 represents 100% runoff and noinfiltration. Other models, such as the COE Flood Hydrograph Package HEC-1, separatelycompute infiltration losses within a certain period of time to arrive at a runoff amount during thattime period.

In computing the peak flow rate for the design of the rock riprap erosion protection at thedisposal site, DOE used the Rational Formula (USBR, 1977). In this formula, the .runoffcoefficient was assumed by DOE to be unity; that is, DOE assumed that no infiltration wouldoccur. Based on a review of the computations, the staff concludes that this is a veryconservative assumption and is, therefore, acceptable.

4.2.3 Times of Concentration

The time of concentration is the amount of time required for runoff to reach the outlet of adrainage basin from the most remote point in that basin. The peak runoff for a given drainagebasin is inversely proportional to the time of concentration. If the time of concentration is


computed to be small, the peak discharge will be conservatively large. Times of concentrationand/or lag times are typically computed using empirical relationships such as those developedby Federal agencies (USBR, 1977). Velocity-based approaches are also used when accurateestimates are needed. Such approaches rely on estimates of actual flow velocities to determinethe time of concentration of a drainage basin.

Various times of concentration for the riprap design were estimated by DOE using the KirpichMethod (USBR, 1977). This velocity-based method is considered by the staff to be appropriatefor estimating times of concentration. Based on the precision and conservatism associated withthis method, the staff concludes that the times of concentration have been acceptably derived.The staff further concludes that the procedures used for computing the times of concentrationare representative of the small, steep drainage areas present at the site.

4.2.4 Rainfall Distributions

After the PMP is determined, it is necessary to determine the rainfall intensities corresponding toshorter rainfall durations and times of concentration. A typical PMP value is derived for periodsof about 1 hour. If the time of concentration is less than 1 hour., it is necessary to extrapolate thedata presented in the various hydrometeorological reports to shorter time periods. DOE utilizeda procedure recornmended in HMR 49 and by the NRC staff (NRC, 1990). This procedureinvolves the determination of rainfall amounts as a percentage of the 1-hour PMP and computesrainfall amounts and intensities for very short periods of time. DOE and NRC staff haveconcluded that this procedure is conservative.

In the determination of peak flood flows, approximate PMP rainfall intensities were derived byDOE as follows:

Rainfall Duration Rainfall Intensity(minutes) (inches/hr)

2.5 54.05.0 44.0

15.0 24.060.0 8.2

The staff checked the rainfall intensities for the short durations associated with small drainagebasins. Based on a review of this aspect of the flooding determination, the staff concludes thatthe computed peak rainfall intensities are conservative.

4.2.5 Computation of PMF

4.2.5.1- Top.and Side Slopes

The PMF was estimated for the top and side slopes using the Rational Formula (USBR, 1977),which provides a standard method for estimating flood discharges for small drainage areas. Fora maximum top slope length of 600 feet, DOE estimated the peak flow rate to be about 0.66cubic feet per second per foot of width (cfs/ft). For an additional side slope length of 80 feet and

NATURITA TER4 4-3 APRIL 1999

a flow concentration factor of 2, DOE estimated the peak flow rate to be 1.1 cfs/ft. Althoughother slope lengths and configurations produce lower peak discharges, DOE adopted the mostconservative flow rates for design purposes. Based on staff review of the calculations, theestimates are considered to be acceptable.

4.2.5.2 Aprons

The side slopes of the cell discharge directly into diversion channels. Therefore, no aprons arerequired downstream of the side slopes. However, aprons are required at several locationsupstream of the cell and channels to prevent erosion. The aprons are needed where steep,natural side slopes discharge concentrated flows into the diversion channels.

DOE computed peak PMF flow rates for the upstream aprons using assumptions ofconcentrated flow, based on the topography immediately upstream of the cell. Several naturalgullies exist and will further concentrate flood flows. Because the shear stresses produced in agully are likely to exceed the flow depths produced by uniform flow spreading across a planesurface, DOE considered such flow concentrations in the analysis. Staff review of these flowcomputations indicate that the analyses are acceptable, and Open Issue No. 7 is closed.

4.2.5.3 Diversion Channels

Diversion channels are provided to intercept and divert runoff from the upland drainage areas onall sides of the cell. Channels 1, 2, and 3 will be constructed in a horseshoe shape around thecell. An interceptor channel will be constructed north of the cell to intercept runoff before itreaches the other diversion channels or the cell area.

In the PMF analysis, HEC-1 was used to compute peak flow rates at different locations in thechannels. Based on a check of the calculations of drainage area, time of concentration, andrainfall intensity, the staff concludes that the PMF estimates are acceptable.

4.3 Water Surface Profiles and Channel Velocities

Following the determination of the peak flood discharge, it is necessary to determine theresulting water levels, velocities, and shear stresses associated with that discharge. Theseparameters then provide the basis for the determination of the required riprap size and layerthickness needed to ensure stability during the occurrence of the design event.

4.3.1 Top and Side Slopes

In determining riprap requirements for the top and side slopes, DOE utilized the Safety FactorsMethod (Stevens, and others, 1976) and the Stephenson Method (Stephenson, 1979),respectively. The Safety Factors Method is used for relatively flat slopes of less than 10percent; the Stephenson Method is used for slopes greater than 10 percent. The validity ofthese design approaches has been verified by the NRC staff through the use of flume tests atColorado State University. It was determined that the selection of an appropriate designprocedure depends on the magnitude of the slope (Abt and others, 1987). The staff, therefore,


concludes that, the procedures and design approaches used by DOE are acceptable' and reflect

state-of-the-art methods for designing riprap erosion protectiqn-.

4.3.2 Upstream Aprons

DOE has adequately addressed the design of the upstream apron by: .

1. providing riprap of adequate size to be stable against concentrated flows associated withthe design storm'(PMP);

2. providing uniform and/or gentle grades along the apron and the adjacent ground surfacesuch that runoff into the diversion:channels is distributed uniformly ata relatively lowvelocity, minimizing the potential for flow concentration and erosion; and.

3. providing an adequate apron thickness and depth to prevent undercutting.

The rock for the aprons will consist of oversized sandstone blocks. DOE provided a design thatincorporated the concepts discussed above. The rock was sized (actually oversized) based onthe occurrence of concentrated flows, using shear stress methods, as recommended by thestaff. Additional discussion of the riprap design of the' upstream apron can be found in Section,4.4.1.2, below.

4.3.3 Diversion Channels

The COE HEC-2 and normal depth computations were use'd to estimate depths and velocitiesunder the estimated discharge conditions in the. channels. The Safety Factors Method was usedto determine riprap sizes for the ditch. Based on 'staff review of the calculations, the'analysis isacceptable. Additional, detailed information related to the design of erosion protection for theditches may be found in Section 4.4, below.

.4.4 Erosion Protection

4.4.1 Sizing of Erosion Protection

Riprap layers of various sizes and thicknesses are proposed for use at the site. The'design ofeach layer is dependent on its location and purpose. Riprap of the following types, sizes, andlayer thicknesses are proposed for use at the site:

Type Average Size Layer Thickness(inches) (inches)

Type A 1.5' 12•Type*B 5.6 12TypeB 1 7.0 15,Sandstone 21-36 Varies

NATU RITA TER 4-5 APRIL 1999

4.4.1.1 Top and Side Slopes

The riprap on the top slope has been sized to withstand the erosive velocities resulting from anon-cell PMP, as discussed above. DOE proposes to use a 1.0-foot-thick layer of Type A rockwith a minimum D50 of 1.5 inches. The riprap will be placed on a 0.5-foot-thick bedding layer.The Safety Factors Method was used to determine the rock size.

The rock layer on the side slopes is also designed for an occurrence of the local PMP. DOEproposes to use a 1.0-foot-thick layer of Type B rock with a minimum D50 of approximately 5.6inches. The rock layer will be placed on a 0.5-foot-thick bedding layer. Stephenson's Methodwas used to determine the required rock size. Conservative values were used for the specificgravity of the rock, the rock angle of internal friction, and porosity.

Based on staff review of the DOE analyses and the acceptability of using design methodsrecommended by the NRC staff, as discussed in Section 4.3 of this report; the staff concludesthat the proposed rock sizes are adequate.

4.4.1.2 Upstream Aprons

Riprap sizes for the aprons were computed using acceptable assumptions of concentratedsheet flow and gully flows. DOE correctly evaluated the potential for high velocity flows fromupstream drainage areas to impact the apron and will place oversized sandstone rocks todissipate the energy. The required size of the rock varies from 21 to 36 inches, and DOE willuse sizes that are even larger than the required size. Staff review indicates that the rock sizesare conservative, and, therefore, acceptable.

4.4.1.3 Diversion Channels

The design of the diversion channels was analyzed by DOE in the following areas:

1. design of the side slopes for concentrated flows entering the channel from the uplanddrainage area;

2. design for runoff directly through the channel;.

3. design of channel outlets; and

4. sediment considerations.

4.4.1.3.1 Channel Side Slopes

Type B and Type B1 riprap layers are proposed for a substantial length of the ditch. The designof the ditch side slopes considered the effects of PMF sheet flows directly down the proposedside slopes from the upland drainage areas. Using the Stephenson Method for the 1V on 5Hditch side slope, the required D50 was found to be less than the size proposed. The staffconcludes that the proposed rip-rap is conservative and is, therefore, acceptable.


4.4.1.3.2 Channels (Main Section)

For flows directly through the channels, the Safety Factors Method was used to determine the*rock sizes. Based oh a review of the calculations, the proposed riprap layers are considered tobe adequate.

4.4.1.3.3 Channel Outlets

The channel outlets generally will be constructed in competent rock. In several areas, DOE willprovide oversized sandstone blocks to form the outlet of the Channels where discharge-tonatural ground occurs. Therefore', no erosion or headcutting is expected to occur. Based ondirect site observations and review of the construction drawings, the staff concludes that.flowsdischarging from the diversion channels will not adversely affect the Title II cell and will be safelydischarged from the site., DOE has acceptably located the outlets of the channel and hasprovided an acceptable design to"account for flows that could potentially impact the Title Ii cell.Therefore, the staff concludes that Open Issue No. 8 is closed.

4.4.1.3.4 Sediment Considerations

In general, sediment deposition can be a problem in diversion ditches when the slope of thediversion ditch is less than the slope- of the- natural ground where flows enter the ditch. It isusually necessary to provide sufficient slope and capacity in the diversion ditch to flush or storeany sediments that will enter the ditch. In particular, significant design features may benecessary in areas where natural gullies are intercepted by the diversion ditch. Concentratedflows and high velocities could transport large quantities of sediment, and the size of theparticles transported by the natural gully -may be larger than the man-made diversion ditch caneffectively flush.

For this site, a considerable amount of sediment from the upland drainage area can be expectedto enter the diversion ditch, for the following reasons:

1.' The upland drainage areas.have steep slopes, whereas, the diversion channels havebeen designed with relatively flat slopes. Flowrvelocities in the ditches may not be as highas those occurring on the natural ground. Therefore, sediment, cobbles, and bouldersmay be transported to the ditch and may not be easily flushed by the lower velocitiesinthe ditch.

2. The potential for gully development (and resulting high flow velocities) in the uplanddrainage area and subsequent transport of bed-load material, into the diversion channelsis high. Based on review of topographic maps of the area and a staff site visit to the area,gullies and areas of flow concentration are evident upstream of the diversion channels.Flows moving toward the diversion channels will tend to concentrate in these. gullies,increasing the potential for gully incision and transport of sediment.

To document the acceptability .of the channel design, DOE demonstrated that: (1) the channelswill have some sediment-carrying capacity; (2) potential sediment deposition in the channels will


not significantly affect the flow capacity; (3) any blockages in the channels will not have anadverse effect on the stability of the contaminated tailings; and (4) the riprap in the channelsprovioes adequate protection.

First, DOE provided analyses that indicated that the channels will be able to flush out much ofthe sediment. Using storm events of various magnitudes, DOE calculated the velocities neededto transport materials of various sizes. DOE determined that the slopes of the channels aresufficient to transport muchof the deposited materials during most flood events;

Second, DOE estimated the amount of sediment that will be deposited. DOE determined thatthe channels will have adequate flow capacity, evenif a significant amount of blockage occurs.

Based on review of the sediment analyses provided by DOE, the staff considers that sedimentaccumulations in the, diversion channels have been adequately addressed. As discussedabove, acceptable analyses of the effects of sediment buildup in the channels have been'provided. Therefore, the staff concludes that Open Issue No. 9 is closed.

4.4.2 Rock Durability

EPA standards require that control of residual radioactive materials be effective for up to 1000years; to the extent reasonably achievable, and, in any case, for at least 200 years. Theprevious sections of this report examined the ability of the erosion protection to withstandflooding events reasonably expected to occur in 1000 years. In this section, rock durability isconsidered to determine if there is reasonable assurance that the rock itself will survive andremain effective for 1000 years.

Rock durability is defined as the ability of a material to withstand the forces of weathering.Factors that affect rock durability are: (1) chemical reactions with water; (2) saturation time;(3) temperature of the water; (4) scour by sediments; (5) windblown scour; '(6) wetting anddrying; and (7) freezing and thawing.

DOE identified several sources of rock in the immediate site vicinity. The suitability of theserocks as a protective cover was then assessed by laburatory tests to determine the physicalcharacteristics:. DOE conducted the tests and used-the results of these tests to classify therock's quality and to assess the expected long-term performance of the rock. In accordancewith past DOE rock-testing practice, the tests included:

1. Petrographic Examination (ASTM C295). Petrographic examination of rock is used todetermine its physical and chemical properties. The examination establishes if the rockcontains chemically unstable minerals or volumetrically unstable materials.

2. Bulk Specific Gravity (ASTM C127). The specific gravity of a rock is an indicator of itsstrength or durability. In general, the higher the specific gravity is, the' better the quality ofthe rock.

3. Absorption (ASTM C127). A low absorption is a desirable property and indicates slowdisintegration of the rock by salt action and mineral hydration.


4. Sulfate Soundness (ASTM C88). In locations subject to freezing or exposure to salt water,a low percentage is desirable"

5. Schmidt Rebound Hammer. This test measures the hardness of a rock and can be usedin either the field or the laboratory.

6. Los Angeles Abrasion (ASTM C131 or C535). This test.is a measure of rock's resistanceto abrasion.

7. Tensile Strength (ASTM D3967 or ISRM Method). This test is an indirect test of a rock'stensile strength.

DOE then used a step-by-step procedure for evaluating durability of the rock, in accordance withprocedures recommended by the NRC staff (NRC, 1990), as follows:

Step 1. Test results from representative samples are 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 is multiplied by a weighting factor. The effect of the weighting factor isto focus the scoring on those tests that are the most applicable for the particularrock type being tested.

Step '3. The weighted scores are totaled, divided by the maximum possible score, andmultiplied by 100 to determine the rating.

Step 4. The rock quality scores are then compared to the criteria that determines itsacceptability, as defined in the NRC scoring procedures.

In accordance with the procedures suggested by-the staff, DOE determined from preliminarytesting that the rock proposed for the disposal site scored above 80. The staff concludes thatthe rock will be of sufficient quality to meet EPA standards.-

4.4.3 Testing and Inspection of Erosion Protection

DOE provided a detailed inspection and testing program for the selection and placement of rock.in the RAIP. The staff evaluated these testing and inspection quality control requirements forthe erosion protection materials and concludes that the proposed testing program is acceptable.

For the large blocks of sandstone.to be used, DOE applied additional testing and inspectionprocedures to ensure the quality of each large rock. Each piece was inspected by a trainedgeologist, who verified that:

1. The sandstones were fine-grained and cemented with quartz.


2. The rock porosity was low with few fractures that would increase the potential for freeze-thaw processes to affect the rock.

3. There were no significant joints, fractures, partings, or seams that would induce icewedging.

4. The sandstone was derived from massive, bedded formations, reducing the potential forsignificant bedding planes.

Based on staff review of the overall testing and inspection plan for all types of rocks that wereproduced and placed, the staff concludes that the program is acceptable.

4.5 Upstream Dam Failures

There are no impoundments near the site whose failure could potentially affect the site.

4.6 Conclusions

Based on review of the information submitted by DOE, NRC staff concludes that the site designwill meet EPA requirements as stated in 40 CFR 192 with regard to flood design measures anderosion protection. The staff concludes that an adequate hydraulic design. has been provided toreasonably assure stability of the contaminated material at the disposal site for a period of 1000years, or in any case, at least 200 years.


5.0 WATER RESOURCES PROTECTION

5.1 Introduction

The Naturita processing site is located in the San Miguel River Valley and is underlain byunconsolidated alluvial floodplain deposits and fill material. The alluvium is the upper-mostaquifer at the processing site and is contaminated from former processing-site activities. Thealluvium is underlain by the Brushy Basin and the Salt Wash Members of the MorrisonFormation. The Brushy Basin consists of interbedded shale, sandstone, and conglomerate.lenses. The Salt Wash consists predominantly of sandstone with some shale. The BrushyBasin and the Salt Wash have not been affected by uranium processing activities. Existinggroundwater contamination does not presently represent a risk to human health or theenvironment.

However, DOE is required to demonstrate that cleanup or control of existing processing-relatedgroundwater contamination at the Naturita site will comply with the EPA groundwater protectionstandards in Subpart B of 40 CFR Part 192. Groundwater cleanup at the former processing sitewill be addressed under a separate DOE program and a National Environmental Policy Actprocess, using strategies and options outlined in a programmatic environmental impactstatement that has been developed for the UMTRA Project. The need for and extent ofgroundwater cleanup at the Naturita site will be evaluated based on the extent of existingcontamination, the potential for current or future groundwater use from the uppermost aquifer,and protection of human health and the environ'ment.

At the Upper Burbank Disposal site, DOE must comply with the final standards (40 CFR 192.20)issued by the EPA on January 11, 1995. From a review of the information submitted; it appearsthat the site will comply with the requirements of Subpart A of the EPA groundwater protectionstandards. However, the NRC staff has yet to reach a determination on the long-termsurveillance plan, which the DOE has not yet submitted to the NRC.

5.2 Hydroqeolocqic Characterization

5.2.1 Identification of Hydrogeologic Units

A. Processing Site

At the Naturita processing site; unconfined groundwater occurs within the alluvial flood plaindeposits from 3 to 18 ft (0.9 to 5.5 m) below the land surface. The saturated thickness isapproximately 15 ft (4.6 m) in the vicinity of the site. The next deepest aquifer at the site is theSalt Wash Member of the Morrison formation, which consists predominantly of sandstone withsome shale. The Salt Wash aquifer is separated from the alluvial aquifer by the Brushy BasinMember of the Morrison formation. Under the site, the Brushy Basin Member'is considered anaquitard and consists of thick, laterally extensive, interbedded shales with some sandstones. Itranges in thickness from 110 to 165 ft (33.5 to 50.3 m). The top of the Salt Wash aquifer isapproximately 130 to 165 ft (39.6 to 50.3 m) below land surface near the site. The totalthickness of the Salt Wash aquifer has not been determined, but is at least 80 ft (24.4 m) thick inthe vicinity of the processing site.

NATURITATER 5-1 APRIL 1999

B. Disposal Site

Five principal hydrostratigraphic units occur within the upper 800 ft (240 m) of sedimentsbeneath the disposal site. From the land surface down, these are: (1) sandstones and shalesof the Salt Wash Member of the Morrison Formation; (2) shales and siltstones of theSummerville Formation; (3) sandstone of the Entrada; (4) sandstones of the Kayenta; and (5)sandstones of the Wingate Formation.

The Salt Wash Member directly underlies the disposal site and has a thickness of about 120 ft(37 m). This unit is predominantly comprised of sandstone with some interbedded shale layers.The Summerville Formation underlies the Salt Wash Member. This unit is considered anaquitard and is 90 ft (27 m) thick. It is composed of massive clayey mudstones, silty shales,clayey siltstones, and minor, interbedded sandstones. The Entrada Formation underlies theSummerville Formation and has a thickness of approximately 160 ft (49 m). The SummervilleFormation is a sandstone. Underneath the Summerville formation is the Kayenta Formation,which has a thickness of approximately 180 ft (95 m). This formation consists of interbeddedlayers of sandstone, siltstone, shale, and some conglomerate. Below the Kayenta Formation isthe Wingate Formation. This formation is about 250 ft (76 m) thick and is a sandstone. TheKayenta Formation together with the Wingate Formatic. form the first saturated aquifer beneaththe disposal site.

Below the Wingate Formation is the Chinle Formation. The Chinle Formation is about 400 ft(120 m) thick and is predominantly a siltstone. Because of it's low permeability, the ChinleFormation acts as an aquitard to vertical groundwater movement.

5.2.2 Hydraulic and Transport Properties

A. Processing Site

The occurrence of shallow groundwater in the alluvial aquifer is limited by the lateral extent ofthe alluvium in the vicinity of the Naturita processing site. The average hydraulic conductivity forthe alluvial aquifer is 3.0 ft/day (0.001 cm/sec) and the average linear groundwater velocity is0.06 ft per day (2x10 5 cm/sec). The groundwater flow direction in the alluvium is subparallel(northwest) to the San Miguel River. Groundwater from the alluvial aquifer discharges into theSan Miguel River northwest of the site.

The Salt Wash aquifer is a major regional groundwater system in the area. The potential area ofnatural discharge from the Salt Wash aquifer is the San Miguel River northwest of theprocessing site. For the Salt Wash aquifer, hydraulic conductivities averaged 0.06 ft/day (2x10 5

cm/sec) and the average linear groundwater velocity is estimated to be 0.002 ft/day (7x10 7

cm/sec). The Salt Wash aquifer is separated from the alluvial aquifer by the Brushy BasinMember, which locally is considered an aquitard. Groundwater in the Salt Wash aquifer isconfined, and has a potentiometric surface that is higher in elevation than the water table in thealluvial aquifer. Therefore, if any significant flow were to occur between the Salt Wash aquiferand the alluvial aquifer, water movement would be upwards from the Salt Wash aquifer throughthe Brushy Basin Member and into the alluvial aquifer.


'• ',•. •,'•m•,'-•'•, •',•"t" •

B. Disposal Site

The disposal site is underlain by approximately 600 ft (180 m) of unsaturated sandstone,siltstone, and shale. The Summerville Formation, composed of shale and siltstone, is about120 ft (37 m) below the site and has a hydraulic conductivity of less than 0.01 ft/yr(1.0xI0a cm/sec). This 90 ft (27m) thick layer function.i as an aquitard: and should prevent any.potential groundwater contamination from the disposal site from reaching the Kayenta/Wingateaquifer.

The KayentaNVingate Formation is the uppermost aquifer beneath the disposal site. Only theKayenta/Wingate aquifer is saturated beneath the disposal site. The aquifer is unconfined andat a depth of approximately 600 ft (180 m). Average hydraulic conductivity of the Wingateformation is 0.12 ft/day (4.2x!0' cm/sec). Groundwater flow beneath the repository is towardthe north at velocity of about 8 ft/yr. Primary recharge to the Kayenta/Wingate aquifer isnortheast of the San Miguel River along the Uncompahgre Plateau. Secondary recharge to theWingate portion of the aquifer is from the Paradox Valley south of the site. Discharge from theaquifer is to the San Miguel River.

5.2.3 Extent of Ccntamination

A. Processing Site

To determine whether uranium processing activities at the Naturita processing site haveinfluenced groundwater qualityin the alluvial aquifer, DOE collected samples from on-site anddown gradient monitor wells and analyzed these samples for the constituents (including lead,nitrate, and silver) listed in Table 1 to Subpart A and Appendix I of 40 CFR Part 192. Based onthis analysis, arsenic, cadmium, chromium, fluoride, methylene chloride, molybdenum, selenium,strontium, thallium, tin, toluene, uranium and vanadium, radium-226 and -228, and gross alphamay be contaminants in the alluvial aquifer groundwater. Of these constituents; arsenic,cadmium, molybdenum, selenium, uranium, radium-226 and -228, and gross alpha were foundto exceed the EPA maximum concentration limits. Based on uranium concentrations, acontaminant plume extends at least 1500 ft (460 m) down gradient from the former mill yard andhas a maximum width of approximately 900 ft (275 m). Contaminated groundwater from thealluvial aquifer discharges into the San Miguel River, where no impacts on the river water qualityhave been observed to date.

Groundwater in the Salt Wash aquifer was f(und to not be contaminated as a result of millingoperations at the processing site.

B. Disposal Site

Groundwater at the disposal site is presently uncontaminated by the disposal of contaminatedmaterial.


5.2.4 Water Use

A. Processing Site

Eight wells are located within 2 miles (3.2 kilometers) of the processing site. Water from thesewells are used for domestic purposes. Five of these wells are located up gradient from theprocessing site (four obtain water from the alluvial aquifer and one from the Salt Wash aquifer).The two remaining wells are located down gradient of the site, but are located on the oppositeside of the river. There should be no threat to up gradient wells from contaminated groundwaterfrom the processing site in the alluvial aquifer as groundwater flow is in the opposite directionfrom these wells. Groundwater pollution in the alluvial aquifer should not be a threat to downgradient wells because the river represents a discharge point for the alluvial aquifer. Sincethese wells are located on the other side of the river, g:oundwater contamination in the alluvialaquifer should not reach them. Therefore, the staff concludes that Open Issue No. 12 is closed.

No impacts to groundwater have been observed or are expected in the Salt Wash aquifer fromthe processing site. No impacts to surface water quality have been observed from contaminatedalluvial groundwater at the site.

Future use of groundwater in the alluvium for domestic consumption is not expected. This isbecause the alluvial aquifer has a very low potential for use as a source of water, since it islimited to the small area of alluvium in and adjacent to the San Miguel River. Alternativesupplies of reliable, good-quality water are available from the town of Naturita, from surfacewater, and from deeper groundwater aquifers.

B. Disposal Site

Four wells produce groundwater within two miles (3.2 kilometers) of the disposal site. All ofthese wells are owned by Umetco Minerals Corporation. These wells are no longer being usedand will be plugged prior to deeding the land in and .around Uravan-to the federal government.Five additional wells are within a radius of five miles from the site. All of these wells areup gradient of the disposal site and, therefore, cannot be impacted by the site. Future use ofgroundwater beneath the Upper Burbank site is limited by the poor water quality and lowpermeability of the Wingate Formation and significant depth [600 ft (180 m)] to groundwater. Inthe future, land will be deeded to the federal government, which will limit the development ofgroundwater resources by the general public.

There are no agricultural or domestic surface-water users within a 2-mile (3.2-kilometer) radiusof the site. Umetco Minerals Corporation does have water rights on the San Miguel River forindustrial uses.. Within a 5-mile (8-kilometer) radius of the site, water use is limited to springsused for stock water. The closest spring used for stock watering is located about 4 miles(6 kilometers) northeast of the site.


5.3 Conceptual Design Features to Protect Water Resources

A. Processing Site

Groundwater contamination does not represent a risk to human health or the environmentbecause there is currently no consumption of the conta~minated groundwater in the alluvial.aquifer. The distribution of hazardous constituents in groundwater will decrease with time,because contaminated material is being moved off site to another location and because thealluvial aquifer discharges to the San Miguel River. This means that existing contamination inalluvial aquifer groundwater will eventually be flushed out of the aquifer and diluted by the waterin the San Miguel River. Groundwater cleanup at the former processing site will be addressedunder a separate DOE program and a National Environmental Policy Act process, usingstrategies and options outlined in a programmatic environmental impact statement that has beendeveloped for the UMTRA Project

B. Disposal Site

The climate in the vicinity of the disposal site is semiarid. Under natural conditions deeppercolation at the disposal site is less than 0.01 ft3ift2/yr and may for all practicable purposes bezero. The lack of a perched zone under the disposal site and the lack of springs and seepsalong the canyon walls further indicate that the site has a very low infiltration rate. The disposalsite was modeled by DOE to determine possible infiltration rates after cover.construction.Modeling results suggest a very low infiltration rate of about 0.028 ft3/ft 2/yr through the cover.This infiltration rate equates to a flow of approximately 0.1 gpm (9660 ft3/yr) through the base ofthe 8-acre disposal cell. This indicates that very little deep percolation should occur underneaththe disposal cell. Travel time for liquid from the base of the disposal cell through theSummerville Formation was calculated to be in excess of 1,000 years.

The residual radioactive materials that will be disposed of at the site are principally contaminatedsoils. The contamination of these soils should be relatively low due to the mixing of the originaltailings materials with surficial soils. Batch tests performed on this soil material confirm that thismaterial has relatively low concentrations of radionuclides and heavy metals. Geochemicalattenuation of any leachate from the disposal site would occur as contaminated water flowsthrough the bedrock formation.

5.4 Disposal and Control of Residual Radioactive Materials

5.4.1 Water Resources Protection Standards For the Disposai Site

The EPA groundwater standards (40 CFR 192.02) require three basic elements for setting thegroundwater protection standards. These are: (1) determination of hazardous constituents;(2) proposal of a concentration limit for each hazardous constituent found to exist in the tailingsor leachate; and (3) specification of the point of compliance. The DOE analyzed groundwatersamples from the alluvial aquifer beneath the Naturita processing site and conducted laboratorybatch leach tests of contaminated soil material from the Naturita processing site. Based onthese tests, DOE identified 25 hazardous water quality parameters that are reasonably expected


to be in or derived from residual radioactive material to be disposed of at the site. Theseparameters were selected to be monitored at the point of compliance and are presented in Table5-1. ,2or these parameters, the DOE has established concentration limits (Table 5-1). Theproposed concentration limits are either the maximum concentration limit or, for thosehazardous constituents without maximum concentration limits, the statistical maximum ofbackground groundwater quality derived from water samples collected from Wingate wellsCM93-1 and CM93-2. Concentration limits for strontium and tin will be determined by routinesampling of CM 93-1 and CM 93-2 during long-term site surveillance activities., Since DOE willsample for many other parameters other than tin and strontium, the ground-water protectionprogram should detect any potential contamination in the ground water from the disposal site,during the period when tin and strontium concentration limits are being established.

Wingate well CM93-2 is designated as the point of compliance for the disposal site. This well isimmediately down gradient of the disposal cell.

5.4.2 Performance Assessment for the Disposal Site

DOE must demonstrate that the performance of the disposal unit will comply with EPA'sgroundwater protection standards in 40 CFR 192 Subparts A and C. The disposal cell designshould minimize and control releases of hazardous coistituents to groundwater and surfacewater to the extent necessary to protect human health. The following are important toperformance of the disposal site:

1. The uppermost aquifer, the Wingate Formation, lies approximately 600 ft (180 m)below the base of the disposal cell and is hydrogeologically'isolated from surfacerecharge or initial transient drainage from the disposal cell by low permeability shalesand mudstones overlying the aquifer.

2. The Summerville Formation, the principal aquitard beneath the site, is approximately90 ft (27 m) thick and effectively isolates groundwater in the underlyingKayenta/Wingate aquifer from potential contaminants in the disposal cell.

3. Geochemical properties of the bedrock materials attenuate hazardous constituentspossibly associated with leaching of the residual radioactive materials.

4. The multi-layered cover reduces the infiltration rate and minimizes long-termseepage from the cell.

5. The disposal cell will be contoured to provide efficient drainage of precipitation awayfrom the disposal cell and to minimize excess moisture in the cover and associatedinfiltration.


5.4.3 Closure Performance Demonstration for the Disposal Site

DOE must demonstrate that the p'oposed disposal design will:. (1) minimize and controlgroundwater contamination; (2) minimize the need for further maintenance; and (3) meet initialperformance standards of the design, in accordance with the closure performance standards of40 CFR 192.02. The disposal cell design uses a multi-layered cover to reduce the infiltrationrate and minimize long-term seepage from the cell. The disposal cell will be contoured toprovide efficient drainage of precipitation away-from the disposal cell and to minimize excessmoisture in the cover and associated infiltration. In addition, natural stable material will be usedin constructing the disposal cell to minimize the need for further maintenance.

5.4.4 Groundwater Monitoring and CorrectiveAction Plan at the Disposal Site

The DOE is required by 40 CFR 192.03 to implement groundwater monitoring during thepost-disposal periodfor the purpose of demonstrating that the disposal cell will perform inaccordance with the design. The regulation 40 CFR 192.04 requires the implementation of.acorrective action program if the monitoring shows an exceedance of concentration limits. Themonitoring plan required under 40 CFR 192.03 should be designed to include verification of thesite-specific assumptions used to project the disposal system performance. Prevention ofgroundwater contamination may be assessed by indirect methods, such as measuring themoisture migration within various components of the cover, tailings, or beneath the tailings, aswell as direct groundwater monitoring.

At the disposal site, DOE will monitor potential repository seepage using wells at the contact ofthe Salt Wash and Summerville Formations near the disposal cell for a period of time followingcompletion of remedial action. Monitoring any perched groundwater on the top of theSummerville from the disposal cell includes well BR95-1, BR95-2, and BR95-3. If seepage isdetected in these monitor wells, performance monitoring of wells CM93-1 and CM93-2 will beconducted.

5.5 Clean-up and Control of Existing Contamination at the ProcessinQ Site

The DOE is required to demonstrate that cleanup or control of existing processing-relatedgroundwater contamination at the Naturita site will comply with the EPA groundwater protectionstandards in Subpart B of 40 CFR Part 192. Groundwater cleanup at the former processing sitewill be addressed under a separate DOE program and a National Environmental Policy Actprocess, using strategies and options outlined in a programmatic environmental impactstatement that has been developed for the UMTRA Project. The need for and extent ofgroundwater cleanup at the Naturita site will be evaluated based on the extent of existingcontamination, the potential for current or future use of groundwater from the uppermost aquifer,and protection of human health and the environment.


5.6 Conclusions

The staff concludes that the proposed remedial action for the Naturita sites will acceptablycomply with the EPA groundwater standards, with the exception of the following open issues(Nos. 13 and 18) that may be deferred until the groundwater cleanup phase of the project.

1. DOE rmust demonstrate compliance with EPA's groundwater clean-up standards in40 CFR 192, Subparts B and C at the Naturita prpcessing site (deferral provided bythe UMTRCA amendment of 1982).

2. DOE must provide the details of its groundwater monitoring program (samplingfrequency, etc.) for the disposal site to demonstrate compliance with 40 CFR 192.03.This information can be included when DOE submits the long-term surveillance planto the NRC for review.


Table 5-1 Hazardous Constituents and Concentration' Limits for the Disposal Site

Constituent

Aluminum

Antimony'

Arsenic

Barium

Beryllium

Cadmium

Chromium

Copper

Cyanide

Fluoride

Gross alpha (excluding uranium and radon)

Lead

Mercury

Molybdenum

Nickel

Nitrate (as N)

Radium-226 and -228

Selenium

Silver

Strontium

Thallium

Tin

Uranium

Vanadium

Zinc

Concentration Limit

0.1 mg/L (background)


0.05 mg/L (maximum concentration limit)








44.7 pCi/L.(background)




0.05 mg!L (background)

10 mg/L(maximum concentration limit)

5.0 pCi/L (maximum concentration limit)









NATURITA TER 5-9 APRiL 19991

6.0 RADON ATTENUATION AND SITE CLEANUP

6.1 Introduction

This section of the TER documents the staff evaluation of the radon attenuation design for thedisposal cell and the processing site cleanup plan for the remedial action at the Naturita,Colorado, UMTRA Project site (DOE, 1998a and 1998b). The evaluation includes review of thematerial characterization, radon barrier design, site radiological characterization, proposedremedial actions, and site cleanup verification plan to ensure compliance with the applicableEPA standards. The review followed the NRC SRP for UMTRCA Title I sites (NRC, 1993).

6.2 Radon Attenuation

To meet the EPA standards for long-term control of radiation and limiting release of radon fromresidual radioactive materials to the atmosphere, the contaminated material will be relocated tothe Upper Burbank disposal site at Uravan, Colorado, and covered with the following layers:3-foot radon barrier, 5.5-foot frost protection, 6-inch bedding, and 12-inch riprap. The radonbarrier layer of the cover has been designed to limit the long-term average release of radon fromthe disposal cell to meet the EPA flux standard of 20 pCi/m 2/s and to attain released radonlevels as low as reasonably achievable (ALARA).

Because radon (Rn-222) is a gas with a short half-life (3.8 days), the amount of radon fromuranium mill tailings reaching the atmosphere-is reduced by restricting the gas movement longenough so that radon decays to a solid daughter that remains within the disposal cell. Thephysical and radiological parameters influencing the amount of radon available to the soil porespaces and its movement are incorporated into a .computer code. The staff evaluated theestimation of the long-term (at least 200 years) average (over the entire cell surface, over atleast 1 year) radon flux from the disposal cell cover by utilizing the RADON computer code.Most of the code input values are parameter values derived during characterization of thevarious materials that will make up the cell and/or based on conservative estimates. Thecombination of input parameter values and underlying-assumptions comprise the radon fluxmodel. Staff also reviewed the construction specifications for materials placement forconsistency with the radon flux model assumptions (material sequence and compaction) andevaluated the other layers of the cover for their ability to protect the radon barrier layer fromdrying, natural weathering, and biointrusion.

An additional aspect of the staff review considered that the radon barrier layer is also designedto satisfy criteria for construction and infiltration of surface water. In addition, the potential forcracking of the barrier layer due to settlement or heaving within the cell and the potential forfreeze-thaw and erosional damage to the coyer were evaluated. These aspects of the celldesign are evaluated in Sections 3 and 4 of this TER.

6.2.1 Evaluation of Parameter Values

The staffs review addressed the adequacy of the parameter values (i.e., code input) byevaluating the justification or assumptions made for each value to confirm that each value wasrepresentative of the material or a conservative estimate, consistent with site construction

NATURITA TER 6-'1 APRIL 1999

specifications, and based on long-term conditions. Design parameters of the contaminated andbarrier materials that were evaluated include: material placement sequence; layer thickness;bulk density; specific gravity; porosity; long-term moisture content; and radon diffusioncoefficient. In addition, the radium concentration and radon emanation fraction of thecontaminated materials were evaluated. The sampling and testing methods for the materialswere also reviewed to determine their appropriateness and to ensure that the data wereadequate.

6.2.1.1 Contaminated Materials

Although the Naturita processing site no longer held a tailings pile, areas of the site containresidual contamination. These areas are:

1. former tailings pile area (27 acres, at the lowest elevation)2. mill yard and ore buying station (14 acres, on higher terrace)3. ore storage area (12 acres, west of Highway 141)4. windblown/waterborne materials (196 acres)

The volume of contaminated material is estimated to be 548,000 cubic yards (cy), includingapproximately 8000 cy of processing site debris to be placed in the disposal cell. Approval ofthe application of supplemental standards (no remedial action) associated with the processingsite proposed by DOE will reduce the volume of disposed material by approximately 147,000 cyof mainly windblown material. The proposed application of supplemental standards is discussedin Section 6.3.3 and the impact of its approval and implementation on the radon barrier analysisis discussed in Section 6.2.2.

The disposal cell design indicates that contaminated material from the mill yard (includesretention basin and ditch soils, vicinity property materials, demolition debris, and ore buyingstation) and ore storage area will be placed at the bottom of the cell and covered by soil from theformer tailings pile area. Windblown material will be placed last (DOE, 1995; Figure 1.6, Page1-10). The windblown material comprises approximately 39 percent of the material to bedisposed, if the supplemental standards application for the processing site is approved, and55 percent, if the application is not approved (DOE calculation 17-737-01-02).

Radon model parameter values for the contaminated material were derived from DOE (1995)RAP calculation 17-741-02. Most of these values were determined from laboratory testingperformed on material compacted to 90 percent (Standard Proctor), as the material is to beplaced in the cell at this level of compaction. Staff is concerned that some of the contaminatedmaterial parameter values are based on limited testing or non-conservative estimates.However, staffs concern is mitigated by the proposed thickness of the radon barrier and frostprotection layers of the cell cover, so that the contaminated material parameter values are notan issue (see Section 6.2.2 of this TER). For documentation purposes, the'evaluation of eachparameter value follows.

Average maximum dry density and specific gravity measurements for each material type wasused to calculate porosity. The values for mill yard and ore storage area materials were


combined (volume weighted), because these materials will be combined during placement in thecell. The resulting parameter values (below) are acceptable to staff.

Material Density* #:Tests Spec. Gravity # Tests Porosity

mill yard/ore storage 1.60 11 2.69 10 .40tailings area 1.61 9 2.63 7 .39windblown 1 51 11 2.58 6 .42

g/cc at 90 percent compaction

The long-term moisture content parameter value of each material was based on the average ofminus 15-bar capillary moisture test results. The tailings pile area (five samples) averaged5.1 percent by weight moisture, mill yard material averaged (five samples) 10.8 percent, one orestorage sample yielded 11.1 percent, and windblown material (four samples) averaged 13.0percent. The high moisture value for windblown soil is considered reasonable because of thehigh clay content (3 samples averaged 26 percent) of the material. To be conservative, staffused a windblown material moisture value of 9.0 percent in its radon model.

A single soil sample each from the mill yard,. ore storage, and windblown contaminated materialwas measured for radon diffusion coefficient. Each sample was tested at five different moisturecontents and a best fit curve prepared. The diffusion coefficient value corresponding to theestimated long-term moisture of the material was selected. An average radon diffusioncoefficient of 0.0188 cm 2/s represents the mill yard/ore storage layer in the cell and 0.0136 cm 2/swas derived for the windblown material. A value of 0.025 cm 2/s was estimated for the tailingspile area. Because of the. limited data, staff used the more conservative code-calculateddiffusion coefficient value for windblown material (0.031 cm 2/s) in its modeling.

Twelve radon emanation fraction measurements on contaminated material ranged from 0.06 to0.35. The volume weighted average emanation fraction for the mill yard/ore storage soils-(four.samples each) was 0.33, and for windblown material (four samples) the value was 0.22. Notests were performed on former pile area soil, so the mill yard/ore storage value was assumed tobe representative of this material. These values appear reasonable, but staff utilized moreconservative values in its model.

DOE determined the Ra-226 content of the contaminated materials primarily by gammaspectroscopy. Incremental Ra-226 depth.profiles were constructed for each measurement gridpoint. The average Ra-226 concentration was determined for each subarea by integrating theprofiles over the volume, based on the excavation depth. Based on these~data, volume-weighted average Ra-226 concentrations were calculated for each layer in the disposal cell asfollows:


Area Ra-226 (pCi/g) # Samples Volume (x1000 cy) Thickness (cm)

Mill Ya -!,debris/ 78Ore Storage 133 27 134.6 119", 122tailings pile 90 56 116.1 113Windblown 38 281 294.1 171", 402(if supplemental standards applied)

Higher Ra-226 values than the average measured values were modeled. A value of 59.5 pCi/gwas used for windblown material and 94.1 pCi/g for former tailings pile soil. This approach isconservative and, therefore, is acceptable to staff.

6.2.1.2 Radon Barrier

The parameter values for the radon barrier material were selected based on the results oflaboratory testing of samples from the Club Mesa borrow site.

The summary table of geotechnical design parameters in the RAP (DOE, .1998) calculation 010(sheet 8), indicates that radon barrier material.has an average of 50 percent fines. However, theconstruction specifications do not contain a requirement for a minimum percent fines (materialpassing the No. 200 sieve) for radon barrier soil, although calculation 006 (sheet 107) indicatesthat the radon barrier soil will have a minimum of 50 percent fines. In addition, the actualmaterial tested contained an average of 86 percent and a minimum of 80 percent fines(calculation 006 sheet 108).

Barrier material was tested at 95 percent compaction, but will be placed at 100 percentaccording to the design and construction specifications. The moisture test value derived frommaterial at the lower compaction may not be conservative for the radon flux model moistureparameter, because the looser soil would hold more water. Therefore, staff modified the valuefor this parameter in its flux model.

The density and porosity parameter values for the radon barrier material appear to be based onthe average measurements of two samples (calculation 010 sheet 6). However, the RAP (DOE,1995; Section 6.3.4) indicates that 10 samples were tested, although the summary of soil testresults (calculation 006 sheet 108) indicates that 5 samples tested for maximum densityaveraged 1.60 g/cc (99.64 pcf) and 4 samples tested for specific gravity averaged 2.70, resultingin a calculated porosity of 0.41. Calculation 010 sheet 6 states that the density value for designis 1.50 g/cc, but the radon flux analysis uses the less conservative 1.60 g/cc value. Staff utilizedthe conservative values of 1.5 g/cc and 0.44 for density and porosity in its model.

The long-term moisture content parameter value was based on two minus-1 5-bar capillarymoisture tests that averaged 19.4 percent. At this moisture value, a radon diffusion coefficient of0.0063 cm 2/s was derived. However, a code-calculated value of 0.0021 cm2/s was used in theflux analysis, which is not conservative. Staff normally would use the Rawls and Brakensiekequation to estimate the long-term moisture content, but data on the organic content of thebarrier soil were not available. The material tested had a high fines content that may produceunreliable or unrepresentative capillary moisture test results. Therefore, staff used a moisture


value of 16 percent, deemed reasonable for clayey soil, and a calculated diffusion coefficient.value of 0.0097 cm2/s in its model. -In addition, DOE provided as built calculations which showedsufficient protection.

The' thickness of the radon barrier layer is set by the design at 3 feet to satisfy ALARAconsiderations. This, is acceptable to NRC staff because this thickness provides reasonableassurance that the.long-term radon flux standard can belmet, as discussed. below.

6.2.2 Evaluation of Radon Attenuation Model

DOE provided two radon flux models and utilized the RADON computer code to evaluate theradon attenuation capacity of the barrier. One model assumed that the upper 16 feet (500 cm)of contaminated material was composed of windblown material, and the other assumed thislayer was composed of material from the former tailings pile area. Both models assume that theside slopes of the cell have the same layer sequence and thickness. To be conservative,neither model considers the radon attenuation ability of the frost protection layer. Each modelwas run first to estimate the average long-term radon flux from a 3-foot-thick barrier and secondto determine the required barrier thickness to achieve a flux' of 20 pCi/m 2s. The resulting valuesare:

Contaminated Layer Flux (pCi/m 2s) Required Barrier Thickness

Windblown Material 1.3 2.4 inches (6 cm)

Tailings Pile Area 9.1 8.5 inches (21 cm)

Staff modeled the more conservative parameter values discussed in previous sections and useda conservative, but realistic layer sequence and thickness. The layers modeled were"(1) 4.5 feet (138 cm) mill yard/ore storage material; (2) 3.5 feet (106 cm) tailings pile area soil;(3) 4 feet (122 cm) windblown material; and (4) 3 feet (90 cm) of radon barrier. This modelreflects a minimal amount of material with low-levels of Ra-226 (assumes that supplementalstandards are approved) and, therefore,'there is a higher total Ra-226.concentration than isexpected to be present-. The staff s modeling resultediin an estimated long-term radon flux of11.8 pCi/m 2/s. This provides reasonable assurance that the radon barrier design meets the EPA'radon flux standard.

6.2.3 Durability of the RadonBarrier

One aspect of barrier durability that can be evaluated by radon flux modeling is freeze-thawdamage. DOE calculated that the frost penetration into the cover would extend 44 inches(conservatively modeling ,the frost protection layer at its long-term moisture content). With the.proposed 66-inch-thick frost protection layer and-the 18-inch-thick bedding and riprap cover, theradon barrier soil would not'be affected by freeze-thaw events (see further discussion in TERSection 3.3.4). Therefore, flux modeling with parameter values altered to reflect a frostdamaged'radon barrier was not necessary. Evaluation of the potential for cracking of the radonbarrier due to desiccation or cell instability is addressed in Section 3.4.


Another aspect of the evaluation of the long-term integrity of the radon barrier is estimating thelikelihood of intrusion by burrowing animals or deep-rooted plants. This aspect of cell designwas not addressed, but staff considers that biointrusion of the radon barrier will, be restricted bythe unfavorable environment of the rock layer in the final cover. Although, it is recognized thatsome volunteer plant growth will occur on the cover, significant root penetration 7 feet deep, tothe radon barrier, is not anticipated.

6.3 Site Cleanup

6.3.1 Radiological Site Characterization

Field sampling and radiological surveys at the Naturita processing site and adjacent areasresulted in the identification of contaminated materials covering 133 acres. In Section 6.5.1 ofthe DOE RAP for the processing site (DOE, 1998) the discussion of site characterizationmentions that data have not indicated a potential for preferential mobilization of Th-230 at thesite. Staff considered that characterization of soil Th-230 and U-238, as described in the RAP,is inadequate. NRC staff estimated from the coordinates given in Table B-3 of Calculation 17-730-01-01 that only one sample each from the former tailings pile and ore storage areas wereanalyzed for Th-230. However, DOE states (DOE, 1994; Section 6.5.1) that furthercharacterization of Th-230 and uranium will be performed in conjunction with test pitting of thecobbly soil. DOE subsequently. provided additional Th-230 and U-238 data obtained with thecobbly soil study to substantiate that adequate characterization of these radionuclides wasperformed.

Soil background levels of Ra-226 were measured in the Naturita area and DOE stated that theaverage value is 2.3 pCi/g. The value is based on four samples ranging from 1.1 to 3.4 pCi/g.Since little was known about the location of the site and the various processes, the RemedialAction Contractor randomly located test pits across the mill site and adjacent vicinity propertiesfor soil extraction and radioactive characterization. In order to provide adequatecharacterization of uranium and radium at the processing site, a sampling protocol wasestablished prior to remediation, DOE-provided -additional soil background data and establishedthe Ra-226 background to be 1.5 pCi/G in the final report and vicinity property reports.

6.3.2 Cleanup Standards

DOE committed to excavate contaminated soil to meet the EPA standard of 5 pCi/g (surface)and 15 pCi/g (subsurface) plus background for Ra-226 in soil and. to. place the contaminatedmaterials in an engineered disposal cell. Excavation will be monitored to ensure that cleanupefforts are complete. The cleanup plan is to.stockpile the debris and vicinity propefty material inthe mill yard and begin site excavation at the higher elevations.

All buildings on the site will be demolished, and all contaminated debris will be placed in thedisposal cell. Therefore, cleanup of buildings is not required.

DOE stated that subsoil conditions in the tailings pile area generally consist of a high percentageof cobbles and gravels greater that a Number 4 sieve. Therefore, DOE proposes use of thegeneric procedure for determining the bulk, Ra-226 and Th-230 content of cobbly soil for


excavation'control and verification. NRC concurred on the generic procedure, but stipulated thata report detailing the site-specific procedures used should be provided for NRC review in aseparate report or in the Completion Report. DOE provided corrected and updated cobbles-to-fines information in the update to the RAP, and the staff finds this additional informationacceptable.

6.3.3 Supplemental Standards

DOE submitted (DOE, 1994; Appendix A, including calculation 17-730-02-02) an application forsupplemental standards to exclude remediation of some windblown tailings areas and tailingsburied around a gas line. DOE also provided the same information by letter dated October 7,1994, and NRC staff responded on April 19, 1995, with two general and six specific commentsresulting from its review of the application. DOE provided a response to those comments onDecember 21, 1995. At the time of completion of this TER, those responses were treated andresolved as Vicinity Properties.

The Vicinity Properties under consideration for supplemental standards total approximately142 acres and contain approximately 119,600 cubic yards of contaminated soil. The generaljustification for not excavating these Vicinity Properties is that cleanup would be difficult andcostly, and the material does not pose a significant health risk. The application of thesupplemental standard of "no remedial action" for these Vicinity Properties is based on meeting40 CFR 192.21 (a-f) criteria that represent circumstances that would result due to remedialaction. The Part 192 criteria applied by DOE are:

a. clear and present risk of injury to Workers or the public;

b. environmental harm that is excessive (long-term, manifest) compared to the healthbenefits; and

c. high cost relative to long-term benefits at a vicinity property, and the residual radioactivematerials do not pose a clear present or future hazard.

The type of Vicinity Properties and the above criteria that DOE applied to each VicinityProperties are: River Front Wetlands (Former Pile Area and Area E) - Criterion b; Former OreStorage Area Steep Slopes - Criteria a, b, and c; Steep Slopes with Windblown RadioactiveMaterial (Areas B, C, D, E, F, G1, and G2) - Criteria a, b, and c; and High-Pressure Gas Line -Criteria a, b, c.

NRC staff provided specific comments on each Vicinity Property type, as well as the generalcomment that all Vicinity Properties proposed by DOE for the application of supplementalstandards include the criterion of environmental harm without adequate justification. DOEaddressed-how partial remediation of the areas proposed for-"no remediation" would cause"environmental harm that is clearly excessive compared to the health benefits to persons livingon or near the site, now or in the future" as required by 40 CFR 192.21(b). DOE providedindividual assessments and applied the appropriate criteria for supplemental standards in eachvicinity property completion report.


1 '!) ; .

DOE indicates that the river front wetlands (3.8 acres) are under the jurisdiction of the COE, andareas with cottonwood and willow seedlings that occur next to the river are to be protected.However, the UMTRA Project has replaced wetlands vegetation at other sites. DOE alsoindicates that spillage of, contaminated material during excavation could contaminate the river,but some of this material probably enters the river with each flood. As indicated above, DOEaddressed how remediation of the river front wetlands "would, notwithstanding reasonablemeasures to limit damage, directly produce environmental harm that is clearly excessivecompared to the health benefits to people living on or near the site, now or in the future," asrequired by 40 CFR 192.21(b).

For Vicinity Properties with steep slopes, DOE indicated that there are relatively flat portions, butthat the extra cost to gain access with equipment would .exceed the long-term benefits. DOEprovided detailed discussion of the cost to benefit information and limited health risk for eachindividual vicinity property completion report for justification and use of the supplementalstandards.

The steep slopes of Areas B, C, and E border the east side of the highway. RAP Figure 3indicates that, typically, a 50-foot-wide strip beside the highway will not be excavated. Area Dcovers 114.5 acres on the west side of the highway. It appears that some portions of theseareas could be remediated without excessive cost or risk, assuming that the elevated radonreadings are not due to natural (in situ) deposits. Because final excavation limits for all areasare determined by the DOE contractor in the field, DOE should provide guidance (possibly areminder on the extent of excavation map) indicating that the remediation will come as close tomeeting the otherwise applicable standards as is reasonable under the circumstances. DOEprovided discussion of the cost to benefit information in the individual .vicinity propertycompletion report for justification and use of the supplemental standards.

In addition, the construction of a golf course on the east side of the highway at the Naturita site(Area E) and a recreational vehicle park on the west side of the highway (Area D) has beensuggested (February 22, 1995, letter from D. Crane, Chairman, Naturita Citizens Group toW. Woodworth, DOE, Project Site Manager for Naturita). There was no consideration of thesepossible future uses of the areas in the original information provided by DOE. DOE was askedto provide a discussion of possible future uses of all the supplemental standard areas in thediscussion of potential health risks to persons that might occupy the areas. DOE provided thisinformation and discussed the potential health risk in each individual vicinity property completionreport.

One steep windblown area, labeled G2, has an average Ra-226 concentration of 53 pCi/g (10samples) and the highest value was 206 pCi/g. DOE provided discussion of the health risk andof the cost to benefit information in the individual vicinity property completion reports forjustification and use of the supplemental standards.

For the gas line, DOE proposes that a 5-foot-wide area on either side of the line remainunexcavated. Notes of a conversation with an employee of the Natural Gas Company indicatethat excavation must be by hand for 3 feet on either side of the line. DOE indicates that the costand time for hiring specialized workers or providing workers extra training and specialequipment for work near the gas line may not be warranted because of the low risk of public


radiation exposure, but specialized workers or training may not be necessary for work severalfeet away from the line. Also, DOE has not provided information to indicate what entity (theState of Colorado, City of Naturita, or Natural Gas Company) would have the responsibility ofdisposing of the contaminated material should the gas line be dug up. In addition,Ra-226 data were not provided for the assessment of potential health risk, because DOEassumed the remote location would prevent public exposure. DOE treated the gas line area asa vicinity property and provided justification for the use of supplemental standards in thecompletion report for this area,

A record of a conversation with a representative of the Natural Gas Company was the only landowner comment originally provided by DOE. DOE's submittal stated that a record ofnegotiations with the other owners is documented in the Remedial Action Agreement, but nocopies of these agreements or discussions were provided. As required by 40 CFR 192.22(c),DOE provided NRC with copies of comments from land owners regarding the proposedapplication of supplemental standards to portions of their property. DOE provided copies of thediscussions and agreements in the vicinity property completion report, which was reviewed bythe staff and found acceptable.

6.3.4 Verification

The final radiological verification survey for land cleanup will be based on 100-square-meterareas. The standard method for Ra-226 verification is analysis of composite soil samples bygamma spectrometry, but DOE may use several other measurement techniques, depending onparticular circumstances. DOE indicates that the nine-point composite gamma measurementtechnique or the RTRAK detection unit may be used in the windblown areas. NRC haspreviously agreed to the use of these procedures with adequate quality control in specific cases.

DOE stated that verification for Th-230 will follow the generic thorium policy. Also, any uraniumcleanup verification will.be derived as part of a supplemental standard.

No on-site structures at the processing site will require radiological verification, because allstructures will be demolished and the debris will be buried at the disposal cell.

6.4 Conclusions

Based on review of the design and analyses presented in the RAP (DOE, 1998) and associateddocuments, NRC staff concludes that the radon attenuation model has some short-comings, butmodeling by the staff demonstrates that the radon barrier design is conservative: Radon.attenuation provided by the frost protection layer was, conservatively, not considered in eithermodel. In addition, DOE has committed to do further testing of materials and will perform a final-radon flux analysis with-as-built parameter values to verify the design. This final analysis will beprovided for NRC review as part of the Completion Report. Therefore, assuming all cell stabilityissues will be. resolved, staff is assured that the average surface radon flux will be below theEPA standard.


The staff finds that the radiological characterization program, the proposed processing sitecleanup, and Verification plans have been addressed in the changes to the Remedial ActionPlan and the Vicinity Property Completion Reports.


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.,~ if.-

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