ML20153H328

Draft Technical Evaluation Rept for Proposed Remedial Action at Grand Junction Tailings Site,Grand Junction,Co

ML20153H328
Person / Time
Issue date:	08/31/1988
From:	NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS)
To:
Shared Package
ML20153H251	List: ML20153H249 ML20153H328
References
REF-WM-54 NUDOCS 8809090151
Download: ML20153H328 (50)

Text

Enclosure 1 s

DRAFT TECHNICAL EVALUATION REPORT FOR THE PROPOSED REMEDIAL ACTION AT THE GRAND JUNCTION TAIUNGS SITE GRAND JUNCTION, COLORADO August,1988 DIVIS10tl 0F LOW-LEVEL WASTE MANAGEMENT AND DECOMMISS10 Nil 1 OfflCE OF NUCLEAR MATERIAL SAFETY AND SAFEGUARDS U.S. ItVCLEAR REGULATORY COMMISSION R8R'92in WM 54 **

• PDC

1 ORAFT TECHNICAL EVALUATION REPORT FOR THE PROPOSED REMEDIAL ACTION AT THE GRAND JUNCTION TAILINGS SITE GRAND JUNCTION, COLORADO I

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1.0 INTRODUCTION

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1.1. EPA Standards..................................... 5 t 1.2. Site and Proposed Action.......................... 6 i 1.3. Review Process.................................... 6 1.4 T E R O rg a n i z a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 ,

1.5. Summary of Open Items............................. 10 t i

2.0 GEOLOGIC STABILITY...................................... 13 .

2.1. Introduction...................................... 13 1 2.2. Location.......................................... 13  ;

2.3. Geology........................................... 13 l 2.3.1. Stratigraphic Setting.................... 13 '

2.3.2. Structural Setting....................... 14 2.3.3. Geomorphic Setting....................... 15 2.3.4. Seismicity............................... 15 l 2.4. Geologic Stabt11ty................................ 17 ,

2.4.1. Bedrock Suitabi11ty...................... 17 i

! 2.4.2. Geomorphic Stabt11ty..................... 17 i j 2.4.3. Seismotectonic Stability................. 18 l 2.5. Conclusions....................................... 19 l

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3.0 GEOTECHNICAL STABILITY.................................. 20 >

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3.1. Introduction...................................... 20 [

4 3.2. Site Characterization............................. 20  :

3.2.1. Grand Junction Characterization -  !

I Description of Site...................... 20  !

) 3.2.2. Grand Junction Site-Site Investigations.. 20 l

! 3.2.3. Cheney Reservoir Disposal Site - l' Description of Site...................... 21 3.2.4. Cheney Reservoir Site - Site {

Investigations........................... 21 l 3.2.5. Cheney Reservoir Site-Site Stratigraphy.. 22 [-

l 3.2.6. Testing Progras.......................... 23 3.3. Geotechnica~1 Engineering Evaluation..s............ 23 3.3.1. Stability Evaluation..................... 23

j. 3.3.2. Liquefaction............................. 24 i 1 3.3.3. Cover Design............................. 24 }

3.4. Geotechnical Construction Criteria................ 25 i 3.5. Conclusions....................................... 25 I j

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4.0 SURFACE WATER HYOROLOGY AND EROSION PROTECTION.......... 26 4

' b 1 4.1. Hydrologic Descriptien and Site Conceptual Design. 26 i 4.2. Floedi ng 0eterminati cns. . . . . . . . . . . . . . . . . . . . . . . . . . . 26 4.2.1. Probable Maximum Precipitation (PMP)..... 26 4.2.2. Infiltration Losses.................-.... 27 4.2.3. Time of Concentration.................... 27 4.2.4 PMP Rainfall Distributions............... 27  :

4.2.5. Computation of PMF. . . . . . . . . . . . . . . . . . . . . . . 27 [

4.2.5.1. Onsite Drainage..................... 27  !

, 4.2.5.2. Diversion Ditches................... 27  !

l 4.2.5.3. East Side Creek..................... 28  !

l 4.3. Water Surface Profiles and Channel Velocities..... 28 I

! 4.3.1. Top $1 opes............................... 28 i

! 4.3.2. Side $1 opes.............................. 29 i

4.3.3. East Side Creek.......................... 30

i 4.3.4 Diversion 0 itches........................ 31 i 4.4. Erosion Protection................................ 32 l 4.4.1. Sizing of Erosion Protection............. 32 ,

4 4.4.2. Rock Durabt11ty.......................... 33 (

i 4.5. Upstrerm Dam Failures............................. 33 l

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5 4.6. Conclusions....................................... 33 j 5.0 WATER RESOURCES PROTECTION.............................. 34 a

l I 5.1. Introduction...................................... 34  !

J 5.2. Disposal and Control of Residual Radioactive

) Materia 1..........................................34 l 1 5.2.1. Groundwater Protection Standard.......... 34 i 1 5.2.1.1. Hazardous Constituents.............. 34 4 5.2.1.2. Concentration Limits................ 35  :

j 5.2.1.3. Point of Compliance. . . . . . . . . . . . . . . . . 35

, 5.2.2. Performance Assessment................... 35 l 5.2.2.1. Design Analysis of the Disposal Unit................................ 36 5.2.2.2. Hydrogeologic Characteristics and Performance Assessment.............. 36

5.2,3. Closure Performance Standard............. 37 5.2.4. Groundwater Monitoring and Corrective Action................................... 38  ;

Cleanup and Control of Existing Contamination..... 38

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! 6.0 RADON ATTENUATIOR AND SITE CLEAN-UP..................... 40

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6.1. Introduction...................................... 40 i 6.2. Radon Attenuation................................. 40 1 6.2.1. Parameters Evaluation.................... 40 i l

6.2.2, Radon Barrier Evaluation................. 42 [

6.3. Site C1ean-up..................................... 43

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7.0 S tJfM RY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , 4 4

8.0 REFERENCES

AND BIBLIOGRAPHY............................. 45 l

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1.0 INTRODUCTION

i The Grand Junction site was designated as one of 24 abandoned uranium mill j tailings plies to receive remedial action by the U.S. Department of Energy 1

(00E) under the Uranium / M1 Tallings Radiation Control Act of 1978 (UMTRCA). [

UMTRCA requires, in part, that NRC concur with DOE's selection of remedial  ;

action, such that the remedial action meets appropriate standards promulgated l by the U.S. Environmental Protection Agency (EPA). This draft Technica) l Evaluation Report (TER) documents the NRC staff's review of the DOE preliminary final design and remedial action plan and outlines the resulting outstanding j issues.

1.1 EPA Standards f 1

As required by UMTRCA, remedial action at the Grand Junction site must comply ,

with regulations established by the EPA in 40 CFR Part 192, Subparts A-C. t j, These regulations may be summarized as fo11ews: i

1. The disposal site shall be designed to control the tailings and other f residual radioactive material for 1000 years to the extent reasonably i

i achievable and, in any case, for at least 200 years [40 CFR i 192.02(a)).

2. The disposal site design shall prevent raden-222 fluxes from residual i

radioactive materials to the atmosphere from exceeding 20 .

picoeuries/ square meter /second or from increasing the annual average concentration of radon-222 in air by more than 0.5 picoeuries/ liter  :

I (40CFR192.02(b)). l The remedial action shall ensure that radium-226 concentrations in j 3.

land that is not part of the disposal site averaged over any area of j 100 square meters do not exceed the background level by more than 5 picoeuries/ gram averaged over the first 15 centimeters of soil below the surface and 15 picoeuries/ gram averaged over any 15-centimeter i

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thick layer of soil more than 15 centimeters below the land surface  !

[40CFR192.12(a)). [

< On September 3, 1985, the U.S. Tenth Circuit Court of Appeals remanded the i groundwater standards (40 CFR Part 192.2(a)(2)-(3)) and stipulated that EPA  !

promulgate new groundwater standards. EPA proposed these standards in the form i

< of revisions to Subparts A-C of 40 CFR Part 192 in September 1987. The proposed standards consist of two parts; a first part governing the control of a any future groundwater contamination that may occur from tailings piles after l remedial action, and a second part that applies to the clean-up of .

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contamination that occurred before the remedial action of the tailings. (

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6 1.2 5,ite and proposed Action The Grand Junction mill site is a 104-acre property adjacent to the south side of tne city of Grand Junction, Colorado, and adjacent to the north side of the l Colorado River (See Figure 1.1). The site consists of the tailings pile, mill l site, and effluent ponds of the former Climax Uranium Mill site, which was  !

operated by the Climax Uranium Company between 1951 and 1970. The State of Colorado presently uses a portion of the site (the State Repository) for temporary storage of contaminated material obtained from remedial action at vicinity properties in the Grand Junction area.

The Grand Junction site contains an estimated 4.1 million cubic yards of contaminated materials in the form of finely ground sand and slimes and contaminated soils. The tailings are covered with approximately six inches of soil; the site is sparsely vegetated. Concrete and brick from demolished mill buildings were placed as riprap along the north bank of the Colorado River.

The proposed disposal site is on Bureau of Land Management (BLM) land located off U.S. Highway 50, 18 miles southeast of Grand Junction, near Cheney i Reservoir (See Figure 1.2).

The proposed remedial action consists of the following major activities:

• Movement of all contaminated materials (uranium mill tailings, windblown contaminants, and demolition debris) to a disposal site located near Cheney Reservoir.

• Stabilization of contaminated materials in an embankment, which will rise a minimum of 50 feet above the surrounding terrain and will extend approximately 20 feet below grade.

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' Disposal of stabilized tailings in one layer, overlain by a layer of vicinity property material.

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• Coverage of the tailings embankment with a multilayered cover system on the top and sideslopes. Starting from the layer directly over the '

tailings, the topslope cover system consists of a two-foot-thick radon / moisture infiltration barrier covered by a geomembrane layer, which is in turn covered by a one-foot-thick sand bedding / drainage I layer, a choked rock layer, and finally topped by a two-foot-thick ,

l vegetated soil layer, The sideslopes are designed similarly except ['

the cover system has no soil layer on top and the riprap layer is not choked.

1.3 Review process l

l The NRC staff review was performed in accordance with the Standard Review plan  :

for UMTRCA Title I Mill Tailings Recedial Action Plans (Reference 1) and 6 consisted of comprehensive assessments of DOE's proposed preliminary final l

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9 design and remedial action plan. Staff review of preliminary final data and designs submitted by DOE indiente that there are still outstanding items as outlined in Section 1.5 and discussed in further detail in Chapters 2 through 7 of this TER. All open items of concern must be addressed before concurrence l with the proposed remecial action can be granted by NRC. The NRC .111 review all appropriate data suomitted by DOE in this regard. Upon resolution of the open items, the NRC staff will revise this TER into final form to include evaluations and conclusions with respects to the additional information submitted by DOE.

'The remedial action information assessed by the NRC staff was provided '

primarily in the following documents (References 2-11):

1. Remedial Action Plan and Site Design for Stabilization of the Inactive Uranium Mill Tatlings Site at Grand Junction, Colorado; ,

Final, Volumes I and II, March 1988, UMTRA-DOE /AL 050505.0000.

2. Uranium Mill Tailings Remedial Action Project (UMTRAP), Grand Junction, Colorado; Calculations, Final Design for Review, Volumes I, II, III, IV, and Addendum (Radon Barrier Thickness Design Calculations), February 1988.

3. Uranium Mill Tat 11ngs Remedial Action Project (UMTRAP), Grand Junction, Colorado; Information for Bidders, Volumes I, II, !!!, and IV, February 1988.

4. Uranium Mill Tailings Remedial Action Project (UMTRAP), Grand ,

Junction, Colorado; Subcontract Documents, Final Design for Review, February 1988.

5. UMTRA Project - Grand Junction, Calculation, Disposal Site Erosion Protection; MKE Occument No. 5025-GRJ-C-01-00787-02.

6. UMTRA Project, Grand Junction, Rock Source Evaluation.

7. UMTRA-Grand Junction, Changes Between Preliminary and Final Design i for qeview of Phase !! Subcontract Documents; and Response to NRC comments on draft Remedial Action Plan; Letter from W. John Arthur, 00E to Paul Lohaus, NRC, March 25, 1988. )

8. Water Resources Protection Strategy for Tailings Disposal at Cheney i Reservoir Disposal $1*=; Addendum to Remedial Action Plan and Site Design for Stabili:ation of the Inactive Uranium Mill Tailings Sites  ;

at Grand Junction, Colorado; May 1988. i

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9. Grand Junction, Colorado Cheney Reservoir Disposal Site; Conceptual  ;

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Design Calculations for the Proposed Vegetative Cover, June 1988, 1 i I

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10. Guidance Document for the Grand Junction Final Design for Review,  !

Jve 1988.

1.4 TER Organization The purpose of this draft Technical Evaluation Report is to document the NRC [

staff review of DOE's preliminary final remedial action plan for the Grand  ;

Junction Site and discuss the open items resulting from this review. The  !

following sections of this report have been organized by technical discipline l 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 staff's conclusions and identification of remaining open items with respect to the long-term stability l standard in 192.02(a). Section 5, Water Resources Protection, summarizes the t NRC staff's conclusions and remaining open items regarding the adequacy of  !

DOE's compliance demonstration wnh respect to EPA's groundwater protection l requirements in 40 CFR Part 192. Section 6 provides the basis for the staff l conclusions and identification of open items with respect to the radon control

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standards in 192.02(b).

1.5 Summary of Open Items The NRC staff review of the proposed DOE preliminary final design and remedial action plan has identified open items, which are discussed in more detail in the following chapters. A brief summary of these open items is provided in Table 1.1. .

11 TABLE 1.1

SUMMARY

OF OPEN ITEMS TER Regulatory Explanation Subsection citation _

1. 00E has not adequately addressed 2.4.2 192.02(a)(1) the potential impact of headwater extension of nearby deep gullies.

2. DOE has not completed long-term 3.2.6; 192.02(a)(2)(1) moisture and permeability testing 3.3.3; 192.02(a)(3) of the radon / infiltration barrier 6.2.1 material necessary to demonstrate the hydraulic conductivity and radon attenuation assumed in the design.

3. DOE has not used values of bulk 6.2.1 192.02(a)(2)(1) density and porosity for the radon barrier (layer 2) that are supported by the laboratory testing.

4. 00E has not completed the full 3.3.3 192.02(a)(1) analysis of frost penetration on the side slopes and impacts on cover design.

5. 00E has not provided adequate 3.3.3; 192.02(a)(3) demonstration that the entire cover 5.2.2.1 system can achieve the infiltration performance that is assumed in the  ;

groundwater impacts assessment.

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6. DOE has not completed radtological 3.2.6; 192,02(a)(2)(1) characterization of the ponds area 6.2.1 material and impacts to radon barrier thickness.

7. DOE has not finalized slope stability 3.3.1 192.02(a)(1) l analysis due to the conceptual nature t of the multilayered cover (layer thick-l ness variation and analysis of effects of geomertrane),

i j 8. 00E has net adequately designed 4.3.1 192.02(a)(1) l the riprap for the top slopes (gully formation assumptions).

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9. DOE has not adequately designed the 4.3.2 192.02(a)(1) riprap for the side slopes (flow spreading assumptions).

10. DOE has not adequately designed 4.3.3 192.02(s)(1) erosion protection of the outlet to diversion ditch D-1 to prevent erosional impacts from East Side Creek.

11. DOE has not adequately analyzed the 4.3.4 192.02(a)(1) effects of gully flows into the diversion ditches and the potential for diversion ditch clogging and sedimentation.

12. DOE has not adequately addressed the 5.2.1.1 192.02(a)(3);

selection of harardous constituents. 264.93

13. DOE has not clearly indicated the 5.2.1.2 192.02(a)(3);

concentration limits they propose. 264.94 14 DOE has not proposed a monitoring 5.2.1.3 192.02(a)(3) scheme at the point of compliance.

15. DOE has not provided adequate 5.?.2.2 192.02(a)(3) support for hydrologic assumptions used in the performance assessment (recharge and discharge scenarios, hydraulic conductivity).

16. DOE has not demonstrated that the 5.2.3 192.02(a)(4);

proposed cover design minimizes the 264.111 need for further maintenance (con-sideration of mounding),

17. DOE has not proposed a groundwater 5.2.4 192.02(a)(4)(b) performance monitoring program.

18. DOE has not presented an evaluation 5.3 192.12(c) of cleanup of existing contamination.

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O 13 2.0 GEOLOGIC STABILITY 2.1 Introduction This section of the TER documents NRC staff's revi n of geological information l for the proposed remedial action at the Grand Junction uranium mill tailings .

disposal site. Background information for this TER is derived from DOE's Remedial Action Plan (Ref. 2), DOE's Final Design for Review (Ref. 3),

supplementary information provided during the review process, staff's site visits, and independent sources as cited, 2.2 Location For this remedial action, site characterization is required for two areas in  :

Colorado: (1) the abandoned mill and tailings pila in Grand Junction, located i in western Colorado, on the Colorado River and aleng Interstate 70, 250 miles 1 west of Denver, and (2) a proposed disposal site near Cheney Reservoir, located approximately 18 miles southeast of Grand Junction, in the Gunnison River valley.

2.3 Geology t

EPA standards listed in 40 CFR 192 do not include generic or site-specific requirements for the characterization of geological conditions at UMTRA Project sites. Rather, 40 CFR 192.02(a) requires control shall be designed to be effective for up to 1,000 years, to the extent achievabis, and in any case for at least 200 years. NRC staff have interpreted this standard to mean that certain geological conditions must be met in order to have reasonable assurance that this long-term performance objective will be achieved. Guidance with regard to these conditions is specified in NRC's UMTRAP Standard Review Plan (SRP) (Ref. 1).

I 2.3.1 Stratigraphic Setting l DOE characterized regional and site stratigraphy by reference to published work and original field investigations as recommended in SRP section 2.2.2.1 (Ref.

, 1). Both the processing and disposal sites occur in broad valleys developed along strike of the Cretaceous Mancos Shale. The Mancos is a thick sequence of fissile shale containing sparse siltstones and sandstones. The Mancos i underlies the entire Grand Valley area, and has a thickness in excess of 3,800 feet (Ref.12). Each site occurs near the base of the Mancos, which is in turn underlain by Cretaceous Dakota Sandstone and the Burro Canyon Formation. The s Mesaverde Formation occurs bp-section and crops out near the tops of Grand Mesa i and the Book Cliffs to the east and north. Tertiary volcanic rocks form the i caps of Battlement and Grand Mesas to the east. The staff finds DOE's regional  :

characterization is sufficiently accurate upon which to base a review of the  !

detailed alternate site characterization. The abandoned mill tailings are underlain by up to 20 feet of unconsolidated Colorado River alluvium. In general, the alluvium consists of an thin upper layer of silty deposits and a

14 thicker lower layer of coarser sand and gravel. Only a few wells penetrate the Mancos Shile beneath the tailings, and it appears to extend down to 60 feet in depth. Botn Mancos and Oakota crop out on the southern benk of the rive.r and the Mancos pinches out rcmpletely within one half mile southwest of the site.

Details of the mill area's stratigraphy, as it affects hydregeological and geetechnical conditions of the site and ability of the remedial Action to met UMTRA Project ground-water standards, are discussed in other sections of this TER.

The Cheney disposal area is located on the Grand Mesa piedmont in the Gunnison River valley, Deposits beneath the site consist of mud- to gravel-sized material with 25 to 50 feet thickness. While detailed site stratigraphy is poorly known, 005 determined that the deposits consist mainly of poorly stratified debris flows and secondary fluvial and eolian deposits. The fine grained matrix material appears to be derived from Mancos, Mesaverde, and Wasatch formation rocks below Grand Mesa. The gravelly fraction is predominantly vesicular and scoriaceous basalt derived from the mesa's cap.

Mancos Shale underlies the deposits and crops out along arroyo exposures. The Mancos is underlain by the Dakota and older strata which are not of significance to the remedial action. The staff find reasonable assurance that detailed subsurface geological conditions at Cheney will not affect the site's ability to meet remedial action standards.

2.3.2 Structural Setting DOE characterized the region's structural setting by reference to published regional geological maps, aerial reconnaissance, and field observation and mapping of features critical to assuring long-term stability of the remedial action. Thet,e studies were recommended in SRP section 2.2.2.3 (Ref. 1). The Grand Junction area is situated on the northeast flank of the Uncompahgre Upitft. The Uncompahgre Uplift is a large, northwest-trending, asymmetrically tilted block cored by Precambrian rocks. It is bounded on the northeastern and southwestern flanks by abrupt, locally faulted monoclines. The uplift was active as early as Pennsylvanian time, and is known to have experienced repeated uplift as recently as Miocene or Pliocene time, and may presently be undergoing continued deformation (Ref. 13). Potentially active faults associated with the northeast side of the uplift were mapped by Kirkham and Rogers (Ref.13) and lie 6 to 25 miles from the Cheney disposal site.

The Uncompahgre Uplift is bordered to the north by the Piceance Basin. Strata underlying the Grand Junction area dip northward and form a transitional :ene between the two structural features. The Piceance Basin formed in Laramide time and has undergone gradual uplift through Pliocene time (Ref. 2). The basin is bounded on all sides by uplifts of Laramide age, and developed over 8,200 feet of stratigraphic section since the Late Cretaceous.

15 2.3.3 Geomorphic Setting 00E characterized the region's shysiography by reference to published literature and topographic maps, as reco meaded in SRP section 2.2.2.2 (Ref.

1). Site geomorphic conditions were characterized by aerial photographic interpretation and field observations. The area is located in the Canyonlands section of the northeastern Colorado Plateau physiographic province (Ref. 14).

The Book Cliffs, a few miles to the north, form the northern boundary of the Canyonlands Section and the southern edge of the Vinta Basin. The Colorado and Gunnison Rivers occur along strike valleys in the Mancos Shale.

The Grand Junction mill site and tailings pile are located on a 114-acre site en the Colorado River's floodplain. Approximately 4 million cubic yards of I tallings are currently protected from the river by a 30-foot berm of concrete

! blocks and other debris (Ref. 2). In some places, the river approaches directly to the berm. Elsewhere, the river bank shows evidence of recent ,

erosion, such as development of transverse cracks near the water's edge and mass wasting into the river. A constant need for bank maintenance and other measures to isolate the tailings from erosion is a principal reason for  !

proposed removal of all contaminated material from the present disposal site. [

J The Cheney disposal site occurs on one of a series of nine pediment levels l lying below and west of Grand Mesa. The pediments are graded to ancestral levels of the Gunnison River or its tributaries. Each pediment surface is separated from adjacent ones by an erosional scarp. The pediments are eroded on shallowly dipping Mancos Shale and include up to 40 feet of Quaternary deposits in the proposed disposal area. The deposits are poorly sorted, .

consist of clayey to bouldery material, and appear to be derived from l Cretaceous strata and Tertiary volcanics that flank Grand Mesa. Grain-size r sorting and stratigraphy of the surficial deposits indicates they are mainly colluvial in origin.

Surface-water drainage from the disposal area is mainly by sheet flow.

However, ficw becomes channelized in many places, especially where drainage area or surface gradient is high, and gullies have formed in many areas. Four  !

gullies occur adjacent to or down gradient from the proposed disposal site.  !

Headward erosion and widening of the gullies are the most significant [

geomorphic process with which the remedial action must be concerned (Ref. 2).  ;

2.3.4 Seismicity l 00E characterized regional seismicity by obtaining data bases provided by the National Oceanographic and Atmospheric Administration (NOAA), by applying accepted techniques to determine earthquake magnitudes, and by employing methods suggested in SRP section 2.2.2.3 (Ref. 1) for calculating peak horizontal ground accelerations generated by a design-basis event.

Grand Junction and the Cheney site are each located in the northeastern portion '

of the Colorado plateau, bordered to the east by the Rocky Mountain r

16 physiographic province. Historical and instrumental seismic events have been concentrated along the margins of the Plateau, where it meets the Basin and Range or Rocky Mountain physiographic provinces (Ref. 2). The plateau includes a scible interior and several border zones which experience elevated seismicity, thinner crust, higher terrestrial heat flow, normal faults, and high occurrence of Tertiary and Quaternary volcante rocks. Nearly all large historic earthquakes of the plateau are associated with the border zones. The disposal sites are located in the Colorado Plateau's bcrder zone with the western Rocky Mountains.

NOAA's compilation of historical earthquake epicenters includes only five .

events within 65 km of the site. Calculated Richter magnitudes of the quakes i was as high as 4.4 However, faults responsible for the earthquakes have not been identified with certainty (Ref. 2). I DOE's analysis of potential earthquake magnitudes for the interior Colorado Plateau included determination of both the Maximum Earthquake (ME) and Floating Earthquake (FE) for the region. To augment its analysis of Colorado Plateau seismicity. 00E studied four regional structures for the occurrence of capable faults. First, faults in the Piceance Basin were determined through preliminary study to be not capable. Faults in the Paradox Basin, while displaying evidence of Neogene movement, are associated with salt dissolution l l and collapse, are not associated with lithospheric tectonism, and are not  :

capable of generating earthquakes in excess of Richter magnitude 5. Staff find these two areas do not present a seismic risk to long-term site stability.

l Based on literature review, DOE assumed several faults on the flanks of the Uncompahgre Uplift were potentially capable. Field examination of these faults l within 40 miles (65 km) of Cheney resulted in no observations of evidence that i any of these f aults have experienced Quaternary movement (Ref. 2). Seismic l activity in the western Rocky Mountain province is mainly associated with the ,

San Juan Mountains and Grand Hogback, each of which form the border with the l i

Colorado Plateau, Despite discovery of no capable faults in the Uncompahgre area, it appears that the Uncompahgre Uplift may be experiencing regional tectonic movement at this time. DOE concludes that the association of faults in the study area with an active regional structure requires that the faults de considered capable, i regardless of surficial expression of such. NRC staff find this conclusion an  !

acceptable and conservative basis upon which to calculate maulmum credible ,

earthquake magnitudes and peak horizontal ground acceleration values. See the  !

Seismotectonic Stability section for a discussion of DOE's analysis of the design earthquake and peak horizontal ground acceleration value for the Cheney disposal site. l l

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17 2.4 Geologic Stability r Geological conditions and processes at the sites are characterized tn determine  !

the ability to meet 40 CFR 192.02(a). In general, site lithologic, i stratigraphic, and structural conditions are considered for their suitanlity  !

i as a disposal foundation and their potential interaction with tat 11rgs lea: hate and ground water. Geomorphic processes are considered for their potential i impact upon long-term tailings stabilization and isolation. Potential geologic  ;

hazards, including seismic shaking, liquefaction, on-site fault rupture, ground '

collapse, and volcanism are identified for the purpose of assuring the long-term stability of the disposal cell and success of the remedial action. i 2.4.1 Bedrock Suttability DOE's proposed remedial actions are influenced mainly by charactwistics of l unconsolidated floodplain deposits at Grand Junction's mill site and colluvial .i deposits at Cheney. The staff conclude that bedrock stratigraphic and i structural conditions at the sites should have no affect on DOE's ability to j meet remedial action standards.  ;

l 2.4.2 Geomorphic Stability I

Stabiltration of stil tailings in their present location would require constant ,

maintenance and repair of existing erosion control features (Ref. 2). Proposed [

removal of Grand Junction's tailings will result in elimination of the site's [

major geomorphic hazard: erosion of tailings during a catastrophic flood event in the Colorado River basin.

Adequate characterization and interpretation of surficial deposits and bedrock conditions at Cheney presented a major concern early in NRC's review process. ,

I Geomorphic issues addressed by NRC centered on (1) evidence at the site that I the Cheney ares has experienced long-term landscape stability in the past, and [

(2) potential for future channel incision and site instability.

l Geomorphic features observed by site investigators, and attributed to past I

long-term landscape stability, included relic bar-and-swale topography, desert pavement, desert varnish on surficial stones, and well-developed sotis with argillic B and calcic C horizons. Staff found that presentation of DOE's ,

observations and interpretations were not clear or complete, and made comments &

on the draft RAP regarding landscape stability at Cheney. Careful review of the Remedial Action Plan, reference to applicable geological literature, discussion between staff and DOE's geomorphic consultant, requests for additional information, and staff site visits resulted in a better l understanding of the site's features as described in the RAP. Site visits by i NRC staff confirmed the existence of several of the features, and interpretations that the pediment surface is at least late Pittstocene in age ,

(Ref. 2) appears to be accurate. Staff, however, suggested the bar-and-swale  !

features could be evidence of recent overland flow concentration and incipient l

i

[

18 I

l a formation Thers. ore, the NRC staff find that potent ai l channel growth

. :icn of the site should be accounted for in the site design.

f. 2) considers that the greatest geomorphic hazard at the Cheney site Jward extension of deep gullies occurring southwest of the proposed r osal area. Four principal channels exist in the area, and are expected to widen or erede headward toward the proposed disposal location. One channel (Creek C; Ref. 2) approaches within 1,100 feet of the location with a distinct '

v-shape prefile. It is assumed this channel is headcutting toward the site.

Another channel (Creek 0; Ref. 2) has steep side slopes within 450 feet of the proposed disposal location.

NRC staff considered in its early reviews that formation of new gullies was a hazard which 00E naeded to consider. Calculations and designs (Ref. 3) attempted to analyze depths of current gullies in the disposal area, and design a rock tpron around the disposal cell to limit future erosion. NRC staff consider that the analysis did not take into account the extent of erosion that may occur during the performance period of the remedial action.

DOE's analysis took into account only swales, up to five feet in relief, which already drain the disposal area. 00E (Ref. 3, calculation 05-659-01-02) analyses concluded that rock aprons are designed to halt erosion from gullies up to the five-foot depth. The analysis, however, did not account for actual incised channels 10 to 20 feet deep only a few hundred feet from the proposed disposal cell.

DOE needs to reevaluate the potential depth of gull'es which could develop near the disposal cell's edges. Then, it must be shown that the erosion protection features will accommodate potential gully erosion, and that long-term tailings stability and isolation will be achieved.

I 2.4.3 Seismotectonic Stability In order to select a design earthquake and estimate on-site horizontal ground acceleration for use in subsequent engineering analyses, DOE employed attenuation relationships of Campbell (Ref. 15). NRC staff considered that use

of Campbell (1981) relationships were unaccept4 Jly restrictive, and were biased toward geologic and seismic conditions of tha 'alifornia area. The staff's original review finding perceived a failure t.. employ current and germanc methcds that are acceptable to the seismologic community in ger,eral.

Based on a further analysis, however, accounting for regional variations of

, attenuation (Ref. 16), staff determined that calculated peak ground acceleration varied only 0.019 between the two methods. Therefore, the original calculations are considered to be reasonably conservative for design calculations, and further analysis is unnecessary.

Based on fault and seismicity analyses described above, DOE concluded that faults near Cheney are associated with modern tectonic activity in the i

"f - --- . . _ _ _ , _ _. _ _ - _- _ _ , _ _ _ , _ _ . , , _ . , _ _ - _ , - , - . - , - _ _ _ _ _

19 Uncompahgre Uplift. 00E employed published methods to determine an expected magnitude (Ref.17) and on-site peak horizontal ground acceleration (Ref.15) resulting from rupture on any fault associated with the Uncompshgro Uplift or other faults considered capable. As a result, DOE adopted the nearest fault (number 8; Ref. 2; Plate E.3.2) as the design fault for the Cheney site. Fault number 8 is credicted to experience a maximum credible earthquake of magnituce 6.8 and produce an on-site peak horizontal bedrock acceleration of 0.42g.

These criteria were derived through reasonable and conservative means, and the staff accept their adoption as design criteria for the Cheney dispesal site.

2.5 Conclusions Based upon review of the Final Remedial Action Plan and Final Design for Review, and DOE's response to NRC comments on drafts of these documents, staff has reasonable assurance that regional and site geological conditions have been characterized adequately to meet 40 CFR 192. The potentf for future gully erosion of the tailings embankment, however, has not been thoroughly examined, and the staff do not have reasonable assurance that the requirement for long-term stability will be met by the proposed erosion protection design.

Design criteria for the disposal cell's rock apron remains an open issue at 1

this time.

s 20 3.0 GEOTECHNICAL STABILITY 3.1 Introduction This section presents the NRC staff review of the geotechnical engineering aspects of the remedial actions at the Grand Junction, C0 UMTRAP site. The review results consist primarily of evaluations of the site characterization and geotechnical stability aspects of the stabilized tailings embankment and the cover design. The staff review of related geological aspects such as geologic, geomorphic, and seismic characcerizations of the site is presented in Section 2.0 of this report. The staff review of the ground water conditions at this site is presented in Section 5.0 of this report.

3.2 Site Characterization 3.2.1 Grand Junction Characterization - Description of Site The uranium mill tailings at the Grand Junction site were placed in one pile covering the southwestern and central area of the site. The pile forms a deposit that is approximately 10 feet thick at the western end of the site and is as much as 52 feet thick in the northeastern part. Shortly after the mill was shut down, efforts were made to stabilize the pile by the placement of concrete and brick from demolished mill buildings as riprap along the river.

The settling ponds were also covered with material from demolished buildings and then were contoured with an estimated 174,000 tons of tailings transferred from the main tailings pile. The tailings' pile was then covered to a minimum thickness of six inches of soil and revegetated, though little of the vegetation now remains. Contamination of material below the tailings pile has occurred d;e to tha movement of tailings liquids into the subpile materials.

As discussed in Section 1.2, the State of Colorado has placed contaminsted material from cleanup of vicinity properties in the Grand Junction area adjacent to the tailings pile, and will add to this pile as cleanup of the properties continue.

The Grand Junction site is on a young alluvial terrace a few feet above the present level of the Colorado River. Bedrock beneath the site consists of the

! Cretaceous Mancos Shale, Oakota Sandstone, and Burro Canyon Formation, which dip to the northeast under the site. A detailed site geological study at the n111 site was not conducted since the tailings and other contaminated materials will be relocated for stabilization.

3.2.2 Grand Junction Site - Site Investigations Seve/al subsurface investigations have been performed at the Grand Junction UMTRAP site in order to characterize the tailings and contaminated materials for geotechnical engineering and radiological chararteristics. These investigations have included:

21

1. A study by Bendix Field Engineering Corporation (1985) to determine the extent of contamination that resulted in data from 358 shallow soil samples, 177 boreholes, and 175 in-situ Ra-226 measurements. Addendum 01 to Appendix 0 of the final RAP (Ref. 3) is the Bendix report detailing the results of this investigation. Results of this investigation were used in estimating the volume of contaminated material to be removed from the Grand Junction mill site and relocated to the Cheney Reservoir disposal site. Additional radiological characterization of tailings and contaminated materials at the Grand Junction mill site were conducted by Chem-Nuclear Systems, Inc. (1987) results of which are presented in Volume IV of Information for Bidders (Ref. 4).

2. Investigations conducted by Sergeant, Hauskins, and Beckwith (1981),

Colorado State University (1980), Jacobs Engineering Group (1984),

Chem-Nuclear Systems, Inc. (1987), and Lincoln-DeVore (1987), which included 199 augur borings, 5 test pits, and monitoring wells from which samples for laboratory analysis were obtained. Geotechnical engineering characteristics of the tailings and contaminated materials have been l

determined through the lab analysis of the samples from these I investigations. Volumes I, II, and IV of the Information for Bidders (Ref. 4) present detailed information on the field investigations, logs, and lab analysis of these studies.

3.2.3 Chenty Reservoir Disposal Site - Description of Site The Cheney Reservoir disposal site lies about one mile north of the Cheney Reservoir, which is utilized for livestock and wildlife watering. The terrain at the site is very flat and the area is sparsely covered with grasses and shrubs. The average elevation of the disposal area is about 5255 feet. The surficial material at the site is an eolian derived silt with some clay and sand and an occasional gravel to boulder size basalt fragment ranging from zero to three feet thick. Underlying the silt is a mixture of alluvium and colluvium deposits consisting of interlayered clay, silt, sand, and gravel with occasional layers of basalt cobbles and boulders. This layer apparently represents mixed alluvium and debris flow deposits.

3.2.4 Cheney Reservoir Site - Site Investigations Investigations conducted by Jacobs Engineering Group (1984), Lincoln-Devore (1986), and Western Engineers (1987), were performed at the Cheney Reservoir Site in order to characterize ihe soils and subsurface materials for l geotechnical engineering and radiological characteristics. These l investigations included borings, test pits, and monitoring wells from which samples for laboratory analysis were obtained. Geotechnical engineering characteristics of the materials and certain radiological characteristics were determined through laboratory analysis of samples from these investigations.

Volume III of the Information for Bicders (Ref. 4), and the Water Resources Protection Strategy document (Ref. 9) for disposal at the Cheney Reservoir site

i l

l 22 present detailed information on the field investigations, logs, and lab analysis of these studies.

3.2.5 Cheney Reservoir Site - Site Stratigraphy The site stratigraphy can be divided into four zones as defined by the soil borings described in the previous section. These four zones are: (1) the surficial layer of unconsolidated deposits described in sectic.1 3.2.3 above; (2) The upper weathered zone of the Mancos Shale; (3) the lower, less weathered portion of the Mancos Shale; (4) and,the Dakota Sandstone and other formations underlying the Mancos Shale.

The unconsolidated deposits of the surficial layer range in thickness from 23.5 feet to 42.0 feet based on the borings. Idealized cross-sections of these materials divide the zone into three layers: (1) lean sandy clay or sandy silt, underlain by; (2) clayey to silty gravel, underlain by; (3) hard, lean clay.

The tailings will be placed partially below grade in the disposal cell; the base of the excavation will be at an elevation of from 5235 to 5240 feet. The foundation of the excavation, therefore, will consist of an average of 15 to 20 feet of the natural, unconsolidated surficial soil layers of the Cheney Reservoia site. Refer to Section 2.0 of this report for detailed evaluation of the geolo9y and bedrock conditions at the Cheney Reservoir site.

The earthen materials for the layered cover system will be obtained from the excavated materials, with the possible exception of erosion protection rock for the top slope. Radon barrier materials will br. composed of silty clays and clayey silts from layer 1 of the surficial soil:, and from minus 1-inch materials from layer 2 sieving. The drain ruterial will be obtained from crushed Type "A" material passing the 3-P.ch sieve but retained on the 1-inch sieve. The choked rock layer will also oe obtained from the sievlng process.

Erosion protection rock will be obtabed from the sieving process as well, however, it is possible that not enough rock is available at the Cheney Reservoir site. The remedial action plans on using borrow from other nearby I DOE UMTRAP projects to fill this need if it arises.

A thin perched ground-water t.ble exists at the Cheney Reservoir site in the upper weathered Mancos Shale and in the lower portion of the overlying alluvium. The perched system lies approximately 10 to 15 feet below the bottom of the excavated disposal cell. See Section 5.0 of this report for detailed evaluations of the ground water conditions of the Cheney Peservoir site.

The investigations discussed in Section 3.2.4 above included a total of 32 test pits and 4 auger borings, plus a 1760 foot deep explor,atory water well from which the stratigraphy of the Cheney Reservoir site was determined and the availability and suitability of the soil materials for the proposed uses was determined. The staff has reviewed the details of the test pits and borings as well as the scope of the overall geotechnical exploration program. The staff concludes that the geotechnical investigations conducted at the Cheney Reservoir disposal site adequately establish the stratigraphy and the soil

l 23 conditions at the Cheney Reservoir site, that the explorations are in general 1 conformance with applicable provisions of Chapter 2 of the NRC SRP, and that they are adequate to support the assessment of the geotechnical stability of the stabilized tailings and contaminated material in the disposal cell.

3.2.6 Testing Program The staff has reviewed the geotechnical engineering testing program for the Grand Junction mill site and the Cheney Reservoir disposal site. The testing program included physical pro?erty tests, compaction tests, triaxial shear strength tests, permeability tests, and particle size and gradation '

measurements on samples of tailings and contaminated materials and soils from the disposal site. The staff finds that the testing program employed was l appropriate for support of necessary engineering analyses and that the scope of '

the testing program and the utilization of the test results to define the material properties are in general agreement with applicable provisions of the NRC SRP. However, the DOE has not submitted all the test data for long-term moisture content and permeability of the radon / infiltration barrier, or all of the test data to characterize the ponds area materials that will include future material from vicinity properties. NRC's evaluation of the radon / infiltration barrier can not be completed until the staff is able to review all the test data on the materials.

1 3.3 Geotechnical Engineering Evaluation 3.3.1 Stability Evaluation f The staff has reviewed the exploration data, test results, critical slope characteristics and methods of analyses pertinent to the slope stability aspects of the remedial action plan for the Grand Junction UMTRAP site. The analyzed cross section with the 5 horizontal to 1 vertical slope has been compared with the exploration records and the design details. The staff finds '

that the characteristics of the slope have been properly represented and the most critical slope section has been considered for the stability analysis.

Soil parameters for the various materials in the stabilized embankment slope i have been adequately estabitsbed by appropriate testing of representative t material. Values of parameters for other earthen material have been assigned i on the basis of data obtained from geotcchnical explorations at the site and data published in the literature. The staff also finds that appropriate methods of stability analysis (the Modified Bishop's Method and infinite slope) i have been employed and have addressed the likely adverse conditions to which the slope may be subjected.' Factors of safety against failure of the slope for seismic loading conditions and static loading conditions have been evaluated .

for both the short term (end-of-construction) a-d long-term tate. The values of the seismic coefficients (.25g for the long-term condition ard .19g for the short-term condition) were calculated in accordance with the recommerded

methods in the NRC SRP and are acceptable to the staff. The staff firios th.'

the use of the pseudo-static method of analysis for seismic stability of the

(

-.m-r-c-,..,-.-,m - m--m--..--w-r-----,-rer -m e e------e._-- - - , - ,- ---*e m- r , ww-- -7 yr-wm-*- y r-w,r,- -----e- ~ wm vv '-e-~

l 24 1

slopes to be acceptable considering tne flatness of the slopes and the conservatism in the soil paramater values. The minimum factors of safety against failure of the slope were 2.42 and 1.09 for the short term static and pseudo-static conditions, respectively, compared to required minimums of 1.3 ,

and 1.0, respectively. The minimem factors of safety against fa11ere of the  ;

slope were 3.03 and 1.01 for tne long term static and pseudo-static conditions, respectively, compared to required minimums of 1.5 and 1.0, respectively. l However, it is evident that certain design details have not been finalized, ,

particularly the thicknesses of materials in the proposed cover. lJntil these design details are finalized and the effect of the addithnal materials on ,

slope stability fully analyzed, the stability of the slopes cannot be fully .

evaluated by the staff. Also, full details of the method that will be employed .

to ensure critical parameter values of the geomembrane layer with respect to '

, slope stability must be analyzed by the staff before slope stability can be fully evaluated.

3.3.2 Liquefaction The staff has reviewed the information presented on the potential for liquefaction at the site based on the results of geotechnical investigations, including boring and test pit logs, test data, soil profiles, and other information. The compacted dry density of the stabilized tailings material

! layer will be equal to a minimum of 90 percent of maximum dry density as determined by the ASTM 0-698 test, and the tailings pile embankment design provides for the tailings materials to be in an unsaturated condition. The perched ground-water table at the site is estimated to be 10 to 15 feet below the bottom of the excavation. Given these conditions, the staff agrees that i liquefaction at the sie would not be a concen. However, if the infiltration

through the cover cannot be limited to 1E-8 cm/sec., there exists the potential l for mounding of this perched water system to an extent that liquefaction could i occur. The evaluation of the liquefaction potential at the site may have to be j revisited based upon the final cover design and its associated infiltration

analyses (See section 3.3.3). ,

3.3.3 Cover Design The proposed conceptual cover design for the Cheney Reservoir disposal cell employs a multi-layered system of earther and geomembrane materials with a ,

different system of layers on the top slopes and the side slopes. On the top, l 1

in descending order from the surfar.e are: (1) a vegetated three foot thick soil ,

! layer; (2) a 1 and 1/4 foot thick rock erosion barrier including a choked rock l

filter layer; (3) a one foot clean sand drain layer; (4) a geomembrane layer; {

and (5) a two foot thick radon / infiltration barrier. On the side slopes, in 4

descending order are: (1) a one foot thick rock erosion barrier; (2) a one foot i thick clean sand drain layer; (3) a geomembrane layer, and (4) a two foot thick

! radon / infiltration layer. The Water Resources Protection Strategy document  :

assumes a hydraulic conductivity of IE-9 cm/sec. for the cover system. This value is based on assumed performances of the radon / infiltration barrier, the j geomembrane, and the vegetative cover in limiting infiltration through the r J

25 ~

cover system. However, the permeabilities of the geomembrane and the radon / infiltration barrier have not beer ;11y characterized and a full analysis of frost penetration on the st* slopes nas not been completed. This characterization and analysis must be completed, and the results of the permeability characterization used to develop a complete analysis that aemonstrates that the cover system will achieve the desired infiltration properties before the staff can complete an evaluation of the cover system.

3.4 Geotechnical Construction Criteria The staff has reviewed the geotechnical construction criteria contained in Appendix F to the RAP (Ref. 2) for earthwork and placement of materials in order to construct the stabilized embankment. Information on the preparation of the subbase and the construction of the radon / infiltration barrier is acceptable to the staff. However, due to the conceptual nature of the cover design, the construction criteria do not contain sufficient information on the construction of the remaining layers of the multi-layered cover system to permit a full evaluation by the staff, i

3.5 Conclusion Based on the review of the design of the Grand Junction remedial action plan as presented in the RAP and supporting documents, the NRC staff concludes that it cannot yet concur on the plan with respect to long-term stability aspects of the EPA standards (40 CFR Part 192.02(a)) f,or the reasons described in this section of the report.

i i

l

26 i 4.0 SURFACE WATER HYOROLOGY AND EROSION PROTECTION 4.1 Hydrologic Description and Site Conceptual Design The existing tailings in the city of Grand Junction, Colorado will be moved from their present location in the floodplain of the Colorado River to the  !

Cheney Reservoir site. The Cheney Reservoir site is located approximately 15 miles southwest of Grand Junction, Colorado and is situated on an alluvial surface. Small ephemeral streams are located on the east and west sides of the proposed remediated pile. The small stream on the east side of the pile, which has been named East Side Creek, is located immediately adjacent to the downstream end of the diversion ditch (Ditch D-1) on that side of the pile.

In order to comply with EPA standards, which require stability of the tailings for a 1,000-year (or minimum 200 year) period, DOE proposes to stabilize the tailings and contaminated materials in an engineered embankment to protect them from flooding and erosion. The design basis events for protection of the embankment slopes included the Probable Maximum Precipitation (PMP) and the Probable Maximum Flood (PMF) events, both of which are considered to have low probabilities of occurrence during the 1,000 year stabilization period.

The tailings will be consolidated into a single pile, which will be protected by soil and rock covers. The covers will have maximum slopes of 2% on the top ,

and 20% on the sides. The remediated embankment will be surrounded by aprons and diversion channels which will safely convey flood runoff away from the r tailings and prevent gully erosion into the stabilized pile. The top slope of the pile will have both soil and rock covers. A two-foot vegetated soil cover will be placed over a one-foot layer of riprap which will be designed to ,

prevent gully intrusion into the pile once gu11ying is initiated in the soil cover. The side slopes of the pile will be protected by a layer of rock riprap, which will not be covered by soil. ,

I 4.2 Flooding Determinations In order to determine site impacts from flooding, DOE analyzed peak flows and velocities and evaluated the need for erosion protection features. DOE esti-

• mated the PMF peaks resulting from an occurrence of the PMP over the various small drainage areas. These design events meet the criteria outlined in the Standard Review Plan (Ref.1) and are, therefore, acceptable.  !

The details of DOE's flood computations were analyzed by the NRC staff as follows:

4.2.1 Probable Maximum Precipitation (PMP) >

A PMP rainfall depth of approximately 7.9 inches in one hour was used by DOE to  !

compute the PMF for the small drainage areas at the site. This rainfall  ;

estimate was developed by DOE using Hydrometeorological Report (HMR) 49 (Ref. [

f

27 18). Based on a check of the rainfall computations, the staff concludes that the PMP was acceptably derived for this site.

4.2.2 Infiltration Losses In computing the peak flow rate for tne design of the rock erosion protection, DOE assumed that essentially no infiltration losses would occur. Based on a review of the computations, the staff concludes that this is a very conservative assumption and is, therefore, acceptable.

4.2.3 Time of Concentration The time of concentration is the amount of time required for runoff to reach the outlet of a drainage basin from the most remote point in that basin. The peak runoff for a given drainage basin is inversely proportional to the time of concentration for that basin. If the time of concentration is conservatively computed to be small, the peak discharge will therefore be conservatively large.

Various times of concentration (tc) for the aprons and embankments were esti-mated by 00E using methods discussed in Reference 19. The staff concludes that the procedures used for computing tc are representative of the small steep drainage areas present at the site. For very small drainage areas with very short times of concentration, 00E utilized tc's as low as 2.5 minutes, which is considered to be conservative.

4.2.4 PMP Rainfall Distributions 00E derived rainfall distributions and intensities from HMR 49 (Ref. 18), which is acceptable. In the detercination of peak flood flows, rainfall intensities for durations as short as 2.5 minutes were used. Basea on a review of this aspect of the flooding determination, the staff concludes that the computed peak rainfall intensities are conservative, and therefore, acceptable.

4.2.5 Computation of PMF 4.2.5.1 Onsite Orainage DOE utilized the rational formula (Ref. 19) to compute the peak sheet flows down the slopes and PMF flows on the aprons, given the input parameters dis-cussed above. Based on our review of the calculations presented, the staff concludes that this method of computation has been conservatively applied.

4.2.5.2 Diversion Ditches The PMF's for the diversion ditches were estimated using procedures discussed in Reference 19, which provides standard methods for estimating flood discharges. The PMF for Ditch 0-1, which has a drainage area of about 50 acres, was estimated to be approximately 900 cfs. The PMF for Ditch 0-2, which

O 28 has a drainage area of about 62 acres, was estimated to be approximately 1100 cfs. Review of these computations indicates that the peak ficod estimates have been acceptably derived.

4.2.5.3 East Side Creek The PMF for East Side Creek was estimated by 00E using Reference 20, which is a standard computational method for estimating peak flood discharges. Review of the computations indicates that 00E has used conservative and/or reasonable methods for estimating input parameters such as lag times, infilt ation losses, and rainfall distributions. Based on that review and on a comparisen with other peak flood discharge data such as that found in Reference 21, the staff concludes that the estimated peak PMF discharge of about 2800 cfs is acceptable.

4.3 Water Surface profiles and Channel Velocities Water surface profiles, velocities, and shear stresses used in designing erosion protection features were computed using various methods. The NRC staff checked the water level and velocity computations in accordance with standard procedures, such as those given in Reference 22, to determine their accuracy.

Based on this check, the staff concludes that the estimates are generally not appropriate.

4.3.1 Top Slopes

. l The design of the riprap layer for the top slopes of the pile is based on the assumption that a gully of a particular shape will be formed and that the gully will carry a peak discharge of some specified magnitude. It appears, however, that the assumption of a particular gully shape is not supported by the information provided. Additionally, the drainage area tributary to the gully may not have been adequately derived.

The staff fully recognizes that the shape of the gully and the drainage area is  ;

difficult to predict and particularly difficult to justify. However, in cases ,

where a soil cover is provided over a properly-designed riprap layer, it should i be assumed that the soil channel will erode to a critical configuration in a lateral and/or vertical direction until a hydraulically-efficient section is  !

formed. It should be pointed out that the actual section formed and peak ,

i discharge aay not be the most critical parameters affecting the riprap

! calculations; the critical parameter is likely to be the maximum depth of flow i in the gully. Therefore, a much more defensible concept, in this case, would be to assume that the gully' erodes to its maximum depth of two feet into the ,

soil cover and that the critical shear force is produced by this depth of flow, regardless of the width or cross-section shape of the gully. The shear stress

, acting on the riprap layer is then a function of only the depth of flow and can be computed using the formula T = 62.4 x y x S, where T is the shear stress, y is the maximum depth of flow (two feet), and S is the slope of the top cover

29 (0.02). This shear stress can then be used in the Safety Factors Method to arrive at an appropriate riprau size.

4.3.2 Side Slopes The design of the riprap layer for the side slopes of the pile is based on the formation of a gully on the top slope of the pile which then discharges concentrated flood flows onto the side slopes. The flow rate which was calculated for the desi:n of the riprap for the side slopes, however, does not appear to be conservatively derived. It appears that the actual amount of ficw spreading may be significantly less than the amount assumed to occur, resulting in higher peak discharges at the top slope / side slope interface (slope break).

First, the assumption that flow spreading will begin at a point 100 feet upstream of the slope break, at the end of the gully, is unsupported. It is likely that the gully could end closer to the slope break. Because the 10-foot rock shoulder will not be an impermeable barrier, some drainage from the assumed gully will occur through the rock layer. This will result in a lowering of the bsse level at the rock shoulder / soil cover interface, since flow in the gully will be able to drain through the rock. The elevation of the soil cover at the rock / soil Interface is more likely to be at the elevation of the rock layer on the top slope, which is two feet lower than assumed in the calculations. Therefore, the staff concludes that it is possible for a gully to exist immediately at the rock / soil interface. If a gully exists at this location, very little or no flow spreading will occur, and the design flow rate for the side slope riprap will be much higher than assumed.

Second, the rate of flow spreading that was a wmed does not appear to be appropriate. The computed rate of 160 feet of widening in a distance of 100 feet is unsupported by verified computational procedures or standard design practice. For example, in designing a diverging spillway chute, the U.S. Army Corps of Engineers utilizes a flow spreading angle of 1/3F, where F is the Froude Number of the incoming flow (See EM 1110-2-1o01, Hydraulic Design of Spillways,1965). Use of such a rate of flow spreading will result in a much smaller width of flow at the slope break.

Third, even if flow were to spread uniformly in a given distance, it is very unlikely that the flow rate in any one-foot width of embankment will be identical to the flow rate in the adjacent one-foot width. Such uniform flow rates could only occur if the embankment were perfectly level and the depth of flow over the rock layer is uniform across the entire width where flow spreading is assumed. This is very unlikely to occur on a riprapped slope; typical construction techniques do not permit such uniformity.

In order to resolve these concerns, DOE should revise the estimates of peak discharge for designing the riprap on the side slopes. These revisions should include consideration of the peak flow which could occur in a gully which is assumed to form on the top slope of the pile. The staff notes that the rock for the top slopes is designed for a much higher discharge than the rock for

30 the side slopes. It would be acceptable if the rock for the side slopes is designed for the maximum flow which could occur in a gully on the top slopes; this peak flow rate (in a one-foot width) can be determined using the Manning Equation where the area of flow (two square feet) and the hydraulic radius (two feet) are determined by the maximum depth of flow (two feet) in any one-foot width in a gully of any shape. Thus, the computations are not dependent on the assumption of a particular gully shape, drainage area, gully discharge, or amount of flow spreading (all of which are almost impossible to justify). The computations therefore are based on a flow rate which is the maximum that can be conveyed by a gully of any size, shape, or configuration. The rock size for the side slopes can then be determined using the Stephenson Method and this peak flow rate. The peak flow rate determined would also be acceptable for designing the rock for the top slope, using the Safety Factors Method; use of this flow rate should result in a shear stress approximating the shear stress calculated in accordance with the discussion in 4.3.1, above.

4.3.3 East Side Creek NRC staff review of the erosion protection provided for the outlet of Diversion Ditch 0-1 indicates that the design is rot adequate to prevent erosion from the flow velocities and scour produced in the East Side Creek. It appears that the computational procedures used to design this erosion protection were not appropriately applied, resulting in under-designed rock sizes and toe depths.

First, the use of existing cross-sections may not be representative of the sections which will exist during the occurrence of a major flood event. Due to the steepness of the stream causing supercritical flow, it is likely that significant erosion will occur which could alter existing sections. The sections could be scoured, which would result in a greater deptn of flow and

. higher velocities in the scoured area or could be eroded laterally which could

! result in larger flow areas and lower velocities. The actual amount of erosion, scour, and channel change are very difficult to predict. Therefore, it is necessary that the channel section that is used for design purposes has been carefully selected; the use of an average section interpolated between existing sections is generally not appropriate.

Second, if HEC-2 is used to develop water surface profiles between sections, it is usually necessary to use more than three cross-sections to compute the profile. This is particularly true when the sections change as drastically as those used in this application, where the bottom width of the channel changes from 0 to 80 feet in a horizontal distance of only 260 feet and where the flow velocities change significantly. Additionally, the assumed Manning's n value of .05 is generally considered to be inappropriate in an earth channel.

Third, the use of an average slope and velocity may not be representative of l

the actual slope and velocity that will exist immediately at the sectiori in question.

31 Fourth, a considerable amount of turbulence can be expected to occur in this irregular channel, causing an increase in the shear forces which will need to be resisted. With such irregularities, localized hydraulic jumps, eddies, vortices, etc can be expected to occur, causing increases in the shear stresses

~

on the riprap.

Fifth, additional increases in the shear force can be expected as a result of the location of the erosion protection on the outside of a bend in the channel.

This stream curvature can result in an increase in the riprap size required.

Review of the information provided indicates that rock larger than the proposed 20 inches may be difficult to locate within a reasonable distance of the site.

The staff also fully recognizes that the proposed riprap serves as backup protection for the energy dissipation area (EDA) and is located a significant distance away from the tailings area.

In order to resolve our concerns, we suggest that the most effective approach may be to perform minor regrading in the East Side Creek. The creek channel could be widened, straightened, aligned, and generally protected in a manner which would allow the use of 20-inch rock as a measure to protect against flood velocities in the channel. The width, depth, and shape of the channel necessary to reduce velocities and shear stresses to acceptable levels could be readily computed using the Safety Factors Method and normal depth procedures.

Additional protection and safety margins could also be provided by grading the channel so that (1) the minimum invert elevation occurs on the east side of the channel, i.e. the channel bottom is sloped to the east; (2) the channel is straightened or re-aligned so that the EDA is not on the outside of a bend; (3) a relatively uniform section exists both upstream and dowmstream of the EDA; (4) gradual transitions are constructed from the natural channel to the man-made portions of the channel; and (5) measures are taken to assure that hydraulic jumps and/or excessive turbulence occur well upstream or downstream of the EDA area.

The design of the riprap and the grading in the East Side Creek should be revised accordingly. Alternatively, larger riprap should be provided, taking into consideration each of the concerns mentioned above. If riprap is provided to protect the existing channel in the vicinity of the end of the EDA, it will probably require riprap considerably larger than the proposed 20 inches, and the toe will need to extend to a depth equal to the expected depth of scour.

4.3.4 Dhersion Ditches There appears to be a potential for concentrated gully flows to enter the diversion ditches. The staff considers it important to analyze the effects of gully inflows on the design of the riprap for the diversion ditches and to analyze the potential for clogging and sedimentation of the diversion ditches.

Review of DOE responses to the NRC staff's previous questions indicates that DOE concludes that sedimentation and clogging of the ditches will not be a

l l

32 problem and that concentration of runoff has been appropriately considered.

The staff does not agree with DOE's conclusions regarding either of these concerns, since DOE has not provided any technical justification of their conclusions.

First. It is not clear how the ditches will be self-flushing, since the_ro:k ditches are flatter and have a higher roughness coefficient than the earth gullies. If clogging of the ditch begins, it is not apparent what prevents the clogging from worsening or what causes the sediment to be flushed from the ditches.

Second, DOE's statement that no boulders will be transported into the ditches is not supported, especially in light of the fact that boulders have been observed in the gullies. Additionally, the entire rock source for the site riprap is expected to be derived locally from the pile excavation; it seems unlikely that there are no rocks present in the ditches or in locations.which could be eroded.

Third, DOE has addressed the problem of flow concentration only from the standpoint of increased flow rates due to rapid channelization; 00E has not addressed the problem of inflows directly into the diversion ditches. Such inflows may cause erosion of the ditch riprap, particularly on the side slope of the ditches which will receive gully flows directly down the side slopes.

If a gully discharges directly onto the ditch side slope, it is unlikely that the riprap can resist these flow velocities, since the rock is designed only for thne flow velocities which would occur longitudinally along the ditch and

, is not designed for the velocities and flow concentratiens produced in the gullies parpendicular to the side slopes.

l 00E should revise the riprap design of the diversien ditches, in light of the concerns discussed above. Acceptable approaches for designing the riprap to resist flow velocities caused by gully inflows are very similar to the approaches for designing the rock for the side slopes of the pile, where gully i

flows are accounted for in the design of the rock on steeper side slopes.

Steepening of the ditches to increase self-cleaning velocities may be one i e:ceptable solution to the sedimentation problem. Alternatively, DOE needs to further justify the ability of the riprsp design to withstand erosive forces produced in the natural earth gullies and the ability of the ditches to be self-cleaning and not require maintenance to perform their intended function.

Such justifications should be accompanied by pertinent technical analyses which document the ability of the designs to meet EPA long-term stability requirements. ,

4.4 Erosion Protection l 4.4.1 Sizing of Erosion Protection

. As discussed above. DOE has not correctly determined appropriate flow rates,

water surface profiles, velocities, shear stresses, and other parameters

l l

33 l

-\

l necessary to correctly design the erosion protection for the top slopes, side  !

slopes, diversion ditches, or the East Side Creek. It will be necessary for DOE to either completely re-design the crosion protection or to provide additional justification for the design proposed.

4.4.2 Rock Durability 00E has determined that the rock will be produced from the excavation of the  !

site. Gradation and rock durability criteria were presented, including the  :

results of several durability tests. Using the criteria provided in References 23 and 24, 00E has documented that the rock, while not of excellent quality, is of relatively good quality and is the most economical source that can reasonably be found. Based on our review of tne assessment., data, and criteria provided, the staff concludes that the rock durability criteria proposed and the rock to be found at the site are adequate.

4.5 Upstrean Dam Failures There are no impoundments near the site whose failure could potentially affect the site.

4.6 Conclusions Based on its review of the information submitted by DOE, the staff concludes that the site design will ng meet EPA requirements as stated in 40 CFR 192 with regard to flood design measures and erosion protection. An adequate hydraulic design has m been provided to reasonably assure stability of the contaminated material at the Cheney Reservoir site for a period of up to 1,000 years. 00E should revise the designs of the riprap for the top slopes, side slopes, ditches and East Side Creek. Alternatively, DOE should provide additional information which documents the adequacy of the design proposed.

34 5.0 WATER RESOURCES PROTECTION 5.1 Introduction The NRC staff has reviewed the Final Remedial Action Plan ( RAP) (Ref. 2) and the Water Resources Protection Strategy (WRPS) (Ref. 9) for the Grand Junction /Cheney Reservoir, Colorado UMTRA site in accordance with the NRC Oraft Technical Fosition on Information Needs to Demonstrate Compliance with EPA's Proposed Groundwater Protection Standards in 40 CFR Part 192, Subperts A-C (June, '2988). The purpose of the WRPS is to document DOE's strategy for complying with the EPA groundwater protection standards and to document groundwater impacts that may result from tailings disposal with respect to the standards. Based on our review, we consider that 00E has not provided sufficient information on groundwater p"otection to determine whether the proposed remedial action will be adequate to meet the EPA standards. Our review of groundwater information is documented in the following paragraphs.

5.2 Disposal and Control of Residual Radioactive Material 5.2.1 Groundwater Protection Standard EPA standards in 40 CFR Part 192.02(a)(3) require that disposal units be designed to control residual radioactive material in conformance with site-specific groundwater protection standards established by 00E. The groundwater protection standard consists of three components: 1) a list of hazardous constituents, 2) a corresponding list of concentration limits for the constituents, and 3) a point of compliance.

5.2.1.1 Hazardous Constituents 00E is required to select hazardous constituents based on characterization of the composition of the residual radioactive material, groundwater quality data, processes and reagents used in processing uranium, and an assessment of constituents reasonably expected to be in the waste. The list could include any of the 375 constituents listed in Appendix VIII of 40 CFR Part 261, along with molybdenum, radium, uranium, nitrate, and gross-alpha particle activity.

In the WRPS, DOE identified the following constituents as contaminants of concern due to their detection in tailings pore fluid: As, Ba, Ca, Pb, Mo, Ni, Se, Ra-226 and 228, U-234 and 238, and gross-alpha particle activity. 00E appears to have constrained their list of hazardous constituents to include only those for which EPA has proposed a Maximum Concentration Limit (MCL) in 40 CFR 192.02(a)(3). DOE did'not indicate in the WRPS whether these constituents or other constituents are expected to be in or derived from residual radioactive material at the Grand Junction site, as required in 40 CFR 192 Subpart A. DOE should revise Section 4.1.1 of the WRPS to discuss their ,

identified hazardous constituents with respect to the composition of the tailings, and if necessary, expand the list to include additional constituents which are likely to be derived from residual radioactive material at the site.

1

l 35 5.2.1.2 Concentration Limits DOE is required to propose concentration limits for all hazardous constituents which are not to be exceeded in groundwater at the Point of Compliance (POC).

The proposed concentration limits may be specified as background concentrations, Maximum Concentration Limits (MCLs) or Alternate Concentration limits (ACLs).

DOE does not clearly indicate in the WRPS what concentration limits they propose. Based on the information provided in Section 4.2.4 of the WRPS, NRC staff cannot determine whether DOE is proposing MCLs, or plans to request some other limits under Supplemental Standards. For example, 00E indicates that if the cover can limit infiltration to a rate of 1 E-9 cm/s, then MCLs for most hazardous constituents can be met at the POC. However, if the cover design can only achieve a flux rate of 1 E -8 cm/s (WRPS, p. 47), MCLs for at least five constituents will be exceeded at the POC. In this case, 00E claims that Supplemental Standards will be requested because the uppermost equifer is a Class III aquifer, 00E also states that, "...the proposed Supplemental Standards shall include maximum concentrations at the P00..." for constituents analyzed. DOE's intent is not clear to NRC staff. If DOE requests Supplemental Standards (or ACLs), they should provide information to justify their selection, demonstrate that the aquifer is Class III, demonstrate that concentrations are as low as reasonably achievable, and demonstrate that the proposed remedial action is sufficient to protect public health and the environment. ,

5.2.1.3 Point of Compliance DOE is required by 40 CFR Part 192.02 (a)(3) to propose a Point of Compliance for each disposal site. The POC is a vertical surface that extends downward into the uppermost aquifer along the hydraulically downgradient limit of the disposal area. DOE's selection of the POC should include a demonstration that a series of groundwater monitor wells along this surface will provide early warning of the release of hazardous constituents to the uppermost aquifer.

In accordance with 40 CFR Part 192.02(a)(3), 00E has specified in the WRPS that the POC at the Cheney site is the downgradient edge of the tailings waste management unit. However, 00E has not proposed a monitoring scheme at the POC or demonstrated that the monitoring design will be adequate to provide early warning of release of hazardous constituents to the uppermost aquifer. DOE should revise the WRPS to discuss how the POC will be monitored.

5.2.2 Performance Asses'sment In accordance with 40 CFR Part 192 Subpart A, 00E is required to demonstrate that the overall performance of the proposed disposal unit and disposal design is adequate to comply with the groundwater protection standard discussed in section 5.2.1, above. The demonstration should consist of an integrated analysis of the performance of the natural and engineered features of the

36 disposal. site, and include the following: 1) an assessment of the hydrogeologic characteristics of the disposal site suf ficient to support analysis of disposal unit designs and disposal performance, 2) a design analysis of the disposal unit, and 3) a performance assessment of the disposal system. The overall performance assessment should be a defensible, conservative analysis, taking into account realistic failure sceanarios of engineered components. 00E should evaluate in their assessment the distribution and amounts of rainfall, rates dnd distd butions of infiltration into the disposal unit. And leaching and transport of constitusnts downgradient of the disposal unit.

5.2.2.1 Design Analysis of the Disposal Unit 00E has not provided a quantitative analysis of infiltration into the tailings through the proposed cover design. Although DOE has described in the WRPS the mutually reinforcing components of the cover designed to limit infiltration to a flux of 1 E-9 cm/s, they have not performed a quantitative analysis, considering realistic failure scenarios, to demonstrate that this can be achieved. Until 00E demonstrates that the cover can achieve an operative flux of 1 E -9 cm/s, 00E should select and justify a groundwater protection standard (such as Supplemental Standards or ACLs) based on performance assessment results using a more conservative flux estimate.

5.2.2.2 Hydrogeologic Characteristics and Performance Assessment Although 00E has attempted to characterize the flow regime of che uppermost aquifer at the Cheney site, the hydrogeologic model used in support of DOE's performance assessment presented in the WRPS appears to be founded on an inadequate understanding of the site hydrology. NRC staff consider that 00E has not provided adequate support for the following hydrologic assumptions used in the performance assessment presented in the WRPS:

a) The assumption that the perched aquifer is a consequence of leakage l

from Whiting's Ditch.

Based on a visual inspection of Whiting's Ditch during an NRC staff visit to the Cheney site in August, 1988, the ditch was dry, and there was no evidence to support DOE's theory that the ditch serves as the principle recharge source I to the shallow aquifer as described in DOE documents (FRAP, FEIS, and WRPS).

In addition, Whiting's Ditch does not divert water from Indian Creek as described in the WRPS and FRAP. In reality, the ditch diverts water from the creek west of Indian Creek (Creek 0), which appears to get very little flow 1 based on NRC staff observations in the field. At one time Creek 0 diverted water from Indian Creek further up stream, but the diversion dam on Indian l creek appears to have been breached a number of years ago. NRC staff suggest that 00E revise the WRPS to examine alternate recharge scenarios, such as percolation from infiltration, and discuss the importance of these results with respect to EPA's standards in 40 Part 192.

37 b) The assumption that the aquifer is discharged by direct evaporation from depth or deep percolation into the Mancos Shala.

Because there is insufficient information concerning aquifer discharge to fully understand the fate of potentially contaminated groundwater, NRC staff suggest that 00E consider other possible discharge scenarios, such as downgradient discharge of the aquifer flowing under the site into Indian Creek and its tributaries. NRC staff consider that this scenario cannot be dismissed based on current available information. 00E should either consider this s:enario in their analysis to demonstrate that the public and environment will be protected (i.e., perform simple dilution calculations at the creek), or demonstrate why this scenario need not be considered, c) The assumption that a hydraulic conductivity of 3.5 ft/ day, calculated from the Whiting's Ditch recharge scenario, is applicable.

00E indicates in the WRPS that a minimum effective aquifer hydraulic conductivity of 3.5 ft/ day (1.2 E-3 cm/s) was calculated based on an assumed age of the ditch (70 years) and an assumed downgradient extent of the recharge front (7000 ft). The assumed downgradient extent of the perched aquifer was based on several dry wells on site. 00E states that the hydraulic conductivity could be much higher than this (if the system is in steady-state and water is evaporating or percolating into Mancos), but this value should provide a conservatively low estimate of the dilution potential of the aquifer, and consequently, a conservatively high estimate of leachate concentrations at the POC in their performance assessment.

However, actual measured in-situ hydraulic conductivity values based on slug-withdrawal tests in two of the wells are much lower than this, on the order of 2.0E-5 to 5.0E-6 cm/s (Table E.7.3, FRAP). Use of these values in the performance assessment should result in reduced potantial for dilution by the aquifer, and consequently, higher concentrations of constituents at the POC.

1 NRC staff suggest that DOE revise the WRPS to include additional analysis based on the measured, less conservative hydraulic conductivity values to calculate concentration ratios for hazardous constituents at the POC, and discuss the results of the analysis with respect to the EPA standards, b summary, NRC staff consider that 00E has not adequately charactsrized the shallow groundwater flow regime, including recharge and discharge, areal extent of the aquifer, and rate and directions of flow, or conducted a performance assessment analysis adequate to demonstrate compliance with the proposed EPA standards in 40 CFR 192.02(a)(3).

5.2.3 Closure Performance Standard In accordance with the closure performance standard of 40 CFR Part 192.02(a)(4), 00E is required to demonstrate that the proposed disposal design:

38  :

1) minimizes the need for further maintenance as required in 40 CFR Part 264.111(a); and 2) controls, minimizes, or eliminates releases of hazardous constituents to groundwater as required in 40 CFR Part 264.111(b). ,

With respect to 40 CFR Part 264.111(a) DOE has not demonstrated in the WRPS .

that the pruposed cover design will not require active maintenance to assure  !

ccmpliance with the groundwater protection standard. Failure of the cover components to perform according to design could result in groundwater mcunding i below the pile, subsequent pile instsbility, and ultimate failure to comply with the long-term stability standard in 40 CFR Part 192.02(a). DOE should consider in their analysis how potential mounding could result in the need to rely upon active maintenance of the cover.

1 With respect to 40 CFR Part 264.111(b), 00E has presented results of an assessment to demonstrate that the disposal unit is adequate to protect groundwater resources. However, NRC staff consider these results to be l i inconclusive until DOE provides additional constituent transport calculattens i based on alternative scenarios and assumptions, as described in Section 5.2.2,  !

above, and demonstrates stability of the cover as noted above.

5.2.4 Groundwater . Monitoring and Corrective Action  ;

DOE is required to describe an integrated monitoring program to be conducted before, during, and after completion of the disposal action to demonstrate that 2 the initial disposal performance complies with the groundwater protection standard and closure performance standards under 40 CFR Parts 192.02(a)(3) and '

(4).

O 00E has not provided details of the groundwater monitoring program to be t i implemented before, during, and after disposal of the tailings at Cheney (including monitoring at the POC). DOE states in the WRPS that the details of ,

the monitoring program will be provided in a separate document. NRC staff cannot riview the monitoring program for its adequacy until this document is submitted,  !

l

! $.3 Cleanup and Control of Existing Contamination [

i i

DOE is required to demonstrate compliance with EPA standards in 40 CFR Part [

', 192, Subparts B and C for cleanup and control of existing contamination. DOE's  ;

cleanup evaluation should consist of a

1) groundwater cleanup standard, 2) i cleanup demonstration, and 3) cleanup monitoring program.

DOE has not addressed ir, the' FRAP how groundwater cleanup will comply with EPA requirements in Subparts B and C of 40 CFR Part 192. NRC staff consider that

groundwater cleanup, however may be deferred until after EPA promulgates final j groundwater protection standards, provided that DOE demonstrate that disposal

, and clianup activities may proceed independently of each other. When the final l EPA standards are promulgated DOE should submit a cleanup assessment that F

I l

39 describes a groundwater cleanup standard, cleanup demonstration, and cleanup monitoring program as required in 40 CFR Part 192.

)

1 i

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l 1

40 6.0 RADON ATTENUATION AND S0IL CLEANVP 6.1 Introduction This section of the TER documents the staff evaluation of the radon attenuation design and the radiation survey plan for the remedial actions at the Grand Junction, C0 UMTRAP site. The review results consist primarily of evaluations of :he material characterization, radon barrier design, and soil cleanup aspects of the proposed reniedial action to assure compliance with the appropriate EPA standards.

6.2 Radon Attenuation As described in previous sections of this report, the radon / infiltration barrier will be composed of material excavated from the Cheney Reservoir disposal site and placed over the stabilized tailings embankment. The design thickness of this barrier is 2 feet.

The review of the cover design for the radon attenuation included evaluation of the pertinent design parameters for both the tailings / contaminated materials and the radon / infiltration barrier, and calculations of the radon barrier thickness.

The design parameters for the tailings, contaminated materials, and radon barrier materials evaluated include: long-term moisture content, material thickness, bulk density, specific gravity,' porosity, and radon diffusion coefficient. Radium content and radon emanation coefficient parameters were evaluated for the tailings and other contaminated materials. The computer code RAECOM was used to calculate the radon barrier thickness, and the input that included the above parameters was evaluated.

6.2.1. Parameter Evaluation The material properties and radiological parameters used in the design of the stabilized tailings pile and the radon / infiltration barrier at the Grand Junction site have been reviewed.

The material thicknesses used in the analysis are based on the conceptual design of the the remedial action plan and the available data. The main pile tailings and contaminated materials will be placed in the disposal cell as one layer, with tailings from the ponds area and vicinity property cleanup placed in a separate layer on top of the main pile tailings. The design assumes these layers are uniform and average property values are used for the materials. It is possible that some of the details of the design will change. However, the thicknesses of the contaminated materials are not likely to be altered.

Therefore, the thicknesses of these layers used in the analysis of the radon carrier are reasonable representations of the field conditions and are acceptable to the staff.

41 The bulk density and specific gravity were determined by field and laboratory tests, and the corresponding porosity was calculated. The bulk density and porosity for the tailings are 1.39 gm/cc and .492 respectively. These values were determined from representative samples of the materials and the staff finds these values to be acceptable. The values for these parameters for the ponds area material and the vicinity properties materials that will he placed as a separate layer in the stabilized emeankment are 1.87 gm/cc and .304 These values require further justification from characterization of representative ponds area and vicinity property materials for full evaluation of the radon barrier thickness. The bulk density and porosity for the layer 1 radon / infiltration barrier material are 1.65 gm/cc and .399 respectively. These parameter values are acceptable to the staff. The bulk density and porosity values for the layer 2 sieved radon / infiltration barrier material are 1.89 gm/cc and .327 respectively. These values are not supported by the lab measurements presented. 00E needs to either provide further lab tests that justify the values of these parameters used, or use values which are supported by the existing data before the staff's full evaluation of the radon / infiltration barrier design can be completed.

The design assumes the following long-term moisture contents: 18% for the tailings materials; 9% for the ponds area materials; 17% for the radon / infiltration barrier material that will be derived from layer 1 soils; and 10% for the radon / infiltration barrier material that will come from layer 2 materials. The laboratory tests conducted to date on layer 1 materials at 15 bar capillary pressure indicate a moisture saturation (0.760-0.820) that is significantly different than the one that is calculated using a method provided in the NRC SRP (0.394-0.496). Also, the in-situ moisture content of the material in layer 1 to be used for the radon barrier material is given in the final RAP as 12.0%, which is significantly lower than the 17.0% value used in the analysis. Results are needed from the additional capillary pressure tests on the radon barrier mate als before NRC's evaluation of the radon / infiltration barri e can be completed. The value of 10% for the layer 2 materials to be used in the radon / infiltration barrier requires a similar justification through the results of additional capillary pressure tests. The moisture contents assumed for use in the analysis for the two contaminated materials layers are determined from representative samples of the materials and are acceptable to the staff.

Radon diffusion coefficents for the cover material and tailings were derived from correlation curves of moisture saturation versus radon diffusion coefficisnt. These curves were developed using diffusion coefficients and moisture saturation data from laboratory measurements of soil samples that are intended to be representative of conditions in the stabilized pile. Further characterizatier of the radon / infiltration barrier materials, as described above, must b;. conducted and the results analyzed before NRC's evaluation of the radon barrier thickness can be completed. The values of the radon diffusion coefficient for the tailings material have been determined adequately, and a very conservative value of the radon diffusion coefficient based on the measured values has been used in the analysis for the ponds area

a 42 material. The use of these values in the analysis is, therefore, acceptable to the staff.

The radon emanation coefficient for the tailings material was measured in the laboratory on samples representative of field conditions and the value of 0.359 was conservatively determined based on the measured values and is acceptable to the staff. However, the radon emanation coefficient for the ponds area material was determined with limited data, and the value used is not conservative. Analyses with the RAECOM model indicate that the thickness of the radon barrier is extremely sensitive to this value. Therefore, further characterization of this parameter will need to be accomplished before a full evaluation of the radon / infiltration barrier design can be completed.

The radium content of several matericls at the site was measured. The average radium content to be used in the analysis was determined by weighted averaging with depth in a measurement hole than averaging over an area at any given depth. A weighted average value of the radium content for the main tallings pile material was calculated and a conservative value of 575 pCi/gm was chosen for radon / infiltration barrier thickness calculations. A value of 50 pC1/gm was conservatively estimated from limited data for the ponds area materials.

The value for the main tailings materials results from an adequate characterization of the radiurs content of the pile and is acceptable to the staff. The value for the ponds materials is conservative based on adequate characterization of the current conditions of the area and considering that vicinity property materials will be deposited there in the future and is adequate for purposes of performing calculations on the conceptual design.

However, since the radon / infiltration barrier thickness is sensitive to this parameter value, the planned additional characterization of the ponds area material to determine the average radium content should be done in order to ensure proper design of the radon / infiltration barrier thickness.

The ambient air radon concentration is a required parameter value for the RAECOM modeling and has been measured at the Grand Ju etion site as 0.8 pei/1.

The technique used to measure the radon concentrc* ion and the result is acceptable to the staff.

6.2.2 Radon Barrier Evaluation The radon / infiltration barrier thickness necessary to comply with the radon efflux limit was calculated using the RAECOM computer code. For a given assumed thickness of the radon barrier, the RAECOM code calculates the radon gas release rate. The EPA standard requires that the release of raden-222 from residual radioactive material to the atmosphere not exceed an average release rate of 20 picoeuries/mr/sec. DOE has analyzed the ra' don / infiltration barrier in two layers, one corresponding to the layer 1 materials and one corresponding to the layer 2 materials that will result from the sieving process. Sirce this approach represents the actual layered placement of the materials, the staff finds this approach to the analysis to be acewptable. The RAECCM modeling with the parameter values utilized from the previous discussions result in a

. t 43 redon-222 release rate of 15.39 picoeuries/m2/sec. However, as discussed above, further characterization of certain material preparty parameters is necessary before NRC's evaluation of the raden/ infiltration barrier thickness can be completed.

6.3 Site Clean-up Site characterization surveys have been conducted at the site to identify the subsurface boundary of the tailings pile, as well as, the depth and area of the mill yard, ore storage, emergency spill ponds, and windblown centaminated areas. The results of the site characterization survey are being u;ed to plan the control monitoring for the contaminated material excavation, as well as the final radiological vertftcation survey at the processing site. 00E has committed to the clean-up of the processing site in accordance with the EPA standard in 40 CFR 192 Subpart B (see Section 1.1).

Further, the procedures identified in the rap for the final radiological verification survey are consistent with generic procedures (RAC-015) that have been reviewed and approved by the staff. Therefore, the NRC staff is prepared to concur with the site clean-up aspects of the proposed remedial action.

. l c.,

m 44 7,0

SUMMARY

This Technical Evaluation Report (TER) summarizes the NRC staff review of the proposed remedial action for the itiactive uranium mill tailings site at Grand -

Junction, Colorado. Addiuional information is needed prior to unconditional concurrence by NRC. The deficient areas have been noted in the text and summarized in Table 1.1 of this document. The NRC staff review of additional information provided by 00E will be presented in the Final TER or supplements to the TfR and will include the NRC concurrence position on the proposed remedial etion.

4

.--e,g-~~ - - , - - -

45

8.0 REFERENCES

AND BIOLIOGRAPHY t

1. NRC, 1985, Standard Review Plan for UMTRCA Title I Mill Tailings Remedial ,

Action Plans: U.S. NRC, Division of Waste Management, October, 1985. l

2. Remedial Action Plan and Site Design for Stabilization of the Inactive Uranium Mill Tailings Site at Grand Junction, Colorado; Final, Volumes I .L and II, March 1988, UMTRA-00E/AL 050505.0000. j i' 3. Uranium Mill Tatlings Remedial Action Project (UMTRAP), Grand Junction, Colorado; Calculations, Final'Oesign for Review, Volumes I, II, III, IV, and Addendum (Radon Barrier Thickness Design Calculations), February .

, 1988.

t l 4. Uranium Mill Tallings Remedial Action Project (UMTRAP), Grand Junction,

Colorado; Information for Bidders, Volumes I, II, III, and IV, February ,

4 i

1988. (

5. Uranium Mill Tailings Reuedial Ac.tien Project (UMTRAP), Grand Junction, Colorado; Subcontract Documents, Final Design for Review, February 1988.

I 6. UMTRA Project - Grand Junction, Calculation, Otsposal Site Erosion  :

i Protection; MKE Document No. 5025-GRJ-C-01-00787-02. j 1

l 7. UMTRA Project, Grand Junction, Rock Source Evaluation.

8. UMTRA-Grand Jurction, Changes Between Preliminary and Final Design for t

Review of Phase II Subcontract Documents; and Response to NRC comments l

on dr4f t Remedial Ac61on Plan; Letter f rom W. John Arthur, 00E to i Paul Lohaus NRC, March 25, 1988.

f

9. Water Resources Protection Strategy for Ta111ngst Oisposal at Cheney }

Reservoir Disposal Site; Adddendum to Remedial Action Plan and Sites at {

j Grand Junction, Colorado; May 1988.

l 10. Grand Junction, Colorado, Cheney Reservoir Disposal Site; Conceptual {

Design Calculations for the Proposed Vegetative Cover, June 1986. l i

i

11. Guidance Document for the Grand Junction Final Design for Review, June i 1988. [

, 12. Lohman, S.W. ,1965, Geology and artesian water supply, Grand Junction f J area, Colorado: U.S. Geological Survey Professional Paper 451.  ;

13. Kirkham, R.M. and Rogers, W.P., 1981. Earthquake potential in Colorado, a i preliminary evaluation: Colorado Geological Survey Bulletin number 43. [

i

14. Hunt, C.B., 1974, Natural regions of the United States and Canada: }

San Francisco, W.H. Freeman and Company, 725 p. l l

i t

e ,

46

15. Campbell, K.W., 1981, Near-source attenuation of peak horizontal ground  ;

accel e r4 *. ion : Bulletin of the Seismological Society of America, v. 71,

p. 2039-2070.

16. , 1982, A preliminary methodology for the regional zonation of peak-ground acceleration: Proceedings of the 3rd International Ecrthquake Microzonation Conference, Seattle, Washington, v. 1, p. 365-376.

17. Bonilla, M.G. , Mark, R.K. , and Lienkaemper, J.J. ,1984, Statistical .

relations among earthquake magnitude, surface rupture, length, and l surface fault displacement: Bulletin of the Seismologicc1 Society of America, v. 74, p. 2379-2411.

18. U.S. Department of Commerce, U.S. Army Corps of Engineers, H o a .trea-logical Report No. 49, ' Probable Maximum Precipitation Esm.tes, ,

Colorado River and Great Basin Drainages," 1977.

19. 0.5. Bureau of Reclamation, U.S. Department of the Interior, Design of ,

Small Dams, 1973.

20. U.S. Army Corps of Engineers, Hydrologic Engineering Center, "Flood '

Hydrograph Package," HEC-1, continuously updated and revised.

21. Crippen, J.R. and Bue, C.D., "Maximum Floodflows in the Conterminous  :

3 United States," USGS Water Supply Paper 1887(1977). f f 22. Chow, V.T., "Open Channel Hydraulics," McGraw-Hill Book Company, New York, )

1959. ,

1

23. Nelson, J.D. et al., "Methodologies frr Evaluating Long-Term Stabilt ration

Designs of Uranium Mill Tailings Impoundments," NUREG/CR-4620, June i 1986.  ;

2A, Johnson, T.L., "Oversizing of Less Durable Erosion Protection," Draft Document, August 1988. ,

25. U.S. Nucler,r Regulatory Commitsion, Regulatory Guide 1.59, "Design Basis Floods for Nuclear Power Plants," January 1983.

26. Staff Technical Position WM-8201, "Hydrologic Dasign Criteria for Tailings ,

I Retention System," January 1983.

27. U.S. Army Corps of Eng'ineers, Hydrologic Engineering Center, "Water Surf 6ce Profiles, HEC-2," continuously updated and revised. l

28. U.S. Army Corps of Erigineers, "Hydraulic Design of Flood Control r Channels," EM 1110-2-1601, 1970.

I I

I <

a

O O

47

29. L'.S. Army Corps of Engineers, "Additional Guidance for Riprap Channel Protection," EM 1110-2-1601, 1970.

30. U.S. Department of Commerce, U.S. Army Corps of Engineers, Hydrometeore-logical Report No. 43, "Probatle Maximum Precipitation, Northwest States," 1966.

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

32. Simons, D.B., and Senturk, F., Sediment Transport Technology, Fort Collins, Co'orado, 1976.

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

34. Stephenson, D., Rockfill Hydraulic Engineering Developments in Geotechnical Engineering #27, Elsevier Scientific Publishing Company, 1979.

= -.

t-wiesv e n 7

Specific Connents

1. WRPS,,p. 45, Table 4.3 The subpile concentration for As is reported incorrectly as 1.10 mg/1; the actual calculated value using the equation on page 43 is 0.10 mg/1.

2. FRAP, Table E.7.5 Water Leval Measurements Water level measurements reported in Table E.7.5 for well 508 range from approximately 32 feet below the ground surface to 103 feet below ground surface, while the total depth of the well is only 52 feet, as reported in Table E.7.1. DOE should revise Table E.7.5 to reflect accurate information.

3. WRPS, Figure 2.1, Hap of Cheney Reservoir, aM Corresponding Text DOE should revise the map of the Cheney site shown in Figure 2.1 to accurately reflect the location of Whiting's Ditch, and revise the text of the FRAP and WRPS to consider more viable recharge scenarios to the shallow aquifer, other than the Whiting's Ditch scenario.

4. WRPS and fRAP, Missing Information on Wells and Borings Based on NRC staff review of groundwater information in the FRAP, WRPS, Information to Bidders's Volume III, and the FEIS, we cannot locate the following information:

1) map showing location of all borings, wells, and test pits constructed to date at Cheney site; I 2) well logs for wells 507, 508, 509, and 728; i information on wells installed in Nov-Dec 1986, referenced by 00E in their i 3) response to NRC comments on the DRAP. 00E indicated that wells were installed south-southeast of the disposal area across from Indian Creek, and east of the disposal ares, which were apparently dry. NRC staff cannot find any reference to these wells in DOE documents, such as well !.D. numbers, locations, and Iogs.

DOE should attempt to consolidate the information listed above into a single document (such as the WRPS), with a consistent labeling system for boreholes and wells (i.e., use 500 series vs. GCH, and GWCH) to facilitate NRC review, or explain why the data cannot or need not be provided.

5. WRPS, p.17, Source Concentration Values DOE indicates in the WRPS that conservative values of source concentrations for hazardous constituents were estimated using the geometric mean of resu hs frcm lysimeter samples and column leaching analyses of tailings pore fluid.

D

0 2-The maximum value for each constituent, however, would be more conservative.

DOE should consider maximum measured concentration values for each constituent in the performance assessment to ensure conservative results.

6. WRPS. pp. 40-50. Performance Assessment Modelin2 DOE has not justified several of the assumptions and input 1arameters used to calculate contaminant concentration ratios at the base of tie pile, or described the basis for model results. Forexample,NRCstaffdoasnot understand how the "atvisua concentration ratios of 0.056 for constituents was calculated. Also, DOE has not described information such as dis)ersivity -

coefficients, and distance to the base of the pile (POC). DOE s1ould describe and justify all of the input parameters and model results so that NRC staff can independently review the adequacy of the model and model results.

7. General DOE has not analyzed impacts to the shallow groundwater from disposal of For example, in addition constituents for which EPA has not established MCLs.

to those constituents for which DOE has listed as hazardous constituents in the WRPS, DOE lists C1, F1, Fe, Sulphate, Ca, gross beta, K, Sr, ammonium, specific conductance, Ma, T0X and Vanadium in the FEIS (Insert GW7), as constituents whose concentrations exceed background and/or EPA drinking water limits in the alluvial grounenater at Grand Junction. Although MCLs have not been established for these constituents, and they may not be listed in Appendix VIII of 40 CFR PArt 261, DOE should consider analyzing their impact to the groundwater regime at Cheney with respect tc the State of Colorado groundwater standards.

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