ML20217A064
| ML20217A064 | |
| Person / Time | |
|---|---|
| Issue date: | 11/30/1990 |
| From: | NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| To: | |
| Shared Package | |
| ML20217A051 | List: |
| References | |
| REF-WM-54 NUDOCS 9011200174 | |
| Download: ML20217A064 (60) | |
Text
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1 1 l l l ORAFT TECHNICAL EVALUATl0N REPORT ,
-FOR THE PROPOSED REMCOIAL ACTION ,
AT THE GRAND-JUNCTION TMI.INGS SITE GRAND JUNCTION, COLORACO N. ! 1[; l .-,e. , l 1 L
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-Section Page l
- 1. 0 '7NTRODUCTION.......................................... 5' j 1.1. EPA Standards.................................... 5 1.2. Site and Proposed Action......................... 6 -
1.3. Review Process................................... 6 s 1.4. T E R O rg 1 i z a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -. . 9 !
- 1. 5. S umma ry o f Op e n I s s ue s . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
~ 2. 0 - G E0 LOG I C ST AB I l iTY . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . 15 ;
' 2.1. ~ Introduction..................................... 15 1 2.2. Location......................................... 15 i 2.3. Geo1ory.......................................... 15 j 2.3.1. Stratigraphic Setting................... 15 .i o *
'2.3.2. Structural Setting...................... 16. 1 2.3.3. Geomorphic Setting...................... 17.
.2.3.4,. Seismicity.............................. 17 2.4. . Geologic Stability............................... 19 2.4.1. Bedroc k Sui tabi l i ty.' . . . . . . . . . . . . . . . . . . . . 19 i
.2.4.2. Geomorphic Stability.................... 19 l 2.4.3. Seismotectonic" Stability................ 20 -l 2.5. Conclusions................ ..................... 21 4
3.0' GE0 TECHNICAL STABILITY................................. 22 i
, 3.1. Introduction..................................... 22' l 3.2. Site and. Material Characterization............... 22 3.2.1. . Processing Site Description............. 22 i 3.2.2. Processing Site Investigations. . . . . . . . . . ' 22 .
- 3. 2. 3.' Cheney Reservoir Disposal Site De s c ri pti o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 3 j 3.2.4. Cheney Reservoir Disposal Site i Investigations.......................... 23 ,
3.2;5. Cheney Reservoir Disposal Site
' Stratigraphy............................ 23
'3.2.6. . LTesting Program......................... 24 r
'3.3. Geotechnical Engineering. Evaluation.............. 25 3.3.1. Stability 1 Evaluation.................... 25
'3. 3. 2. Settlement.............................. 26
- 3. S . ' . Liquefaction............................ 26 3.3.4. Cover-Design............................ 27 E
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,, 3.4.1. Construction Methods and Features....... 28 '
3.4.2. Testing and Inspection.................. 28
- 3. 5. Conclusions...................................... 29 f
4.0 SURFACE WATER HYOROLOGY.AND EROSION PROTECTION......... 30 4.1 -Hydrologic Description and Site Conceptual Design.30 4.2. Flooding 0etermirations.......................... 30 4.2.1. Selection of Design Rainfall Event...... 31 4.2.2. Infiltration Losses..................... 31
.4.2.3. Time of Concentration................... 32 4.2;4. Rainfall Distributions.................. 32 4.2.5. Computation of PMF...................... 33 4.2.5.1. Topslopes, Sideslopes and Aprons... 33 4.2.5.2. Diversion Channel.................. 34 4.3. Water Surface Profiles and Channel Velocities.... 34 4.3.1. Top Slopes.............................. 34 1 4.3.2. Side Slopes and Aprons / Toes............. 35
'4.3.3. Diversion Channe1....................... 35 4.4. E ros i on Protecti on. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 i 4.4.1. Sizing of Erosion Protection............ 38- >
4.4,2. Rock 0urabilitv......................... 38 4.4.3. Testing and Inspection of Erosion
. Protection................ ............. 38
-4.5. Upstream Dam Failures............................ 40 4.6; Conclusions....................................... 40 5.0 WATER RESOURCES PROTECTION,............................ 41 5.1. ' I n t ro d u c t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . 41 5 5.2. Hydrogeologic Characterization................... 41 '
5.2.1. Identification of Hydrogeologic Units. . . 41 5.2.2. Hydraulic and Transport Properties...... 43-5.2.3.- -Geochemical Conditions and Extent o f Contami nati on. . . . . . . . . . . . . . . . . . . . . . . . 45 5.2.4. Water Use........................ .... 46
- 5. 3. . Conceptual Design Features to Protect ' water Resources.-....................................... 47 5.4..-Disposal and Control of. Residual Radioactive Materials'........................................ 49
- 5.4.1, Water Resources Protection Standards for Disposal............................ 49 {
5.4.1.1. Hazardous: Constituents............. 49 5.4;1.2. Concentration Limits............... 50 5.4.1.3. Point of Compliance................ 50 ! 5.4.1.4. Supplemental Standards............. 50 j 5.4.2. _ Performance Assessment. . . . . . . . . . . . . . . . . . 51 l 5.4.3. Closure Performance Demonstration. . . . . . . 52 5.4.4. Groundwater Monitoring and Corrective L Action Plan............................. 52 1 I
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- 5. 5. Cleanup and Control of Existilig Contamination.... 53
- 5. 6.' Conclusions...................................... 54 6,0 -RADON ATTENUATION AND SITE CLEAN-UP.................... 55 6.1. Introduction..................................... 55 l
- 6. 2, Radon Attenuation................................ 55 -!
- 6. 2.1. - Parameter Evaluation.................... 55 .;
6.2.2. Radon Barrier Evaluation................ 57 1 6.3. S i t e C 1 e a n- up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
7.0 REFERENCES
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1.0 INTRODUCTION
The Grand Junction site was designated as one of 24 abandoned uranium mill tailings piles to receive remedial action by the U.S. Department of Energy (DOE) under the Uranium Mill Tailings 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 by the U.S. Environmental Protection Agency (EPA). This draft Technical Evaluation Report (TER) documents the NRC staff's review of the DOE preliminary final design and remedial action plan and outlines the resulting outstanding issues. 1.1 EPA Standards
-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.
These regulations may be summarized as follows:
- 1. The disposal site shall be designed to control the tailings and other residual radioactive material for 1000 years to the extent reasonably achievable and, in any case, for at least 200 years [40 CFR 192.02(a)].
- 2. The disposal site design shall prevent radon-222 fluxes from residual radioactive materials to the atmosphere from exceeding 20 picocuries/ square meter /second;or from increasing the annual average concentration of radon-222 in air by more than 0.5 picocuries/ liter
[40 CFR 192.02(b)].
- 3. The remedial action shall ensure that radium-226 concentrations'in i land that_is not part of the disposal site averaged over any area of 100 square meters do not exceed the background level by more than 5 picocuries/ gram averaged over the first 15 centimeters of soil belo..
the surface and 15~picocuries/ gram averaged over any 15-cent;.neter thick layer of soil more than 15 centimeters below the land surface [40 CFR 192.12(a)]. On_ September 3, 1985, the.V.S. Tenth Circuit Court of Appeals remanded the l 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 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 any future groundwater _ contamination that may occur from tailings piles l after remedial action, and a second part, governing the clean-up of l contamination that occurred before the remedial action of the tailings. In l'
accordance with UMTRCA Section 108(a)(3), the remedial action shall comply with the EPA proposed standards until such time as the final standards are l promulgated._LAt that time, 00E has committed to re-eraluate its groundwater L protection plan and undertake such action as necessary to ensure that the l l final EPA standards are met. l l
y . .. 4 6 1.2 Site and Proposed Action The Grand Junction mill site is a 114-acre property adjacent to the south side of the city of Grand Junction, Colorado, and adjacent to the north side of the . Colorado River (See Figure 1.1). The site consists of the tailings pile, mill
. site, and effl_uent 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 present estimate of total
- contaminated materials to be placed 4. the disposal cell is.5.7 million cubic yards. The tailings on the site are covered with approximately six inches of soil,.and the site is sparsely *,egetated. 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 Reservoir (See Figure 1.2). The proposed remedial action consists of the following major activities: Movement of all contaminated materials, by a combination of rail and truck, to a disposal site located near Cheney Reservoir. Stabilization of contaminated materials in an embankment, which will , rise approximately 30 feet above the surrounding terrair, and will extend up to 40 feet below existing grade. Coverage of the tailings embankment with a multilayered cover system on the top and sideslopes. Starting from the layer directly over the contaminated materials, the topslope cover-system consists of a two-foot-thick radon / infiltration barrier, covered by a six-inch-thick sand bedding / drainage layer,= a one-foot-thick rock biointrusion layer, a three-inch-thick choked rock layer, and finally topped by a two-foot-thick vegetated soil layer with rock mulch. The sideslopes consist of a 42-inch-thick radon / infiltration barrier, covered by a six-inch-thick sand bedding / drainage layer, and finally a one-foot-thick rock erosion protection layer. Restoration of the processing site with uncontaminated fill from the' disposal sito excavation.
'1.3 Review Process i The NRC staff review was performed in accordance with the Standard Review Plan
- for UMTRCA Title I Mill Tailings Remedial Action Plans (SRP) (NRC, 1985) and
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9 consisted of comprehensive assessments of DOE's proposed preliminary final remedial action plan and site design. Staff review of preliminary final data
'and designs submitted by 00E indicate that there are still open issues as presented in Section 1.5 and discussed in further detail in Chapters 2 through 6 of this TER. All issues must be addressed before concurrence with the proposed remedial action can be granted by NRC. The NRC will review all appropriate data submitted by 00E in this regard. Upon resolution of the open issues, the NRC staf f will revise this TER into final form to include evaluations and conclusions with respect to the additional information submitted by DOE.
The remedial action information assessed by the NRC staff was provided primarily. in the following documents (00E,1990a-f), (MK-Ferguson,1990):
- 1. DOE, " Remedial Action Plan and Site Design for Stabilization of the Inactive Uranium Mill Tailings Site at Grand Junction, Colorado,"
Preliminary Final, UMTRA-00E/AL 050505.0000, August 1990 (Grand Junction RAP), Remedial Action Selection Report (RAS).
- 2. Grand Junction RAP, Attachment 1: Contract Documents, Design and
, Engineering Calculations (Calculations Volumes I-V).
- 3. Grand Junction RAP, Attachment 2: Geology Report
'4. Grand Junction RAP, Attachment 3: Groundwater Hydrology Report and Appendix A, Volumes I-IV.
- 5. Grand Junction RAP, Attachment 4: Water Resources Protection Strategy'
- 6. Grand Junction RAP, Attachment 5: Summary of Field Investigations,- 4 Volumes I and II.
- 7. -MK-Ferguson Company, "UMTRA Project, Grand Junction, Colorado, Remedial Action Inspection Plan," September, 1990.
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 processing site and the designated disposal site, Cheney Reservoir; and discuss the open items resulting from this review. The following sections of this report have been organized by technical discipline relative to the EPA standards in'40 CFR Part 192, Subparts A-C. Sections 2, 3, and 4 provide the technical basis for the NRC staff's conclusions and identification of remaining open issues with respect to the long-term stability standard in i 192.02(a). Section 5, Water Resources Protection, summarizes the NRC staff's conclusions and remaining open issues regarding the adequacy of DOE's compliance demonstration with respect to EPA's groundwater protection l
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r 'r l._ requirements.in 40 CFR Part 192. Section 6.provides the~ basis for the staff I conclusions and-identification of open issues with respect to the-radon
, scontrol. standards in 192.02(b):and soil cleanup in.192.12.
i Summary of Open Issues
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1--5.
-1 lThe NRC -staff review:of:- the. proposed:00E preliminary final design and remedial -f
- action plan has identified open issues, which are discussed in more detail in ;
'A brief summary of these open issues-is provided in l
- 'm l Table l.1.th,7 following chapters. ~
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SUMMARY
OF OPEN ISSUES Open Issue: TER Subsection
- 1. Information provided in the subcontract documents 3.3.1
' indicates' that-the supporting calculations do not reflect the current excavation plan,.i.e. an additional 6 feet of 1 excavation into the Mancos shale. 00E needs to address
,the effect ofEthis design change on slope stability in
.the Final' Remedial Action Plan. I c2.'The supporting calculations do not reflect the current 3. 3. 2 ~
excavation plan. -00E needs to address the effect of this
' design change onLthe settlement / cracking ' analysis in the F.inaliRemedial Action Plan.
3.' The. selected' gradation requirements in the specifications 3.3.4 appear- to' allow for radon / infiltration barrier material that is incorsistent with the expected design permeability.
.Furtherm0re, it- is not exactly clear what'value is proposed ,
for the design permeability i.e., 5.02E-8 cm/sec as given in 4
.the summary:4f; design' parameters, or'1E-7ecm/sec as given in the wateriresources' protection. strategy. In order;to: bring c'larity to'this aspect ~of the radon barrier' design, 00E
- needs to provide a discussion that presents the-expected material make-up of the radon barrier, the design permeabi.ity, the basis for. selection.of the permeability,.
L the resulting-gradation; specifications,:and' justification of how the specifications will ensure a. radon barrier'with the design permeability. '
, 4.SThe; RAS indicates th't-the a layer 1immediately above the ' 3. 3. 4
>> radon barrier <is to be a six-inch-thick sand bedding / drain
< ' layer, intended to drain water laterally off the cell and~
Lprotect.the radon barrier from the riprap. The gradation
. specifications and drawings show two separate materials, a drain material and a bedding material'. The RAS does not
-clearly' identify:the design basis = for the two.different
- materials, and the-calculations do not clearly lay out how;
- the gradations are established from-the design criteria (permeability, filter' criteria). ' DOE needs to clarify p these aspects of the cover. design in the final RAP.
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4 12 u-i TABLE 1.1 (cont.)
SUMMARY
OF OPEN ISSUES s, Open. Issue TER Subsection I5.: Thef calculations provide -the basis for the gradation 3.3.4
-design of the choked rock layer. However, the resulting gradation is not consistent with the gradation presented in the constructionLspecifications. -There is no basis for the gradation-providedEin the specifications. DOE needs to reso~1ve this discrepancy in the final RAP.
m._ 6. 00E'needs to address two additional aspects'of the 3.4.2
. disposal-cell construction in the RAIP. The specifications indicate that compaction requiremet ' er the. bedding, drain, and choked rock layers are metru
.(number.of passes)1rather than numerical (% maximum densi ty). The RAIP should contain discussion of the-plans"toLinspect and document the placement of these-matertals.- The: specifications.also include r;quirements
.for placement of the rooting soil, rock mulch, 'and vegetation. The.RAIP should contain plans to inspect
=these aspects of the cover.
- 7. It does.not appear that care was taken to ensure 3.4.2
_ consistency between=the specifications and the RAIP. DOE:needs_to review the. specifications, making appropriate revisions'to ensure l consistency with the RAIP.
- 18. 00E needs to provide a redesign of the erosion 4.2.5.1; protection for the top slopes of the disposal cell, 4.3.1 addressing flow concentration considerations, or provide additional' justification,for the design proposed.
9.' DOE'needs'to_ provide a redesign of the erosion 4.2.5.1;
-protection for the side slopes of the disposal cell, 4.3.2 revising assumptions for peak flows and dispersion by>the 20-foot. rock cover extention, or provide additional Ljustification for the design proposed.
'10. 00E'needs to provide a~ redesign of the erosion 4.3.2 protection;for.the toes.and aprons of the disposal cell, considering revised peak flows from the side slopes
.and potential for gully'headcutting, or provide additfonal justification for the design proposed.
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SUMMARY
OF OPEN ISSUES
- $..II$$......................................................!.ER}gbygg_qgn .. . . 11. DOE needs to provide a redesign of the erosion 4.3.3
_ protection for the diversion channel, considering erosion protection at, the channel outlet, potential. for-gully inflow to the channel, and clogging / sedimentation, or provide < additional justification
-for the proposed design.-
- 12. 00E 'needs to demonstrate. that by deferring 5.2.4;
. groundwater cleanup at the. Grand Junction processing 5. 5 site'public health and safety will-not be affected.
DOE needs'to take additional. water quality samples from the Colorado River (especially at low flow) and test for all hazardous constituents. Further, 00E F needs to define.the area potentially affected by the present contamination,.and the-groundwater usage (not just for drinking' purposes) within that area. 13.-DOE needs to clearly' state.in the RAP exactly what 5.4.1.2 the supplemental standard is 00E also needs to demonstrate that:their proposed supplemental. standards
-come as close to meeting the otherwise. applicable standards as is reasonable under-the circumstances.
00E needs to provide a list of the concentration limits ' of the hazardous constituents that they have identified.
- 14. 00E needs .to perform additional vertical permeability 5.3; testing on the foundation material,"at the final 5.4.2 excavation: depth. The permeability tests should~be, performed on compacted Mancos: Shale material, since it 4 is'likely that the heavy,. moist tailings will compact
.the: friable shale material.
-15. 00E.needs to correct the Rawls method (long-term 6.2.1
_ moisture) calculations, and provide discussion of the
- basis' for not factoring the results-of the Rawls method into'the selection of the design long-term moisture.
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14 1 i i TABLE 1.1 (cont.) I
SUMMARY
OF OPEN ISSUES Open Issue' TER Subsection = 16.'The' concept of adjusting the average Ra-226 6.2.1
, concentration values for-the design is acceptable q
- os 'to the NRC staff; however, the' Standard Error of the Mean does not adequately represent the variability i
-of the data. DOE needs to re-evaluate parameter ;i adjustment. to better_ represent the-variability of {
- the> data. The range'of~Ra-226_for the main tai',ings
-and'off pile' materials should be added to Table 6.3.
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y; m , w 1 15 2.0 GEOLOGIC STABILITY 2.1 Introduction b This section of the TER dor.uments NRC staf f's review of geologic information i for the proposed remedial action at the Grand Junction uranium mill tailings disposal site. Background inforOction for this TER is derived from DOE's Remedial Action Plan (00E,1990a-f), supplementary information provided during the review process, staff's site visits, and independent sources as citet 2.2 Location For this remedial action, site characterization is required for two areas in Colorado: (1) the processing site, consisting of an abandoned mill and tailings pile located in Grand Junction Colorado, on the Colorado River and
, along Interstate 70, 250 miles west of Denver, and (2) the proposed disposal site near Cheney Reservoir, located approximately 18 miles southeast of Grand ,
J _ Junction, in the Gunnison River valley. ) 2.3 Geology The EPA standards listed in 40 CFR 192 do not include generic or site-specific requirements for the characterization of geologic conditions at UMTRA Project sites. Rather, 40 CFR 192.02(a) requires control shall be designed to be effective far up to 1,000 years, to the extent achievable, and in any case for at least 200 years. NRC staff have interpreted this standard to mean that l
.certain geologic conditions must be met in order to have reasonable assurance that- this long-term performance objective will be achieved. Guidance with p
_ , regard to these conditions is specified in NRC's UMTRA Project Standard Review Plan (SRP) (NRC, 1985).' 1
, 2.3.1 Stratigraphic Setting 1 DOE characterized regional and site stratigraphy by reference to published u work and original field investigations as recommended in SRP Section 2.2.2.1 (NRC,1985). Bedrock in the region of the processing and disposal sites consists of a thid sequence of marine and continental sedimentary rocks, and is overlain by surficial deposits which include alluvium, terrace gravels, and j colluvium. Both the processing and disposal sites occur in broad valleys
. developed along strike of the Cretaceous Mancos Shale. The Mancos is a thick l sequenca of fissile shale containing sparse siltstones and sandstones. The Mancos underlies the entire Grand Valley area, and has a thickness in excess !
of 3,800 feet (Lohman, 1965). Each site occurs near the base of the Mancos, which is in turn underlain by Cretaceous Oakota Sandstone and the Burro Canyon formation. The Mesaverde Formation occurs up-section and crops out near the - tops of _ Grand Mesa and the Book Clif fs' to the east and north. Tertiary _ volcanic rocks form the caps of Battlement and Grand Mesas to the east. The staff finds that DOE has adequately characterized the regional stratigraphy.
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9 16 At the processing site, 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 thicker lower layer of y coarser sand and gravel. Only a few wells penetrate the Mancos Shale beneath y the tailings, and it appears to extend down to 60 feet in depth. Both Mancos s and Dakota crop out on the southern bank of the river, and the Mancos pinches out completely within one-half mile southwest of the site. Details af t.e } s mill area's stratigraphy, as it affects hydrogeologic and geotechnical conditions of the site and ability of the remedial action to meet 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. Surficial deposits beneath the site consist of unconsolidated l alluvial material, approximately 15 to 30 feet thick in the disposal cell 4 area. DOE determined thet these deposits consist mainly of mixtures of silty gravel with cobbles and boulders derived from the basalt rocks that cap Grand Mesa. Mancos Shale, approximately 800 feet thick, 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 00E characterized the region's structural setting by reference to published regional geological maps, aerial reconnaissance, and field observation and napping of features critical to assuring long-term stability of the remedial action. These studies were recommended in SRP section 2.2.2.3 (NRC, 1985). The Grand Junction area is situated on the northeast flank of the Uncompahgre Uplift. The Uncompahgre Uplift is a large, northwest-trending, asymmetrically tilted b.ock cored by Precambrian rocks. It is bounded on the northeastern and southwestern flanks by abrupt, locally faulted monoclines. The uplift was active as ee Iy as Pennsylvanian time, and is known to have experienced repeated uplif t as recently as Miocene or Pliocene time, and may presently be undergoing continued deformation (Kirkham, 1981). Potentially active faults associated with the northeast side of the uplift were mapped by Kirkham and Rogers (1981) 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 zone between the two structural features. The Piceance Basin formed in Laramide time and has undergone gradual uplift through Pliocene time (00E, 1990c). The basin is bounded on all sides by uplifts of Laramide age, and developed over l 8,200 feet of stratigraphic section since the ', ate Cretaceous. ; i L d
t i 17 2.3.3 Geomorphic Setting 00E characterized the region's physiogrcphy by reference to published literature and topographic maps, as recommeaded in SRP section 2.2.2.2 (NRC, 1985). Site geomorphic conditions were characterized by aerial photographic interpretation and field observations. The area is located in the Canyon 13nds section of the northeastern Colorado Plateau physiographic province (Hunt, 1974). 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 on the Colorado River's floodplain. The tailings are currently protected from the river by a 30-foot berm of concrete blocks and other debris (00E, 1990a), 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 rM r 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. The Cheney disposal site occurs on one of a series of nine pediment levels 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 pootly sorted, consist of clayey to bouldery material, and appear to be oerived from Cretaceous strata and Tertiary volcanics that flant Grano Mesa. Grain-size sorting and stratigraphy of the surficial deposits indicates they are mainly colluvial.in origin. Surface-water drainage from the disposal area is mainly by shee't flow. However, flow becomes channelized in many places, especially where drainage area or surface gradient is high, and gullies have formed 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 (DOE, 1990c). 2.3.4 Seismicity 00E characterized regional seismicity by obtaining data bases provided by ti.9 National Oceanographic and Atmospheric Administration (NOAA), by applying accepted techniques to determine earthquake magnitudts, and by empicying methods suggested'in SRP section 2.2.2.3 (NRC, 1985) for calculating peak horizontal y.'ound accelerations generated by a desitn-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
I 4 18 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 (00E, 1990c). The plateau includes a stable interior and several border zones which experience elevated seismicity, thinner crust, higher terrestrial heat flow, normal faults, and high occurrence of Tertiary and Quaternary volcanic rocks. Nearly at? large historic earthquakes of the plateau are associated with the bordet zoned The disposal site is located in the Colorado Plateau's border 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 was as high as 4.4. However, faults responsible for the earthquakes have not been identified with cert 6inty (00E, 1990c). DOE's analysis of potential earthquake magnitudes for the interior Colorado Plateau included determination of both ' a Maximum Earthquake (ME) and floating Earthquake (FE) for the region To augment its analysis of Colorado Plateau seismicity, DOE studied four regional structures for the occurrence of capable faults. First, f6ults in the Ph.eance 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 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 piesent a seismi- sk to long-term site stability. Based on literature review, DOE m omed several faults on the flanks of the Uncompahgre Uplift were potentially capable. Field examination of these faults within 40 miles (65 km) of Cheney resulted in no observations of evidence that any of these faults have experienced Quaternary movement (DOE, 1990c). Seismic 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 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 be considered capable, regardless of surficial expression of such. NRC staff find this conclusion an acceptable and conservative basis upon which to calculate maximum 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.
o .D 19 2.4 Geologic Stability Geological conditions and processes at the proposed site are characterized to determine the ability to meet 40 CFR 192.02(a). In general, site lithologic, stratigraphic, and structural conditions are considered for their suitability J as a disposal foundation and their potential interaction with tailin0s leachate and ground water. Geomorphic processes are considered for their potential impact upon long-term tailings stabilization and isolation. ' Potential geologic hazards, including seismic shaking, liquefaction, on-site I fault rupture, ground collapse, and volcanism are identified fer the purpose of assuring the long-term stability of the disposal cell and success of the , remedial action. ) 2.4.1 Bedrock Suitability DOE's proposed remedial actions are influenced mainly by characteristics of 1 unconsolidated floodplain deposits at Grand Junction's mill site and colluvial i deposits at Cheney. The staf f conclude that bedrock stratigraphic and I structural conditions at the sites should have no effect on DOE's ability to meet remedial action standards. I 2.4.2 Geomurphic Stability Stabilization of mill tailings in their present location would likely require constant maintenance and repair of existing erosion control features. Proposed removal of Grand Junction's tailings will result in elimination of the processing 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.- Geomorphic issues addressed by NRC centered on (1) evidence at the site that ' the Cheney area has experienced long-term landscape stability in the past, and (2) potential for future channel incision and site instability. Geomorphic features observed by site investigators, and cited as evidence of past long-term landscape stability, included relic bar-and-swale topography, desert pavement, desert varnish on surficial stones, and well-developed soils 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 Rer.edial 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 understanding of the site's features as described in the RAP. Site visits by NRC staff confirmed the existence of several of the features, and interpretations that the pediment surface is at least late Pleistocene in age (00E, 1990c) appears to be accurate. Staff, however, suggested the bar-and-swale features could be evidence of recent overland flow concentration
~~
l o l 20 . 1 and incipient channel formation. Therefore, the NRC staff concludes that potential channel growth and erosion of the site should be accounted for in , the site design. I Based on a compilation of erosion rates from an extensive literature study, DOE (1990c) considers that the greatest geomorphic hazard at the Cheney site is headward extension of deep gullies, one of which occurs south of the edge of the proposed disposal area. NRC staff considered in its early reviews that formation of new gullies was a hazard which DOE also needed to consider. DOE's analysis of this hazard includes discussion of several conditions which enhance geomorphic stability at the site. These include diversion of overland surface flow by placement of the cell, backfilling of the south-side gully, and naturally-armoring site conditions. DOE also proposes that the disposal cell be surrounded by rock aprons designed to safely convey flood runoff away from the tailings and prevent gully erosion into the stabilized pile. Section 4.3.2 of this report presents concerns with the design of the rock for the apron, but concludes that if the apron design is revised to adequately - withstand peak flood flows from off the pile, the required rock size will be sufficient to prevent headward gully advancement. The staff concludes that a revised apron design, which acceptably resolves erosion protection concerns, coupled with the conditions listed above, will provide adequate protection against off pile gully intrusion. 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 00E employed attenuation relationships of Campbell (1981). NRC staff considered that use of Campbell (1981) relationships were unacceptably restrictive, and were biased toward geologic and seismic conditions of the California area. The staff's original review finding perceived a failure to employ current and germane methods that are acceptable to the seismologic community in general. Based on a further analysis, however, accoun;ing for regional variations of
,'.ttenuation,. staff determined that calculated peak ground acceleration varied only 0.01g 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, 00E concluded that faults near Cheney are associated with modern tectonic activity in the Uncompahgre Uplift. 00E employed published methods to determine an expected magnitude (Bonilla,1984) and on-site peak horizontal ground acceleration (Campbell, 1981) resulting from rupture on any fault associated with the Uncompahgre Uplift or other faults considered capable. As a result, DOE l l l l
1. 21 f, adopted.the nearest f ault (number 8; 00E,1990c; Plate 2.1) as the design 7 fault for the Cheney site. Fault number 8 is predicted to experience a maximum credible earthquake of magnitude 6.8 and produce an on-site peak i horizontal bedrock acceleration of 0.42g. These criteria were derived through reasonable and conservative means, and the staff accepts their adoption as design criteria for the Cheney disposal site, t 2.5 Conclusions ; Based upon review of the Preliminary Final Remedial Action Plan and associated i documents, and DOE's response to NRC comments on drafts of these documents, the staff has reasonable assurance that regional and site geological
-conditions have been characterized adequately to meet 40 CFR 192. As discussed in Section 2.4.2, the concern regarding the potential for future I gully intrusion into the tailings embankment will be resolved through >
resolution of the erosion protection apron issue. Other conditions which I would hinder long-term stability have been identified and mitigated by the design features. . f L f
+
.- ~ ,..a.-, -.g. - -
22 3.0 GE0 TECHNICAL STABILITY 3.1 Introduction This section presents the NRC staff review of the geotechnical engineering aspects of the proposed remedial actions at the Grand Junction, CO UMTRAP site, as detailed in DOE's Preliminary Final Remedial Action Plan (DOE, 1990a-f) and Remedial Action Inspection Plan (MK-Ferguson,1990). Tile 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 geologic aspects such as stratigraphic, structural, geomorphic, and seismic characterizations of the site is presented in Section 2.0 of this report. The staff review of the - groundwater conditions and protection strategy at this site is presented in Section 5.0 of this report. 3.2 Site and Material Characterization i 3.2.1 Processing Site Description 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 demolisted 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 by a minimum thichess of six inches of soil and revegetated, though little of the vegetation now remains. Centamination of material below the tailings pile has occurred due to the movement of tailings liquids into the subpile materials. As discussed in Section 1.2, contaminated material from cleanup of vicinity properties in the Grand Junction area is being placed in an area adjacent to the tailings pile. The Grand Junction site is on a young alluvial terrace a few feet above the present level of the Colorado River. Bedrock beneath th: site consists of the Cretaceous Mancos Shale. Oakota Sandstone, and Burro Canyon Formation, which-dip to the northeast under the site. A detailed geologic study at the mill site was not conducted since the tailings and other contaminated materials will be relocated for stabilization. 3.2.2 Processing Site Investigations Several subsurface investigations have been performed at the. Grand Junction processing site in order to characterize the tailings and contaminated materials for geotechnical engineering and radiological aspects of the l
]
I 23 remedial action. A study by Bendix Field Engineering Corporation (1985), to determine the extent of contamination, consisted of 358 shallow soil samples, 177 boreholes, and 175 in-situ Ra-226 measurements. Results of this investigation were used in estimating the volume of contaminated material to be relocateci to the Cheney Reservoir disposal site. Additional investigations conducted by Sergeant, Hauskins, and Beckwith (1981), Golder Associates (1982), Colorado State University (1980), Jacobs Engineering Group (1984 and 1989), and Lincoln-DeVore (1987), resulted in over 240 borings, 5 test pits, 27 lysimeters, and monitoring wells, from which samples for laboratory analysis were obtained. Geotechnical engineering characteristics of the tailings and contaminated materials have been determined through laboratory analysis of the samples from these investigations. 3.2.3 Cheney Reservoir Disposal Site bscription The Cheney Reservoir disposal site lies between Grand Mesa and the Gunnison River, 18 miles southeast of Grand Junction a.'ong U.S. Highway 50. The terrain at the site is very flat and the area is t.parsely covered with grasses and shrubs. The average elevation of the disp) sal area is about 5230 feet. The zero- to three-foot-thick layer of surficial material at the site is an eolian derived silt with some clay and sand with gravel to boulder size basalt fragments. Underlying the silt is a mixture of clluvium with colluvium deposits and mudflow debris consisting of interlayered clay, silt, sand, and gravel with occasional layers of basalt cobbles and boulders. 3.2.4 Cheney Reservoir Disposal Site Investigations Investigations conducted by Jacobs Engineering Group (1984 and 1989), Lincoln-Devore (1986), and Western Engineers (1987), were performed at the Cheney Reservoir Site in order to obtain geotechnical engineering and groundwater characterization data. These investigations included over 130 borings, 158 test pits, 7.nd 38 monitoring wellr. from which samples for laboratory analysis were obtained. Geotechnical engineering charactraristics and certain radiological characteristics of the materials were determined through laboratory analysis of samples from these investigations. In addition, 1200 linear feet of continuous trench were excavated and a surface geophysical survey was conducted to learn the nature of the shallow groundwater beneath the disposal site. 3.2.5 Cheney Reservoir Disposal Site Stratigraphy 15e site stratigraphy can be divided into four zones af, defined by the soil bo*ings described in the previous section. These four zones are: (1) the surficial layer of unconsolidated deposits described in section 3.2.3 above; (2) The upper weathered zone of the Mancos Shale; (3) the lower, les!.-weathered portion of the Mancos Shale; (4) and the Dakota Sandstone and othor formatiors underlying the Mancos Shale.
-. . 1 t
24 , The unconsolidated deposits of the surficial layer range in thickness from 15 feet to 50 feet based on the borings. Soils of this unit range from clays to large boulders. Finer grained materials consist of clays (CL), silt and clay mixtures (CL-ML), and sandy silts and clays (SM and SC). These materials are intermixed and interlayered with sand and gravel deposits that are cemented to varying degrees. Larger cobbles and boulders are frequent and randomly mixed throughout the entire thickness of the deposit. Generally, the clays and silts range from low to medium plasticity. The coarse grained materials are usually rounded to subrounded and contain the full distribution of sizes. Substantial gypsum deposits resulting from evaporG1on of transient waters in paleochannels are present within this unit Tne upper unit is underlain by the Mancos Shale, which extends to depths on the order of 750 feet. The surface of the Mancos Shale was eroded before the surficial materials were deposited, creating gullies in the Mancos. Groundwater in the Cheney Reservoir disposal site area occurs in isolated, thin paleochannels within the basal portion of the alluvium, in fracture systems in the underlying unweathered Mancos Shale, and in the Dakota Formation. Detailed field investigations, however, identified a large area suitable for the disposal cell that is devoid of water-filled paleochannels (see Section 5.0). The staff has reviewed the details of the test pits and borings as well as the scope of the overall geotechnical exploration program discussed in Section 3.2.4 above. The staff concludes that the geotechnical investigations conducted at the Cheney Reservoir disposal site adequately establish the stratigraphy and the soil conditions at the Cheney Reservoir site, that the explorations are in general 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 l The staff has reviewed the geotechnical engineering testing program for ; materials from the Grand Junction processing site and the Cheney Reservoir ! disposal site. The testing program included specific gravly, Atterberg limits, particle size distribution, moisture / density relationships, shear , strength, permeability, and consolidation tests on samples of tailings and l contaminated materials and soils from the disposal site. The staff finds that ! the testing program employed was 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. ! l
O 25 3.3 Geotechnical Engineerino Evaluation 3.3.1 Stability Evaluation 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 I vertical slope has been compared with the exploration records and the design details. The staff finds that the most critical slope section has been considered for the stability analysis.
Soil parameters for the various materials in the stabilized embankment slope have been adequately established by appropriate testing of representative material. Values of parameters for other earthen material have been assigned on the basis of data obtained from geotechnical explorations at the site and data published in the literature. The staff also finds that appropriate methods of stability analysis (the Morgenstern-Price Method and infinite slope) have been employed and have addressed the likely adverse conditions to which the slope may be sut.,ected. 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) and long-term state. The values of the seismic coefficients used in the analysis are .25g for_the long-term condition and .19g for the short-term condition. These values were derived from the 0.42 g peak horizontal bedrock acceleration (see Section 2.4.3) in accordance with the recommended methods in the NRC SRP and are acceptable to the staff. The staff finds that the use of the pseudo-ctatic method of analysis for seismic stability of the slopes is acceptable considering the flatness of the slopes and the conservatism in the soil parameter values. The minimum factors of safety against failure of the slope were 2.35 and 1.06 for the short term , static and pseudo-static conditions, respectively, compared to required minimums.of 1.3 and 1.0, respectively. The minimum factors of safety against failure of the slope were 3.29 and 1.03 for the long term static and pseudo-static conditions, respectively, compared to required minimums of 1.5 and 1.0, respectively.
'However, information provided in the subcontract documents indicates that the supporting calculations do not reflect the current excavation plan, i.e. an additional 6 feet of excavation into the Mancos shale to accomodate an additional 1.1 million cubic yards of contaminated materials. The effect of this design change on slope stability needs to be addressed in the Final Remedial Action Plan. This may be accomplished either by additional stability analysis using the revised profile, or by discussion (most likely in Section 3.3.2 of'the Remedial Action Selection Report) of why che change will not affect. for the worse, the previous analyses and the resulting stability conclusions.
26 3.3.2 Settlement - The staff has reviewed the analysis of total end differential settlement of the disposal cell and foundation materials and the resulting potential for cracking of the radon barrier. Calculations indicate that all settlement due to placement of the main pile tailings, off-pile tailings, and radon barrier will have taken place by the time the radon barrier construction is completed. Therefore, the primary concern is the settlement due to the placement of the erosion protection materials. Settlements due to the placement of the erosion protection were calculated at three profiles along an east-west partial cross section through the disposal cell. The staff agrees that an appropriate section has oeen chosen to assess the most critical conditions for differential settlement. Calculated settlements along the profile varied from
.03 incSes to 4.28 inches, with a resulting maximum horizontal strain of .01%.
The calculated tensile failure strain for the proposed radon barrier material (PI=19.3%) was 0.108 %. 00E has concluded that total and differential settlement of the materials comprising the proposed disposal cell will not have an adverse effect on the ability of the cell to meet the stability standards. The staff agrees that settlement will. generally be small due to the compaction of the materials in the cell and the granular nature of much of the material. Differential settlement should not cause por. ding concerns due to the sloping configuration of the cell. Cracking of the cover due to settlement should not occur, since the resulting maximum strain is well below the calculated tensile failure strain. However, as indicated in Section 3.3.1 above, the supporting calculations do not reflect .. ' current excavation plan, i.e. an additional 6 feet of excavation into the Mancos shale. The effect of this design change on the settlement / cracking analysis needs to be addressed in the Final Remedial Action Plan. 3.3.3 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 consolidated shale bedrock foundation material is nc-l susceptible to liquefaction.- The compacted dry density of the stabilized tailings. and contaminated materials will be equal to a m%imum of 90 percent of maximum dry density as determined by the ASTM D-698 test, and the tailings pile embankment design provides for the tailings materials to be mostly in an unssturated condition. DOE bas. indicated that a portion of the tailings may l- become saturated for a time. A two-dimensional, finite element method flow analysis of transient drainage of. tailings pore water shows that the maximum depth of saturation in the tailings (at the base of the disposal cell) will range' from zero to 12.3 feet within one to two years af ter completion of the
! remedial action. However, given the compacted nature of the tailings, the conservatism applied in the worst-case transient drainage analysis, and the L unliklihood of a heavy earthquake during the period of saturation, the staff concludes that the stability of the disposal cell will not be adversely affected by seismically induced liquefaction.
l
D 27 3.3.4 Cover Design The proposed conceptual cover design for the Chercy Reservoir disposal cell employs a multi-layered system of earthen and geomembrane materials with a different system of layers on the top slopes and the side slopes. On the top, in descending order from the surface are: (1) a vegetated two-foot-thick soil rooting medium with surficial rock mulch layer; (2) a 1.25-foot-thick rock biointrusion barrier including a choked rock filter layer; (3) a 6-inch-thick clean sand bedding / drain layer; and (4) a two-foot-thick radon / infiltration barrier. On the side slopes, in descending order are: (1) a one-foot-thick rock erosion protection layer; (2) a 6-inch-thick clean sand bedding / drain layer; and (3) a 3.5-foot-thick radon / infiltration barrier. This cover system provides a total of from 5 to 5.75 feet of cover over the contaminated material, and collectively is designed to limit infiltration of precipitation, protect the pile from erosion, and control the release of radon from the cell. Details of the staff review of the cover's performance related to limiting infiltration are addressed in Section 5.0 of this report; the review of the cover's erosion protection features is presented in Section 4.0; and the review of the radon attenuation aspects of the cover is presented in Section 6.0. However, there are certain other aspects of the cover (frost protection, gradation / filter design, etc.) that are addressed here. The Remedial Action Selection Report (RAS) (DOE, 1990a) indicates that the radon / infiltration barrier will consist of compacted clay that will limit infiltration and inhibit radon emanation. The specifications provide for the use of excavated oilty clay material from depths of about 10 to 15 feet, or if necessary, screened material from the overlying gravelly layer. These two materials are quite different based on the results of gradation and permeability tests. The selected gradation requirements in the specifications appear to allow for material that is inconsistent with the expected design permeability. Furthermore, it is not exactly clear what value is proposed for the radon barrier design permeability i.e., 5.02E 8 cm/sec as given in the summary of design parameters, or IE-7 cm/sec as given in the water resources , protection strategy. In order to bring clarity to this aspect of the radon I barrier design, 00E needs to provide a discussion that presents the expected j material make-up of the radon barrier,-the design permeability, the basis for selection of the permeability, the resulting gradation specifications, and justification of how the specifications will ensure a radon barrier with the !
-design permeability. l The RAS indicates that the layer immediately above the radon barrier is to be i a six-inch-thick sand bedding / drain layer, intended to drain water laterally i off the-cell and protect the radon barrier from the riprap. The gradation i specifications and drawings show two seprate materials, a drain material and a bedding material. The RAS does not clearly identify the design basis for '
the two dif ferent materials, and the calculations do not clearly lay out how the gradations are established from the design criteria (permeability, filter criteria). Thet,e aspects of the cover design need to be clarified in the . final RAP. l
28 i The top layer of cover on the side slopes is proposed to consist of one foot of Types B and and C riprap (d5n>6in). The proposed erosion protection for the top slope is a combination Of a two-foot-thick vegetated natural soil layer and an underlying one-foot-thick rock biointrusion layer (Type A riprap). Details of the review of the erosion protection design are found in Section 4.0 of this report. On the top slope, a three-inch-thick layer of choked rock is proposed between the vegetated layer and the biointrusion layer to prevent piping of soil into the rock of the biointrusion layer. The calculations provide the basis for the gradation design of the choked rock layer. However, the resulting gradation is not consistent with the gradation presented in the construction r specifications. There is no basis for the gradstion provided in the specifications. This discrepancy needs to be ret.olved in the final RAP. The cover does not contain a layer constructed solely for the purpose of protecting the radon barrier against frost damage. However, a computer analysis of the depth of frost penetration, using Rifle, Colorado weather data, indicates that the thickness of the other la)ers of material and the radon barrier itself will provide adequate frost piotection. The staff - concurs that no additional frost protection is necessary. Based on the geotechnical review of the disposal cell cover design, the staff has identified several issues which preclude a detertaination that the cover has been adequately designed from a geotechnical en;.neering perspective to provide the necessary protection for the long term. Items, as described above, remain-to be clarified on aspects of the radon / infiltration barrier, the bedding / drain layer, and the choked rock filter. 3.4 Geotechnical Construction Details 3.4.1 Construction Methods and Features The staff has reviewed and evaluated the geotechnical construction criteria provided in Attachment I to the RAP. Based on this review, the staff concludes that the plans and drawings clearly convey the proposed remedial action design features. In addition, the excavation and placement methods and specifications represent accepted standard practice. 3.4.2 Testing and Inspection The staff has reviewed and evaluated the testing and inspection quality control requirements provided in the Remedial Action Inspection Plan (RAIP). In general, the RAIP is found to provide a program for testing and inspection that is consistent with the Staff Technical Position on Testing and Inspection (NRC, 1989a). However, there are two additional aspects of the disposal cell construction that need to be addressed in the RAIP. The specifications
. 1 29 l
t! indicate that compaction requirements for the beddirg, drain, and choked rock layers are method (number of r sses) rather than numerical (% maximum
- density). The RAIP should contain discussion of the plans to inspect and document the placement of these materials. The specifications also include requirements for placement of the rooting soil, rock mulch, and vegetation.
The RAIP should contain plans to inspect these aspects of the cover. , , In addition, the staff has reviewed the field quality control portions of the > specifications to assess consistency with the RAIP. Based on this revied4 it
'does not appear that care was taken to ensure consistency . For example, the RAIP indicates that the radon barrier will be tested for gradation once every 1000 cubic yards placed; the specifications indicate this frequency to be once every 2000 cubic yards. Another example is that the specifications do not require all of the erosion protection durability tests that are required in
- the RAIP.
Prior to the staff concurring in the program for testing and inspection. DOE needs to address the two RAIP items identified above, and thoroughly rt.iew the' specifications for other inconsistencies, making appropriate revisions to ensure consistency with the RAIP.
- 3. 5 Conclusions ;
Based'on the review of the geotechnical engineering aspects of the design of the Grand Junction remedial action as presented in the Preliminary Final : Remedial Action Plan and the Remedial Action Inspection Plan, the NRC staff
- concludes that in light of the open items identified in this section, it cannot concur on the plan with respect to long-term stability aspects of the. EPA standards (40 CFR Part 192.02(a)).
1 e 2
.6 e 30 4.0 SURFACE WATER HYDROLOGY AND EROSION PROTECTION 4.1 fjydrologic Description and Site Conceptual Design DOE proposes to move the existing tailings in the city of Grand Junction, .
Colorado, from their present location in the floodplain of the Colorado River l to the Cheney Reservoir site. The Cheney Reservoir site is located approximately 18 miles southeast of Grand Junction. The site is in a remote, relatively flat area and is located on a pediment surface that forms a divide between two small ephemeral washes. These washes are 1400 feet north of the pile and 1000 feet south of the pile and merge with Indian Creek approximately 2/3 of a mile below the site. Indian Creek flows into Kannah Cr0ek, which discharges into the Gunnison River. A local drainage area of about 240 acres drains toward the pile. Slopec in this watershed average about three percent. Flows from about 145 acres of this drainage area will be intercepted by a diversion channel, located ' northeast of the remediated pile. Some gullying is occurring in the small , ephemeral streams in the site vicinity. ' In order to comply with EPA standards, which require stability of the tailings j' for a 1,000 ye.r (or minimum 200 year) period, 00E 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. As proposed by'00E, the tailings.will be consolidated into a single pi a , which will be protected by soil and rock covers. The covers will have mcximum slopes of 2% on the top and 20% on the sides. The remediated embankment will be surrounded by aprons which will safely convey flood runoff away from the tailings and prevent gully erosion into the stabilized pile. The top s1cpe of i the pile will have both soil and rock covers. DOE has provided conflicting information regarding the cover design; however, it appears that a two-foot ; vegetated soil cover will be covered with a layer of rock mulch to enhance vegetation growth. The side slopes of the pile will be protected by a layer of rock riprap, which will not be covered by soil. 4.2 Flooding Determinations The computation of peak flood design discharges for various design features at , the site was performed by DOE in several steps. These steps included (1) l selection of a design rainfall event, (2) determination of infiltration i losses, (3) determination of times of concentration, and (4) determination of appropriate rainfall distributions, corresponding to the computed times of
31 concentration. Input parameters were derived from each of these steps and were then used to determine the peak flood discharges to be ustd in water surface profile and velocity modelling and in the final determination of rock size for erosion 7 Setion. 4.2.1 Selection s a sign Rainfall Event One of the most disruptive phenomena affecting long-term stability is surface water erosion. DOE has recognized that it is very important to select an appropriately conservative rainfall event on which to base the flood protection designs. DOE has concluded (DOE, 1989) and the NRC staff concurs (NRC, 1990) that the selection of a design flood event should not be based on the extrapolation of limited historical flood data, due to the unknown level of accuracy associated with such extrapolations. Rather, DOE utilized the Probable Maximum Precipitation (PMP), which is computed by deterministic methods (rather than statistical methods), and is based en site-specific hydrometeorological characteristics. The PHP has been defined as the most severe reasonably possible rainfall event that could occur as a result of a combination of the most severe meteorological conditions occurring over a watershed. No recurrence interval is normally assigned to the PHP; however, DOE and the NRC staff have concluded that the probatility of such an event j being equalled or exceeded during the 1000 year stability period is small. Therefore, the PMP is consioered by the NRC staff to provide an acceptable design basis. ; Prior to determining the runoff from the drainage basin, the flooding analysis requires the determination of PMP amounts for the specific site location. Techniques for determining the PMP have been developed for the entire United States primarily by the National Oceanographic and Atmospheric Administration (NOAA) in the form of hydrometeorological reports for specific regions. These techniques are widely used and provide straightforward procedures with minimal , variability. The staff, therefore, concludes that use of these reports to i derive PMP estimates is acceptable. 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 Cheney Reservoir disposal site. This rainfall estimate was developed by DOE using Hydrometeorological Report (HMR) 49 (Department of Commerce, 1977). The staff performed an independent check of the PMP value, based on the procedures given in HMR 49. Based on this check of the rainfall computations, the staff concludes that the PMP was acceptably derived for this site. ; 4.2.2 Infiltration Losses i Determination of the peak runoff rate is dependent on the amount of precipitation that infiltrates into the ground during the cccurrence of the rainfall. If the ground is saturated from previous rains, very little of the rainfall will infiltrate and most of it will become surface runoff. The loss l rate is highly variable, depending on the vegetation and soil characteristics of the watershed. 1
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~ 32 l Typically, all runof f models incorporate a variable runoff coefficient or variable runoff rates. Commonly-used models such as the Rational Formula (Bureau of Reclamation, 1973) incorporate a runoff coefficient (C); a C value > of I represents 100% runoff and no infiltration. Other models such as the U.S. Army Corps of Engineers Flood Hydrograph Package (HEC-1) separately compute infiltration losses within a certain period of time to arrive at a runoff amount during that time period. In computing the peak flow rate for the design of the rock riprap erosion protection at the proposed disposal site, DOE used the rational formula. In l this formula, the runoff coef ficient (C) was assumed by DOE to be unity; that is DOE assumed that no infiltration losses would occur. Based on a review of the computations, the staff concludes that this is a very conservative assumption, as discussed above, 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 of that basin. If the time of concentration is computed to be small, the peak discharge will be conservatively large. Times of concentration and/or lag times are typically computed using empirical relationships such as those developed by Federal agencies (Bureau of Reclamation, 1973). Velocity-based approaches are also used when accurate estimates are needed. Such approaches rely on estimates of actual flow velocities to determine the time of concentration of a drainage basin. Within the computerized design procedure used by DOE to estimate riprap sizes (M.K. Ferguson,1938), the times of concentration for the pile top and sides , were estimated by computing the actual flow velocity and dividing the length of the design segment by that velocity. Such a velocity-based method is considered by the staff to be appropriate and very precise for estimating times of concentration. Based on the precision and conservatism associated with such a method, the staff concludes that the tc's have been acceptably derived. The staff further concludes that the procedures used for computing tc are representative of the small steep drainage areas present at the Cheney Reservoir site. For very small drainage areas with very short times of. concentration, DOE utilized tc's as low as 3.7 minutes; the staff considers such tc's to be conservative. 4.2,4 Rainfall Distributions After the PMP is determined, it is necessary to determine the rainfall intensities corresponding to shorter times of concentration. A typical PHP value is derived for periods of about one hour. If the time of concentration is less than one hour, it is necessary to extrapolate the data presented in
33 the various hydrometeorologir;al reports to shorter time periods. DOE utilized a procedure recommended by NOAA and endorsed by the NRC staff. This procedure involves the determination of rainfall amounts as a percentage of the one-hour PMP, and computes rainfall amounts for a very short periods of time. 00E and the NRC staff have concluded that this procedure is conservative. In the determination of peak flood flows, rainfall intensities for durations as short as 2.5 minutes were used. The distribution of PMP rainfall is derived by plotting and extrapolating the following relationships that were recommended by the NRC staff: Rainfall Duration % of 1-hr PMP (min) 2.5 27 5 45 15 74 30 89 45 95 60 100 The staff checked the rainfall amounts for the short durations associated with small drainage basins. Based on a review of this aspect of the flooding determination, the staff concludes that the computed peak rainfall intensities are conservative. 4.2.5 Computation of PMF 4.2.5.1 Top Slopes, Side Slopes, and Aprons The peak runoff rates for the top slopes, side slopes, and aprons were estimated using a computerized design procedure for riprap sizing (MK-Ferguson,1988), which iteratively computes the riprap size required. The rational formula (Bureau of Reclamation, 1973) forms the basis for computing the peak sheet flows down the slopes. Based on a review of the calculations
-presented, the staff concludes that the peak rates of runoff have not been acceptably derived.
DOE indicated that a flow concentration factor (FCF) of 3 was used to design the top slopes of the pile. However, staff review of the calculations
.provided indicates that no flow concentration was assumed for the design of the top slopes.- Under flow concentration conditions, the top slopes (including the 2-inch layer of rock mulch) and side slopes, as designed, cannot withstand a PMP/PMF event.
DOE further assumed that extending the side slope rock 20 feet up onto the top slope would cause dispersion of concentrated flows off the top slope. Such dispersion was assumed by DOE to prevent the formation of concentrated flows on the side slopes. Based on review of the calculations, the staff concludes that the assumptions are unfounded and overly optimistic (see Section 4.3.2).
. o 34 In order to resolve these issues, DOE could use one of the following options:
- a. If the rock mulch is designed as a riprap layer and adequate rock sizes are provided, use FCF = 1 for the top slope and side slopes;
- b. If a vegetated soil cover, with or without a 2-inch rock mulch, is proposed for the top slope, use FCF = 3 for the top slope and side ,
slopes. 4.2.5.2 Diversion Channel lhe PMF for the diversion channel was estimated using the Rational Formula, which provides a standard method for estimating flood tiischarges. The PMF at the downstream end of the ditch, which has a drainage area of about 145 acres, was estimated to be approximately 1260 cfs. Based on staff review of the
' computational procedure, this estimate is considered to be acceptable.
4.3 Water Surface Profiles and Channel Velocities Following the determination of the peak flood discharges, it is necessary to determine the resulting water levels, velocities, and shear staesses associated with that discharge. These parameters then provide the basis for the determination of the required riprap size and layer thickness needed to assure stability during the occurrence of the design event. 3 In determining riprap requirements for this site, DOE utilized a computerized design procedure. The procedure is iterative in nature and first assumes a trial D RO size. Various parameters, such as time of concentration, rainfall intensity .and flow velocity, are then computed for individual slope segments. The procedure assumes the occurrence of sheet flow on a onn~ foot-wide strip of a'given slope. length. The Safety Factors Method is used foe slopes less than 10 percent, and the Stephenson Method is used for slopes FWer than 10 percent. The validity of these two design approaches was aerified by the NRC staff through the use of flume tests at Colorado State University. It was determined that the_ selection of'an appropriate design procedure depends on the' magnitude of the slope'(Abt, et al., 1987). The staff therefore concludes that the procedures and design approaches used by DOE are acceptable and reflect state-of-the-art methods for designing riprap' erosion protection. 4.3.1 Top Slopes The information provided by DOE in the RAP and in the calculations is confusing and conflicting. However, the design of the top slopes of the pile is apparently based on the assumption that the soil cover is sufficiently flat to limit shear stresses and that the rock mulch will provide added protection. These assumptions are unsupported by the information provided. Based on the criteria developed in the NRC Staff Technical Position (NRC, 1990), the staff concludes that the design should be modified (See Section 4.2.5.1, above).
O O I 35 4.3.2 Side Slopes and Aprons / Toes The design of the riprap layer for the side slopes of the pile is based on tt assumption of sheet flow on the top slope of the pile which then discharges flows onto the side s' opes. The flow rate which was calculated for the desigi. of the riprap for the side slopes, however, does not appear to be conservatively derived. Without sufficient justification, DOE has given too much credit to the 20-foot layer of rock which extends up onto the top slope. DOE optimistically assumes that this rock layer will disperse the flow so that no flow concentration will occur. It also appears that the actual amount of flow may be significantly more than the amount assumed to occur, resulting in , higher peak discharges at the top slope / side slope interface (shape break). In order to resolve these concerns, 00E 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 form on the top slope of the pile. The staff also notes that the peak design discharge for the top slopes is much higher than the design discharge for the side slopes (e.g. see , Calculation 05-504-01-00, Sheet B-37, where the peak discharges are 2.5 and 1.2 cfs for top and side slopes, respectively, even though the total flow length for the side slope is greater). It would be acceptable if the rock for the side slopes is designed for the maximum flow which could occe. on the top slopes, assuming that a rock layer is provided on the top slope. 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. The rock sizes for the design of the aprons and toes will also have to be increased accordingly. The design of the rock toe will also need to address the potential for gully intrusion into the tailings area due to headcutting and upstream advancement of a potential gully. The staff considers that if i the toe design is revised to adequately withstand peak flood flows from off the pile, then the required rock size will be sufficient to prevent headward gully advancement. The potential for gully intrusion is further discussed in Section 2.4 of this TER. . l l 4.3.3 Diversion Channel Flow depths and rock sizes for the diversion channel were estimated by-00E using procedures developed by the U.S. Army Corps of Eaqir.eers. Flow depths L were estimated to range from 0.8 to .'.1 feet; velocitin ranged from 1.4 to l 4.1 feet per second. Based on the sta'f review of the calculations, these estimates have been acceptably derived. 1 NRC staff review of the RAP indicates that erosion protection has not been l provided for the outlet of the diversion coannel to prevent erosion from the I flow velocities and scour produced in the adjacent large gully. It appears l ll i
36 that rock will be needed to prevent damage to the diversion channel outlet. Assuming that the pile can be affected in a 1000 year period due to this erosion, the following procedures should be considered in the design of erosion protection at this location: First, the use of existing gully 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 secticns could be scoured, which would result in a greater depth 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 cross-section change are ve:y difficult to predict.
Therefore, it is necessary that the section that is used for design purposes be carefully selected; the use o' 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 where the sections change as drastically as those could change in this design, where the bottom width of the gully changes in a relatively short horizontal distance and where the flow velocities change significantly. Additionally, a Manning's n value of less than .05 is generally considered appropriate in an earth channel (gully). Third, the use of an average slope and velocity may not be representative of the actual slope and velocity that will exist immediately at the section in question. Fourth, a considerable amcunt of turbulence can be expected to occur in this irregular gully, causing an increase in the shear forces which will need to be resisted. With such irregularities, localized hydraulic jumps, eddies, and vortices 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 gully. This stream curvature can result in an increase in the riprap size required. Review of the information provided indicates that large rock may be difficult to locate within a reasonable distance of the site, The staff also fully recognizes that the riprap required in this area would serve as backup protection and would be located a significant distance away from the tailings area. Therefore, in order to resolve the staff's concerns, the most effective approach may be to perform minor regrading of the existing gully. The gully could be widened, straightened, aligned, and generally protected in a manner l- which would allow the use of 20-inch rock as a measure to protect against j flood velocities in the gully. The width, depth, and shape of the gully i
, o 37 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 gully so that (1) the minimum inv<-t elevation occurs on the east side, i.e. the bottom is sloped to the eae (2) the gully is straightened or re-aligned so that the downstream end of the diversion channel is not on the outside of a bend; (3) a relatively uniform section exists both upstream and dowmstream; (4) gradual transitions are constructed from the natural portion to the man-made portions of the gully; and (5) measures are taken to assure that hydraulic jumps and/or excessive turbulence occur well upstream or downstream of the area.
The design of the riprap and the grading should be revised accordingly. Alternatively. larger rip'ap should be provided, taking into consideration each of the concerns rnchtioned above. If riprap is provided to protect the existing gully in the vicinity of the diversion channel discharge, it will probably require large riprap and the toe will need to extend to the expected depth of scour. Additionally, there appears to be a potential for concentrated gully flows to enter the diversion channel. The staff considers it important to analyze the effects of gully inflows on the design of the riprap for the diversion channel and to analyze the potential for clogging and sedimentation of the diversion channel. Review of DOE responses to the NRC staff's previous questions indicates that 00E concludes that sedimentation and clogging of the channel will not be a 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 00E has not provided any technical justification for those conclusions. First, it is not clear how the channel will be self-flushing, since the rock channel is flatter and may have a higher roughness coefficient than the earth gullies. If clogging of the channel begins, it is not apparent what prevents the clogging from worsening or what causes the sediment to be flushed from the channel. Second DOE's statement that no boulders will be transported into the channel 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 locations which could be eroded. If a gully discharges directly onto the channel side slope, it is unlikely that the channel side slopes can resist these flow velocities, since the channel is designed only for those flow velocities which would occur longitudinally within the channel and is not designed for the velocities and flow concentrations produced in the gullies perpendicular to the side slopes. i
q l 38 l 00E should revise the riprap design of the diversion channel, in light of the concerns discussed above. Acceptable approaches for designing 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 flows are accounted for in the design of the rock on steeper side slopes. Steepening of the channel to increase self-cleaning velocities may be one acceptable solution to the sedimentation problem. Alternatively, 00E needs to further justify the ability of the present design to withstand erosive forces produced in the natural earth gullies and the ability of the channel to be self-cleaning and not require maintenance to perform its intended function. Such justifications should be accompanied by pertinent technical analyses which document the ability of the design to meet EPA long-term stability requirements. 4.4 Erosion Protection 4.4.1 Sizing of Erosion Protection As discussed above, 00E has not correctly determined appropriate flow rates, water surface profiles, velocities, shear stresses, and other parameters necessary to correctly design the erosion protection for the top slopes, side slopes, aprons, or the diversion channel. It will be necessary for 00E to either completely re-design the erosion protection or to provide additional justification for the design proposed. 4.4.2 Rock Durability
.The EPA standards require that control of residual radioactive materials be effective for up to 1000 years, to the extent reasonably achievable, and, in any case, for at least 200 years. The previous sections of this report examined the ability of the erosion protection to withstand flooding events reasonably expected to occur in 1000 years. In this section, rock durability is considered to determine if there is reasonable assurance that the rock itself will survive and remain effective for 1000 years.
Rock durability is defined as the ability of a material to withstand the forces of weathering. Factors that affect rock durability are (1) chemical reactions with water, (2) saturation time, (3) temperature of the water, (4) scour by sediments, (5) windblown scour, and (6) wetting and drying. DOE conducted investigations to identify acceptable sources of rock within a reasonable distance of the site. The suitability of the rock as a protective cover was then assessed by laboratory tests to determine the physical characteristics. The results of these tests were used to classify the "ock's
39 quality and to assess the expected long-term performance of the rock. The tests included:
- 1. Petrographic Examination (ASTM C295). Petrographic examination of rock is used to de% rmine its physical and chemical properties. The examination et ablishes if the rock contains chemically unstable minerals or volumetrically unstable materials.
- 2. Bulk Specific Gravity (ASTM C127). The specific gravity of a rock is an indicator of its strength or durability; in general, the higher the specific gravity, the better the quality of the rock.
- 3. Absorption (ASTM C127T A low absorption is a desirable property and indicates slow disint-gration of the rock by salt action and mineral hydration.
- 4. Sulfate Soundness (ASTM C88). In locations subject to freezing or exposure to salt water, a low percentage loss is desirable.
- 5. Freeze-Thaw (AASHTO 103). A low percentage loss is indicative of resistance to weathering resulting from the crystallization process.
- 6. Schmidt Rebound Hammer. This test measures the hardness of a rock and can be used in either the field or the laboratory.
- 7. .Los Angeles Abrasion (ASTM C131 or CS35). This test is a measure of rock's resistance to abrasion.
- 8. Tensile Strength (ASTM D3967). This test is an indirect test of a rock's tensile strength.
All samples for testing were taken in accordance with Standard Practices for Sampling Aggregate (ASTM D75). DOE used a step-by-step procedure for evaluating rock durability, in accordance with procedures recommended by the NRC staff (NRC, 1990), as follows: Step 1.- -Test results from representative samples were scored on a scale of 0 to 10. Results of 8 to 14 are considered " good"; results of 5 to 8 are considered ". fair"; and results of 0 to 5 are considered " poor". Step 2. The score was multiplied by a weighting factor. The effect of the weighting factor is to focus the scoring on those tests that are the most applicable for the particular rock type being tested. Step 3. The weighted scores were totaled, divided by the maximum possible , score, and multiplied by 100 to determine the rating. l ! I 1 l l l l 0 l l l-
e _ e i 4 1 40 1 Step 4. The rock quality scores were then compared to the criteria which I determines its acceptability, as defined in the NRC scoring I procedures. 00E has determined that the rock will be produced from the excavation of the l site. Gradation and rock durability criteria were presented, including the ! results of several durability tests. Using the criteria provided in the Staff , Technical Position or: erosion protection (NRC, 1990), 00E has documented that I the rock, while riot of excellent quality, is of relatively. good quality and is the most economical source that can reasonably be found. Based on our review of the assessments, data, and criteria provided, the staff concluc'es that the rock durability criteria proposed and the rock to be found at the sit.e are adequate. 4.4.3 Testing and Inspection of Erosion Protection The staff has reviewed and evaluated the testing and inspection quality , control requirements for the erosion protection materials, as provided in the Remedial Action Inspection Plan (RAIP). Based on the results of the durability tests to characterize the proposed rock, the staff concludes that the proposed testing program detailed in the RAIP is acceptable. The RAIP requirements for inspection during placement are also acceptable. 4.5 Upstream Dam Failures There are no impoundments near the site whose failure could potentially affect ' the site, 4.6 Conclusions Based on its. review of the information submitted by DOE, the staff concludes that the site. design will not meet EPA requirements as stated in 40 CFR 192 with regard to flood design measures and erosion protection. An adequate hydraulic design has not been provided to reasonably assure stability of the cuntaminated 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, aprons, and diversion channel. Alternatively, 00E should provide additional-information which documents-the adequacy of the design proposed. l l l l l l
41 5.0 WATER RESOURCES PROTECTIOh 5.1 Introduction The NRC itaff has reviewed the Remedial Action Plan (00E,1990a-f) for the Grand Junction, Colorado UMTRA Project site for compliance with EPA's proposed groundwater protection standards in 40 CFR Part 192, Subparts A-C. To achieve compliance with the proposed EPA groundwater protection standards, DOE has proposed narrative supplemental standards to ensure sufficient protection of human health and the environment. DOE has proposed application of supplemental standards in lieu of the primary standards based upon the limited use (Class III) designation of the groundwater of the uppermost aquifer at the disposal site (Dakota Sandstone aquifer). DOE asserts that the uppermost aquifer is a Class III aquifer due to its naturally occurring high TDS concentration. DOE further assert' that the supplemental standards , proposed will assure protection of human health and the environment, and come as close to meeting the otherwise applicable standards due to the hydrologic isolation of the uppermost aquifer. The NRC staff concurs with DOE's approach of proposing narrative supplemental standards to ensure protection of the uppermost aquifer. Further, the NRC staff concurs with DOE's assessment that the uppermost aquifer is of limited use based upon its Class III designation; therefore, supplemental standards are appropriate. However, DOE has not clearly stated the supplemental standard, and has not adequately demonstrated that the supplemental standards come as close as possible to meeting the otherwise applicable standards; therefore, DOE's proposed remedial action plan cannot be shown to be in compliance with the EPA groundwater protection standards. Consistent with EPA's groundwater protection standards, the NRC staff distinguishes between the. disposal of residual radioactive materials at the d 1posal site and the cleanup of existing groundwater contamination at the p wcessing site. The NRC staff cannot accept DOE's proposal to defer groundwater cleanup until. DOE demonstrates that public health and safety will not be impacted by the existing contamination at the Grand Junction processing site.
- 5. 2 Hydrogeologic Characterization
- 5. 2.' 1 Identification of Hydrogeologic Units
'A. Processing Site The hydrogeologic units that are most susceptible to impacts from the processing site are described below:
(a) The uppermost hydrogeologic unit is the unconfined alluvium aquifer, which has a range'of thickness of approximately 5 to 15 feet depending
42 1 upon its location with respect to the Colorado River. The alluvium is comprised principally of silts, sands, gravel, and cobbles. Groundwater level: in the alluvium range from 4 to 20 feet below the ground surface, o and fluctuate two to five feet throughout the year. The groundwater flow pattern is controlled by the river, with groundwater closest to the river generally flowing parallel to the viver and that farther away generally flowing toward the river. Groundwater in the alluvium is believed to discharge into the river at the site. (b) The Mancos Shale fc,rmation underlies the alluvium and varies in thickness from zero to greater than 100 feet. The formation is comprised primarily of shale, but contains some thin sandstone beds. DOE states that although the Mancos Shale is saturated it behaves as an aquitard because of its low permeability and low well yields. (c) The Dakota Sandstone / Burro Canyon Formation (D/BC) aquifer consists of beds of sandstone, conglomeratic sandstone, shale, and beds of coal. Groundwater occurrence and movement has not been character 1 zed at the site. DOE considers the confining properties of the overlying Mancos Shale to be adequate to prevent contaminants from reaching this aquifer. Groundwater level data for three wells drilled into the Dskota Sandstone appear to support this argument, since water level data show the potentiometric elevat;on of the D/BC aquifer being several feet above the potentiometric elevation of the alluvium aquifer; this would tend to have the effect of limiting downward migration. B .- Disposal Site g The Cheney disposal site is located on a broad pedim nt surface on the west flank of the Grand Mesa. From a hydrogeologic stanopeint, the stratigraphy at the site is described as follows: (a) The uppermost aquifer occurs in paleochannels formed by perched water in a gravel deposit at the base of the alluvium deposits. The alluvium deposits consist mostly of mixtures of silty gravel with some cobbles and boulders, with a thickness ranging from 5 to 40 feet. The paleochannels were formed by erosional processes into the upper surface of the weathered Mancos Shale bedrock. DOE concludes that recharge to the paleochannel does not come from direct rainfall based upon caliche deposits within the soils and gypsum deposits within the upper 10 to 15
- feet of alluvium. DOE believes that recharge to the paleochannels is derived fro.a drainage out of the bottom of Indian Creek and surface runoff in Creek C (north of the site). Of the three paleochannel systems
. identified by DOE, only one has sustained-flow near the disposal cell area; this system has flow within 100 feet of the northwest corner of the disposal cell footprint. Discharge from the paleochannels is believed to occur through evapotranspiration and infiltration into the t weathered zone of the Mancos Shale through fractures.
I 1
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4 .i
'k' s f
..- 43 a4 DOE proposes to-construct a partially below grade disposal cell by-excavating.up to.35 feet of surface materials; the base of the cell will be in unweathered Mancos Shale. The purpose of.this is to eliminate the 2 -possibility of any ponded water within the cell seeping into the surrounding alluvial paleochannels. By installing the base of the
; disposal cell into the bedrock, the uppermost aquifer, in t:rms of complia Ne at the point of compliance (POC), will be the Da w ca Sandstone aquifer-(see Section (c) below).
.(b)- Underlying the alluvium.is 700 to 750 feet of shale which constitute
'the Mancos Shale formation. The upper portion of the Mancos Shale is n, fractured and weathered, while the lower portion is generally fairly competent.' Thin limestone and sandstone beds are scattered throughout
.the, formation. Although it contains isolated areas of perched water, DOE has characterized the Mancos $ hale as an equitard. It is considered an aquitard because of its low permeability, low yield to wells, and zones of.unsaturation.. In addition, it acts as a confining unit for the e underlying Dakota Sandstone'. based upon the large pressure heads evidenced in wells in'the Dakota Sandstone, and based on age dating of the water.1
,(c) Groundwater in the Dakota Sandstone is believed to occur primarily in fractures within the. upper part of the formation. -The highly dense
. matrix of.the sandstone material. limit. groundwater from occurring-due to primary porosity. .The dense matrix also acts to help confine water
~' occurring within the.-formation. 00E suspects that recharge to this
- aquifer; occurs through an outcrop near the Gunnison River.
c . 5. 2. 2 . Hydraulic and Transport Properties 4 : Based onLinformation from DOE, the hydraulic conductivity at the processing. and! disposal, s,ites a're sunnarized below: P Table-5;11- Hydraulic conductivity, ll. , Gre.nd Junction Processing Site - Unit: Hydraulic Conductivity ' Method ft/d cm/s 1,
; Alluvium; . 85 3E-2. Pump test Mancos Shale: .1 1.1E-2L 4E-6 Slug DakM& Sandstone-. 7.1E-2~ 2.5E-5 Slug l
i
.' ).
u s
), 1 tb sit y o
t . 44 .y
" Table 5.2 - Hydraulic conductivity,.
,1 Cheney Reservoir Disposal Site
# Unit Hydraulsc Nnductivity Method Direction j U
-ft/d cm/h l Alluvium 4.8E-1 1.7E-4 R H&V Weathered Mancos 1.4E-1 5.06E-5 F&C H 1.4 5.06E-4 Packer H L ,
'Unweathered Mancos 7.74E-3 2.73E-6 R,F, & C H a 1.63E 5.75E-6 Packer H 2E-7 SORI V o
note: R = Rising head' test F = Falling head test C = Constant head test SDRI:= Standard double ring infiltrometer H = Horizontal direction V.= Vertical-direction DOE lcalculatesit. heave'rageflineargroundwatervelocityinthealluviumatthe p ocessing. site to; range from 0.2 to.5.0 feet per day (6.35-4 to 1,74E-3 ; cm/s); however, no:information.'is provided on the. assumed hydraulic gradient i:e and effective: porosity used in making this determination. .The average linear
. groundwater velocity estimated forithe paleo:hannels at the Cheney disposal "7' site is 0.34 feet'per day (1.2E-4'cm/s); based upon using an average hydraulic < 1 conductivity of 3.4 ft/ day, a hydreulic gradie.nt :of. 0.025 9 t/ft , and an 3 K ,
effective; porosity lof:0.25.' No estimates'were made of the t, age linear '
/ groundwater velo-ny withint the -Dakota Sandsune, 'at either site, because of i' N; ' insufficient linfopwation to determine the hydraulic gradients.
The NRC staff d$fers comm(nt'on the calculations for the processing' site
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becausa DOE proposes to defer gro.undwater cleanup to..a later phase'of the.
~
1 remedial action project. ' d~
, The2NRC staff concurs that 00E.has" adequately char cterized the hydraulic and .
, stransport properties at'the Cheney disposal'. site.' Although DOE.has not
gE , ,
- characterized the hydraulic and transport properties of the Dakota Sandstone
,V L' aquifer,,NRC' staff considers'cha'racterization;of this. aquifer unnecessary given that-DOE:has adequately shown'that-this-is a Class III aquifer and.that J <
(transport- to. this aquifer l will bellimited by. the' confining units. 4 " ;; y m
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t 45 5.2.33 Geochemical Conditions and Extent of Centamination A. . Processing Site DOE has concluded that seepage from tailings fluids has contaminated the alluvium aquifer at the processing site. The contamination plume is estimated to extend westward from the tailings area to a distance of 2500 feet, and discharge.into the Colorado River. Concentrations of several hazardous constituents have been determined to be above background concentrations within the Colorado River, immediately at the' site and down gradient to a distance of 1640 feet.- DOE did not test for all hazardous constituents in the river. In addition, DOE provided no information on river discharge at the time of the
. sampling; therefore, no inference can be made as to whether or not concentrations will be higher at a lower stream discharge. DOE has determined that uranium, molybdenum, and gross alpha concentrations, in the groundwater, down gradient from the tailings area are elevated above background concentrati ons~. . No determination has been made of the extent of contamination 1 , in the lakota Sandstone aquifer; DOE considers contamination of this aquifer '
to be unlikely given the degree of confinement offered by the Mancos Shale. The NR.C staff defers comment on the geochemistry assessment of the processing site because DOE proposes to defer groundwater clean-up until a later p%se of
'the remedial action project.- .At such time, DOE will need to better define the extent-of contamination by identifying all constituents that exceed background ;
concentration.. DOE's choice of sampling locations for determining down gradient contamination.is insufficient for identifying contamination at the source (i.e,, the tailings and vicinity property material areas). Therefore, either additional wells will have to be insta? led in the sotrce
. area, or better!use of existing wells.will have to be made to determir H whether-concentrations are considered to have exceeded background. In addition, because of the' dynamic nature of the contamination plume, DOE must i x redefine the plume at a later time when the remediation of the aquifer is to ;
, take. place. ,
e: L B[ Disposal Site ' $ 100ELh as present'ed. data to show that the Dakota Sandstona aquifer, at the , i' , Cheney' Disposal site,-is saline, with total dissolved solids concentrations exceeding 10,000'mg/1; therefore,-the aquifer is cm.c dered a Class III
, groundwater under the. EPA definition (40-CFR Part.192.11 (e)). Background
%'" ( Lwater' quality data shows that average combined concentrations of radium-226 Sc J % y' and radium-228 exceed the; EPA proposed MCL. Natural gas and measured redox' fpotentialiindicate=a reducing. environment.
', DGE has also provided information to show;that groundwater in the Mancos Shale.
L' (where it is: present). is in a reducing condition. Geochemical models indicate 7 i" , that arsenic, molybdenum, seleni'um, vanadium, uranium, cadmium, lead, copper,
" anditckel constituents are likely-to be removed from solution by chemical
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't 46 precipitation in such an environment. Laboratory batch tests also show that arsenic and cadmium are almost completely attenuated by the shale matrix, and selenium and molybdenum are partially attenuated.
The NRC staff concludes that DOE has adequately characterized the geochemical-properties of the Cheney Disposal site. 5.2.4 Water Use , A. Processing Site DOE indicates the primary source of drinking water for Grand Junction is the Grand Mesa surface water, which is located far up gradient from the processing site. The Gunnison River serves as an additional source during heavy demands; municipal water intake into the Gunnison River is located immediately up gradient from the processing site. NRC staff reviewed the surface v' iter quality data provided by DOE, and concludes that additional sampling io needed , to 41etermine the level of contamination within the Colorado River and its potential for impact to the public. DOE needs to sample for all o' the hazardous constituents identified within the tailings. In addition, due to the high variability of surface water quality, further testing under low flow 1 conditions are needed. DOE indicates there is only one unregistered well, completed in the alluvium i aquifer, in'the vicinity of the tailings. This well is. located up gradient from the tailings, and is used for dewatering purposes. In addition, DOE states that the potential for future use of groundwater in the alluvial and . Dakota Sandstone aquifers will be minimal because of the availability of city. water, and the poor water quality-(seasonally for the alluvial aquifer).
- Although 00E indicatesnthat-there is-no existing usage of shallow: alluvial-groundwater on Dakota. Sandstone groundwater in the area, the. area considered is' undefined; therefore,-the potential impact to' users outside the=immediate
- area cannot'be determined. In-addition, it is difficult to determine from DOE's reports whether they are concluding that there are no wells in the area z (i.e., used'for something other.than as'a drinking source) or that there'are no wells'used as'a drinking' source. One well not. identified by DOE is listed .
on the construction drawings as remaining after construction. Field verification determined that'this is not a well, but part of an aqueduct system and there are plans-to use this as a source of water. 00E needs to better define.the' area potentially af fected-by the present contamination, and- L the present and future water usage (drinking and other) within that area. . As ; discussed in TER Section 5.5,-the NRC staff considers this an open issue. B. Disposal Site'
. Based on the information provided by 00E, there are no registered wells within two' miles of the Cheney Dispost.1 site. Existing groundwater use in the area is minimal due to the following factors: 1) the current population density is
9: g.. 47 low; 2) the availability of shallow groundwater is limited; and 3) shallow groundwater is too poor in quality for domestic use. it is reported that residents in the area receive their water by hauling it in from nearby communities and collecting rainfall in cisterns. DOE has not projected what groundwater usage will be in the future; however, . based upon the reasons given for existing minimal usage and the fact that groundwater in the Dakota Sandstone is saline and fairly expensive to drill to, it is unlikely that future groundwater usage in the area will change greatly. 5.3 Conceptual Design Features to Protect Water Resources 00E proposes to relocate the tailings and vicinity property materials from the Grand Junction processing site to the Cheney disposal site. Construction
. dewatering will be required at the processing site to excavate the conta.hinated materials below the water table. A slurry trench will be constructed around-the site to facilitate the dewatering. At the completion ,
of the excavation, windows will be installed in the slurry wall to restore natural flushing. The processing site will be restored with uncontaminated fill from the disposal site, and then revegetated and mulched. A wetland
. system will.be created at the down gradient edge of the site, along the river.
Disposal of the tailings and vicinity property materials.wili uccur in a 60 acre cellipartially below grade. The disposal cell will be excavated up to 35~ feet below the existing grade, through the alluvium, into the Mancos Shale. Clean-fill dikes will be constructed tu'surrcund the contaminated materials. :These dikes,.which~will extend above the original grade, are designed to minimize the risk of mounded leachate within the pile reaching one
;of the paleochannels'in the alluvium. The contaminated materials will be placed in the disposal cell in such a way as to minimize infiltration into and through the cell, and to minimize mounding during transient drainage.- To
. accomplish this,.00E proposas to place the lower permeability vicinity property materials over the higher permeability tailings. This will create a a
#lproperty capillary barrier,will materials i.e.ha',e
, suction within thebefore to be overcome partially saturated water can movevicinity down into the coarser grained tailings.
The cover design' for the facility consists.of, in ascending order: (a) a 2-foot radon barrier constructed of alluvial clay -from the disposal site, with a saturated hydraulic' conductivity of 1E-7 cm/s; (b) a 6-inch-sand drain layer, with a hydraulic conductivity of IE-4 cm/s; (c) a 15-inch erosion , protection / biobarrier layer; and (d) a 2-foot layer of rooting soil. The erosion protection / biobarrier and rooting soil medium will also serve.to , provide frost and freeze protection for the radon barrier. Grasses, cacti, l and sage will be planted on the top of the cover to increase evapotranspiration and thus. reduce infiltration into the pile. , L I 1
y, s 48 L Because of the great depth to the uppermost aquifer, the geochemical attenuation properties of the Mancos Shale, and the poor quality of the Dakota Sandstone groundwater, NRC staff is primarily concerned, in terms of the cell design, with the potential for perched contaminated water reaching one of the highly transmissive paleochannels. The closest reported paleochannel to the disposal cell, with sustained groundwater flow, occurs along the northern edge of the pile. Flow in this channel is reported to be within 100 feet of the northwestern edge of the pile. DOE has redesigned the cell to eliminate potential seepage from the northwest corner of the disposal cell. 00E has determined that the vertical hydraulic conductivity of the foundation ! material is 2E-7 cm/s, which is only slightly more permeable than the design saturated hydraulic conductivity of the radon barrier; however, ponding within the disposal cell is not expected to be a problem for the following reasons: (a) DOE has calculatad the expected maximum ponding depth in tne cell to be 12.3 feet, which is below the depth of any nearby paleochannels; and (b) The clean-fill dikes surrounding the contaminated materials will minimize lateral migration of leachate.
'It should be noted that DOE has changed their original plans by proposing to excavate an additional six feet into the Mancos Shale. As a result of this design change,-additional permeability testing of the Mancos Shale is needed at this lower depth.
The NRC-staff agrees with DOE's assessment that ponded leachate should not reach any nearby paleochannelt for the following reasons: (a) Conservative calculations by NRC staff show that nearly 45 feet of water
'would be required to obtain a sufficient hydraulic gradient for lateral migration'of leachate at a rate equal to the saturated conductivity of the barrier. Given the huge volume of the disposal cell, it is estimated that it.would.take over 200 years of infiltration at a flux equal to the saturated hydraulic conductivity of the barrior to achieve such a head;
-(b) The expected infiltration through the. cover is-expected-to be less than the saturated hydraulic conductivity because the other components of the cover will reduce the flux received by the barrier. One component of the cover which will help reduce infiltration will be the veaetation at the top of the cover. DOE proposes to design the vegetatic- 9r similar to ambient conditions. The ambient vegetation cover appea.e - limit.
infiltration.into the ground as evidenced by caliche deposits within the-soils andLgypsum deposits within the alluvium; (c). DOE has indicated their intintion to excavate down an additional 6 feet below the. grade specified in their design; this additional 6 feet will l l provide additional storage for any ponded leachate. l 1 +
s r >
=,; I 49 (d) Independent calculations by NRC staff confirm that seepage out of the
-base of the cell will exceed influx into the cell. These calculations were based upon an influx equal to the saturated hydraulic conductivity of the radon barrier (i.e., 1E-7 cm/s) and a vertical hydraulic conductivity of the foundation material equal to 2E-7 cm/s; and (e) Placement of the lower permeability vicinity property material over the ,
coarser grained tailings will create a capillary barrier, as long as the vicinity property material is partially saturated. . 54 Disposal and Control of Residual Radioactive Materials 3 EPA's proposed. standards in Subparts A and C of 40 CFR Part 192 require DOE to demcnstrate that the disposal of residual radioactive material complies with site-specific groundwater protection standards and closure performance standards in four areas: Water Resources, Protection Standards for Disposal (Subsection 5.4.1); Performance Assessment (Subsection 5.4.2); C wsure i Performance St=ndards.(E.4.3); and Groundwater Monitoring and Corrective W Action Program (Subsection 5.4.4). J
, .i Water Resources-Protection Standards for Disposal
. 5) 4cl-1
- EPA. standards in_40 CFR Part 192,02(a)(3) require-that disposal' units be l!
designed to' contro11 residual radioactive material in conformance with
- site-specific groundwater protection standards established by DCE. The
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groundwater protection standard consists of three components:'1) a list' of > hazardous constituents, 2) a.co'rresponding. list of concentration' limits for
-the' constituents, and 3) a point ~of' compliance. -
g X 5. 4.1.1 - Hazardous Constituents Based,on!the characterization'of the tailings pore fluids,'at the_ Grand 1 Junction processing site,-00E. identified'the following inorganic constituents: ! g ar. ony, arsenic,-beryllium, barium, cadmium,4 chromium, cobalt, copper, net ,
: gt a.s alpha activity, lead,; mercury, molybdenum' . nickel, nitrate,' radium -266 ,
m cand -228Eselenium. si.ver,.and uranium' ' Additionally, the following elements. Hie icontainedsin hazardous, constituent compounds'were, identified: aluminum,- . y o , cyanide, fluoride',l strontium,-sulfide,' tin, vanadium,'and: zinc. A scan of i 4
, groundwaterL samples from three wells. revealed no'. volatile, ' semi-volatile. or-1 other organic compounds'present i'n,the-groundwater.
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The:NRCsstaff-has reviewed DOE's assessments-of the-hazardous constituents using,the following three criteria to. select hazardous constituents::1)
>whether or not the constituents are reasonably, expected to be inor derived
-from the tailings; 2)'whether or not they.are listed in Appendix'VIII of 40 ;
CFR Part 261, with the addition.of radium -226 and -288, uranium,Lnitrate, j i
..l
=,- m- 1 50 molybdenum, and net gross alpha particle activity as specified in 40 CFR 192.02(a)(3)(1); and 3) whether or not they were detected in the tailings or groundwater at the site. Based upon an independent analysis of the information provided by DOE, the NRC staff concludes that for the Grand Junction. site, the list of identified hazardous constituents is appropriate.
5.4.1.2 Concentration Limits DOE proposes to comply with the propo.ed EPA groundwater protection standards, at the Chenay Disposal site, by achieving a narrative supplemental standard (TER Section 5.4.1.4). In implementing supplemental standards DOE must demonstrate that the supplemental standards come as close to meeting the otherwise applicable standards as is reasonably achievable under the circumstances. DOE has not indicated concentration limits for the hazardous constituents identified in TER Section S.4.1.1. Therefore, no determination can be made as to whether or not they have come as close to meeting the otherwise applicable standards.as is reasonably achievable. DOE needs to provide concentration ' limits for the hazardous constituents identified in TER Section 5.4.1.1. The NRC staff considers this an open issue, 5.4.1.3 Point of Compliance DOE is proposing no monitoring of groundwater in the Dakota Sandstone because-the aquifer is designated Class III (TDS greater'than 10,000 mg/1).
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Accordingly, DOE is proposing no point of compliance. The NRC staff concurs that;no groundwater monitoring is required in this aquifer, and therefore, no pointLof compliance is required. 5.4.1.4 Supplemental Standards
=In lieu of.the primary standards, 00E-has proposed-application of supplemental standards for the Grand' Junction UMTRA site, based on the Class III criterion ,
lin 40 CFR Part '192.21(g). 00E asserts-that the uppermost aquifer is a Class III aquifer ~due to the TDS-concentration being greater'than 10,000 mg/1; this
'is=in accordance with 40 CFR Part'192.11(e). i T
To' establish-supplemental staadards under the 40 CFR Part 192.11(e) criterion, 40 CFR Part 192.22(a):and.(d; .equire that the standards must: 1) come as close to meeting the otherwise applicable standard:as is reasonable under the
~
y circumstances; and 2) assure-protection of. human health and the environment. DOE states that these requirements are met since the uppermost aquifer is isolated from the potential = source of contamination, and the design of the cell will'be isolated from the paleochannels.
.The NRC stuff concurs with DOE's assessment that the uppermost aquifer is n essentially hydrologically isolated, The uppermost aquifer is considered
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- . 6' y, hI - t Y -isolated from contaminants leaching from the cell because of the following '
, -- f actors: l
, !(a) The. upward pressure gradient and confinement of the Dakota Sandstone ?
U should keep contaminants from migrating to that zone; L (b); The ' geochemical ' attenuation properties of the thick Mancos Shale and any L perched' water. systems within the Mancos Shale should effectively remove contaminants; prior to reaching the Dakota Sandstone; and
,g (c) -Age dating indicates that groundwater in the Dakota Sandstone is not from !
immediate recharge from the overlying Mancos Shale aquitard. 1
- Al'though'00E 'provides an acceptable basis for the hydrologic' isolation
- conclusion, the ' narrative supplemental standard is never clearly stated. The .
TRAP needs:to make clear exactly what the supplemental standard is. As i indicated in Section 5.4.1.2 above,; DOE also I:as not provided .information .on , what;they, consider to be the otherwise applir.cble standards. Therefore, no 4 determination can.be made as to whether or not the supplemental standards come , 9 Jas close to those standards as is reasonable under the circumstances, j a 5,l4. 2 : jPerformanceAssessme't t i
, DOE must demonstrate that the pe, srmance of the disposal unit will comply :
, with' EPA's groundwater protection' standards in 40 CFR 192. Subparts A and C.
iTo comply withSthe groundwater protection standards, DOE has proposed . J
# narrative: supplemental; standards (as discussed in TER Subsection 5.4,1.4).
P The narrative: supplemental standardsLwill be achieved by the hydrologic c y [ isolation:of the uppermost 1 aquifer. DbEihasprovided,informationtoishowthatinfiltrationthrough.thecovergunderf L , h 1*7' l? -
! average climatic conditions will'be 5.6E-8 cm/s;- under long term conditions,- ,
L' .c. infiltrati.on Lis: predicted-to beiessentially zero.: In. addition,100E has-fE
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' presented information i.ndicating that the geochemical properties;ofithe Mancost Shale and perch'ed water zones within the Mancos1 Shale effectively limit
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l OM : migration"of contaminants tolthe uppermost aquifer. J
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-The:iNRC staff does not.agreeiwith DOE's estimates on' infiltration through the:
E cover for the' followingireascns:' :1) DOE's prediction for infiltration under
. average climatic; conditions.(i'.e., 5.6E-8 cm/s).used a' hydraulic conductivitp.
S 'value- for'the barrierithat isoless than the design hydraulic conductivity;; and 7 2) 00EJdid~nots pro l vide.their calculations to:show how they obtained the. ls .infiltN u v rate?under'the long-term conditions. However, these.differe*:es are 'not a :ssue' becauselthe NRC staff. concludes that the' hydrologic isolation- % of:thelJ @ aLSandstone:and1the geochemical attenuation properties ofsthe' Mancos' Shale! adequately negate concerns about performance within the uppermost-aquifer.t"Further; if contaminant's were to reach the Dakota Sandstone aquifer,
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L LDOE has, adequately l, documented that' this aquifer is a Class III aquifer,L and ~
- :therefore,fis not a' water supply source for domestic-use .
1 S T l_ _ _ _i
y 52 00E has provided calculations to show that mounded water within the cell, during transient drainage, will not reach any nearby paleochannels. The
-maximum predicted mounding is 12.3 feet, which will take place in the toe area of the cell. Transient drainage is predicted to last roughly 12-14 years.
Transient drainage calculations were made using a flux equal to the saturated hydraulic conductivity of the radon barrier-(i.e., IE-7 cm/s), and a vertical hydraulic conductivity of 2E-7 cm/s for the foundation material (i.e., competent Mancos Shale). Since DOE has proposed to excavate an additional six feet within the Mancos Shale, the NRC staff cannot agree that mounding will not be a oblem until DOE has completed additional vertical permeability tests at tnis depth. In addition, considering the highly friable nature of the Mancos Shale when exposed to the atmosphere for even short periods of time, it is important that DOE perform their permeability tests on the Mancos Shale after it has been compacted. It is. expected-that the heavy-moist tailings material will compact the foundation material. The NRC staff considers this to be an open issue. l 5.4.3 Closure Performance Demonstration In accordance with the closure performance standards of 40 CFR Part 192.02(a)(4), DOE is required to demonstrate that the proposed disposal design will (1) minimize and control groundwater contamination, (2) minimize the need for further maintenance, and (3) meet initial performance standards of the design. As discussed in TER Section 5.3, the primary concern that NRC staff has with the' performance of the disposal cell is the potential for mounded leachate to reach one of the nearby paleochannels. Based upon DOE's proposed cell design, the likelihood of mounded leachate reaching one of the nearby paleor.hannels is minimal; however, DOE still needs to perform additional hydraulic tasting of the foundation material. In terms of minimizing the need for further maintenance, 00E has proposed to use natural, stable materials in their construction of the cell. 1 5.4.4 Groundwater Monitoring and Corrective Action Plan Pursuant to.the proposed EPA groundwater protection standards in 40 CFR Part. 192.02(a) and-(b), 00E is required to implement a groundwater monitoring and corrective action program to be carried out'during the post-disposal period. As part of licensing the long-term care of the completed disposal site, DOE will: provide a Long-Term Surveillance Plan (LTSP), which includes a discussion of the groundwater monitoring program and any necessary. groundwater protection activities or strategies. DOE has proposed to do no groundwater monitoring at the Cheney Disposal site, since~no point of compliance is designated in the uppermost aquifer (see TER 1
,o~,
53 Section 5.4.1.3). The NRC agrees that no groundwater monitoring of the-uppermost aquifer is needed, because it is designated as a Class III
-groundwater. Provided that DOE's additionti permeability testing of the foundation material confirms that mounding vill not reach any paleochannel, no monitoring of the paleochannels is necessary.
Although 00E has proposed no groundwater moritoring at the Cheney Disposal site, they do intend to visually check for seeps or other surface exposures during routine surveillance of the site. Pcssible corrective action identified may include the following: 1) constructing a sump or other device to collect the contaminated' groundwater and treating or evaporating the collected water; and 2) controlling access to the contaminated water by covering'it. DOE will provide information on the corrective action plan in the LTSP submitted to the NRC. NRC staff will review the proposed corrective action plan as part of the review of the LTSP. In the LTSP, 00E should consider
. corrective action to be taken in the event of failure of the cover in addition to the development of seeps. ,
00E has conceptually proposed to monitor the groundwater at the Grand Junction processing site during remedial _ action to assess the effects of the-remedial-act-lon.on water quality. The NRC staff recommends.that 00E also monitor the Colorado- River, at the processing site, during' their remediation activities. , 5.5 Cleanup and Control of Existing Contamination 00E-needs to demonstrate compliance with the EPA standards listed in 40 CFR
?P art 192, Subparts-B and C.for cleanup and control of existing contamination.
00E proposes tondefer the. demonstration of cleanup and. control of existing-
. contamination to a later phase of the remedial. action project, as provided for
- in thelUMTRCA amendment of 1982. The.NRC staff agrees that groundwater-cleanup may be deferred; however, in order to defer cleanup of the Grand Junction processing site, 00E must demonstrate that 1) future cleanup of the >
processing site will not be impacted by the disposal and thus is separable from the disposalEactions, and 2) that public health and-safety will be protected.
'By:v'trtue of. moving the tailings to the Cheney Disposal site, DOE has
. demonstrated that the disposal of the tailings will: not impact groundwater cleanup of the Grand Junction processing site. However, 00E-has not-adequately-addressed the potential effect on public health and safety of delaying cleanup of-the contaminated groundwater at the processing site. As.
discussed in TER Section 5.2.4, the NRC staff is' concerned that'00E has not adequately _ demonstrated that _there no existing withdrawals within the immediate area of the processing site. Further, DOE has not adequately
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, 1 54 i
J 3: [ determinedithe' extent of' contamination in the Colorado River and the potential
, f E- impacts to users 1of the. river. The NRC ataff considers this an open issue and.
=' -
~ cannot concur on deferral of groundwater cleanup at the Grand Junction
, . processing site until'this issue is resolved.
' 5.6'~ Conclusions Based upon the review of the Preliminary Final Remedial Action Plan, the NRC staff concludes that DOE's proposed remedial: action has not been shown to be in compliance with the EPA groundwater standards. The following open issues remain to be resolved: -;
DOE must demonstrate =that by deferring groundwater cleanup at the Grand 1.- 3 Junction processing site _public health and safety will not be affected. 00E
.needs:to take additional uater quality samples from:the Colorado River (especially at'lowfflow)'and test for all hazardous constituents. Further,
. 00E needs to define the-area potentially affected by the present contamination and theigroundwater usage.-(not just for drinking purposes) within that area..
- 2. . - Doe needs 'to clearly;st' ate in the RAP exactly what the supplemental
- standard..is.. 00E must also demonstrate that their proposed supplemental >
standards.come as close.to meeting the otherwise applicable standards as is
; reasonable under the: circumstances. 00E needs tc~ provide a list of the .
; concentration ~ limits of the hazardous constituents that they.have identified.
l 3. -00E must perform additional vertical' permeability testing on the a
. foundation' material, at'the finalJexcavation depth. .The.permeabit4ty i tests ,
should be p'erformed-onicompacted Mancos Shale. material, since it ls likely ci y: .that: the -heavy, . moist tailings will~. compact' the friable shale material.
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e 6.0 RADON ATTENUATION AND SITE CLEANUP 6.1 Introduction
'This section of the TER documents the staff review of the radon attenuation design and tM radiation survey plan for the remedial actions at toe Gem d Junction, 00 UMTRA Project site. The review consists primarily of evaiuations of the material characterization, radon barrier design, and soil cleanup aspects of the proposed remedial action to assure compliance with the appropriate EPA standards.
6.2 Radon Attanuation 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 ic 2 feet for the top slopes of the pile and 3.5 ff feet for the side slopes. The review of the cover design for 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 evaluated for the tailings, contaminated materials, and radon barrier materials 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. 00E used the computer code RAECOM to calculate the radon barrier thickness. The NRC-evaluated thel input, including the above-parameters, and performed an L lindependent' analysis;of the design using;the RAD 0N1 code (NRC,.1989b), which is p fa simplified versio'n of the REACOM: code.
1 li b
'6.2.1. Parameter Evaluation ,
?' LThe material' properties and radiological parameters used in the design of the f
- stabilized: tallings pile ano the radon / infiltration-barrier at the Grand 1 L iJunction site have been reviewed.
kM m. .. . _The material thicknesses used in the analysis are based on the conceptual Ls x ;
, , . ; design-of.the.the remedial action plan and-the available data. The main' pile N , tailings and contaminated materials.will be placed in the disposal cell in two
.' stages; the: tailings from the ponds, area and vicinity praperty cleanup
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nj materials,_ referred to~as the off pile, contaminated: materials, will be_placed: E in a. separate layer on top of the main pileitailings. _The design assumes Li these layers are uniform and avarage parameter values are used for the materials. It is.possible that.some'of the de hils of the design will change. H L e
56 However, the thicknesses of the contaminated materials are not likely to be ' significantly altered. Therefore, the thicknesses of the layers used in the analysis are reasonable representations of the expected field conditions. 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. The values of these parameters for the off pile contaminated materials that will be placed as a separate layer in the stabilized embankment are 1.87 gm/cc and
.304, The bulk density and porosity for the radon / infiltration barrier material are.l.73 gm/cc and .375 respectively. These values were determined from representative samples of the materials, and the staff finds these values to be acceptable.
The design assumes the following long-term moisture contents: 18% for the tailings materials; 9.74% for the off pile contaminated materials; and 13.79%- for the radon / infiltration barrier material. In selecting these values, 00E considered the results of capillary moisture laboratory tests, the SWRDAT computer' code (USSCS, 1985), an empirical relationship developed by Rawls and Brakensiek (1982), and specifications for placement moisture. The laburatory tests support.the use of chese moisture contents. The use of the SWRDAT code for predicting water retention capacity at different suction pressures does not apmars to conflict with.the methods in the SRP (NRC, 1985). A check of the Ra:* , method and subsequent discussions with DOE indicated that instead of porosit.es, void ratio values were used in the analysis, resulting in incurrect moisture contents. A correct Rawls analysis would result in an
= average moisture value of 10.6%. However, the calculations seem to ignore the Rawls results anyway. The staff concludes that DOE _needs to correct the Rawls method calculations, and provide discussion of the basis for not factoring ie results of the Rawls method into the selection of the design long-term moisture.
. Radon diffusion coefficents for the cover material'and tailings-were derived' from correlatior. urris of moisture saturation versus radon diffusion
. coefficient. TLse curves were developed using diffusion coefficients and i m
l moisture saturation data from' laboratory measurements of soil samples representativeofconditions,ipthestabilizedpile. A' conservatively high
- diffusion coefficient (0.01 cm /s) was assumed for the-off pile contaminated materials because of the material property' uncertainties. The values of the
-radon diffusion coefficients have been determined adequately and are acceptable to.the staff.
The radon emanation coefficient for the tailings material was measured in the e laboratory on samples representative of field conditions. Values of 0.37.for the main tailings,_and 0.38 for_the off pile contaminated materials, were
. conservatively.-determined based on the measured values ~and are acceptable to
=the staff. <
( w,' 4 57 LThe radium content of several materials at the site was measured. The average radium content used by DOE in the analysis was deterinined by weighted averaging with depth in a measurement hole, then averaging over an area at any given depth. A weighted average value of the radium content for the main tailings pi'le material was calculated and a value of 600 pCi/g (570 pCi/g plus
-the Standard Error of the Mean (SEM) of 30 pCi/g) was chosen for the radon barrier thickness calculations. A value of 81 pCi/gm was, likewise, estimated from limited data for the off pile contaminated materials. Although the DOE adjusts this and other average parameters by adding or subtracting the SEM
- (whichever is more conservative), these avereqe paramater values are not always representative of the spread of the parameter values. For example, the Ra-226 concentrations in the main pile tailings average 574.8 pCi/g, but the standard deviation is 613.7 pCi/g, and the off pile meterials averaged 461 pCi/g with a standard deviation of 1008.8 pCi/g. The values chosen for the main tallings and off pile materials inherently assume an optimistically uniform mixing of the materials. The concept of adjusting the average Ra-226 concentration values for the design is acceptable to the NRC staff; however, the SEM does not adequately represent the variability of the data. 00E needs i
to re-evaluate parameter adjustment to better represent the variability of the data. A suggested method would be to compile relative frequency distributions to characterize the data, then use an upper limit that bounds two-thirds of
+
the data. In additlen, Table 6.3 of the RAS should be revised to include the range of Ra-226 soil contamination in the main tailings pile and off pile materials.
~The ambient air radon concentration is a required parameter value for the RAECOM modeling and has been measured at the Grand Junction site as 0.8 pci/1, The technique used to measure the radon concentration 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-radon-222 from releaseresidual radioactive rate of;20 materj/sec.al to00E picocuries/m the atmosphere not has analyzed exceed the radonan average
/ infiltration barrier in a manner that represents-the actual layered placement of the materials. The staff finds this approach to the analysis to be acceptable.
DOE's RAECOM modeling, using the parameterfvalues discussed in the previous sections result in a conclusion that 2 feet of radon bayrier will be more than adequate to-reduce the radon-flux to below the 20 pCi/m -sec standard. However, as' discussed above, reevaluation of long-term moisture and radium-226 concentration parameter values is_necessary prior to1 NRC concurrence-in the design of the radon barrier, p 4 6
m' , o - -
-.- q P"
58
- 6. 3 Site Clean-up Site characterization surveys have been conducted at the processing 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 '
contaminated areas. The results of the site characterization survey are being used to plan the control monitoring for the contaminated material excavation, as well as-the final radiological verification survey for the land and the buildings. . DOE has committed to the clean-up of the processing site in accordance with the EPA standard in 40 CFR 192 Subpart B. DOE states in the RAP that as the remedial action progresses, excavation control monitoring will be performed to insure 'that the contamination will be removed from the processing site to the levels imposed in the EPA standards. 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 staf f is prepared
- to. concur with the site clean-up aspects of the proposed remedial action.
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8.0 REFERENCES
Abt, S.R., et al., 1987, " Development of Riprap Design Criteria by Riprap Testing In Flumes, Phase I," NUREG/CR-4651. Bonilla, M.G. , Mark, R.K. , and Lienkaemper, J.J. ,1984, " Statistical Relations Among Earthquake Magnitude, Surface Rupture, Length, and Surface Fault Displacement," Bulletin of the Seismological Society of America, v. 74,
- p. 23/9-2411.
Sureau of Reclamation, U.S. Department of the Interior, 1973, Design of
'5 mall Dams.
Campbell,. K.W. ,1981, "Near-Source Attenuation of Peak Horizons.al Ground Acceleration," Bulletin of the Seismological Society of America, v. 71, ;
- p. 2039-2070.
Department of Commerce, U.S. Army Corps of Engineers,,1977,
-"Hydrometeorological Report No. 49, " Probable Maximum Precipitation Estimates, Colorado River and Great Basin Drainages."
00E .(U.S. 03partment of Energy),1989, " Technical Approach Document,"
- UMTRA-00E/AL-050425. 0002, DOE UMTRA Project Office, Albuquerque Operations Office, Albuquerque, New Mexico.
00E,r1990a, " Remedial Action Plan.and Site Design.for Stabili:ation of the Inactive Uranium Mill Tailings Site at-Grand Junction, Colorado," Prelimiaary Final, UMTRA-00E/AL; 050505.0000,- AugustL1990 (Grand Junction RAP), Remedial" Action Selection' Report.
~
00E,1990b Grand Junction RAP,- Attachment 1;- Contract- Documents,- Design and
! Engineering Calculations (Calculations Volumes I-V).
DOE,31990c. Grand.vunction RAP, Attachment 2: Geology Report
; DOE,.1990d,iGrand Junction RAP,; Attachment 3: Groundwater Hydrology Report and
, Appendix A, Volumes I-IV.
,v
, l DOE',J3990e, Grand Junction RAP,: Attachment 4: Water Resources Protection
, Strategy .
D)C. 1990f,, Grand' Junction RAP,' Attachment 5: Summary of Field Investigatiuns, l tVolumesLI'and-II. , Hunt, C.B.,L1974;-Natural Regions of the United States and Canada. W.H. Freeman and Company, San Francisco, California,.725 p. I}}