ML20214X211
| ML20214X211 | |
| Person / Time | |
|---|---|
| Issue date: | 06/08/1987 |
| From: | Weber M NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| To: | Fliegel M NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| References | |
| REF-WM-86 NUDOCS 8706160380 | |
| Download: ML20214X211 (46) | |
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.t SLICK ROCK MEM0/ COMMENTS M 08 W Y;" Ruxud h3 VN Mvt-Lc.a LN L_
MEMORANDUM FOR: Myron H. Fliegel ggo.
Operations Branch Division of Low-Level Waste Management-
~j and Decommissioning g ;;;,gy.33)-
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Michael F. Weber, Acting Section Leader Siting Section, LLTB Division of low-Level Waste Management and Decommissioning
SUBJECT:
COMMENTS ON THE SLICK ROCK DRAFT REMEDIAL ACTION PLAN AND DRAFT ENVIRONMENTAL ASSESSMENT Enclosed please find comments prepared by the Siting Section, LLTB, on the Draft Remedial Action Plan (dRAP) and Draft Environmental Assessment (oEA) for the Slick Rock site located in Slick Rock, Colorado. The comments identify significant deficiencies of the dRAP in the areas of groundwater protection, erosion protection, and geologic stability. The review was performed by Joel Grim, Ted Johnson, and Michael Young in cooperation with Mark Haisfield of your staff. Please contact Kristin Westbrook, our UMTRAP review coordinator, if you have any questions or comments about this review.
Original Signed By Michael F. Weber, Acting Section Leader Technical Branch Division of Low-Level Waste Management and Decomissioning
Enclosure:
Comments on Slick Rock dRAP/ DEA 8706160300 B70600 PDR WASTE PDR WM-86
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SECTION 1 Site:! Slick Rock',-C0 Date: June 1987-
. Document: d RAP w
4 Commentor: NRC/ Hydrology Comment:
1 Page: D-90 Examination of the geomorphic aspects of the site (p. D-90)-indicates that th'e.-
g site may be subject to lateral migration and erosion of Corral Draw. The RAP, however, does not demonstrate that the rock apron will be able to withstand the' i
flood velocities produced in Corral Draw.
The design of the rock apron should J
be.re-examined, particularly southwest of the pile where the Corral-Draw channel is not incised into bedrock.
Documentation should be provided to show Z,,
that the apron will not be eroded by large floods in Corral Draw. Assumptions VW regarding the location, depth, and extent of future channels (or overbank '.
[k..l areas) should be carefully documented with appropriate design bases provided.
cMW Additionally, the HEC-1 and HEC-2 printouts for the PMF on Corral Draw should.
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be provided for NRC staff review.
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3 UMTRA DOCUMENT REVIEW FORM SECTION 1 Site: Slick Rock, C0 Date: June 1987 Document: d RAP Commentor: NRC/ Hydrology Comment:
2 Page:
53 Figure 4.3 and accompanying text indicates that the rock apron for the stabilized pile will be keyed into either bedrock or the cemented terrace gravel.
It is not clear that the bedrock or cemented terrace gravel will be competent and/or durable. The RAP should be revised to demonstrate that bedrock and, particularly, the cemented terrace gravel will be competent or to revise the pile design to accomodate this deficiency. The demonstration should provide, as a minimum, results of durability tests using representative samples of bedrock and terrace gravel. See also NRC geology comment number G5.
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UMTRA DOCUMENT REVIEW FORM SECTION 1 Site: Slick Rock, C0
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Date: June 1987 Document: d RAP (Calculat1ons Volume 1)
Commentor: NRC/ Hydrology Comment:
3 Page: Calc. #SRK-04-87-05-03-00 We note from examination of the civil engineering calculations that'the-rock apron will be designed to resist PMF flow velocities due to runoff from the watershed in the vicinity of the trailer park. We further note that the design of the riprap for the apron.is based on flow velocities occurring on a slope of approximately 0.5%.
However, at the extreme northern and eastern portions of the pile, the flow will be channelized on slopes that will be approximately 20%. The design of the riprap in these areas should be re-evaluated to demonstrate stability of the apron on the steeper slopes.
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UMTRA DOCUMENT REVIEW FORM SECTION 1-Site: Slick Rock, C0 Date: June 1987 Document: draft Remedial Action Plan Commentor: NRC/ Ground Water (Water Use)
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Comment: GW1 Page: D-279 i
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DOE concluded that no known users of potentially affected ground water are l
located near the UC or NC sites, even though nearby residents are withdrawing ground water for consumption from a single water supply well located NW of the
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UC tailings. DOE claims that this.well is completed in the artesian Navajo i
Sandstone, which is unaffected by tailings leachate. However, after reviewing the construction and completion data for this residential well (submitted to the State of Colorado on 13 May 1959), NRC staff noted that this well is actually screened from the the alluvial aquifer down to the Navajo Sandstone.
During phone conversations between Michael Young (NRC) and John-Dupuy (TAC) on-l 22 May 1987, Mr. Dupuy stated that no hydraulic connection exists between the i
contaminated Dolores River Alluvium and the alluvium yielding water to the residential well because the alluvial deposits are not hydraulically connected.
The dRAP provides no information supporting this claim. The dRAP should be 1
revised to 1) include correct completion information for the community well, and 2) demonstrate that this well will not be affected by tailings leachate in the future.
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9 UMTRA DOCUMENT _ REVIEW FORM I
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Site: Slick Rock, C0 Date: June 1987 Document: Draft Remedial Action Plan Commentor: NRC/ Ground Water (Well Construction)
-Comment: GW2 Page: General DOE utilized a set of monitor wells constructed in 1983 (as well as more recently installed wells) to characterize aquifer properties and ground water quality at the NC and UC sites. During a NRC staff site visit to the Slick i
Rock site, in October, 1986, the staff observed two potential deficiencies in construction of the 1983 wells.
Firstly, the well casings material appeared to be composed of ABS Plastic (Acrylonitrile Butadiene Styrene), which is inappropriate material for monitor wells due to the potential sorption of metals onto the well casing and screen (Basdekis, 1964).
Secondly, with respect to well 510 (possibly well 508), the staff observed this well to be i
completed without grout cement at the surface, with well casing extending only several feet below land surface.
These deficiencies may preclude the collection of representative samples of ground water, thus biasing characterization of ground water quality at the sites.
NRC staff commented on this well and the construction material for the other 500 series monitor wells in comments on the final CADSAR. The dRAp should be revised either to l
demonstrate that well completion for the 500 series well is adequate to ensure that ground-water samples collected from these wells are representative of water quality in the alluvial aquifer or to characterize ground water quality based on samples from new, appropriately constructed monitor wells.
1 Reference Basdekis, C., 1964, ABS Plastics, Reinhold Publishing Co., New York, New York.
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11 UMTRA DOCUMENT REVIEW FORM SECTION 1 Site: Slick Rock, C0 Date: June 1987 Document: draft Remedial Action Plan Commentor: NRC/ Ground Water (Future Infiltration)
Come.ent : GW3 Page: General The draft Remedial Action Plan (and DEA) do not provide estimates of the future performance of the tailings embankment with respect to infiltration through the cover or of subsurface drainage of leachate after piacement and compaction of the tailings. These long-term projections are necessary to evaluate the proposed cover design and determine whether the remedial action will protect ground water adequately. The dRAP should be revised to respond to the following comments:
A.
DOE is placing considerable credit in the ability of the
" low permeability" Entrada Sandstone to preclude downward movement of leachate into bedrock (dRAP, Page 58). No permeability measurements of the Entrada Sandstone are included-in the dRAP to support this claim.
DOE should characterize the in-situ hydraulic conductivity of the Entrada Sandstone to evaluate the ability of this sand unit to preclude downward percolation.
B.
No estimates of infiltration into or seepage from the, tailings embankment are included in the dRAP. NRC staff expect infiltration into the embankment to occur after completion of the remedial action. Long-term estimates of infiltration and seepage should be included in the dRAP to demonstrate that significant generation of leachate and seepage will not occur.
C.
The dRAP does not assess the fate and movement of leachate from the tailings.
For example, DOE stated that the tailings will be disposed partially below grade and that the Entrada Sandstone will prevent downward movement of ground water. He.ever, the dRAP does not describe where leachate is expected to migrate after leaving the disposal cell.
If the Entrada Sandstone is a low permeability unit, then leachate may accumulate within the embankment resulting in surface discharge of contaminated ground water and decreasing long-term stability of the tailings.
Alternatively leachate may migrate into the Entrada Sandstone along fractures and result in additional contamination.
The dRAP should be revised to evaluate infiltration into the tailings embankment and movement of leachate from the pile, including direction and rate of flow, to demonstrate that the tailings will not become a source of
12 contamination in the future.
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UMTRA DOCUMENT REVIEW FORM SECTION 1 Site: Slick Rock, C0 Date: June 1987 i
Document: Draft Remedial Action Plan Commentor: NRC/ Ground Water (Water Quality)
Comment: GW4 Page: D-62 The water quality results presented in the dRAP indicate inconsistencies in the analyses of constituents and potential analytical errors on the part of the performing laboratory.
The following points further describe these concerns:
A.
Concentrations of contaminants in ground water have not been analyzed consistently during site. characterization.
For example, high concentrations of ammonium were found in samples collected in downgradient l
wells at the UC site in February 1986. However, ammonium was not analyzed in samples collected subsequently, precluding conclusions about trends of ammonium contamination. The program used to characterize ground water at the Slick Rock site is not consistent with that outlined in the Technical' Approach Document (DOE, 1986). The dRAP should be revised to justify j
departure from the TAD or to characterize' water quality based on additional monitoring, especially for constituents that occur at elevated concentrations.
B.
The dRAP did not include an anion / cation balance for the water quality l
results.
Ion balances can be used to assess the' accuracy of the j
analytical results. Omission of ion balances from the RAP precludes NRC staff assessment of the reliability of the water quality analyses. The I
dRAP should be revised to include anion / cation balances for all water quality results.
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i 15 UMTRA DOCUMENT REVIEW FORM SECTION 1 Site: Slick Rock, C0 Date: June 1987 Document: draft Remedial Action Plan Commentor: NRC/ Ground Water (Discrepancy in Logs)
Comment: GWS Page: 0-285 NRC staff note a discrepancy between the cross-section in Figure 0.5.7. and the lithologic logs (Page 0-175) collected during well drilling.
This figure does not accurately represent information in the lithologic logs, which indicate that up to 40 feet of unconsolidated sand and terrace gravels may be present in certain wells. DOE should modify the figure accordingly to make it consistent with the lithologic well logs.
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16 UMTRA DOCUMENT REVIEW FORM _
SECTION 1 Site: Slick Rock, C0 Date: June 1987 Document: draft Remedial Action Plan Commentor: NRC/ Ground Water (Material Testingl Comment: GW6 Page:
0-268 3
The dRAP contains laboratory results of capillary moisture tests for two samples (#SRK03-506 and #SRK03-509) for determining unsaturated hydraulic conductivity. The purpose of the tests is to characterize the conductivity-moisture content relationship of potential radon barrier material and tailings, which is needed to estimate infiltration into and through the tailings embankment. However, neither sample was retrieved from the borrow material test pits or from the tailings piles. The dRAP does not demonstrate that these moisture characteristic relationships are representative of material at the Slick Rock sites. Therefore, the capillary moisture tests are not relevant to remedial actions at the Slick Rock sites. DOE should collect and analyze representative radon barrier and tailings material in order to estimate potential infiltration into and through the tailings embankment. The dRAP should be revised to demonstrate that representative materials are tested and to provide representative characteristics of Slick Rock materials.
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18 UMTRA DOCUMENT REVIEW FORM SECTION 1 Site: Slick Rock, C0 Date: June 1987 Document: draft Remedial Action Plan Commentor: NRC/ Ground Water (Well Abandonment)
Comment: GW7 Page:
59 DOE states that characterization monitor wells will be abandoned, but does not state when and which wells will be abandoned (i.e., before or af ter remedial actions). Monitoring these wells for ground-water quality will provide primary data about the status of ground water clean-up during the remedial action and surveillance and maintenance phases. The dRAP should be revised to clarify which wells will be abandoned and what effects this will have on future ground-water monitoring.
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O 3 20 UMTRA DOCUMENT REVIEW FORM SECTION 1 Site: Slick Rock, C0 Date: June 1987 Document: draft Remedial Action Plan Commentor: NRC/ Ground Water (Future Ground-Water Quality)
Comment: GW8 Page: General DOE has not provided long-term projections of ground-water quality or natural clean-up rates in the DEA.
Such information is necessary to assess the effectiveness of remedial actions in protecting ground-water resources. DOE should consider the different hydrochemistries of the NC and UC groundwater contaminant plumes in assessing long-term contaminant transport.
For example, the NC contaminated ground water contains high levels of uranium, whereas the UC contaminated ground water contains high levels of nitrate and ammonium.
Because these contaminants differ in their sorption characteristics and concentration distributions, natural restoration will require different lengths of time to reduce contaminant levels to acceptable levels. The dRAP should be revised to evaluate leachate migration and natural restoration rates, 3
considering differences in the hydrochemistries of the plumes and tailings.
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22 UMTRA DOCUMENT REVIEW FORM SECTION 1 Site: Slick Rock, C0 Date: June 1987 Document: draft Remedial Action Plan Commentor: NRC/ Ground Water (Background Water Quality)
Comment: GW9 Page: General DOE utilized seven monitoring wells to characterize background alluvial water quality and concluded that the alluvial water is fresh to slightly brackish in quality. The dRAP, however, includes observations that suggest background ground-water quality has not been established adequately:
A.
00E determined background quality based on only two sampling rounds in February and June-July 1986. These data are inadequate to assess seasonal affects likely to be experienced in relatively fast moving alluvial ground water. Consistent with the TAD, 00E needs to sample ground water at least quarterly for a minimum of one year to assess adequately seasonal changes in ground-water quality or justify why such monitoring is unnecessary.
The dRAP should be revised to include this minimum information to characterize seasonal changes of background ground water quality.
B.
Ground water samples from well 509, located SE of the UC tailings, contained 80 mg/l of ammonium, which is much higher than samples collected from other background wells and considerably greater than concentrations expected in unaffected shallow ground water. Also, units of conductance, magnesium, sulfate and total dissolved solids, are greater than those reported for samples collected in nearby well 505, suggesting that water sampled from well 609 has been affected by the tailings. Therefore, available water quality data indicate that ground-water samples from well 509 cannot be considered representative of background ground water quality. The dRAP should be revised to reevaluate the determination of background ground-water quality.
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UMTRA DOCUMENT REVIEW FORM SECTION 1 Site: Slick Rock, C0 Date: June 1987 Document: draft Environmental Assessment Commentor: N_RC/ Ground Water (Flux Calculations)
Comment: GW10 Page:
B-59 DOE calculated the flux of water through the alluvial aquifer in order to demonstrate that recharge into the Dolores River will not significantly affect-surface water quality. NRC staff notes that the aquifer length was used in the calculations instead of the aquifer width.
The width value used for the NC site calculation was 1600 feet, whereas the actual _ aquifer width at the tailings material is approximately 340 feet. Although the resultant flux value is conservative for assessing impacts to surface water quality, it is almost five times higher that the expected rate of pore water replacement (i.e.
natural restoration).
DOE should utilize conservative parameter values for flux calculations when estimating aquifer restoration rates and include these results in the revised RAP /EA.
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25 UMTRA DOCUMENT REVIEW FORM, SECTION 1 Site: Slick Rock, C0 Date: June 1987 Document: draft Environmental Assessment Commentor: NRC/ Ground Water (Contaminant Distribution)
Comment: GW11 Page: 94 DOE claims that the full vertical extent of the alluvial aquifer is contaminated from the tailings. Water quality information present in the DEA, however, is inadequate to support this conclusion. Ground water quality descriptions in the EA are based on analyses of samples taken from monitor wells that are screened through the entire alluvial unit. These samples probably represent a composite of water quality throughout the entire screened portion of the wells.
Samples collected within discretely screened intervals, the type of samples necessary to characterize the vertical distribution of contaminants, were not collected. Therefore, vertical contaminant distributions cannot be determined. The DEA should be revised to characterize accurately the vertical extent of ground-water contamination.
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1 27 UMTRA DOCUMENT REVIEW FORM SECTION 1 Site: Slick Rock, C0 Date: June 1987 2
Document: draft Environmental Assessment 4
Commentor: NRC/ Ground Water (Bivariate Plot)
Comment: GW12 Figures: B.2.16 and B.2.17 The bivariate plots of water quality designate contaminated ground water samples with corresponding well numbers, but label all other points with 'B' for background. The current use of the symbol 'B' precludes interpretation of background information and trends. The background samples should be identified with their corresponding well numbers to better evaluate potential trends in 4
i the data' results. The EA should be revised to include actual well numbers for j
all plotted samples.
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28 UMTRA DOCUMENT REVIEW FORM, SECTION 1 Site: Slick Rock, CO Date: June 1987 Document: draft Environmental Assessment Commentor: NRC/ Ground Water (Surface Water Quality)
Comment: GW13 Page:
B-30 The DEA discusses surface water quality in the vicinity of the tailings piles, but does not include a table of values presenting the laboratory analyses.
Surface water quality is important at the Slick Rock site because of the connection between the Dolores River and the shallow alluvial. ground water.
The EA/ RAP should be revised to provide tabulated surface water quality data to demonstrate that contaminated ground water discharge has not degraded surface water quality and to evaluate ground water /suface water interactions.
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I 29 UMTRA DOCUMENT REVIEW FORM i
SECTION 1 Site: Slick Rock, C0 Date: June 1987-Document: draft Remedial Action Plan Commentor: NRC/ Ground Water (Water Use)
Comment: GW14 Page: D-279 The dRAP does not identify or describe the source of water for the gas sweetener plant located NW of the UC tailings. This information is important because the plant may be using contaminated ground water for human consumption at the plant or may be stressing the ground water system, which could influence flow direction in the alluvial and/or Navajo Sandstone aquifers. The dRAP.
should be revised to identify and characterize the source of the plant's water, including rates of use, zone of withdrawal (if ground water), purpose of use, and otnar pertinent information.
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UMTRA DOCUMENT REVIEW FORM SECTION 1 Site: Slick Rock, C0 Date: June 1987 Document: draft Environmental Assessment Commentor: NRC/ Ground Water (Statistical Tables)
Comment: -GW15 Page: General The DEA contains several tables that statistically summarize ground-water quality in the alluvial and Navajo Sandstone aquifers (Tables B.2.9., B.2.10.,
B.2.11. and B.2.12.).
Compatible with the comment on the Green River, UT DEA, DOE did not consider the statistical characteristics of the water quality data before assuming that parametric statistics would yield meaningful results.
Prior to the use of parametric statistical techniques, DOE should determine whether the data are normally distributed, independent, and corrected for seasonality and serial correlation (Harris, et al.,1987, and Montgomery, et al.,1987). Such determinations require at least 24 samples. The DEA should be revised to justify use of parametric statistical methods for water quality data assessment or to assess the data.using more appropriate methods.
References Harris, J., J.C. Loftis, R.H. Montgomery,1987, Statistical Methods for Characterizing Ground-Water Quality, Ground Water, vol. 25, no. 2, pp. 185-193.
Montgomery, R.H., J.C. Loftis, J. Harris,1987, Statistical Characteristics of Ground-Water Quality Variables, Ground Water, vo. 25, no. 2, pp.176-184.
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32 UMTRA DOCUMENT REVIEW FORM SECTION 1 Site: Slick Rock, Co Date: June 1987 j
Document: draft Remedial Action Plan Commentor: NRC/ Geochemistry (Characterization)
Comment: GCH1 Page: General Review of the draft Remedial Action Plan and draft Environmental Assessment indicate that the' DOE has not adequately considered geochemistry in evaluating environmental transport of contaminants for the remedial action proposed at the Slick Rock site. The subject documents do not characterize site hydrochemistry i
and soil geochemistry,. including a description of the baseline geochemical conditions, the contaminant source term, the extent and mobility of contaminants, and supporting quantitative and representative site-specific geochemical data (e.g. dispersion coefficients, attenuating capacities) as required for site characterization by DOE's Technical Approach Document (TAD). The dRAP should be revised to characterize site hydrochemistry and soil geochemistry or justify why such characterization-is not necessary.
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34 UMTRA DOCUMENT REVIEW FORM, SECTION 1 Site: Slick Rock, C0 Date: June 1987 Document: draft Remedial Action Plan Commentor: NRC/ Geochemistry (Salt Dissolution) i Comment: GCH2 Page: General i
Similar to comments on the Green' River, UT UMTRA Project site, the dRAP does not adequately consider potential dissolution of salts within the tailings pile and resulting physical instability of the pile during the design life of 200 -
1000 years.
Following the review of DOE's response to NRC comments on the Grand Junction RAP, NRC staff agreed in principle with DOE that salt dissolution and transport due to geochemical disequilibria leading to failure of the disposal cell and. radon barrier could be moderated under certain site conditions. These conditions include, but are not limited to: a water table sufficiently below the bottom of the pile to preclude upward movement of water into the tailings, salt concentrations in the tailings low enough so that dissolution will not promote settlement of the pile, and a sufficiently moist cover system which will preclude the development of strong upward hydraulic gradients.
The dRAP should be revised to demonstrate that instability due to salt dissolution and related processes will be negligible during the design life of 200 - 1000 years or to modify the pile design to mitigate the effects of salt dissolution. Specifically, DOE should determine representative salt concentrations in the tailings and evaluate the potential for shallow ground water accumulating beneath the pile in the Entrada Sandstone.
Further, DOE should demonstrate that the long-term hydraulic gradients in the tailings will be downward.
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36 UMTRA DOCUMENT REVIEW FORM SECTION 1 Site: Slick Rock, C0 Date: June 1987 Document: Draft RAP Commentor: NRC/ geology Comment: G1 Page: general Data from geologic test pits provided in the dRAP are ambiguous and inadequate to support demonstrations of geologic stability of the proposed tailings embankments at the Slick Rock site.
First, lithologic symbols shown on the geologic test pit logs are not defined in an index with detailed lithologic descriptions. Second, several logs for the proposed disposal area are missing from Appendix D.
Third, identification numbers of samples collected in the disposal area are duplicated with those from borrow areas (for example, pits 505 and 506). The dRAP should be revised to clarify the description of existing test pit data to demonstrate the site's geologic, geomorphic, and geotechnical suitability for long-term stability of the tailings.
In addition, NRC staff suggest that DOE review sample locations and numbers, and logs from wells and test pits and make appropriate revisions to correct deficiencies prior to their inclusion in the revised RAP.
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38 UMTRA DOCUMENT REVIEW FORM, SECTION 1 Site: Slick Rock, C0 Date: June 1987 Document: Draft RAP Commentor: NRC/ geology Comment: G2 Page: 23 and D-73 The NRC staff disagrees with DOE's distinction between surficial deposits of the floodplain (Qfp) and a low terrace (QT1). Unit Qfp is mapped (page D-122) only where water normally occurs in the channel of the Dolores River, as shown on the USGS topographic map. The actual floodplain, however, is much more extensive and here includes virtually all areas mapped as QT1 (for example, compare this geomorphic map with the dRAP's designated floodplain on page 61).
Therefore, unit QT1 does not occur as an abandoned terrace level and its unit designation should be revised to Qfp.
An accurate designation of the alluvial deposits at Slick Rock is important because DOE's proposed disposal plan requires removal of all contaminated materials from the " floodplain." In addition, inaccurate identification of the distribution of floodplain deposits may preclude demonstration of adequate protection of groundwater and geologic stability. Therefore, the RAP should be modified to designate the floodplain accurately and consistently, or demonstrate that identification of the floodplain is not important to the proposed remedial action.
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40 UMTRA DOCUMENT. REVIEW FORM SECTION 1 Site: Slick Rock, C0 Date: June 1987.
Document: Draft RAP Commentor: NRC/ geology Comment: G3 Page: D-60 and D-74 and appropriate figures Based on geologic data presented in the dRAP,'the NRC staff considers that the widespread deposits labeled as eolian may actually be of fluvial origin. The characteristics and genesis of sedimentary deposits at the Slick Rock site may significantly influence long-term stability of the stabilized pile and groundwater transport of tailings contaminants.
NRC staff's position on the origin of-the " eolian" deposits is based on the following observations:
(1) supposed eolian deposits are described in the dRAP as silt and clay rich, whereas such sediments are not likely to be deposited in semiarid eolian environments (for example, see Reineck and Singh,1980; Cooke and Warren, 1973); (2) these sediment descriptions are very similar to bedrock lithologies in Corral Draw, their likely source; and (3) no evidence was seen of eolian bedforms or landforms during staff's site visit, October 2, 1986.
Based on the above observations, staff consider the deposits shown as Qe on page 0-124 are a facies of QT2 terrace deposits transported as fine grained -
sediment from Corral Draw to the ancestral Dolores River. This interpretation is supported by the consistent slope of the Qe/QT2 surface from the trailer park area to the Dolores River, the disappearance of QT2 gravel as one traverses the exposed deposits up Corral Draw, and the general configuration of other landforms resulting from the Dolores' former channel position. The RAP should be revised to characterize the extensive sedimentary deposits sufficient to demonstrate geologic stability of the Slick Rock site or justify why such characterization is not necessary.
Cooke, R.U. and Warren, A., 1973, Geomorphology in deserts: Berkeley, University of California Press, 374 p.
Reineck, H.E. and Singh, I.B.,1980, Depositional sedimentary environments:
Berlin, Springer-Verlag, 549 p.
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42 UMTRA DOCUMENT REVIEW FORM SECTION 1 Site: Slick Rock, C0 Date: June 1987 Document: Draft RAP Commentor: NRC/ geology Comment: G4 Page: D-73 and D-124 In conjunction with comments regarding the extent of deposits Qe, QT1, and Qfp, the staff believe that deposit QT2 is more extensive than shown in the dRAP, and perhaps thould be renamed. Unit QT2 is composed of fluvial gravel apparently deposited in an ancestral Dolores River which occurred 70 feet higher than modern base level. Unit Qe appears to be fine grained sediment derived mostly from Jurassic strata in Corral Draw. Both deposits form one distinct terrace sloping parallel to Corral Draw.
Therefore, each facies of this deposit formed during the same period of geologic time, each was graded to the same level of the Dolores River, and the sedimentologic differences between them are due only to their source areas.
Facies relationships of unit QT2 are important because the facies contact underlies the proposed pile location. Differences between the facies may have an impact upon groundwater conditions in the area, and erosional and geologic stability of the pile. On the other hand, existence of eolian deposits in the disposal area may suggest future eolian activity. Thus, long-term stability of the pile would depend on certain design elements not being affected by eolian deposition. The RAP should be revised to take into account the stratigraphic relationships between units Qe and QT2 or justify the existing distinction between them.
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44 UMTRA DOCUMENT REVIEW FORM, SECTION 1 Site: Slick Rock, C0 Date: June 1987 Document: Draft RAP Commentor: NRC/ geology Comment: G5 Page:
53, 56, and D-73 The dRAP describes unit QT2 as coarse grained alluvium with strong carbonate cement. DOE's site conceptual design includes rock aprons keyed to this gravel. Based upon lack of stratigraphic information noted in comment G1, however, the dRAP does not provide sufficient data to verify the characteristics of unit QT2.
Field data which are missing include characteristics of the gravel (unit thickness, grain-size analysis, clast relations) and of the cement (thickness, stage of induration, origin, etc.).
The text implies that the carbonate cement is pedogenic and, therefore, is likely to occur only as buried soil horizons not much thicker than one or two meters. Thus, the dRAP does not demonstrate that the cemented gravel is sufficiently competent to maintain the overlying erosion protection apron to assure long-term stability of the pile. The RAP should be revised to characterize the properties and distribution of the cemented gravel to demonstrate the suitability of QT2 gravels as a disposal-area foundation material.
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UMTRA DOCUMENT REVIEW FORM I
SECTION 1 Site: Slick Rock, C0 Date: June 1987 Document: Draft RAP Commentor: NRC/ geology Comment: G6 Page: 24, 25, and D-120 Geologic maps and cross sections in the dRAP indicate occurrences of the Carmel Formation in the site area.
Stratigraphic descriptions of the area (pages 22, D-52, and D-72), however, do not identify the presence of this unit.
In addition,. general geologic literature for the region indicates that the Carmel i
Formation does not occur in the site area. The presence'and distribution of i
the Carmel Formation is important because it is composed of relatively incompetent lithologies and would underly part of the proposed tailings emban kment. The RAP should be revised to characterize the presence or absence of the Carmel Formation or to demonstrate that its presence does not adversely effect the stability of the proposed tailings embankment.
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