ML20148F928
| ML20148F928 | |
| Person / Time | |
|---|---|
| Issue date: | 02/23/1988 |
| From: | Starmer R NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| To: | Fliegel M NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| References | |
| REF-WM-58 NUDOCS 8803280325 | |
| Download: ML20148F928 (10) | |
Text
/A)ny.52 a
FEB 2 31988 PEMORANDUM FOR: Myron Fliegel, Section Leader Operations Branch Division of low-level Waste Managerrent and Deconmissioning, hMSS FROM:
R. John Starmer, Section Leader Technical Branch Division of Low-Level Waste Managenent and Decenmissioning, hMSS
SUBJECT:
SHIPROCK TECHNICAL EVALUATION MEMORANDUM In accordance with your recent request, we have revised the grourd water protection portion of the Shiprock Technical Evaluation Memorandum (TEM).
These revisions were made to the draft TEM which was transmitted to you in flovember 1987. These revisions reflect your suggested changes to the TEM which you provided to us in the form of a marked-up copy, and also incorporate correents made by Michael Weber.
The enclosed TEM was prepared by Michael Young.
If you have any questions, he may be reached at X23443.
cctyinal Signed 39 R. John Starmer, Section Leader Technical Branch Division of Low-level Ucste Management and Deconsissioning, HMSS Eaclosure: Shiprock Technical Evaluation Pemorandum DISTRIBUTION:
LLWM/SF LMSS r/f LLTB r/f MYoung KWestbrook DGillen, LLOB RJStanner MRKnapp JJSurrreier JGreeves JFC : LL'IB
- LLTB 4AME :MHYoung M HI: RJStanter 3 ATE :02/23/88
- 02p/88 0FFICIAL RECORD COPY 8803280325 880223 PDR WASTE
[///) FO+
r 3 WATER RESOURCES PROTECTION 3.1 Surface Water 3.1.1 Surface Water Characterization The Shiprock UMTRA site is located within the drainage area of the San Juan River with a drainage area of approxinately 12,900 square miles upstream of the site. The site is bounded on the west by Bob Lee Wash, on tho north and northwest by the San Juan River and on the southeast by Many Cevil's Wash.
The yearly average flow of the San Juan River is 2,193 cubic feet per second and controlled by the havajo Dam located 50 miles upstream (00E, 1984a; BLM, 1983).
3.1.2 Surface Water Quality Impacts Water quality in the San Juan River was discussed briefly in the Processing Site Characterization Report (PSCR; DOE, 1984a). Although several constituent concentrations exceed the drinking water Maximum Contaminant Levels (40 CFR Part 141) in water representative of background quality, the San Juan River is used as scurce for municipal drinking water and irrigation near Shiprock.
Drinking water is withdrawn from the San Juan River eight miles upstream from the disposal site (00E, 1984a). DOE sampled the San Juan River in September 1986 to assess possible impacts on surface water quality caused by discharge of contaminated ground water (Miller,1986).
These results indicate little to no increase of dissolved constituent levels between upstream and downstream concentrations.
However, potential impacts on surf ace water quality cannot be fully assessed until DOE characterizes ground-water conditions in the northern area of the floodplain dcwnstream of the site (cf. Section 3.4).
Specifically, DOE needs to characterize ground water flow rates, concentrations of constituents in ground water, and the ground-water discharge rate into the San Juan River to assess potential impacts on the surface water quality.
3.2 Ground-Water Protection 3.2.1 Introduction DOE's hydrogeologic evaluation of the Shiprock processing site identified l
ground-water contamination in terrace alluvium deposits and Mancos Shale beneath the tailings and decommissioned milling facility, and in the San Juan River alluvium located north of the Mancos Shale escarpment (Figure 3.1).
In addition, available ground-water quality monitoring data indicate potential entamination of the floodplain alluvium north of the San Juan River. Although b N has readfly acknowledged the presence of elevated levels of dissolved constituents in ground water beneath and in the vicinity of the site, the extet,t and significance of ground-water contamination caused by milling operations at Shiprock have not been fully assessed.
NRC staff has identified deficiencies in DOE's characterization and assessment of ground-water conditions at the Shiprock site.
00E has not yet characterized the extent of l
ground-water contamination at Shiprock. DOE's recent implementation of an l
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2 expanded ground-water characterization program (Longmire, 1987) should help to address NRC concerns regarding ground-water characterization at Shiprock.
In summary, 00E has not ( Tonstrated ccmpliance with ground-water protection aspects of EPA's stardards in 40 CFR Part 192, which were proposed on Septenber 24, 1987.
Specificelly, DOE has not adeouately (1) characterized background ground-water quality in the ficcdplain alluvium, (2) characterized the extent of grour.c-water contaminaticn in the ficodplain alluvium, (3) predicted future contaminantconcentrationsingroundwater,(4)assessedthepotentialfor ground-water migration in the terrace alluviorr west and south of the Bob Lee Wash nick point, ano (5) selected apprcpriate remedial action for grounc'-water protecticn in accordance with tFe EPA standards.
This section surtrnarizes the technical besis for NRC's conclusions regarding the current status of DOE's characterization, assessment, and selection of remedial action for ground-water protection at the Shiprcck site. NRC witheid concurrence with respect to ground-water protection aspects of the proposed remedial action in Cecember 1984 because of inadequacies of DOE's assessment of grounc-water conditions at Shiprock. Although cleanup and stabilization of the tailings are now complete, issues regarding ground-water assessment and protection have yet to be resolved. NRC staff may revise its conclusions with respect to ground-water protection at Shiprock based on future reviews of additional information to be provided by D0E.
3.2.2 Ground-Water Characterization DOE characterizeo the subsurface hydrogeologic regime at the site using 25 wells constructed on the terrace, and 7 wellpoints and 25 wells constructed on the floodplain.
Additionally, DOE has implemented a fifth well-drilling phase that includes the installation of 10 wellpoints.
00E's site characterizatior, program identified three distinct stratigraphic zones that are relevant with respect to ground-water protection aspects of the EPA standards: (1) terrace alluvium deposits consisting of coarse-grained gravel, sand and silt; (2) the Mancos Shale varying from sandy-shale to shale, with a weathered zone in the upper portion of the unit; enc (3) alluvial floodplain deposits adjacent to the San Juan River consisting of coarse-grained alluvium. The terrace deposits refer to both the alluvium and Mancos Shale that comprise the terrace beneath the tailings. Alluvial sediments in the floodplain north of the San Juan River are similar to those south of the river. Of the 25 wells constructed on the terrace, two were completed solely in the alluvium, eight were completed in both the alluvium and the Mancos Shale, and 15 wells were completed solely in the Mancos Shale.
It is difficult to discern the exact completion lithology for the 32 floodplain wells and well points because DOE did not specify the ccmpletion lithology in the Processing Site Characterization Report (PSCR),
Appendix E (DOE, 1986a). This information is important because the wells may not be completed in the same stratigraphic unit, thus invalidating water quality results.
3 The Gallup Sandstone within the Mancos Sbale is the fourth hydrogeologic unit of potential concern with respect to grobnd-water protection at the Shiprock site, hRC staff evaluations, however, indicate that the Gallup sandstone is hydraulically isolated from the shallow hydrogeologic units. The Gallup sandstone is separated f rom the contaminated alluvium by at least 200 feet of low permeability Mancos Shale.
The Gallup Sandstone is artesian at the site, so the hydraulic gradient is directed upward between the unit and the shallow hydrogeologic units.
Further, the Gallup Sandstont is discontinuous beneath the site and interfingers with the low-permeability Mancos Shale. Therefore, it is very unlikely that the ground-water contamination in the shallcw units, beneath the Shiprock site would cause contamination of the Gallup Sandstone.
3.2.2.1 Terrace Dep-sits Water level measurements taken in the terrace deposits indicate that groundwater generally flows north-northwest towards the escarpment and the San JuanRiver(Figure 3.2).
The recharge zone for the terrace alluvium is most likely south of the tailirgs pile where the Mancos Shale is exposed at the surface and recharged by precipitation.
Discharge occurs primarily as seeps along the escarpment face located above the floodplain surface and to alluvium in Bob Lee Wash.
DOE has asserted that groundwater in the alluvium is perched atop the Mancos Shale.
Field records indicate that wells completed in the Mencos Shale und located east of the tailings were dry, whereas tests in wells west of the pile indicated saturated conditions within the Mancos Shale.
The distribution of saturated conditions within the shale may reflect the presence of seepage from unlined raffinate ar.d tailings ponds. 00E has not characterized ground-water flow ano the extent of ground-water contamination caused by seepage emanating from the unlined ponds on the terrace south and west of the Bob Lee Wash nick point.
DOE determined the hydraulic conductivity of the terrace alluvium and Mancos Shale using packer tests and slug tests using the Skibitzke, Bouwer-Rice, Ferris-Knowles, Cooper-Bredehoeft-Papadopulos, and Hvorslev analytical methods to analyze the slug test data (D0E, 1984a).
These widely used methods yield preliminary hydraulic conductivity values.
Because of the low permeability of the lithologies (caused by partial cementation of the alluvium), however, aquifer pump tests were not performed. The geometric mean of the hydraulic conductivities yielded from the slug tests is 7.3 E-05 cm/s, which is considered by the staff to be reasonable for weathered shale and cemented alluvial sediments. The results of the packer tests produced variable hydraulic conductivities with the highest values at the tops of the unit, with progressively lower conductivities with depth. Although the values were higher than those derived by slug tests, the distribution of the hydraulic l
conductivities is consistent with DOE's conceptual model.
DOE characterized the effective porosity cf the Mancos Shale as ranging from 4%
- 13.6% (D0E, 1984b).
This range of values is considered reasonable for shale.
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3.2.2.2 Floodplain deposits
4 Based on water levels measured in the floodplain wells, groundwater in the southern portion of the ficodplain alluvium flows northwest, parallel to flow in the San Juan River (Figure 3). DOE has not characterized ground-water flow directions in the northern floodplain area. Thus, NRC staff concludes that upgradient flow directions have been adequately characterized, but that ground water flow directions in the northern floodplain, especially north of the drainage channel, have not been adequately characterized.
DOE needs to complete its assessment of groundwater flow conditions in the floodplain, including the ground-water mound that exists at the intersection of Bob Lee Wash and the ficcdplain.
DOE has not characterized the hydraulic characteristics of the alluvium in the floooplain. DOE needs to characterize the hydraulic conductivity, effective porosity, and cther characteristics of the alluvium to assess the significance of contamination in the floodplain deposits.
3.2.3.
Ground-Water Quality 3.2.3.1 Terrace ground-water quality DOE assessed ground-water quality in the terrace and floedplain deposits in three sampling rounds from 1982 to 1984.
The results of this assessment indicate that DOE's "background" wells, specifically wells SGT, 8GT, 12A and 4H, have been impacted by milling operations at Shiprock and are not representative of background ground-water quality.
Thus, DOE has not adequately characterized background ground-water quality in the terrace deposits.
In December 1984, the NRC staff concluded that thorough characterization of background ground-water quality in the terrace deposits is unnecessary because (1) the low permeability of the alluvium and Mancos Shale preclude significant withdrawal of ground water; (2) the aquifer is limited in areal extent; (3) most of the ground water in the alluvium was derived from the nilling operation; (4) most of the alluvial grcund water beneath the site discharges to the floodplain; (5) background gypsum deposits in unsaturated alluvium above the water table indicate that pre-milling ground-water quality, if ground water existed, was poor; and (6) municipal wastes unrelated to the remedial action are being disposed north and south of the site in an uncontrolled manner.
Ground water beneath and downgradient of the site contains elevated levels of ammonium, sulfate, TOS, uranium, selenium, nitrate, magnesium, and strontium (DOE, 1984a). Although oround water assessment programs should generally characterize temporal fluctuations of constituent levels, NRC staff concludes that characterization of temporal changes in ground-water quality are not necessary at Shiprock because these changes are not expected to be significant with respect to the selection of remedial actien. Ground water flows through the terrace alluvium at an average rate of approximately 13 ft/ year. This flow rate is not necessarily representative of contaminant transport rates, however, because contaminant migration may be retarded compared with the flow velocity. Although contaminant migration to the floodplain deposits may be of limited importance, DOE needs to assess migration of contaminated ground water to the west past the nick point of Bob
5 Lee Wash because it could result in contamination of useable off-site ground-water resources.
3.2.3.2 Floodplain ground-water quality DOE attempted to characterize ground-water quality in the floodplain alluvium in three sampling rounds from 1984 through 1986 (DOE, 1986; Miller, 1986). The sempling rounds indicate that ground water in tFe floodplain alluvium has been cegraded directly, for example, by seepage of effluents from a pond in the alluvium and indirectly by discharge of contaminated ground water from the terrace alluvium into the floodplain deposits. Ground-water quality sempling in these deposits indicates elevated levels of chloride, nitrate, sulfate, selenium, chromium, TDS, zinc, anc uranium. DOE has not adequately determined background ground-water quality in the floedplain alluvium. The wells currently used for characterizing background conditions (e.g., wells 608, 609, 610) yielded water samples in September 1986 containing average TDS and sulfate levels of 15,100 and 8,480 mg/1, respectively. Although water quality in the alluvium should approximate the quality of the San Juan River, concentrations of dissolved constituents in the alluvial grcund water are orders of magnitude greater than the surface water concentrations. DOE needs to characterize background ground-water quality in the floodplain alluvium.
In addition, DOE has not adequately assessed the extent and significance of ground-water contamination in the floodplain alluvium north of the drainage channel and on the opposite sice (north side) of the San Juan River.
Limited sampling south of the drainage channel indicates that plumes of contaminated ground water migrated north of the channel. DOE has not, however, determined their extent because of difficulties in constructing wells in the northern portion of the floodplain (D0E, 1986b).
DOE has also ackncwledged that levels of molybdenum and vanadium are elevated in wells 631 and 632 in the floodplain on the north side of San Juan River (D0E, 1983a).
00E needs to characterize the extent of contamination in the northern portion of the floodplain on the south side of the San Juan River and in the floodplain on the north side of the river. Based on this characterization, DOE then needs to assess the significance of the contamination with respect to ground-water protection aspects of the EPA standards.
3.2.3 Ground-Water Impacts and Restoration l
COE has not evaluated adverse effects of human and environmental exposure to existing and potential contaminated ground water.
DOE proposed implementation of institutional controls to preclude human use of contaminated ground water in the floodplain alluvium. NRC staff review of this proposal indicated that the
(
proposed controls were inadequate to demonstrate compliance with the EPA standards because they were incomplete and unenforceable.
00E needs to assess the significance of existing and potential ground-water contamination at the site and select appropriate remedial action in compliance with the EPA l
standards in 40 CFR Part 192.
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6 3.2.4 Conclusions NRC staff concludes that 00E has not adequately assessed the extent ano significance of ground-water contamination caused by) uranium milling operations at the Shiprock site. Specifically, DOE needs to (1 characterize background ground-water quality in the floodplain alluvium, (2) assess the extent of contamination in the floodplain alluvium en the south ard north side of the San Juan River and west of the nick point of Bob Lee Wash, (3) preaict long-term ground-water quality impacts asscciated with the remedial action, (4) select apprcpriate remedial action to protect grcund water in accordance with the EPA standards in 40 CFR Part 192.
3.3 References (add to ena section of TER)
BLM (U.S. Bureau of Land Management), 1983, Second Draft San River River Regional Coal Environmental Irrpact Statement, U.S. Department of the Interior, Bureau of Land Management, Albuquerque, New Mexico.
COE,1984a, Final Processing Site Characterization Report for the Uranium Mill Tailings Site at Shiprock NM, UMTRA-00E/AL-0042, Uranium Mill Tailings Remedial Action Project Office, Albuquerque, New Mexico.
ECE,1984b, Remedial Action Plan for the Stabilization of the Inactive Uranium Mill Tailings Site at Shiprock, NM, UMTRA-00E/AL-050504.0039, Uranium Mill Tailings Tailings Retredial Action Project Office, Albuquerque, New Mexico.
00E, 1986a, Final Processing Site Characterization Report for the Uranium Mill Tailings Site at Shiprock NM, Appendix E. LMTRA-DCE/AL-0042, Uranium Mill Tailings Remedial Action Project Office, Albuquerque, New Mexico.
00E, 1986b, draft Surveillance and Paintenance Plan Shiprock, New Mexic UMTRA-DOE /AL 350204.0000 Uraniurr Mill Tailings Remedial Action Project Office, Albuquerque, New Mexico.
00E, 1986c, Technical Approach Document, 050425.0000, Uranium Mill Tailings Remedial Action Project Office, Albuquerque, New Mexico.
DOE, 1987, Final Draft Shiprock, NM, Uranium Mill Tailings Site Rercedial Action Completion Report, prepared for 00E by MK-Ferguson, UMTRA i
Project Office, Albuquerque, NM.
Knapp, M.P., (NRC), 1986, NRC Coments on 00E Surveillance and Maintenance Plan, sent to J. Themelis (DOE) dated 18 August 1986.
Longmire, P. (00E/ TAC),1987, Monitor Well Installation Scope of Work, sent to Masud Zaman (Navajo Nation) with M. Young (NPC) on carbon copy, dated 17 February 1987.
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