ML20214X285

Forwards Comments on Lowman Umtrap Draft Comparative Analysis of Disposal Site Alternatives Rept

ML20214X285
Person / Time
Issue date:	06/05/1987
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-43 NUDOCS 8706160415
Download: ML20214X285 (11)

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JUN 05 IMF LOWMAN MEM0/ COMMENTS WM Rccord File WM PrcNt_

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MEMORANDUM FOR: Myron H. Fliegel Operations Branch M.iU@M, 623 Sj) d' Division of Low-Level Waste Management T

and Decomissioning FROM:

Michael F. Weber, Acting Section Leader Siting Section, LLTB Division of Low-Level Waste Management and Decomissioning

SUBJECT:

COMMENTS ON THE LOWMAN DRAFT COMPARATIVE ANALYSIS 0F DISPOSAL SITE ALTERNATIVES REPORT (dCADSAR) i Enclosed please find comments prepared by the Siting Section, LLTB, on the Draft Comparative Analysis of Disposal Site Alternatives Report (dCADSAP,)

for the Lowman UMTRAP site located in Lowman, Idaho. The review was performed by Lynn Deering, Ted Johnson, and Kristin Westbrook in cooperation with Mark Haisfield of your staff. Please contact Ms. Westbrook at telephone extension i

x74543 f f you have any questions or coments about this review.

i Michael F. Weber /

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, Acting Section Leader l-Siting Section, LLTB Division of Low-Level Waste Management and Decomissioning

Enclosure:

Comments on Lowman dCADSAR l

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UMTRA DOCUMENT REVIEW FORM SECTION 1 Site: Lowman, ID Date: June 1987 Document: d CADSAR Commentor: NRC/ Geology-Seismology Comment:

1 Page:

7 Section 3.2 of the draft CADS R states that a portion of soil beneath the tailings is composed of brown to black sandy clay.

It is further stated that

" Steep slopes and the presence of these potentially weak residual soils will require careful consideration during design of the stabilized pile." The NRC staff considers that the seismic stability aspects of the soils beneath the tailings require detailed consideration, especially because this area is seismically active, as evidenced by a 6.1 (ML) event in 1944 only 22 miles from the site, and because there is a potentially capable fault 4 miles west of the site.

SECTION 2 Response: Page By:

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UMTRA DOCUMENT REVIEW FORM SECTION 1 Site: Lowman, ID Date: June 1987 Document: d CADSAR Commentor: NRC/ Geology-Seismology Comment:

2 Page:

9 Section 3.2 of the draft CADSAR provides a seismic design acceleration for the site based on a floating earthquake of magnitude 6.2.

Because a magnitude 6.1 earthquake occurred within 22 miles of the site, a magnitude 6.2 earthquake may not be conservative enough for design purposes. This is further indicated by the existence of a potentially capable fault 4 miles west of the site. The CADSAR should be revised to select a larger seismic design acceleration or to justify the seismic design acceleration based on a magnitude 6.2 earthquake in light of existing site information.

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3 UMTRA DOCUMENT REVIEW FORM SECTION 1 Site: Lowman, ID Date: June 1987 Document: d CADSAR Commentor: NRC/ Geology-Seismology Comment:

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20 Under the heading " Summary of Data Needs" it is indicated that the planned site-specific work may include low-sun-angle aerial reconnaissance of the site area to locate potentially active faults and geomorphic features. The NRC staff considers that low-sun-angle reconnaissance data are necessary for the Lowman site because the site area is seismically active as evidenced by a potentially capable fault located four miles from the site and the magnitude 6.1 earthquake that occurred in 1944 only 22 miles from the site. The draft CADSAR should be revised to identify low-sun-angle data as a definite data need or justify why such data are not necessary.

4 SECTION 2

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4 UMTRA DOCUMENT REVIEW FORM SECTION 1

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Site: Lowman, ID Date: June 1987 Document: d CADSAR Commentor: NRC/ Hydrology Comment:

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15 An examination of the proposed' design for stabilization on-site (Figure 4.1) indicates that the stab,ilized pile will be located on a relatively steep hillside.

It further' appears that diversion ditches will be needed to divert surface water runoff around the pile. At this location, the proposed ditches will have to be very steep (possibly greater than 10%)

and the drainage area upstream of the ditches does not appear to be extremely small. Therefore, it may be necessary to armor the ditches with very large riprap for erosion protection against potential flow velocities greater than 25 feet per second.

NRC staff experience with steep terrain has indicated that it may not be feasible to provide erosion protection riprap of the required size.

It may be prudent for DOE to examine other potential sites to avoid the need for such 3

j extensive and costly hydraulic design measures. We suggest that DOE examine the feasibility of relocating the tailings to other sites and/or examine the fessibility of implementing other design measures at the preferred site. The CADSAR should be revised to assess the feasibility of extensive erosion protection measures in light of the above discussion and to consider more feasible alternatives.

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5 UMTRA DOCUMENT REVIEW FORM SECTION 1 Site: Lowman, ID Date: June 1987 Document: d CADSAR Commentor: NRC/ Hydrology Comment:

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16 Examination of the proposed location of the stabilized pile (Figure 4.1) indicates that the toe of the pile slope will be placed on a very steep slope.

In fact, it appears t' hat the natural ground slope (e.g., in the southeast portion) may be as steep as the side slope of the pile. Unless the slope is composed of bedrock, it appears that this steeper natural slope may also need to be stabilized.

In addition, this slope may need to be protected against flooding by Clear Creek, probably necessitating use of very large riprap because the creek is apparently a large, swiftly-flowing stream.

Based on the potential problems discussed above (assuming that the slope is not composed of bedrock), the CADSAR should be revised to assess stabilization of the natural slope at the toe of the proposed tailings embankment and to consider alternate designs and/or alternate sites. At the very least, the location and extent of bedrock needs to be clearly defined before any other designs are developed.

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UMTRA DOCUMENT REVIEW FORM SECTION 1 Site: Lowman, ID

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Date: June 1987

~ Document: d CADSAR Conmentor: NRC/ Groundwater Comment:

1 Page: general As the draft CADSAR provides no detailed technical information with respect to groundwater at the Lowman site, NRC has no specific technical comments on groundwater' issues at the preferred disposal site. The final CADSAR on the disposal alternative (s) should include details of the hydrogeologic site characterization program, results, and analyses, including: depth to groundwater, groundwater flow directions, hydraulic gradients,-thickaess and extent of aquifer units, recharge and discharge areas, hydraulic properties, water quality, and preliminary assessment of the extent of groundwater contamination resulting from mill operations and tailings disposal.

(concent continued)

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T Comment Number 1, NRC/ Groundwater (Contirued)

If results of the groundwater field investigation confirm that that the water te.ble is close to the ground surface, groundwater will be a significant erVironmental concern at the Lowman site, as indicated in the draft CADSAR.

In this ev nt, NRC staff will review the proposed SOS alternative with several key questions in mind, including:

a.

If the tailings are placed below-grade, is the proposed disposal design (compacted clay liner) adequate to isolate the tailings from a fluctuating near-surface water table? This will be paramount as the shallow aquifer is reported to be of excellent quality and is used as a water source to nearby' residents and businesses.

b.

If the below grade design is infeasible due to a shallow water table, is the above ground stabilization option adequate from a stability standpoint, considering that the pile boundaries will need to be expanded toward the steep slopes on site?

c.

Has it been adequately demonstrated that infiltration through the cover will not result in significant leachate production and subsequent migration into and through the shallow potable aquifer?

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8 UMTRA DOCUMENT REVIEW F0F.M SECTION 1 Site: Lowman, ID Date: June 1987 Document: Draft CADSAR Commentor:__NRC/ Groundwater Comment:

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7 The draft CADSAR states that the tailings from the Lowman site are different from tailings from other UMTRAP sites because they have been mechanically rather than chemically processed. A discussion should be provided regarding what differences are anticipated with respect to leachability and mobility of contaminants between the Lowman tailings and chemically-processed tailings piles. The final CADSAR should include water quality results of groundwater sampling from the unsaturated zone within the tailings to characterize, in part, the contaminant source term.

The final CADSAR should also provide information on groundwater chemistry in support of site characterization as it influences grcundwater contaminant concentrations and site stability.

In addition, the final CADSAR should provide information on soil and sediment geochemistry (i.e., solubility, ion exchange, sorption, and carbonate content) to provide an understanding of the processes affecting contaminant migration and rock and soil chemical stability.

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9 UMTRA DOCUMENT REVIEW FORM SECTION 1 Site: Lowman, ID Date: June, 1987 Document: Draft CADSAR Commentor: NRC/ Groundwater Comment:

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21 The draft CADSAR states that approximately 12 monitoring wells will be installed on and near the Lowman site to locate and characterize groundwater.

It is not clear,whether these 12 wells are part of an initial phase of the field investigation, or represent the entire groundwater monitoring program. Based on previous site characterization programs at UMTRAP sites, NRC recommends that the groundwater characterization program allow for at least two phases of groundwater monitoring well installation in the program schedule, with placement of the monitoring wells as needed in the second phase based upon results obtained from the initial monitoring wells. Such flexibility will facilitate a more efficient and cost effective monitoring program.

In addition, information from operational assessment, aerial photographs, surface geology, soil borings, and geophysical investigations should be used to guide the placement and number of the groundwater monitoring wells.

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10 UMTRA DOCUtiENT REVIEW FORM SECTION 1 i

Site: Lowman, ID Date: June 1987 Document: Draft CADSAR (Statement of Work)

Commentor: NRC/ Groundwater Comment:

4 Page:

6 (of S0W)

Section 5.?, Exhibit A of the 50W indicates that a two-inch diameter monitor wells will be installed in each of 12 borings in order to determine hydrogeologic characteristics underlying the site and to assess the extent of subsurface contamination originating from the mill tailings. Two-inch diameter wells may not be large enough to support hydraulic testing and sampling that may be necessary to characterize site hydrogeology.

For example, the Environmental Assessment for the Green River UMTRAP site (December 1986) indicates that a two-inch diameter casing precluded adequate hydraulic testing because it too small to accommodate a submersible pump capable of pumping at a sufficient rate. NRC staff suggests that DOE consider installing four-inch diameter monitoring wells rather than two-inch wells to ensure that the wells are large enough to accommodate pumping rates required for successful aquifer testing.

In addition, the 50W should be revised to indicate that monitoring wells will be designed and installed to ensure stratigraphic correlation.

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