ML20236A940

Notifies That Encl Draft Remedial Action Plan for Stabilizing Tailings at Spook Site Reviewed by B Jagannath. Format of Comments Revised Per Guidance Provided by Project Manager

ML20236A940
Person / Time
Issue date:	09/30/1987
From:	Tokar M NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS)
To:	Fliegel M NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS)
References
REF-WM-72 NUDOCS 8710230246
Download: ML20236A940 (8)

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MEMORANDUM FOR: Myron Fligel, Section Leader

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Operations Branch Division of Low-level Waste Management and Decommissioning, NMSS FROM: Michael Tokar, Section Leader Technical Branch Division of Low-level Waste Management and Decommissioning, NMSS

SUBJECT:

GE0 TECHNICAL REVIEW COMMENTS - DRAFT RAP, SPOOK SITE In response to your request, the draft Remedial Action Plan for stabilizing the tailings at the Spook site has been reviewed. The review comments are presented in the attachment to this memo. Please note that the revised format of the coments is as per the guidance provided by the Project Manager.

This review was performed by Dr. Banad Jagannath; please contact him should you have any questions.

Original Signed By Michael Tokar, Section Leader Technical Branch Division of Low-level Waste Management and Decommissioning, NMSS

Enclosure:

As stated DISTRIBUTION:

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OFFICIAL RECORD COPY 8710230246 870930 PDR WASTE WM-72 PDR.

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1 GE0 TECHNICAL ENGINEERING REVIEW COMMENTS I DRAFT REMEDIAL ACTION PLAN AND SITE CONCEPTUAL DESIGN FOR INACTIVE URANIV.*4 MILL TAILINGS SITE AT SPOOK, WYOMING

Review by: Dr. Banad Jagannath, LLTB,LLWM.

3 Documents Reviewed (References): ,

4 s 1. Remedial Action Plan and Site Conceptual Design for Stabilization of the N Inactive Uranium Mill Tailings Site at Spook, Wyoming. Draft, Volume 1-Text, Appendices A, B, C; UMTRA-DOE /AL 050515.0000; July, 1987.

2. Remedial Action Plan and Site Conceptual Design for Stabilization of the .

Inactive Uranium Mill Tailings Site at Spook, Wyoming. Draft, Volume II-Appendix D, Addendum D1, Addendum D2, Addendum 03, Plates for Appendix 0; UMTRA-DOE /AL 050515.0000; July, 1987.

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3. Remedial Action Plan and Site Conceptual Design for Inactive Uranium Mill ,

Tailings Site at Spook, Wyoming. Draft, Calculations; August, 1987.

4. Review Comments and Responses to Spook Preliminary Final CADSAR, f

July 1987.

5. Report of Investigation- Abandoned Mined Lands Program 15-3, Prepared for the State of Wyoming, Department of Environmental Quality Land Division; prepared by Hydro-Engineering, August 1987.

GE0 TECHNICAL ENGINEERING COMMENTS

1. Geotechnical Data; Figure 3.6, page 28. ,,

Figure 3.6 does not show the ground water table and the geotechnical data (test

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pits and borings) used in developing the Cross Section-AA'. The figure should be revised to present these.

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2. Bottom of Stabilized Tailings Pile; Section 4.2; Figure 4.2; page 56.

Review Comments and Responses.to final CADSAR (Reference 4) and~ draft RAP 7

(Reference 1)indicatethatthebottomofthestabilizedpilewillbea L minimum of 30 feet above the groundwater level at that location. Figures 3.7, L 3.10..and 3.11 show the groundwater level to be between elevations 4980.0 and L

5000.0 feet. Figure 4.2 shows the bottom of the stabilized pile at elevation 5025.0 feet and does not show the groundwater table at the site. This figure should show the groundwater level and also clearly indicate that the bottom of the stabilized pile should be a minimum of 30 feet above the groundwater table.

3. Low-Permeability Cover on the Stabilized Tailings Pile- Constructability; Sections 4.3.11, 4.3.14 and 4.4.9; pages 66, 70, 71, 72 and 76.

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r The tailings are proposed to be stabilized in to a pile of approximately 30 to 50 feet in height with a side slope of 50 percent gradient (2 horizontal to 1 vertical). This pile is proposed to be covered with a 1.5 feet thick layer of

• low-permeability material. In order to achieve the desired permeability, this material is proposed to be compacted to a minimum dry density of 95 percent of the maximum dry density determined as per ASTM D 698 test method. The NRC staff is concerned with the constructability of a 1.5 feet thick layer of low-permeability material, compacted to the above density requirement, on a 50 percent gradient slope of up to a maximum height of 50 feet. The potential problems of operating the compaction equipment on a steep slope, placing the material in 6 or 8 inches thick layers and compacting it to the specifications to attain the coefficient of permeability values assumed in the design should be evaluated. I

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The draft RAP (Reference 1) states that um alluvial soil (clayey Sand) available

.in the overburden piles at the site can be used for the low-permeability cover over the stabilized pile. There is very little data, besides some sieve I analysis data,'to support the statements on the quantity of the material I available at the site and the expected values of the coefficient of permeability. The draft RAP states that the low-permeability cover over the l stabilized pile will have a maximum coefficient of permeability of-1E-7 cms /sec.(dRAPpage73). However, the report on the proposed work by AML (Reference 5) indicates that the low-permeability material proposed for the cover is expected to have a coefficient of permeability of q i

1E-6 cms /sec.(page 5-12 of Reference 5). The permeability parameter for this material should be established with adequate laboratory and field testing to justify the design assumptions .

4. High-Permeability Material layer On Top of the low-Permeability Material Cover Over the Stabilized Tailings Pile; Sections 4.3.5 and 4.3.14; pages 60, 71 and 72.

The draft RAP proposes placing a 2-feet thick layer of high-permeability material (coefficient of permeability at least 3 orders of magnitude higher than that for the underlying low-permeability material) above the low-permeability material cover over the stabilized tailings pile. This is proposed to be placed by the State of Wyoming under the AML program, and the RAP provides very little information on this item. The report on the AML program by the State of Wyoming (Reference 5) does not mention this item except some statements on the availability of high permeability material at the site. Since this cover is an integral part of the DOE's concept of

• l remedial action (providing a high-permeability material layer to intercept any infiltration before it reaches the low-permeability cover over the tailings pile) to meet the EPA standard, there should be a definitive commitment from L__________._ _ - _ - _ - _ - -

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l SPOOK DRAP/GTEC CMTS/BJ 9/87 the State of Wyoming to construct this layer to the DOE's design criteria. Also, the question of constructability on a 50 percent gradient slope and the sequence of construction (whether this layer will be placed immediately after the placement of the low-permeability cover or at any time suitable for the AML program) should be addressed in detail.

The construction details for the high- and low- permeability layers at the toe of the slope of the stabilized tailings pile should be reviewed to ensure that there is a path for the water collected in the high-permeability layer to flow away from the tailings pile. Also, the need for a filter layer in the vicinity of the high- and low-permeability layers should be evaluated.

Since the work will be done by two agencies, their role at the interface of their work and the potential for confusion at the time of certification by the NRC ought to be thought out at this time.

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5. Slope Stability Evaluation of the Stabilized Tailings Pile; Sections 4.3.10 and 4.3.13; pages 65, 68 and 69. '

In the slope stability evaluation presented in the attachments to the dRAP(Reference 3),mostofthedesignparameterswereassignedandthe conservatism of these values were demonstrated by a parametric analysis of the l

slope stability evaluation. Although this approach is acceptable for the j draft RAP phase the staff would like these design parameters to be supported by adequate testing during the design phase.

The dRAP (Reference 1) states the use of a seismic coefficient of 0.09 (page65)intheseismicstabilityevaluationoftheslopeusingthepseudo static method of analysis. The DOE's design guide (TAD) recommends using a j minimum seismic coefficient of 0.1 for a pseudo static method of analysis.

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However,theTAC' calculations (Reference 3page16of.stabilitycalculations) uses a seismic coefficient of 0.105 which was derived as 50 percent of the peak

- horizontal acceleration of .219 for the design earthquake. The final design calculations for the seismic' stability of the slope should be in compliance with the provisions of the TAD for stability evaluation under the design basis earthquake.

The design basis earthquake is being reviewed by the seismologist / geologist of the siting section; refer to their comments on the magnitude of the design basis earthquake.

6. Stability of the East Wall of the Spook Pit; Section 4.2, 4.3.13 and 5.2; Figure 4.2; pages 56, 70 and 81.

The draft RAP does not address the sequence of removing the tailings material in the immediate vicinity of the east wall of the Spook Pit. The stability of the pit wall for the scenario of removing tne tailings from the foot of the wall (ie. material inside the pit adjaining the east wall) while the tailings '

still remain on the top of the east wall bank should be evaluated. If the east wall stability is found to be critical, the option of requiring the removal of the tailings on the east wall bank before removing the tailings at the foot of the east wall may be considered. A detailed evaluation of this scenario is needed.

7. Backfilling the Abandoned Tunnels; Sections 4.3.6 and 4.3.11; pages 61 and 65.

Both the dRAP (Reference 1) and AHL Program document (Reference 5) indicate that the abandoned tunnels will be backfilled. The documents recommend '

different methods of backfilling, however, it is not clear who is responsible for this work. This item needs to be clarified.

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8. Extent of Buffer Zone; Section 3.3.7; page 25.

The dRAP recomends acquiring a 100 feet wide buffer zone around the edges of the Spook Pit to protect the stabilized tailings in the Spook Pit against

- intrusion by exploration activities in the adjoining areas. The AML program document recommends the use of benches in the pit wall (see Figure 9-19 of Reference 5) for. placing the fill material 'next to the pit wall. The effect of this on the required width of the buffer zone, if any, should be evaluated. The statement on page D-38 (section D.3.7.2) indicates that the '

100 feet buffer zone is around the tailings impoundment rather than around the Spook Pit. This discrepancy should be clarified.

9. Radon Barrier Design The information presented is adequate for the preliminary design of the radon barrier. The NRC staff plans to review this design in detail during the final design of the radon barrier. However, note the following coments; Radon flux computation ignores the contribution form the AML program cover material. Radium content of the AML program cover material should be considered in the radon barrier design.

Will the work done in the AML program (above the stabilized tailings I pile) be in full compliance with the DOE /VMTRAP standards for construction, QA/QC, inspection etc.?

• l Please provide a copy of the complete documentation of the S0lLM0lST '

i code used to evaluate infiltration and the USSSC code used to compute the long-term moisture content of soils.

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.10. Additional Information i

The following information is requested:

1. Plan showing the locations of test pits 031 through 050. The logs of these j are presented in Figtres D.4.1.A through D.4.1.J

2. The ground surface elevation for the borings presented in Addendum 0-3.

Also, the boring logs are not in final form.

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