ML20205Q552

Forwards Addl Comments on Environ Assessment for Disposal of Project Low Level Waste. Need to Develop Fully Calibr & Independently Validated Site Hydrogeologic Sys Model Stressed

ML20205Q552
Person / Time
Site:	West Valley Demonstration Project
Issue date:	04/07/1986
From:	Clark A NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS)
To:	Hannum W ENERGY, DEPT. OF
References
REF-PROJ-M-32 NUDOCS 8605300588
Download: ML20205Q552 (5)

Text

^

DISTRIBUTION:

,  ! Project Fil' M-32 LPerson NMSS r/f LDeering PDR & LPDR FCAF r/f TNicholson APR 07 M JStarmer JPhilip MKnapp RMacmillan RECunningham NDavison Project M-32 SNeuder PJustus Dr. William H. Hannum, Director LSaraka ATClark West Valley Project Office DWidmeyer LA File TJohnson U.S. Department of Energy RBoyle Idaho Operations P. O. Box 191 West Valley, NY 14171

Dear Dr. Hannum:

With this letter we complete our review and comment on the Department of Energy's (DOE or the Department) document, " Environmental Assessment for Disposal of Project Low-Level Waste." Our initial comments were forwarded to you with my letter, dated February 27, 1986. Based on the information in the Environmental Assessment the NRC's Division of Waste Management (DWM) cannot determine if the proposed action would or would not result in a significant impact upon the environment. Further, DWM has indicated that, because of the previous inadequate performance of the disposal area, a clear demonstration is necessary to show that similar problems (solvent transport, trentch overflowing) will not occur.

As may be deduced from our enclosed comments, the details of design and construction for your preferred disposal alternatives are considered to be of fundamental importance to their performance. We should be kept fully and timely informed on these details, if you proceed. We also stress the need to develop a fully calibrated and independently validated model of the site hydrogeologic system as based on collected and analyzed data. Without an adequate understanding of site characteristics and the hydrogeologic system, the design and performance of the disposal alternatives may not be assessed with any degree of confidence. We stress the need to develop an erosinn protection design to prevent gully intrusion into the waste disposal areas.

Although we have not specifically addressed the related topic of the disposal of decontamination and decommissioning wastes, early discussions with the Department and its contractor will be useful for developing a better understanding of the disposal volumes, contamination levels, and techniques which may be considered for these wastes.

i i

Sincm,}g'Umm p A. Thomas Clark, Jr.

Advanced Fuel and Spent Fuel Licensing Branch Division of Fuel Cycle and i Mat ~'-l M t,

Enclosure:

Additional NRC Comments 8605300588 860407 NMSS PROJ (

i

• SEE PREVIOUS CONCURRENCE OFC: FCAF :FCAF :WM .

93  : FC WM l

t C

NAME : ATCla rk * :LCRouse * :LSaraka * :MKnapp * : REBrownin

• LLunni_nj. h_am__JS_t_a_r_mer*

t i DATE:04/1/86 :04/1/86 :04/ 3 /85 :04/ 3 /86 : nuum; : 4/[/86 : 04/3/86 0FFICIAL RECORD C03Y

Record Note (4/3/86)

The following comments are included to clarify DWM staff concerns.

The 3/25/86 memorandum from R. Browning to R. Cunningham should be informally transmitted to DOE in order to clarify the DWM statement on its inability to arrive at a conclusion of no significant impact (paragraph 1 of this letter).

Comment on erosion should be clarified to emphasize that past analyzed gullying rates may not be representative of future gullying rates.

Erosion protection design should be provided to mitigate this potential problem.

Tumulus construction may alter current erosion patterns.

Site characterization should be completed and evaluated before any operations associated with LLW disposal commences.

l l

l i

i i

i

. 1

. l k

ADDITIONAL NRC COMMENTS ON THE DEPARTMENT OF ENERGY ENVIRONMENTAL ASSESSMENT FOR DISPOSAL OF PROJECT LOW-LEVEL WASTE Erosion Comment No. 3 in our letter of February 17 emphasizes the erosional effects produced by local intense storm events. Because of the severe rainfalls there is a potential for significant gully intrusion and head cutting into the disposal areas. Erosion protection design using data beyond estimates based on the last few ybars rainfalls is necessary because of the long terms needed for safe disposal. In addition, the orientation, slope, vegetative cover, and other design aspects of both the trench and the tumulus caps, are all important to site stabilization. Some of these actions are necessary now, as we plan to discuss with you and your contractor soon.

Subsidence The emplacement of a cement slurry or pea gravel a3 fill material around the waste in both the tumulus and/or the trenches is extremely important to subsidence prevention. With respect to Class A waste disposal in trenches, we believe that stabilization of Class A waste is necessary to prevent subsidence.

In this regard some differential settling may be expected in both the tumulus and trench caps. Both disposal methods should be analyzed to determine the effect of subsidence on the performance of overlaying protective clay layers or other features important to inhibiting ground water recharge.

Subsurface Characterization Report The local and/or perched water tables and its fluctuations should be delineated using all available data. The purpose of establishing the water table is to assure that all disposals are below the zone of fluctuation (in the diffusion dominated region). The importance of the fracture zone in the upper portion of the unweathered Lavery Till to ground-water flow and deep infilitration should be determined. The transmittal nature of the fracture zone may affect the modeling analysis and it may be inappropriate to create a sharp boundary at 15 meters for modeling purposes. Further, it would be useful to cite and discuss the specific engineering studies which provided the basis for the modeling assumptions and input, e.g., fracture depths and hydrogeologic property values.

The tensiometric data are erratic, and fail to provide a clear understanding of various infiltration periods and rates. Data collected over the various seasons need to be fully incorporated and explained. It would be helpful to know if the instruments were behaving properly or if the erratic behavior was attributable to some other known cause. Ground water quality and related geochemical characteristics of the Lavery Till should be determined.

)

~2 Modeling w

The NRC staff has been having difficulty in understanding the use of the generic EPA PRESTO code for the specific West Valley site. The EA does not adequately substantiate this use. An explanation of the application of the mathematical algorithms in the generic PRESTO code to the site specific West Valley case should be included. Justification for all input patrameters used in both FEMWATER and PREST 0 should be included. Real time data should be used wherever possible. The technical basis and justification for assumina a specific cap failure rate overtime and for the assignment of a permeability should be provided.

Tumulus Design At present, the DWM staff considers that there are sufficient uncertainties in the tumulus design to question the anticipated performance of the tumulus. If the Department decides to proceed with the tumulus concept, the design features in the following list should be analyzed and implemented carefully for proper perfo rmance.

1. The geotextile strength in both shear and tension as affects its capability to maintain clay layer impermeability.

2. The techniques and materials to be used for backfill around the intruder barrier (dolus at present).

3. Proposed slope of the gravel drain beneath the waste.

4 Capability to achieve adequate compaction of the clay layers without affecting its continuity.

5. Accurate determination of the permeability of the clay layers as emplaced.

6. Use of a ground-water model with adequately supported input parameters to analyze tumulus performance for both design and anticipated failure modes.

7. Spacing of waste containers to optimize backfill emplacement. The use of pea gravel should provide the desired drainage, if properly used.

8. Monitoring instrumentation to determine moisture content at various i locations and detect differential settling should be considered. Early warning of failure should be a predominant consideration in monitor design.

9. The connections between the drainage blanket and the gallery drain should be designed with care.

10. The functional relationship of leak rate to moisture content should be determined.

3 Quality Assurance The success of any of the alternatives you select to adequately confine project low-level waste depends on quality both in design, construction, and operation.

Coverage in each of these areas during all phases of the work is essential for-your quality assurance program.

Source Term The basis for the TRU source term in project waste should be substantiated.

l f

i 9

es