ML20206M430

Forwards Review of Addl Info in Support of Proposed Mods to Salt Lake City Remedial Action Plan.Mod for Rock Cover/ Filter Zone Gradations Acceptable.Elimination of Moisture Requirements for Compacted Contaminated Matls Unacceptable

ML20206M430
Person / Time
Issue date:	06/16/1986
From:	Knapp M NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS)
To:	Themelis J ENERGY, DEPT. OF
References
REF-WM-41 NUDOCS 8607010176
Download: ML20206M430 (6)

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Distribution HN C s/ff WMLU r/f NMSS s/f WM41GNeitssif96fgy. JO Bunting MJ Bell RE Browning DM Gillen g gg g DE Martin MR Knapp S Smykowski E Hawkins, URF0 M Nataraja Mr. John G. Themelis, Project Manager Uranium Mill Tailings Project Office U.S. Department of Energy Albuquerque Operations Office Post Office Box 5400 Albuquerque, New Mexico 87115

Dear Mr. Themelis:

Enclosed are the results of our technical review of additional information submitted in support of two proposed modifications to the Salt Lake City RAP.

The additional information pertinent to moisture control specifications for contaminated material was submitted by your letter dated April 28, 1986, and information on the rock cover / filter zone gradations (letter from Roger Williams to you dated March 26,1986) was hand-delivered by R. Rager to D. Gillen on May 5, 1986.

Based upon our review, we conclude that the proposed modification for rock cover / filter zone gradations is acceptable. However, the proposed elimination of moisture requirements for compacted contaminated materials is not acceptable. Our review has concluded that moisture control is necessary, but the present RAP requirement is too restrictive and can be modified. Increasing the range of placement moisture from minus 3% of optimum to optimum moisture as presently required by the RAP, to new limits of minus 3% to plus 5% of optimum moisture is acceptable to the NRC staff, and will provide the material placement conditions necessary to minimize differential settlement and maintain stability. As indicated in the attached technical review, our technical staff has concluded that adequate moisture control is necessary to have reasonable assurance of meeting the governing EPA standards. Therefore, please be aware that documentation of the necessary moisture control of future compacted contaminated materials at the Salt Lake City site will be reviewed by the NRC during construction site visits. Appropriate documentation by DOE of adequate moisture control for this site will be necessary in the future for our concurrence in completion of remedial action. //M Record file WM Project b Docket No.

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NAME :DM Gillen :DE Martin :MR Knapp  :  :  :  :

DATE 386/06/ :86/06/ :86/06/  :  :  :  :

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-2 Upon our receipt of the appropriate fonnal RAP modification and signature page, we will execute our concurrence. Should you have any questions regarding this transmittal, please contact me or Daniel Gillen of my staff.

Sincerely, s/

Malcolm R. Knapp, Acting Chief Low-Level Waste and Uranium Recovery Projects Branch Division of Wasto Management Office of Nuclear Material Safety and Safeguards

Enclosure:

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DATE:86/06/p :86/06//3 :86/06/lk  :  :  :  :

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ATTACHMENT 1 l

4 I REVIEW 0F THE PROPOSED MODIFICATIONS TO THE SALT LAKE CITY REMEDIAL ACTION PLAN (UMTRAP)

By letter dated July 10,1985(Themelis(DOE)toHigginbotham(NRC)),DOEhad

proposed two modifications to the Salt Lake City Remedial Action Plan (RAP).

The first modification dealt with changes in the rock durability specifications

for the erosion barrier material. A review of the modification was performed

! and the conclusion was that DOE's proposed modification was acceptable.

However, it was recommended that the design of the filter layer be reviewed again since there was a change in the overlying riprap size. DOE has submitted to NRC another evaluation of the grading curves and RAP requirements for filter

and erosion barrier material and has made recommendations based on their

. conclusions. We have reviewed DOE's recomendations and our conclusions are l- included in this enclosure.-

The second proposed RAP modification dealt with the compaction specification l for placement of contaminated material. The requirement identified in the RAP 4

(December, 1984) calls for compacting the tailings to a minimum of 90 percent of the standard Proctor maximum dry density (ASTM D-698) and at a moisture content between minus .3 percent of optimum and optimum moisture. NRC concurred in this requirement at the time concurrence was granted in the RAP. The proposed modification by DOE is that the moisture requirement be eliminated and the 90 percent standard Proctor compaction be the only specification required. '

4 The staff reviewed this proposed modification (letter from L. Higginbotham to J. Themelis dated October 7,1985) and concluded that the modification would j not provide reasonable assurance that the design would meet the EPA standards

without further analyses providing acceptable justification for this modification. As a result, DOE reviewed and analyzed field moisture / density l

data of contaminated fill already placed and also performed laboratory testing on a composite sample of tailings considered representative of the material

! that has been placed. The results of the laboratory testing, analysis of the

! field data, and DOE conclusions and recomended changes to the RAP were

! submitted to NRC for review (letter from Themelis (DOE) to Knapp (NRC) dated l April 28, 1986). The results of our review are included in this enclosure.

! Criteria for Filter & Erosion Barrier Materials Based on a review of the gradation limits for the filter material and erosion barrier rock in accordance with the staff Standard Review Plan, the proposed gradation modifications are acceptable. However, DOE identifies in their

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Technical Approach Document (TAD) that the minimum size rock of the rock l

blanket should equal approximately one-tenth of the blanket thickness. It ,

i should be noted that the minimum size rock observed from their gradation curve does not meet this TAD criterion.

l Moisture Control During Field Compaction When specifications for the placement moisture content and degree of compaction are normally established, their selections are dependent upon required engineering properties that would typically include strength, compressibility, and permeability in order to achieve a certain level of performance and stability (Ref. 1). The typical density requirement for placement of tailings l during remedial action is to compact the soil in the field to a minimum of 90  !

percent of the standard Proctor maximum dry density. In general, compacting soil to this degree of compaction has not been a difficult specification to meet. It can be achieved over a broad range of moisture contents depending i upon the amount of field coinpactive effort applied to the soil (Ref. 2). In conjunction with specifying a density, a range of placement moistures are usually specified and are specified for good reasons. The strength and l

compressibility of a cohesive soil are known to depend on the placement water content and density, and both must be considered (Ref. 3, Ref. 4).

l If enough field compactive effort is applied to a soil, 90 percent of standard Proctor density can be achieved at moistures well below optimum moisture (Ref. 1). However, soils compacted too dry of optimum moisture content have been known to settle considerably upon subsequent wetting (Ref. 5). Without a moisture specification, it is possible that the tailings at'the Salt Lake City site could be compacted to the required minimum of 90 percent of standard Proctor density at moisture contents well below optimum moisture (and less than 70 percent saturation). Significant settlement of the material could occur if

! the tailings were later saturated. If cracking of the cover should occur,

! water could infiltrate the tailings and possibly cause localized areas of saturation. This could lead to pronounced differential settlements which would contribute to additional cracking of the radon barrier and/or the creation of preferential drainage pathways. For these reasons, the staff recomends that

the minus 3 percent specification limit remain as the lower bound for moisture i control.

i Shear strengths of soils compacted wet of optimum are generally less than those obtained from soils compacted dry of optimum, particularly immediately followingconstruction(Ref.2,Ref.3). In addition to reduced strength, l

l soils compacted wet of optimum become more ductile which allows for

significantly larger strains (Ref. 2, Ref. 3). Settlements increase as the placement moisture increases on the wet side of optimum (Ref. 4). This is i

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shown by DOE's test results which indicate that relatively larger strains occur

with those samples compacted at moistures greater than 90 percent saturation.

Reference 5 (p.254) also shows that there is a significant increase in compressibility of soil placed wet of optimum over that of soil placed dry of optimum when both are placed at the same dry densities. We do agree with DOE's statement that the test results indicate that the tailings show increased sensitivity to settlement when placed at moisture contents resulting in j saturations greater than 88-90%. Therefore, in recognition of this soil d

behavior and DOE's own test results, we recommend that an upper bound for moisture control be specified so that 90 percent of standard Proctor density 1 will be achieved and the. required strength and settlement characteristics will be assured. The placement moisture content of the tailings recommended by the staff should not exceed plus 5 percent of optimum moisture.

The DOE should have little difficulty achieving the upper moisture bound recommended by the staff for two reasons. First, the average field moisture content exceeds the average optimum moisture content by 2.1 percent which is less than the NRC recommended upper bound. Secondly, DOE reports that the maximum percent saturation for which compaction could be achieved in the field has been 86 percent. This corresponds to approximately plus 6 percent above optimum moisture for 90% standard Proctor density. Further, it is our

understanding that most of the tailings at the time of excavation are at moisture contents greater than optimum. Therefore, DOE should have little difficulty meeting the lower bounds of the staff's recommended limit.

In summary, based on our review of the information presented, we recommend that the material be placed with a moisture cont'ol r specification. However, we agree that the present RAP requirement is too restrictive and can be modified.

Increasing the range of placement moisture from minus 3 percent of optimum to optimum moisture as originally required by the RAP to new limits of minus 3 percent to plus 5 percent of optimum moisture are acceptable to the staff and will provide the material placement conditions required to minimize differential settlement and maintain stability. We are not able to support DOE's technical argument that the stability of the pile will be assured and l

differential settlement will be minimized if the tailing are placed at moisture contents outside this specification. In order to demonstrate that the modified moisture _ control limits are adequate and acceptable, the staff would agree with D0E's plan for monitoring of embankment settlement and recommend that this be performed as stated in the RAP.

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e REFERENCES

1. Terzaghi, K. and Peck, R. B., Soil Mechanics in Engineering Practice, John Wiley & Sons, Inc., New York, 1967, pp. 440-451.

2. National Engineering Handbook, U.S. Department of Agriculture - Soil Conservation Service, prepared by Geotechnical Engineers Inc., Project 80762, October 1982, Section 7. Chapters 9 & 12.

3. Banks, D.C., " Embankment - Design Concepts: Water Content - Density Relations and Effects on Design Parameters," from Notes for Construction of Earth and Rock-Fill Dams Course, U.S. Army Engineer Waterways Experiment Station, Corp of Engineers, Vicksburg, Mississippi,1980.

4. Sowers, G.F., Introductory Soil Mechanics and Foundations, MacMillan Publishing Co., Inc., New York, 1979, pp. 237-263.

5. Winterkorn, H.F., and Fang, H.Y., Foundation Engineering Handbook, Van l

Nostrand Reinhold Company, New York, 1975, pp. 253-256.

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