ML20236C350

Forwards NRC Comments on Draft Remedial Action Plan & Site Conceptual Design for Stabilization of Inactive U Mill Tailings Site at Spook,Wy.Clarification of Interface Between Aml & U Mill Tailings Control Act Program Designs Needed

ML20236C350
Person / Time
Issue date:	10/15/1987
From:	Lohaus P NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS)
To:	James Anderson ENERGY, DEPT. OF
References
REF-WM-72 NUDOCS 8710270109
Download: ML20236C350 (7)

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YlM Record file WM prehet" 4 OCT 151987 Ddd Noi 7 PDRd James R. A'nderson, Project Manager:

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L Uranium Mill' Tailings Project Office

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u U.S. Department of Energy:

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' Albuquerque OperationsLOffice d_..c f f

P.O. Box 5400

%9.910lV5t#$3S)

Albuquerque,NMl87115

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Dear Mr.. Anderson:

. Enclosed;are NRC' Staff. comments on the'DraftJRemedial' Action Plan and-Site' Conceptual-Design-for Stabilization of the Inactive Uranium' Mill Tailings Site '

H at Spook,' Wyoming. No fatal flaws were identified at this stage however,.

L clarification is needed as.to the interface between the AML and VMTRCAtprogram designs.to assure that.the UMTRCA requirements;will be met.

The staff were unable' to coment on the ground-water aspects of the draft RAP prior to review of the draft Environmental ' Assessment, which is ~ scheduled Jfor'-

review in November. -Ground-water coments on the draft RAP will therefore be transmitted with sta'ff comments on the draft EA.

Please contact Susan Bilhorn at FTS 427-4145.if you'have any. ques.tions regarding the Staff's. coments.

Sincerely, L

-Paul H. Lohaus, Acting Chief l

Operations Branch Division of Low-Level Waste' Management-and. Decommissioning, NMSS

Enclosure:

'As stated

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MF1 e 1 :PLohaus BATE 8h)[b)((8h)[b)h8h)[b)[i 0FFICIAL RECORD COPY 8710270109 871015h PDR WASTE l-WM-72 PDR?

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1 Jg NRC' STAFF COMMENTS ON THE 4 -

DRAFT REMEDIAL ACTION PLAN;FOR S,P00K,LWY0 MING l

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. GENERAL Comment: GEN /I --Integration of UMTRCA and AML-Activities y

NRC Staff are concerned'regarding.the' affect AML program activities may-

have on the ability of proposedi emedial action for Spook to meet-UMTRA r

requirements. While the. draft RAP' refers to the AHL design,'it:is not clear what aspects;of the AMLLdesign will'beirelied on to meet:UMTRA requirements, or that adverse impacts.have.been evaluated.and' considered in DOE's design..

'1 00E needs. to describe the relationship. b' tween the-UMTRCA.and' AML. program; H

e designs and address the following questions:

QA/00. How does DOE plan-to assure that the ' ML aethities'are A

concucted as specified in the design, and not adversely; impact the j

stabilized tailings pile?.

Low-and hic h-permeability layers. ' How will the interface. between the low-anc high-permeability layersL e constructed to en'sure'that b

there'is a path for water collected in the:high-permeability layer will flow away from the tailings? How will DOE assuretthat placement of the high-' permeability layer does not adversely' affect' the;

. stabilized pile or low-permeability layer?l What advantage does 00E plan to derive from the high-permeability layer, if any?

Backfill of mine. tunnels. Which' program is res backfilling the mine tunnels and what' impacts'(ponsible..for positive or negative) could that action have.on long-term stability of thejtailings pile and ground-water protection? '

Overburden material. What benefit does DOE plan to'_ derive from the-proposed AML backfill cover (i.e. radon diffusion and/or erosion.

protection)? Since AML is responsible for conducting this: activity, how'does DOE plan to assure that the. backfill cover will;be placed as designed? Has the ' concentration of radium in 'the cover, material' been considered in calculating the radon flux for design off the radon barrier?'

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~GE0 LOGY Comment: = GS/1 - Site' Erosion By Tributary Headcutting,' pages D-36:and D '37'

.This section' of.the' draft RAP andLFigure D'.3.11 depict headcuttingIby 2

a tributaries which would leadEto' erosion 1of.the; stabilized tailings.' The staff agree that. lateral. erosion and.hea'dcutting by tributaries of: Dry' Fork appear to be the;only significant geomorphic hazards associated with~

the' pit-disposal option.

In the staff's opinion, however,:D0E's!

predictions of future. erosion do not' appear-to be basedLon conservative L

' assumptions and analyses.

. Figure D.3.11 shows a model of future. channel:headcutting_into'the disposal area,from theisite's main wash.

The' analysis.assemesJthat the.

channel will naturally-adopt a slope'similar to that~of the: soil-bedrock-contact, approximately 0.076. As a result it 'shows' that erosion in' the :

main 1 wash.would need to exceed 50 feet to: expose the tailings.

In 3

addition, DOE states that' resistance of!the Wasatch~ Formation.is'likely to' prevent erosion beyond;a 35 to 40 foot depth.

1The slope gradient of 0.076 is extremely steep-for a channel and no justification.has been provided.to show:that it:is. reasonable.' Staff:

analysis indicates 'that a more shal'Iow slope, such as 0.030, would expose the tailings with only 21 feet of downcutting.in.the main' wash. Lateral and vertical erosion will occure entirely in backfill, will not be controlled by.bedrockWand will likelyL result in release.of the: tailings, earlier than anticipated from DOE's analysis.

DOE should revise the erosion protection analysis.for this ' site 'using more conservative assumptions, or should justify the. adequacy of the current analysis.

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SURFACE WATERLHYDROLOGY; j

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Comment: SW/1

-Stabilization'of Abandon'ed'Mine'd Lands! overl C

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The intent of: the? remedial action andLAMLidesign,' as! presentediin t.he draft.RAPJ(pages 60-67),- is to promote positive drainage;from. the cov.o@r y~

order to prevent pondingand limit the amount Lof, infiltration:intoith/r fls.

j tailings' fThe coverJdesi;;n, as presented in!" Report 'of, Investigation '

1 Abandoned. Mined' Lands; Program 15-3"'(Hydro-Engineeririg,1987), includestai vegetated earth l cover surrounded-by diversion. ditches. The' staff:doesonot considerithe proposed' cover adequate l to minimize ' erosion.,' ponding, andi..

.'l infiltration.. Furthermore,-we;concludeLthat'00E hasinot; demons'trated:the:

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effectiveness of.the designiforL1000 years with respect toistability"and 2

ground-water quality.

mo First, the ditches for diversion of-flood-flows around thel pit are-4 designed for 2.4. inches of precipitation in!one-hour, which isTpterported.

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'r to be a-1000-year event. This value11s apparently. based on extrapolation 4

of the precipitation data base' for Wyoming,lhowever, it?is textremely"

1. t doubtful that this data base isisufficient to. perform Ltherextrapolations A

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d necessary to' determine a meaningful 1000-year event; JInladditf ort, i.t, appears unlikely that-the' estimate actually represent a 10DD. year event,

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based on' comparison of. the one-hour,1000-year rainfallM2 Winches);to -

the one-hour-probable maximum l precipitation:(PMP),shichtis a 14 inches (see Hydrometeorological Report;(HMR);55,7 Plate 16)pproximatelyThe 9

it appears that:a:value much larger than<2.4 inches Lshould.beiadopted.as&.

the design rainfall.

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4 J-Second, the proposed soil cover is toibe' protected only. by vegetation.

Since a vegetative: cover is unlikelyico be self-sustaining in the arid-i climate of Wyoming,sthe staff questions' whetherLsuch a. cover caniprevent gullying due.to concentration of runoff during' major precipitation' events.

i The sheet flow assumption used inLthis; design is likely to be' invalid if l

flow concentration ~ occurs. Gullying will likely disrupt the; cover, possibly allowing ponding, erosion, and' increased infiltration'in'ateas j

directly above the tailings.

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DOE should provide a revised cover design.and should justify that*the d

design meets the' EPA criteria established in 40 CFR 192.

Factors!that D0E

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needs to thoroughly address include'the: impacts of. extreme: flood ~ events on the' cover and ditches; the potential for flooding.!if ditches fail; then l',

1 impacts. of gully growth on ' the' integrity' of.the tailings-pile;'and the [

t impacts of increased infiltration:on ground water.. A rock 0 cover and rock-protected diversion charrels, designed in"accordance 'with past UMTRA~

practice, may provide an acceptable approach.=

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h REFERENCE CITED

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-m Hydro-Engineering, 1987. Report of Investigation for Abandoned M'irie ' Land !

Program 15-3, Spook Site;; prepared by Hydro-Engineering, Casper, Wyoming :

q for the: State of Wyoming,( Department of Environmental"Quplity.

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s GE0 TECHNICAL ENGINEERING Comment: GT/1 - Constructability of Low-Permeability Cover, paaes 70 -73 In the draft RAP, DOE proposes to stabilize the tailings in a pile approximately 30 to 50 feet high with a side slope of 50 percent gradient (2 horizontal to I vertical). This pile will be covered with a 1.5 feet thick layer of low-permeability material.

In order to achieve the desired i

permeability, DOE proposes to compact this cover material to a minimum dry density 95 percent of the maximum dry density determined using the ASTM D i

698 test method. NRC staff is concerned regarding constructability of the I

proposed low-permeability layer.

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DOE should evaluate the potential problems associated with placing the material in 6 or 8 inches thick layer, operating the compaction equipment on a 50 percent slope, and compacting the material to attain the coefficient of permeability value assumed in the design.

1 Coment: G_T,/2 - Low-Permeability Cover Material, page 73 This section of the draft RAP states that the. alluvial soil (clayey Sand) available in the overburden piles at the site will be used for the low-permeability cover. There is very little data, other than sieve i

analysis data, to support the draft RAP statements on the expected coefficient of permeability for this material.

In addition, the draft RAP j

states that the low-permeability cover over the stabilized pile will have a maximum coefficient of permeability of IE-7 cm/sec. However, the Hydro-Engineering report on work proposed by AML indicates that the low-permeability co.ver material is expected to have a coefficient of permeability of 1E-6 cm/sec (Hydro-Engineering, page 5-12)

DOE needs to determine the actual coefficient of permeability for this l

material, based on appropriate laboratory and field testing, and justify the assumptions used for the design of the low-permeability cover.

Comment: GT/3 - Slope Stability Evaluation, Pages 68 and 69 For'the evaluation of slope stability, most design parameters were assigned, and conservatism of these values demonstrated, using a parametric analysis. This was noted in #SPK-06-87-03-01-00 (page ? - 3)

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of the calculations provided by DOE in support of the draft RAP. Although u

this approach is acceptable at the draft RAP phase, these design

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parameters will need to be supported by test data to assure that they are adequate when used in the preliminary design.

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s Comment: GT/4-SeisulEStability, pages'64 and 65.

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.g Ths drdft RAP'stptes that th@sefonic coefficien't o'fh}09lw y

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l evaluation %ff seismic' slope [stalilityy performed oJry the pseudo -static,

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i/ l method of analysis. Howeverb a'minimdm seismic bpff jcient-of 0.Ws h

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-recommendedinthe. TAD (00E,1986,cpage'67).,;In 49dition, the;sejimici

& coefficient of-0.09 was calculated based.'on a saxiem peak horizon;tal-i" l..

acceleration (PHA)tof.0.169 (draf t1 RAP, Volb2,' pg./!b42),x while the -

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'7 calculations provided in: support ofathe draft RAP dssume'a seismict g '

a ceafficient of,06105 based on a.PHA of,0.219.(stability;calculationspage 1

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/ Chshould 4xplain why. a. seismic coefficient' has :beopssumed th'atiisiless.

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conservative then thatcrecommended in the TAD.

Alfo the discrepancy -

.4 between the'PHA and. seismic stability values presentd1 in the; draft RAP

.. y and-supporting' calculations needs to be resolved; Y ff '

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Comment: GT/5 Stability of = the Ea'st Pit Wall', Figure 4.2t pages 70 and 8f a

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The ~draf t RAP does not address 'the sequ' ence of'mbvhthe tailings:-

<:l material from the east wall of the Sncok ~ pit. (The;; stability of the pit Q[e wall should be evaluated, especially l f DOE plans [to remove the tailingsD #

from the foot of the wall. (i.e. material inside the pit adjcining the; east' e

wall) while the tailings remain on--the top'of the east wallfbsnk.-

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~l Cpmment: GT/6 Extent of the Buffer Zone, page 25 J

L Th draft RAP recofreends acquiring a,100 foot wide buffer zone around the I

eoses of the Spook pit tp proMct the stabilized pfleiagainst intrusion durir.g future" mining ;actiivities.. The Hydro-Engineering report fo program recommends the-uise of benches in tk pit wall (Hydro-Engineerir,

Figure 9-19)Tfor placing the fill' materia 1 4 DOE should consider the effect th's may have on the width of the buyer zone.

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A statement' on page D-38 of' the draft RAP ydirgtes that th'e proposed 100 '

foot buf fer zone will be around the' around tha Spook pit.

This discrepa,t'ailinguimpoundment rather than ncy shoyld also.be clarified. -

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Comment: GT/7 - Water Table Relative to Tailings, Fig,u_re 4.2, page 56 W

The. draft RAP:(page.36)Pstates that the bottom of the! stabilized' tailings, will'be 30. feet above the water tabl$. Figures 3.7. 3J0,/and 3.11:show

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the water table to is between elevatA ns 4980.01a feet and Figure.

4.2-shows the bottom of: the stabilizd tailings a% 500010 9

, n t: 5025.0 feet, but' does N

not show the-water tabir In contrastaFigure D;3Xshows the water table tobeapproximately.10ie[et.belowtheexistingpitebottom.-

This-inconsistency'needstobe'rehlved.

In addition, the water table should' e be included in Figure 4 2 to show the elevation ofxthe stabilized tailings 0 in, relation to the gros 4 water ' level.

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Comment:- GT/8.- Geotechnical Data, Figure 3.6, page 28 Figure 3.6 presents a cross section of the tailings stratigra not show the geotechnical data points (test pits and borings)phy but does l

used in it's M

development.- This' figure.should be revised to show these data points, and j

also to include the ground-water level for reference.

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REFERENCES' CITED-h<

DOE'(U.S. Department of Energy), 1986a. Technical Approach. Document, UMTRA-

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00E/AL-050425.0000,: prepared'by the U.S. Department of, Energy, UMTRA 4

Project Office,' Albuquerque, Operations Office. Albuquerque..New Mexico.

Hydro-Engineering, 1987. Report of' Investigation for. Abandoned Mine Land-Program 15-3, Spook Site, prepared by Hydro-Engineering, Casper Wyoming for the State of Wyoming,' Department of Environmental Quality..

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