ML19329F293

Submits Draft Critique of Woodward-Clyde & Associates Rept, Investigation of Possible Surface Subsidence at Midland Mi. Investigation Not Considered to Be Conservative Enough to Warrant Acceptance That Subsidence Will Not Be Hazardous

ML19329F293
Person / Time
Site:	Midland
Issue date:	03/05/1970
From:	Waldron H INTERIOR, DEPT. OF, GEOLOGICAL SURVEY
To:	Cardone A US ATOMIC ENERGY COMMISSION (AEC)
References
NUDOCS 8006240660
Download: ML19329F293 (3)

Text

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Mecor idy Report -

To:

A. T. Cardonc, Div. Ecacter Lic. , Atonic Energy Co_ dsnion.

Eethecda, Faryland Fror2:

U.11. Valdron, Engineering Ccology 3rcuch, II.S. Geologien1

• Survey, Denver, Colorado '

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Subject:

Critique of report by lloodvard-Civde & Associates cctitled: *

" Investigation of Possibic SurfudfTuiIcSIEiice'aty.idland, Michigan." (AEC Lochet :26d.30-329 and -333, Av.ciid.s 7)

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.s Based en the simplified assurptions cced in the analytical investi-t,aticn of possible surfaca subsidence at Hidinnd, Michigan, by Voodward-Clyde b Associates, the results presented in their report appear to be u

rescenable and valid. Eovever, owing to the ainoat co plete lack of knociedyc of the actual subrurface cenlitions that c:tist at the cite, the invcatigation is not considered to be conservativa enough to ur.rrant P

its acenptance as proaf positive that surfcco subsidence vill not be a hazard to the ".id1:nd nucicar plant durin;. the operationni tine-spen of the plant. A nore ccuservative opproach to the problen, therefore, scce:s desirabic.

As stated in the introductory paragraph of the report, surface dis-placenent is a function of coveral variabica, cuch ne the siza and depth of the opening, cud the physicci characteristics of the rcck section.

Several other vcriabics also could be cited that night significantly affect the potential for surfcco cubsidence. Unfortunntcly, hcvever, nhout the only hs::ic facts recording subsurfaco site conditions, that THIS DOCUMENT CONTAINS I POOR QUAUTY PAGES i I i

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~are at all ved known at .21s tieso, are the stratigraphy o jhe sedinen-  !

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taiy'forcations involved, the depth of the solutionin;,, and the volume of salt extracted fron each well. Issentially nothing appears ta be knom about such basic data asi the lateral extent of the solutioning; the geosctry of the cavitics produced; the a ount of collapse that has occurred, either during or n!ter cessaticn of nining; the state of stress i that existed in the rccks before eining occurred; the changes in the i

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stress field that I:ay have occurred due to minin2; or whether flevage of l the salt has occurrod, either during or after cessation of mining, and jl if so, what pensible effect thic flovano cight have on subsidence. So e l basic, la citu gcephysical data is availabic fror2 horings, but no detailed investisations apparently have hocn I:ada regarding tha physical ccd en31-neering properties of the difforcat rcch units involved. Consequently, although all the data used in the analyaes by Woodward-Clyde & Associntes er/ be reccenabic, these data are still largely beced en assumptions and very little is based on Ir.oun f acts. .

The present state-of-the-crt in subsidence prediction does not appear

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%. ,. , to justify the use of such slepic assumptiens for a conservative analysia Uf. the probic-1. To assuce, for cannple, that the caterial is a linear elastiY r.sterial simply cay not be valid, as it does not n11ow for any

_tice-dependent deforestion. Such tine-dependent deforcation ray be a significEt Ecetor in the potential for subsidence during the lifo span of the plant.

3,ccauso so rnny of the varlsbica affccting surface cubcidence are l either unkcovn or very poorly known et the site, it is sur.gented that i the cpplicant reevaluate the potential for surface subsidence, but that b

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this ti::e he,6asa his analys'ea\cn the more conservative assump6.on that ,-

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the very worst p,ossible conditlobs way exist at the site. Then, if

.- g '. d these results appear to provTde reasonable assurance that to sudden l

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curface displacercuts will cccur at the site, it is su;gestad that the

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cpplicant consider%.dhTi..-gning to resist possible effecto of subidence, .

and also, that he consider installins a conitoring systcm for detecting ~f t possible future differential displaccrents. The purroce of this monitoring system vill be to assure that, if certa'in specified allovable differential ,

I displacements-the ca::nitude of which will be deternf.ned by the design cugineers-are approached er exceeded at any ti:e during the life span of , .

the propoced plant, the plant vill be shut doun until detailed inspections and analysca can be evaluated to determine the feasibility of,-or the rencdial censures required fer, the cor.tinued safe operation of the plant.

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Waldron EGB (Original and 1 to F..U. Coulter)"

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