1993-04-09_REVISION - M1988112 - Laserfiche WebLink

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iii iiiiuiiiiiiiiii , STATE OF COLORADO DIVISION OF MINERALS AND GEOLOGY Department vi Nuwrul Resources 1 J'. 1 Sh?rnu~n SL. Ruom 21 5 Denrcr. CU t'•U'U; Phone: I lU it 661,-'.567 FA% GO 11 d 1'-H 106 April 9, 1993 Mr. Andre J. Douchane Battle Mountain Gold Company 5670 Greenwood Plaza Blvd. Englewood, CO 80111 Re: San Luis (Permit No. M-88-112) Review of 1/13/93 Response to DMG Adequacy Review of TR-08 Dear Mr. Douchane: pF Cpl ~~~1'al :, ~ ~.. . r~~.~ Ruy Romer Goeernur ~Vichael B. Lon,q Drvis~on Dnenor The Division has confirmed the validity of the plots of contaminant plumes that warn provided by BMR in response to the Division's adequacy letter of November 17, 1992. These plots, using rcascnable input values of seepage velocity, aquifer porosity, contami- nant source strength, and assuming a homogeneous reservoir for modeling purposes, indicate that the existing ground water monitoring network of wells M-9, M-12 and M-13 could oossibly be reached by evidence of leaks from the western margins of the tailings facility and the collection pond within the projected 9- to 1 5-year life-of-mine time span when dispersivity vaiues of Ux iu0, Dy 30 and Dx 200, Dy 60 were used in file modeling. However, for the lowest of the dispersivity values modeled, i.e., Dx 30, Dy 10, the monitoring network may not be reached within anise-year period by detectable amounts of contaminant originating from the western margin of the collection pond. The network would, however, apparently be in a position to detect evidence of leaks from this area of *.he collection pond within 15 years. This estimated 9 to 15 life-of-mine time span is based on a proposed 7 to 10 years of active operating life to which is added 2 to 5 years of reclamation. Monitoring is considered necessary during the reclamation period since the tailings pile will require some time after active deposition of the materials to dewater. Flow of water from the pile wasp estimated in the permit application to cease approximately two years after active deposition of tailings in the ponds had stopped. Since the life of the mine is only estimated to be 9 to 15 years and could extend for a longer period, the Division proposes the following condition to approval of TR-08: 1) BMR will maintain and employ the approved ground water monitoring network according to the approved monitoring plan for a minimum of 15 years after use of the tailings facility and collection pond began or until it can be demonstrated to the Division's satisfaction that water flow from the tailings facility to the collection pond has ceased, whichever period is longer. Should the Division determine that evidence of any significant