1992-06-15_REVISION - M1988112 (4)

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MINED LAND RECLAMATION DIVISION Department of Natural Resources 1313 Sherman St., Room 215 Denver, CO 80203 303 866-3567 FAX: 303 832.8106 STATE OF COLORADO OF' CO~ ~~~q7 Ne~~~g • . ~ ~B'!fi Flay Romer, Governor Michael 8. Long, Division Director DATE: June 15, 1992 T0: Larry Oehler FROM: James Stevens -~' RE: San Luis Project (Permit M-88-112) Technical Revision No. 8 Adequacy I have reviewed proposed Technical Revision No. 8 for adequacy of tme proposed program together with locations, depths, and construction of the additional monitoring wells. Protocols related to actual sampling of the we114 are assumed covered under 7R-6. As regards adequacy of the program, the configuration of the potentio-metric surface in the area and likely direction of ground water flow are essentially unknown. A considerable part of the value of the proposed wells is to provide data to help resolve this problem. The hydrologic situation that may be revealed by the new data, however, could show that Well M-9 and proposed M-13 and M-14 do not in themselves comprise a practical monitoring system for the containment pond and treatment facility. Given the locations proposed for Wells M-1.3 and M-14, should M-9 and either of the new wells have essentially t~1e same static head, neither might be expected to readily capture timely evidence of a leak from the containment pond. The operator should commit to a reevaluation of the proposed monitoring network following drilling, data gathering, etc. and to add additional well locations should the existing net~,vork be determined to be inadequate. As for the current locations of the wells relative to the coilection pond, tailings facility and one another, the proposed network dyes not appear to provide the best expectation of intercepting evidence of a containment leak `rpm the pond and facility. If ground water flow in the area has a strong E to W component as is claimed, the breadth of potential coverage by M-1 is small a<_ a result of its being located so close to the pond and so near a line between M-9 and the tailings facility. On the other hand, M-14 would appear to be too far from M-9 and too far southeast of the pond to be effective in monitoring for ieaks from the pond, even counting on some cispersal. Since the location of Well M-9 is fixed, M-13 and M-14 should be relocated to provide greater breadth cf coverage for east to west flow as well as to provide an apparent ability, comparable to that of M-9, to monitor for containment leaks from the pond and~or tailings facility.