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9/30/93 Responses to Comments San Luis Reclamation Evaluation Report Page 23 continue to compact throughout the life of the operation. A permeability of 10~ cm/sec is equivalent to the requirements for an impermeable earthen liner and therefore little fluid movement is expected. Based on calculations presented in the Reclamation Evaluation Report, approximately eighteen months after cessation of deposition flows from the underdrain will drop to less than 0.5 gallons per minute (gpm). These flows will continue to decrease to less than 0.1 gpm after 24 to 30 months. The tailings surface will be graded to slope at approximately 0.5$. At this slope, runolff flows will not be erosive. Information on the graded tailings surface and potential for erosion was addressed in detail in the approved permit application and associated adequacy responses. Comment: B. Some of the weathered tailings samples have metal concentrations which are at or near the levels for surface water standards for, say, the Rio Grande River. BMRI should explain the high metal concentrations in terms of the site conditions that will exist upon closure. The Division needs certain assurance that, under the present reclamation plan, surface water that leaves the site will not be degraded by weathering of the tailings. Response: An analogy of the EPA 1312 test results to water quality standards is inappropriate for the reasons above in the response to comment 2. In any case, the tailings surface upon reclamation will be graded to 0.5$. This slope has been demonstrated not to be erosive under any flows. Concerns with tailings erosion were addressed as gart of the adequacy review by the DMG of the approved permit amendment and additional infiormation can be found in the adequacy review responses. Comment: Some of the humidity cell test results look odd, although this observation is certainly limited by my knowledge of the mineralogy of the ore body.