1990-01-09_REVISION - M1988112 (6)

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-__ 99 01%ii' IE:17 S 303 ?35 5?47 EFV; DEU~!EP. i+? • BATTLE MOUNTAIN RESOURCES, SAN LUIS PROJECT CMLRD ADF4UACY LETTER RESPONSES Page 7 of 28 Initial deposition will result in tailings solutions being directly in contact with the drain layer. However, the potential increase in head during the short period prior to tails covering the drain will be over significantly less area. Total seepage rates during the first year of operation are calculated to be less than these for the case considered above. The extremely law level of seepage predicted by the calculations above, cannot migrate beyond the subsoil immediately beneath the facility ~;nd, therefore, cannot affect hydrologic resources. The monitoring wells were installed immediately downgradient of the tailings facilities and included screen sections in strc~,ta intervals most likely to intercept groundwater flow coming from beneath the tailings facility. If seepage flow from the tailings facility were to occur it would likely take place along the interface between the Santa Fe formation and the overlying alluvial materials, along any extremely porous zones acting as a conduit, and within the groundwater table. The monitor wells were screened at these intervals and will detect any leaks which create flow sufficie^nt to cause migration of fluids. '?. Please discuss whether the co~apletion of angled drill hales within the coJluvium beneath the tailings facility would pro vice beneficial inf,,rmation regarding Leakage through the Liner System. Another approach to leak detection may be to piece slatted ADS piping within r.he compacted colluvial material with an end open to the^ edge of the tailings facility. In any case, a provision to assess and mitigate leakage should 6e addressed. The tailings facility has been designed with a contaiiment system which includes the low permeability characteristics of the tailings themselves, a drainage layer to promote consolidation of the tailings and reduce the hydraulic head on the synthetic membrane liner and compacted subsoil. As discussed in Response 11 above, the potential leakage from the tacility is predicted to increase i.he moisture content of the subsoils sligh°ly, however, saturation is not expected to occur. Angled drill holes or AOS pipe located in the subsoil are unlikely to detect leakage of solution in the unsaturated subsoil. 13, Vlease define the terms lsinfmal and nominal as used in 5ectlon 0.6.5.7 when discussing potential leakage from the disposal facility. Pease discuss how verification of tosses will occur. RE5P0'~~E: Please refer to the response to question 11.