1998-01-10_REVISION - M1988112 - Laserfiche WebLink

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BATTLE MOUNTAIN RESOURCES, SAN LUIS PROJECT CMLRD ADEQUACY 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 low level of seepage predicted by the calculations ' above, cannot migrate beyond the subsoil immediately beneath the facility and, therefore, cannot affect hydrologic resources. The monitoring wells were installed immediately downgradient of the ' tailings facilities and included screen sections in strata 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 material:c, 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 sufficient to cause migration of fluids. 12. Please discuss whether the completion of angled drill holes within a the coiluvium beneath the tailings facility would provide beneficial information regarding leakage through the liner system. Another approach to Leak detection may be to place slotted ADS piping within ' the 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 be addressed. ' RESPONSE Th t ili f ilit b i d ith i h d t t t : e a ngs ac y as een es gne w a con a nmen sys em 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 facility is predicted to increase the moisture content of the subsoils slightly, however, saturation is not expected to occur. Angled drill holes or ADS pipe located in the subsoil are unlikely to detect leakage of solution in the unsaturated subsoil. 13. Please define the terms minimal and nominal as used in Section D.6.5.1 when discussing potential leakage from the disposal facility. Please discuss how verification of losses will occur. RESPONSE: Please refer to the response to Question I1. 1 I 1