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Mr. Michael R. Neumann October I5, 1997 Page 4 take 30 years for the back-filled pit to fill with water and for water to spill out and flow from RSP-4. The re-established flow from RSP-4 was predicted to be at pre-mining levels, which based on the sample taken 5/ 16/77 was seeping at less than 1 gpm. Ground water flow and quality -Note on ground water flow velocity The operator calculated that the ground water that is monitored in bedrock aquifers in the three wells in the permit azea flows generally northeastwazd at an average rate of 0.0142 feet per day, or approximately 5 feet per year (see Permit Application, Volume IA, Section 2.04.7, Table 16). This velocity of 5 feet per year appears reasonable compared to the velocity range of 0.5 to 30 feet per yeaz that was reported by the USGS for rocks in the region that are of lithologies (siltstones and shales) similaz to those in the HG Mine aquifers, but are stratigraphically lower in the Williams Fork Formation (iJSGS Water Resource Investigations Report 90-4020, page 84). Ground water flow and quality - HG-1 Water levels and parameter concentrations in this well have fluctuated within a narrow range since monitoring began in 1987. Water from this well is suitable for drinking water use. This well is located approximately 175 feet down-gradient from the reclaimed shop area. If ground water is moving at 5 feet per yeaz (see note above), ground water from the reclaimed shop azea may not have reached this well yet because it would take 35 yeazs (175 feet = 5 feet/yeaz) to travel the 175-foot distance. If. fractures aze present in the bedrock aquifer, the traveltime could be reduced to much less than 35 yeazs. Ground water flow and quality - HG-2 Like HG-1, water levels and parameter concentrations in this well have fluctuated within a narrow range since monitoring began in 1987. Water from this well is suitable for drinking water use. This well was drilled as the down-gradient monitoring well for the now spoils-filled pit. This well is located approximately 900 feet east of the reclaimed pit azea, and is probably east of the flowpath ofpre-mining ground water that previously flowed through the pit azea. Since the pit was mined out, ground water has probably flowed into the pit, and not eastward toward the HG-2 well. It is unlikely that any ground water could flow from the pit to the HG-2 well until at least the lower (northern) half of the pit fills with water. Then, water from the pit must overcome the pore-entry pressure of the face of the east high-wall and migrate eastwazd through 900 feet of bedrock to the HG-2 well. If ground water is moving at 5 feet per yeaz (see note above), ground water from the pit will reach this well in 180 years. If fractures aze present in the bedrock aquifer, then the traveltime could be reduced to much less than 180 years. Comparison of data in report with past data and permit requirements. The surface and ground water data contained in the report are consistent with previous monitoring data and support the probable hydrologic consequences (PHC) described in the permit application, with the following exception.