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Mr. Michael R. Neumann <br />October I5, 1997 <br />Page 4 <br />take 30 yeazs for the back-filled pit to fi[I with water and for water to spill out and flow from <br />RSP-4. The re-established flow from RSP-4 was predicted to be at pre-mining levels, which <br />based on the sample taken 5/16/77 was seeping at less than 1 gpm. <br />Ground water flow and quality - Note on~round water flow veloc~ <br />The operator calculated that the ground water that is monitored in bedrock aquifers in the three <br />wells in the permit area flows generally northeastward at an average rate of 0.0142 feet per day, <br />or approximately 5 feet per year (see Permit Application, Volume lA, Section 2.04.7, Table I6). <br />This velocity of 5 feet per year appears reasonable compared to the velocity range of 0.5 to 30 <br />feet per year that was reported by the USGS for rocks in the region that are of lithologies <br />(siltstones and shales) similar to those in the HG Mine aquifers, but are stratigraphically lower in <br />the Williams Fork Formation (USGS Water Resource Investigations Report 90-4020, page 84). <br />Ground water flow and quality - HG-1 <br />Water levels and parameter concentrations in this well have fluctuated within a narrow range <br />since monitoring began in 1987. Water from this well is suitable for drinking water use. This <br />well is located approximately 175 feet down-gradient from the reclaimed shop azea. If ground <br />water is moving at 5 feet per year (see note above), ground water from the reclaimed shop azea <br />may not have reached this well yet because it would take 35 years (175 feet _, 5 feet/yeaz) to <br />travel the 175-foot distance. If fractures are present in the bedrock aquifer, the traveltime could <br />be reduced to much less than 35 yeazs. <br />Ground water flow and quality - HG-2 <br />Like HG-1, water levels and parameter concentrations in this well have fluctuated within a <br />narrow range since monitoring began in 1987. Water from this well is suitable for drinking <br />water use. This well was drilled as the down-gradient monitoring well for the now spoils-filled <br />pit. This well is located approximately 900 feet east of the reclaimed pit area, and is probably <br />east of the flowpath ofpre-mining ground water that previously flowed through the pit azea. <br />Since the pit was mined out, ground water has probably flowed into the pit, and not eastward <br />towazd the HG-2 well. It is unlikely that any ground water could flow from the pit to the HG-2 <br />well until at least the lower (northern) half of the pit fills with water. Then, water from the pit <br />must overcome the pore-entry pressure of the face of the east high-wall and migrate eastwazd <br />through 900 feet of bedrock to the HG-2 well. If ground water is moving at 5 feet per yeaz (see <br />note above), ground water from the pit will reach this well in 180 years. If fractures aze present in <br />the bedrock aquifer, then the traveltime could be reduced to much less than 180 years. <br />Comparison of data in report with past data and permit requirements. The surface and <br />ground water data contained in the report are consistent with previous monitoring data and <br />support the probable hydrologic consequences (PHC) described in the permit application, with <br />the following exception. <br />