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April 2021 MNGW-1 pH Memo+S <br /> 3.2 AQUIFER PROPERTIES <br /> A thin deposit of colluvium, up to approximately 25 feet thick, occurs northeast of the <br /> Henderson Mine surface facilities and overlies granitic bedrock. The colluvium forms a <br /> shallow unconfined aquifer system with seasonal variations in saturated thickness (10 to 23 <br /> feet), with water levels rising during rainfall and snowmelt events. Falling head tests were <br /> conducted on MNGW-3 and MNGW-4 following well installation and development in 2014. <br /> The hydraulic conductivity of the colluvium is estimated at 1 to 3 ft/day based on the results <br /> of these tests. Based on an average hydraulic gradient (0.08 ft/ft) and hydraulic conductivity <br /> estimates derived from the falling head tests, and assuming an effective porosity of 0.2, the <br /> estimated groundwater velocity in the shallow colluvial aquifer is 0.4 to 1.2 ft/day, or 145 to <br /> 440 feet per year. <br />