2020-03-24_PERMIT FILE - C1981019A (2)

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RULE 2 PERMITS and the porosity of the materials within the pit. Published infiltration rates for the area are 0.5 inches per year (Rice, 1979) and 3 inches per year (Williams & Clark, 1992), for an average value of 1.8 inches per year. Calculated inflows, in the above equations, indicate an inflow rate 92 gpm (approximately 150 acre-feet/year from 1.8 inches infiltration over 1,000 acres) from infiltration due to precipitation. (No other water is expected to flow into the reclaimed pit materials since the South Taylor Pit is on a topographic and structural high). The volume of water needed to fill the reclaimed pit divided by the infiltration rate equals the time to fill the pit to form an aquifer necessary for sufficient outflow. The result of this calculation is approximately 45 years for pit resaturation to the elevation of the lowest point of the pit boundary where water could be discharged. This assumes no water infiltrates into the undisturbed Williams Fork Formation on the limits of the reclaimed pit, and the entire pit fill becomes saturated. It is possible that the pit fill will be anisotropic and heterogeneous in a way that can allow a pit spring to form prior to complete saturation of the pit fill. It is also possible that most or all of the pit water will enter the Williams Fork Formation (see discussion below) thereby reducing the time to reach saturation or preventing the full thickness from becoming saturated. Groundwater from the reclaimed South Taylor pit will eventually discharge into Good Spring Creek at the drainage that is above the Sturgeon Flume (the unnamed tributary to West Fork Good Spring Creek in Section 21). This would result in a pit spoil spring and/or discharge through colluvial and shallow bedrock groundwater infiltration. This water would likely have the same characteristics as the water in the Streeter Fill well or the Streeter pond or in similar spoil springs (Williams and Clark, 1994). Analytical data for these sampling points are summarized on Table 2.04.7-31. If all of the water that infiltrates into the pit discharges into Good Spring Creek, then 150 acre-feet per year or 92 gallons per minute (0.21 cfs) of pit spoil water will enter the Good Spring Creek drainage. This is more flow than originates from the potentially -impacted springs, which have an average annual flow of 77 gpm. The alluvial aquifer associated with Good Spring Creek has a high transmissivity and is unconfined. Possible impacts to this aquifer would be associated with the infiltration of water from the pit and water quality deviations caused by infiltration of runoff water. The preferential flowpath of bedrock groundwater from the reclaimed pits would tend to be down -dip through and between the different strata of the Williams Fork Formation. The discharge would be to springs and, thus, some groundwater could eventually recharge the alluvial material of Good Spring Creek. Transmissivity of the Williams Fork Formation is presented in Section 2.04.7. Measured and published transmissivities of the upper Williams Fork Formation average about 50 square feet per day (ft2/d). The average hydraulic conductivity of the formation is about 1 foot per day (ft/d). The values utilized to calculate these averages are presented in Table 2.04.7-26 and are from published data (Robson and Stewart, 1990; tables 5 and 6; upper member Williams Fork Formation). A rectangular infiltration area in the undisturbed pit highwall of 133 feet long by 133 feet high could transmit all of the estimated 92 gpm (approximately 150 acre-feet) of annual recharge from the reclaimed pit. This is calculated as follows: Annual seepage from the pit = (133 ft high)(133 ft long)(1 ft/d) = 17,710 ft3/d = 150 ac-ft/yr. With approximately 400,000 square feet of buried highwall, all of the meteoric water infiltrating into the reclaimed pit that contacts the pit wall is expected to enter the strata of the Williams Fork Formation. South Taylor/Lower Wilson — Rule 2, Page 82 Revision Date: 4/7/17 Revision No.: RN -07