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

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RULE 2 PERMITS Most of this water is expected to eventually contribute to seeps and springs tributary to Good Spring Creek. This suggests that it is possible that a reclaimed pit aquifer (if it develops) will flow entirely into the undisturbed strata, and that there will be no or limited discharge into the surficial alluvium/colluvium from the reclaimed pit. Whether the pit aquifer discharges into the bedrock of the Williams Fork Formation or into surface colluvium, it will eventually contribute to the alluvial aquifer and springs tributary to Good Spring Creek. To evaluate the possible effects of infiltration from the pit areas, a velocity calculation for average groundwater flow can be performed. The calculation is based upon the parameters determined for the Williams Fork Formation as discussed above. Seepage velocity (vs), the true velocity representing the rate the groundwater flows through the pore spaces can be calculated utilizing the following formula (Fetter 2001): vs = Kdh/nedl where: • K is the hydraulic conductivity, • dh is the vertical difference in groundwater elevations between two points, and • ne is the effective porosity, and dl is the distance between the two points. Although the strata between the pit and the creek are discontinuous, the elevation difference between the pit aquifer and Good Spring Creek (500 feet) and the horizontal distance between the edge of the pit and Good Spring Creek (3000 feet) will be used. The gradient would approximate the dip of the lithology in the area. Assuming an effective porosity of 0. 15, with an average hydraulic conductivity of 1 ft/d for the Williams Fork Formation, then: vs = (1 ft/d) (5 00 ft) / (0.15) (3,000 ft) vS = 1.11 ft/d The average groundwater velocity of outflow from the South Taylor pit is calculated to be 1.11 ft/d, with the flow presumed to be predominantly in a southeasterly direction following the dip of the southeast dipping leg of the small anticline (refer to Map 7A). Thus, the first pit outflow through the bedrock strata would take about 2700 days or about 7 years to flow from the pit to the creek. Potential Surface Water Quantity Impacts As described above, diminishment of flow into Good Spring Creek appears to be probable during and for a period after mining and reclamation of the South Taylor pit is finished. The reduction can be estimated by assuming no meteoric water infiltrating into the reclaimed pit will reach the creek from a pit aquifer for approximately 45 years after the end of operations (the time to saturate the pit - see above) or that springs located downgradient from the mine will cease flowing during and for a time after mining. The area of the South Taylor pit is approximately 1,000 acres. Assuming that 1.8 inches of precipitation infiltrates, the pit will receive approximately 150 ac -ft per year, or 92 gpm or 0.21 cfs of recharge from infiltration as shown in the preceding paragraphs. Much of this infiltration may eventually surface at springs, likely in West Fork Good Spring Creek. South Taylor/Lower Wilson — Rule 2, Page 83 Revision Date: 4/7/17 Revision No.: RN -07