2015-08-18_PERMIT FILE - C1982056A (4)

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Park Basin. In these areas the unit is overlain by about 300 feet of bedrock including the Wadge overburden. The quantity of recharge passing through to the Trout Creek Sandstone in these areas is governed primarily by the vertical permeability of the overlying bedrock units and the extent of the potential recharge area. This area is limited to the dip slopes where the Twentymile Sandstone has been removed by uplift and erosion. Vertical permeability of the Wadge overburden has been estimated at 0.013 ft/day, about one -third of the horizontal permeability, from pumping tests. The ratio of average vertical permeability to average horizontal permeability of the lithologic units underlying the Wadge Coal Seam, including the Wadge/Wolf Creek Interburden and Wolf Creek Seam, can reasonably expected to be similar to that of the Wadge Overburden, giving an estimated vertical permeability of 0.0005 ft/day. Vertical leakage is actually influenced primarily by the vertical permeability of the lowest permeability units. The USGS have measured values in the order of 0.0001 ft/day for lithologic units which constitute a large proportion of the sequence overlying the Trout Creek Sandstone. This value is believed to be appropriate for estimating seepage rates. Vertical seepage is calculated from the one - dimensional flow equation: Q =KI where: Q = flow rate (ft/day) K = vertical permeability (ft/day) I = vertical hydraulic gradient (dimensionless) For worst -case conditions we can assume a value for the vertical hydraulic gradient of 1.0 which corresponds to essentially saturated gravity drainage. The vertical seepage rate is thus estimated to be on the order of 0.0001 ft/day. Total seepage, Qtot, is given by: Qtot = QA where: A = area recharge The total area of potential recharge to the Trout Creek Sandstone within the Twentymile Park Basin is estimated to be about 5 square miles. The total quantity of recharge to the Trout Creek is therefore estimated at about 100,000 gpd or 115 acre -ft per year. Discharge from the Trout Creek Sandstone is assumed to be at a rate similar to the calculated recharge rate if the aquifer is in dynamic equilibrium. Most of the discharge from the aquifer is believed to occur in the vicinity of the unit outcrop in the northeastern margins of the basin following the trend of the other bedrock aquifer units. Storage within the Trout Creek Sandstone may be estimated using the same technique as described above. The areal extent of the aquifer in the Twentymile Park Basin is about 75 square miles and the average thickness of the unit is about 75 feet. Assuming a fracture porosity of about 0.1 and a confined storage coefficient of about 0.0001 yields a total storage of about 360,000 acre -ft. The SWMD contains the Fish Creek Sandstone, a local sandstone unit, which is approximately 25 feet thick. Approximately 200 feet of interburden separate it from the Twentymile Sandstone. The Fish Creek Sandstone underlies the Fish Creek Coal Seam, which was mined from the adjacent CYCC's Mine No. 2. The Fish Creek Sandstone is characterized as tan- to white - color, quartz rich, fine - grained, and laminated. In the area of the SWMD it may serve as the source of two springs located in the north half of Section 36, TSN, R87W. The location of these two springs is shown on Map 13. The two springs flow at approximately 5 gpm or less, based upon field survey work completed during the fall of 1991. During the first quarter of 1992, the two springs were monitored and their flow rates were measured at 5 gpm or less. Two wells were completed in the Fish Creek Sandstone, and water levels have been monitored on a quarterly basis from these wells. Hydrologic data for these sites can be found in Exhibit 6A. Alluvial Aquifers Recharge and discharge of alluvial aquifers typically occurs as a seasonal cycle in response to snowmelt and normal variations in precipitation. In the spring, snowmelt and high runoff levels result in recharge of the alluvial. TR13 -83 2.04 -28 11/03/14