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Vertical permeability measurements of the Wadge overburden has been estimated at 0.013 ft/day from pumping tests. <br />• The average vertical permeability of the lithologic units underlying the Wadge Coal Seam is expected to be similar to <br />this value. Vertical leakage is actually influenced primarily by the vertical permeability of the lowest permeability <br />units. The USGS have measured values in the order of O.000I ft/day, for lithologic units, which constitute a large <br />proportion of the sequence overlying the Trout Creek Sandstone. This value is believed to be appropriate for <br />estimating seepage rates. Vertical seepage is calculated from the one-dimensional flow equation: <br />where: <br />Q=KI <br />Q = flow rate (ft/day) <br />K = vertical permeability (ft/day) <br />I = vertical hydraulic gradient (dimensionless) <br />For worst case conditions we can assume a value for the vertical hydraulic gradient of I.0 which corresponds to <br />essentially saturated gravity drainage. The vertical seepage rate is thus estimated to be in the order of 0.0001 ft/day. <br />Total seepage, Qtot, is given by <br />Qtot = QA <br />where: <br />A = area recharge <br />The total area of potential recharge to the Trout Creek Sandstone within the Twentymile Park Basin is estimated to be <br />about 5 square miles. The total quantity of recharge to the Trout Creek is therefore estimated at about 100,000 gpd or <br />115 acre-ft per year. <br />• Discharge from the Trout Creek Sandstone is assumed to be at a rate similar to the calculated recharge rate if the <br />aquifer is in dynamic equilibrium. Most of the discharge from the aquifer is believed to occur in the vicinity of the <br />runt outcrop in the northeastern mazgins of the basin following the trend of the other bedrock aquifer units. <br />Storage within the Trout Creek Sandstone may be estimated using the same technique as described above. The areal <br />extent of the aquifer in the Twentymile Park Basin is about 75 square miles and the average thickness of the unit is <br />about 75 feet. Assuming a fracture porosity of about 0.1 and a confined storage coefficient of about 0.0001 yields a <br />total storage of about 360,000 acre-ft. <br />The southwest mining district contains the Fish Creek Sandstone, a local sandstone unit, which is approximately 25 <br />feet thick. Approximately approximately 200 feet of interburden separate it from the Twentymile Sandstone. The <br />Fish Creek Sandstone underlies the Fish Creek Coal Seam, which was mined from the adjacent Colorado Yampa Coal <br />Compan~s Mine No. 2. <br />The Fish Creek Sandstone is characterized by its tan- to white-color, quartz rich, fine-grained and laminated. [n the <br />area of the southwest mining district it may serve as the source of two springs located in the north half of section 36, <br />TSN, R87W. The location of these two springs is shown on Map 13. <br />The two spring's flow at approximately 5 gpm or less, based upon field survey work completed during the fall of <br />1991. During the first quarter of 1992 the two springs were monitored and their flow rates were measured at 5 gpm or <br />less. Two wells were completed in the Fish Creek Sandstone, and water levels will be monitored on a quarterly basis <br />from these wells. Hydrologic data for these sites can be found in Exhibit 6A. <br />. Alluvial Aquifers <br />Recharge and discharge of alluvial aquifers typically occurs as a seasonal cycle in response to snowmelt and normal <br />variations in precipitation. In the spring, snowmelt and high runoff levels result in recharge of the <br />APPR®11ED APR 2 4 2000 <br />Permit Renewal No. 3 2.04-28 4/1/99 <br />