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excursion of the bulk density curve in these strata, indicating the shale and shaley <br />sandstone have very low porosity. Consequently, they would have low permeability. <br />6. The resistivity curve on the log suite does not reach infinite values as it would in dry <br />rock, thus indicating all beds were water-saturated.(see attached interpreted log copy). <br />Calculation of the till-up time of Apex No. 2 Workings <br />Water is assumed to seep from bedrock in the walls and floor of the Apex No. 2 workings on the <br />downdip (north) side of the workings. The updip (south) side of the workings would be dry <br />because it is neaz the outcrop. Seepage from the downdip side of the workings could occur at a <br />velocity on the order of 0.0018 ft. per day (or 0.91 ft per year) calculated as: [(0.00025 ft/day <br />hydraulic conductivity) / (0.02 effective porosity)][0.14 ft/ft hydraulic gradient]. The values in <br />this formula are based on the following information: <br />1. Hydraulic conductivity of 0.00025 fUday. This is the mean conductivity reported <br />by the USGS for shale and siltstone samples from the Williams Fork formation in <br />Routt County (see page 66 of USGS Water-Resources Investigations Report 90- <br />4020). <br />2. Effective porosity of 0.02. This assumed value is a reasonable value for shale, <br />siltstone, and coal, the lithologies exposed in the walls, roof, and floor of the <br />workings. <br />3. Hydraulic gradient of 0.14 fbft. This is slightly steeper than the northwestward dip <br />of bedrock at the Apex No. 2 Mine. <br />Eventually the water level in the workings would rise to the elevation of the highest <br />potentiometric surface of the strata exposed in the workings. Inflow into the mine would cease <br />upon reaching this elevation because all inflow is from rocks that are downdip from the <br />workings. This elevation can be expected to be approximately 7350 feet, based on the sump <br />elevation of the Apex No. 1 Mine and the potentiometric surface in surrounding bedrock that the <br />permittee estimated from pre-mining drillholes (permit page 64). <br />The Apex No. 2 Mine, covers approximately 32 acres below a depth of 7350 ft. The surface area <br />of the floor, roof, and walls in the workings below 7350 ft. is roughly twice the 32 acres, that is <br />64 acres. Seepage would occur from only half of this surface area (the surface area on the down- <br />dip side of the workings). The seepage velocity of 0.0018 ft per year from the 32 acres of surface <br />area in the workings would produce 12 acre-feet of inflow into the mine per year (0.38 ft. X 32 <br />acres). (During mining operations, the 12 acre-feet of inflow per year is assumed to have been <br />consumed by mine operations and evaporated by air-flow through the workings.) The volume <br />inside the workings in the Apex No. 2 Mine below elevation 7350 ft. is an estimated 256 acre- <br />feet. The ]2 acre-feet of inflow per year would fill up the 256 acre-foot volume in 21 years (256 <br />acre-feet/12 acre-feet per year). The actual fill-up time would be significantly longer than 21 <br />years because of a predicted discharge into a sandstone bed as explained below. <br />Page 2 <br />