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For worst-case conditions, we can assume a value for the vertical hydraulic gradient of I.O, which corresponds to <br />essentially saturated gravity drainage. The vertical seepage rate is thus estimated to be in the order of 0.0001 <br />• ft/day. Total seepage, Q[o[, is given by: <br />Qtot = QA <br />where: <br />A =area of saturated backfill <br />The area of saturated backfill in the Eckman Park and Mine # I operations projected to exist at the end of the <br />mining operation was approximately 4,000 acres. The total quantity of recharge to Trout Creek attributable to <br />vertical leakage from [Ire overlying saturated backfill, was therefore estimated at about 130,000 gpd. <br />During the period when elevated solute concentrations are expected to exist in the overlying backfill areas, <br />approximately 235 years, the total contribution is calculated to be in the order of 34,310 acre-ft. This constitutes <br />less [Iran 2 percent of the total water stored in the Trout Creek Sandstone so that the effects of the backfilled areas <br />at the Eckman Park Tract is anticipated to be localized and, in the long term, [o be negligible. <br />• Data from the ongoing hydrologic monitoring program will be used to quantify any change in dissolved solids <br />concentration of the groundwater system in excess of natural baseline variations which might be related to the <br />mining operations. <br />De~vaferine of the Overburden Aquifer and Changes in the Piezometeric Surface <br />The areas disturbed by mining at the Eckman Park operation are within the unconfined part of the Wadge <br />Overburden aquifer, where the overburden materials are typically only partially saturated. Poten[iometric levels in <br />the Wadge Overburden aquifer are typically less than b0 feet above the base of the Wadge Coal Seam in the mine <br />area. Due to the relatively small elevation difference between the potentiometric <br />r~ <br />L <br />1496 Permit Ren. Permit Renewal 780-144-21 Revised 3/18/97 <br />