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<br />-3- <br />The Eckman Park mine plan calls for an initial boxcut at the deepest planned <br />mining level to be followed by strip mining in incremental stages upslope from <br />the boxcut to the southeast. This will expose the overburden aquifer where it <br />may be under worst case conditions saturated under a maximum piezeometric head <br />of 120 ft. as taken from map 9. The exposed portion of the overburden aquifer <br />will drain water through the highwalls Snto the pit. The applicant used the <br />methods o: Stzlhman to attempt to quantify the rate of dewatering along with <br />the point-sink, constant drawdown equation of Jacob and Lohman. The discharge <br />was found to reach a maximum of 28,000 gpd during the second year of miring in <br />Ecl:man Park. Dewatering will have been reduced to near zero year in the fifth <br />year of mining. This dewatering is not significant since it is only a <br />transient-phenomena. After reclamation the piezeometric surface will begin to <br />recover to approximately its orginal level. However it will no longer be <br />confined. <br />Partial dewatering of the overburden aquifer to the north west of Eckman Park <br />will occur as a result of the construction of the Eckman Park boxcuts. The <br />drawdown will be detected in some of the observation wells but no lowering of <br />water levels is expected because the nearb}• private wells are completed in <br />isolated alluvial aquifers or they are to distant to be affected by mining. <br />Using distance drawdown equations maximum drawdown was calculated for various <br />distances from the boxcut. This data is plotted on [he Twenty mile Park <br />Cumulative Hydrologic Effects (map 53). Water level decline is not expected <br />to be measurable more than 5000 f[. from [lie boxcut. At a distance of <br />approximately 1006 ft. from the boxcut the maximum drawdown will be 7.5 ft. <br />These simplified calculations do not take into account the gradient of the <br />piezometric surface, the effect of faulting, and the preferred direction of <br />ground water flow in the aquifer. Pumping tests performed b}• the applicant <br />indicate that the faults in the Eckman park area are cemented and act as <br />aqui[ards and therefore if accounted for in the drawdown model would decrease <br />the affects of drawdown on distance. In addition, maximum projected <br />dewatering rates were used. Therefore the simulation represents the worst <br />case condition. This minor amount of drawdown will only be temporary and will <br />recover after reclamation when pumping from the boxcuts Ss haulted. <br />The proposed method of mining will result in greater postmining permeability <br />and recharge capacity in the mine plan area. In the undisturbed condition, <br />confining layers of shale overlying the overburden aquifer prevents recharge <br />by downward percolation. !lining in Eckman Park and completion of mining in <br />Energy Mine (~1 will result in an expansion of the postmining recharge area so <br />as to include the entire Eckman Park and Energy Mine t: o. 1 mined areas. The <br />present recharge area of the overburden aquifer is currently a narrow subcrop <br />where the aquifer is exposed beneath the topsoil along the south and west <br />boundaries of the permit area, (Eckman Park Overburden Aquifer Piezometric <br />Surface, map 12). <br />