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<br />backfilled and reclaimed, spoil aquifer systems will develop. A <br />portion of the spoils water will recharge the adjacent Wadge Coal <br />and overburden located immediately down gradient of the mined pit. <br />This recharge water is of poor quality, generally being high in TDS <br />and other dissolved constituents. The concentrations of these <br />constituents will exceed concentrations which existed prior to <br />mining. Finally, the base flow which is contributed to alluvial <br />aquifers and streams in Twentymile Park by the Wadge overburden may <br />be affected by the poor quality recharge from the spoils aquifers. <br />As mining progresses, spoils aquifers develop and eventually <br />discharge to the surface water system. This spoils effluent flows <br />down gradient towards Trout Creek, and depending upon time of the <br />year, recharges the associated alluvial body. The addition of this <br />high TDS water to the eastern bank alluvial aquifer system of Trout <br />Creek will cause a diminution of quality in the immediate vicinity <br />of the Edna Mine site. No impact to the west bank alluvium due to <br />spoils aquifer discharges is likely. <br />Mining adjacent to the Trout Creek alluvium in the West Ridge Area <br />has caused the alluvium to dewater into the mining pit. Only minor <br />quantities of water have been induced to flow into the pit, and <br />then only when mining was closest to the alluvium. As distance <br />between the mining activities and the alluvium increases, <br />dewatering of the alluvial aquifer decreases. No drop in the <br />alluvial aquifer water level was observed when mining was closest <br />to the alluvium. If this gradient reversal occurs, it will be for <br />a limited period of time, and will not significantly lower the <br />water level within the alluvium. <br />As is apparent from the preceding discussion, the major impact to <br />the ground water system is the development of spoils aquifers, and <br />their subsequent discharge. <br />As previously discussed, backfilled mining pits resaturate along <br />the base of the mined coal (top of the underburden) to an elevation <br />equal to that of the lowest point (topographically) of the <br />down-slope highwall. When the elevation head of the spoils aquifer <br />exceeds the elevation of the lowest point of the buried highwall, a <br />spoils spring will develop at that location. These springs <br />discharge water which is typically high in total dissolved solids, <br />sulfate, manganese and sodium. It is thought that the spoils <br />discharge will vary with time, dependent upon local climatologic <br />and hydrogeologic conditions. The quality of the discharge is <br />expected to improve with time, however the length of time required <br />prior to a return to undisturbed water quality conditions is not <br />currently known. <br />The permittee has projected the magnitude of TDS loading which the <br />Trout Creek alluvium will receive. In the West Ridge Area, TDS <br />levels in the discharge leaving the area are expected to increase <br />from 2122 mg/1 to 2828 mg/l. This is substantiated by recently <br />collected data from a spoils well on West Ridge. Total dissolved <br />solids were monitored at 2875 mg/1 at this down-gradient well <br />-25- <br />