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Evaporation of water in mine does occur. It has not been quantified. Most of the water that evaporates does so before the measurement of inflows. Also, the large areas of water storage in the mine are primarily in sealed areas, • which have negligible evaporative losses. Therefore, any evaporative losses do not enter into the water balance calculations as they relate to determining mine discharge to the receiving streams. Evaporation is not included in the mine water balance. While it does contribute to water loss, it has not been measured. Since all mine inflow used in the water balance are measured or based upon measure flows, the amount lost to evaporation does not affect the net calculated amount sent to storage or discharged. It will affect the total amount removed from the formations. This evaporation has been previously estimated to be 8.6 acre-feeUyear per square mile mined. This was based upon measurements in the Belina Mine in Utah and has been used for "Windy Gap" analyses for the Foidel Creek Mine. As of the end of ]998 approximately 5 square miles have been mined. However, approximately most of the area has been sealed. Only the mains and a maximum of two longwall panels are open at any one time. This is equivalent of an area of 1.5 square miles. This yields an estimated evaporative loss from the formation at 13 acre-feet/year (8gpm). Actual evaporative loss will be lower because most of the longwall panels is either solid (pre-mining) or gob (post-mining) which does not get well ventilated. Based upon this water balance [he estimated Fish Creek Borehole pool volume was 546,000,000 gallons (Exhibit 49, Table E49-3). At the end of the water year 1998, the elevation in the FCB pool was 5882 fr. At that elevation approximately 18,000,000 ftz of working were flooded with an average height of 8.5 fr and an extraction rate of 74% within the panel area, yielding an initial void space of 850,000,000 gallons. Since there will be air pockets developed in the void workings and gob and the gob does not saturate instantly, the water balance estimate of 546,000,000 gallons is reasonable. This also means that the inflow estimates are also reasonable. Water Handling Presently, the mine can handle the net underground water four ways: 1) discharge it to Fish Creek, 2) discharge it to Foidel Creek, 3) reuse it by pumping it into the lmillion-gallon tank, 4) store it in the pool below the FCB, or 5) recycle it back to the Prep Plant as make-up water. Map 16, 1998/1999 Mine Water Balance Map; present the current inflow and outflow of water in the mine. All water except the ground water inflow to the WMD, can be directed to Foidel Creek via site 109 by diverting underground dewatering discharge using existing • piping. In May 1999, a system to recirculate water pumped out of the mine via Site 109 was completed. This allows for some of the water recovered from the mine to be reused for water sprays and cooling. It is anticipated that approximately 100 gpm can be recirculated. This will reduce future discharges by the same amount. Water that is captured in the mine can be directed in a number of directions. The water from the 10 Right borehole can either be directed up the North Mains to Site 109 or can be discharged behind the seals into the WMD where it can be discharged to Fish Creek via Site ] 15. The water from the 6 Right area can either be directed up the North Mains to Site 109 or can be discharged behind the seals into the WMD where it will report to the Fish Creek Borehole sump. From Site 109, the water can be directed to Site ] 14, Pond D for discharge into Foidel Creek, to the lmillion-gallon storage tank, or the pit south of Pond D and then pumped directly into Foidel Creek without being routed through Pond D. As of April 1999, the FCB pool had an elevation of 5905 feet. The pool can not be allowed to exceed 5960 feet because it would then overflow against the seals in the WMD. In order to provide a margin of safety, the pool will be pumped down [o at least an elevation of 5800 feet. This will require a reduction of approximately 50% or 273,000,000 gallons. This water plus inflow to the pool will have to be pumped from the FCB. The timing and water quality issues related to this discharge is discussed in Effects on Ground Water Quality of Aquifers and Surface Water Systems Impacts of Mine Water Dischazge below. Dewaterioe and Potentiometric Drawdowo io Bedrock Units The projected inflows to the mine from the Wadge overburden unit will cause dewatering and potentiometric drawdown in the unit. Where the Twentymile Sandstone directly overlies the mine workings, it will also be affected. In fourteen years of mining no impact at the Trout Creek Sandstone has been observed and water quality data from the mine inflow does not indicate any significant connection to either the overlying Twentymile • Sandstone of the underlying Trout Creek Sandstone. Well 006-82-48A, completed in the Twentymile Sandstone, showed a rapid water level decline before being rendered inoperable due to being undermined by a longwall panel. TR 01-39 2.05-138 8/10/01