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y information in a report to the WQCD regarding the mine water inflow event that occurred January 20, 1997, and the direct discharge that was authorized by the WQCD. In regards to Outfall O15 for the Refuse Pile Expansion (RPE) pond, discharge would consist primari/y of surface runoff from the pile as it is built (the RPE has not yet been permitted by the CDMG to be constructed). The RPE pond has been designed to collect surface runoff from the RPE and any water from the underdrain. Design requirements for an underground development waste pile such as the RPE, include an underdrain to capture any water that may percolate through the pile. In addition, there aze a few springs in the area of the pile that will be collected by lateral branches of the underdrain and connected to the main underdrain. Therefore, water that may be dischazged from the underdrain may include leachate, as well as water from springs. The underdrain design of MCC's Lower Refuse Pile (I.RP), which is the refuse pile currently utilized at the West Elk Mine, is the same. Any water from the underdrain, which also may consist of leachate and spring water, is discharged to pond MB-2R (Outfa11004). It has been MCC's experience that there is only enough water in the underdrain to create a damp area where the drain daylights. It is unlikely that this "water" will ever flow into the pond. MCC expects the RPE underdrain will exhibit similaz "flows". The amount of leachate to be produced in the RPE has been very conservatively estimated. This estimate is included in the RPE revision application to CDMG and is included for your information. Leachate volume is a function of the amount of precipitation, runoff, evapotranspiration, and infiltration into the pile, and based upon parameters defining climate, vegetative cover, soil cap, surface grade, and subsurface permeability. The estimate of leachate volume was obtained using the U.S. Army Corps of Engineers "Hydrologic Evaluation of Landfill Performance (I-IELP) Model", Version 3, September, 1994. Please note that leachate production has been conservatively estimated by increasing the monthly precipitation average for May from 1.33 inches to 3.6 inches. Also included in this submittal is a table which summarizes leachate production during the three phases of pile construction (refuse will not be placed in the pile until Phase 2). As you will note, the highest amount of leachate will be produced during Phase 2, but because this phase will last only approximately two months, it is more appropriate to consider the amount of leachate to be produced during Phase 3. Also enclosed, is a table entitled "Refuse Pile Expansion Surface Runoff and Leachate Calculations" which provides a more typical estimation of leachate. The average annual underdrain flow during Phase 3 is predicted to be 0.7 gpm. The underdrain peak flow from a 100-year, 24-hour event during Phase 3 is predicted to be 4 gpm. In comparison, the peak flow surface runoff is predicted to 285 gpm. Therefore, any discharge from the sedimentation pond will be primarily surface runoff. In addition, the pond has been designed to completely contain the runoff and sediment volume from a 100-year, 24-hour storm event. As is the case with Outfall 013, MCC has not experienced high concentrations of "heavy metals" nor expect to. The underground development waste will continue to originate from the B seam, as what is currently being disposed of on the LRP. MCC has not been able to collect a sample from the LRP underdrain because there has never been any concentrated flow. However, MCC has determined the acid-base potential of the strata enclosing the B, E, and F-Seams. The LRP