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As previously discussed, backfilled mining pits will resaturate along the base of the mined coal (top of the underburden) to an elevation equal to that of the lowest point (topographically) of the downslope highwall. When the elevation head of the spoils aquifer exceeds the elevation of the lowest point of the downslope highwall, a spoils spring will develop at that location. These springs discharge water which is typically high in TDS, sulfate, manganese and sodium. It is thought that the spoils discharge will vary with time, dependent upon local climatologic and hydrogeologic conditions. The quality of the discharges is expected to improve with time, however, the length of time required prior to measuring acceptable (i.e. approximating baseline conditions) water quality, is not currently known. When Peabody Coal Company can demonstrate that the reclaimed lands meet the phase II bond release criteria, the sediment ponds, excepting the Wadge, Pond 003, and PeCoCo Impoundments, which are approved permanent impoundments, will be removed from the site. At that point in time, it is assumed that the majority of baseflow to Cow Camp, Bond and Grassy Creeks will be contributed by spoil aquifer discharges to the surface system. In the Grassy Creek Drainage, the quantity and quality of the flows will be similar to present conditions. All of the spoil spring discharges issuing into the Grassy Creek drainage will pass through the Wadge Impoundment, a permanent structure. Dilution and mixing within the impoundment will limit the concentration of dissolved solids discharged to the alluvial system. As mining continues in this drainage, some increase in dissolved constituents is expected. Data collected at NPDES sites 002 and 003, which discharge disturbed area drainage into Grassy Creek, indicate that there has been an increase in TDS, based on monthly average concentration (June through September) on a yearly basis for the years 1982 through 1991. It should be noted, however, that the rate of increase, based on monthly average TDS concentration on a yearly basis, appears to have stabilized during this period. Therefore, it is not expected that the quality of the effluent will further degrade the alluvial water quality in the Grassy Creek Drainage. In the Cow Camp and Bond Creek drainages, Wadge spoils aquifer discharges will contribute flow to these tributary creeks and eventually to Fish Creek. During the months of June and July, Cow Camp Creek and Bond Creek sustain flow their entire length to fish Creek. During this period, each creek contributes water to the associated alluvial aquifers. The spoils spring discharges are sufficiently diluted by snowmelt runoff to preclude degradation to the quality of the alluvial aquifers in these drainages. (See the Surface Water section of this Probable Hydrologic Consequences statement for further discussion regarding surface water impacts.) Information supplied by Peabody Coal Company indicates that at their confluences with Fish Creek, Cow Camp Creek and Bond Creek do not support flow during the months of August and September. It is assumed that during this period of time, Cow Camp and Bond Creek flow for about 2 miles beyond the disturbed area boundary before becoming ephemeral. At the point where the streams become ephemeral, it is assumed, for purposes of this discussion, that the flow in each drainage is 0.2 cfs with a TDS concentration of 2500 mg/1. _27_