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' Ja„uary 1994 /dn Coa! Cwnpa,+y * 199.7 Annual Hydrology Feprnl • .7 ' 3.0 MINE AREA CONFINED GROUND WATER I Confined ground water falls into two categories: Mine Area Coal Aquifer and Mine Area Overburden. The Mine Area Coal Aquifer is monitored at a cell designated as 79-61. This well is located just north of Pit 1, along Bush Draw, in the undisturbed coal seam. ' The Mine Area Overburden wells are designated as 79-1 and 79-2. These wells are located at [he north and south ends of the 720 Pit, adjacen[ w the east crest of the pit. ' Wafer levels were measured and samples taken during October 1992 and April 1993 as designated in the Monitor+ng Plan. The field data from the Confined Ground Water Wells are contained in Exhibit A, 1993 Field Data. The individual analyses of samples collected are I presented in Exhibit B, 1993 Coal Aquifer Water Quality Analyses and Exhibit C, 1993 Overburden Water Quality Analyses. The data are summarized on Table 1, 1993 Ground Water Statistics. I 3.1 MINE WATER COAL AQUIFER During the 1993 water year, a limited amount of ground water was visually observed or ' encountered in Pit 1 (Site 328) indicating no obvious impact on ground water resources, however, the majority of the water that was encountered was a resuh of snowmelt and precipi[ation. The 720 Pit has contained water since mining ceased. The coal seam has been I removed from the north and the south of this pit, therefore the slow accumulation of water in this pit indicated that surface runoff is the prime contributor. I The mine area coal aquifer well (79-tit) was monitored and sampled in October 1992 and April 1993. Table 1, 1993 Ground Water Statisua, presents the water quality summary for the year. The coal aquifer remains much lower in total dissolved solids than the overburden aquifer, I indicating perched aquifers with no intermixing. For comparison purposes, the mean field parameter values and analyses parameter values for the last five years are presented in Table 2, Historic Mine Area Coal Aquifer Water Quality Data. 3.2 MINE AREA OVERBURDEN I As previously stated, limited ground water was encountered during the year, indicating no tmpatt on groundwater resources. Table 1, 1993 Ground Water Statistics presents a summary of the field and lab results for the year from wells 79-1 and 79-2. ' For comparison purposes, the mean field parameter values and analyses parameter values for the last five years are presented in Tables 3 and 4, Historic Mine Area Overburden Wafer Quality Data. As shown, there have been fluctuations in concentration values, but there does not seem to be an identifiable trend. TrrraMarn.r/ACZ La. * P.O. 8os 774018 " Slcamlx~a7 Spru+gs, Colorado 80977 (303J 8196250