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Permit C-81-071 1996 Annual Hydrology Report GROUND WATER MONITORING BEDROCK The Wadge Overburden formation (including the Wadge coal seam) overlies the Trout Creek Sandstone and underlies the Twentymile Sandstone. Four wells in the Wadge Overburden (which includes the Wadge Coal) are monitored in the vicinity of Mines No.1 and Eckman Park. Wells 009-79-4, 006-82-74C, 94M001, and 94M002 require semi-annual monitoring for water levels, field parameters, and water quality samples. Required monitoring for these wells was completed in 1996 with field measurements obtained and water quality samples collected during April, May, and September. Beginning in 1995, monitoring wells 026-79-4 and 026-79-6 were replaced by 94M001 and 94M002. Tables 4 through 7 provide summaries of the 1996 Water Year data collected at each site. Tables 4a through 7a provide period of record statistical summaries of collected data at each site. Tables 4b through 7b provide period of record water level summaries for each site. Figures 4 through 11 provide graphical representations of water levels TDS concentrations recorded at each site. The potentiometric surface in the Wadge Overburden is generally observed to slope from south to north in monitored wells in the vicinity of Mine 1 and Eckman Park as shown by water levels in wells 009-79-4, 006-82-74C, 94M001, and 94M002. During 1996, water levels in wells 009- • 79-4 (Figure 6) and 006-82-74C (Figure 4) returned values comparable to 1995 figures with a more pronounced seasonal fluctuation evident and probably due to the wetter than usual spring occurring in 1996. Well 94M001 (Figure 8) continued to show a steady water level. Well 94M002 exhibited minor seasonal fluctuation (approximately 2') and returned values consistent with previous data. The water quality data for the Mine No. 1 Wadge Overburden wells are summarized on Tables 4 through 7. Plots of dissolved solids concentrations are presented on Figures 5, 7, 9, and 11. The baseline water quality of the Wadge overburden is a mixed type water with a dissolved solids level ranging from 500 mg/I to 3500 mg/L. Elevated dissolved solids levels in wells 006- 82-74C and 009-79-4 appears to correlate somewhat with seasonal recharges from the spoil aquifer following backfilling and reclamation, indicating that they are affected by seepage from the spoils aquifer. Wells showing elevated dissolved solids tend to also have elevated sulfate, calcium and magnesium and reduced SAR compared with undisturbed Wadge Overburden groundwater chemistry. This is consistent with mixing with spoil waters which are typically characterized by elevated dissolved solids, sulfate, calcium and magnesium as discussed below. Well 009-79-4 dissolved solids in 1996 were more typical of the normal levels recorded for this site following higher levels recorded in 1995. TDS levels in wells 94M001 and 94M002 are noted to be significantly lower than those recorded in wells 006-82-74C and 009-79-4. The data does not indicate any significant changes in the trace metals concentrations. No anomalous water quality impacts attributable to mining were evident in data collected from Wadge Overburden wells during 1996. Two monitored parameters at well 009-79-4 (Table 5) were observed to return values beyond the previously established ranges. Anew minimum • SAR value was established in April of 1996, and a new maximum pH was recorded in September. The previously recorded maximum pH was 8.8 for this well. CYCC will continue to monitor this situation as increased pH values have also recently been recorded at other I'\DOCUMENTIAHR\ECKMAN\EP96TE%T.DOC 0928197 Page 2