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Mounmin Coa/ Compam~ 1999 Annual Hydrology Report West Elk Mine • Assessment of Mining Impacts to Hydrologic Resources Surface Water Impacts While MCC maintains a comprehensive network of streamflow gaging stations throughout the permit and lease azeas, few of the monitored streams have been directly within the influence of mining (Map 2) to date. In July 1998, longwall mining progressed into the Minnesota Creek drainage. Flow tables and hydrographs for the surface water stations with continuous recorders aze contained in Appendices A and B, respectively. Water quality and field parameters for all surface water stations aze located in Appendix C. These data indicate that there have been no impacts to surface waters due to mining. Impact of TDS on the North Fork WWE evaluated the concentrations of the individual parameters that collectively constitute the TDS in mine discharges, and determined that the pond discharge water is predominantly sodium carbonate/sodium bicarbonate in nature. Aside from high concentrations of sodium, none of the other parameters, including heavy metals, are found in significant concentrations. There are no applicable numeric standards or criteria for sodium. WWE has reviewed the salinity (TDS) loading analysis in the most recent version of the North Fork Cumulative Hvdrologic Impacts Analysis (CHIA), in the context of MCC's WY99 discharges. In the 1997 CHIA, CDMG calculated the cumulative TDS (salinity) loading to the • North Fork from coal mines located in the North Fork valley. The assumptions used for MCC's contribution were a discharge rate of 1,000 gpm (2.23 cfs) and a TDS concentration of 2,500 m@/L. When assessing WY99, the total volume discharged from ponds MB-l, MB-2R, MB-3, MB-5, SG-1, and Lone Pine pipeline was approximately 511 acre-feet, which translates to an average continuous discharge rate of approximately 317 gpm (0.71 cfs). Based on the 1999 Discharge Monitoring Reports for the ponds, the flow-weighted, maximum TDS concentrations were as follo+as: MB-1 = 0 mg/L; MB-2R = 430 mg/L; MB-3 = 770 mg/L; MB-5 = 290 mg/L; SG-1 = 590 mg/L; and Lone Pine pipeline = 3550 mg/L. Consequently, the annual salinity loading to the North Fork from the West Elk Mine for WY98 was 1,919 tons, which is well below the value assumed in the CHIA as shown in Table ] 0. Table 10 WY99 Salinity Loading Relative to 1997 CHIA Analysis Avg. Continuous TDS Annual Sslt Discbarge Rate Concentration Loading Percent of CHIA Scenario (gpm) (mg/L) (tons/year) Loading WY99 317 2,760 1,920 34 percent 1997 CHIA ],000 2,500 5,670 -- • 831-031.510 Page23 Wright [SalerEngineers