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Mountain Coal Companv 1998 Annual Hydrology Report Wesr Elk Mine <br />. Assessment of Mining Impacts to Hydrologic Resources <br />Surface Waterlmpacts <br />While MCC maintains a comprehensive network of streamflow gaging stations throughout the <br />pemtit and lease azeas, few of the monitored streams have been dtrectly within the influence of <br />mining (Map 2) to date. In July 1998, longwall mining progressed into the Minnesota Creek <br />drainage. Flow tables and hydrographs for the surface water stations with continuous recorders <br />are contained in Appendices A and B, respectively. Water quality and field parameters for all <br />surface water stations aze located in Appendix C. These data indicate that there have been no <br />impacts to surface waters due to mining. <br />Impact of TDS on the North Fork <br />WWE evaluated the concentrations of the individual parameters that collectively constitute the <br />TDS in mine discharges, and determined that the pond discharge water is predominantly sodium <br />cazbonate/sodium bicarbonate in nature. Aside from high concentrations of sodium, none of the <br />other parameters, including heavy metals, are found in significant concentrations. There are no <br />applicable numeric standards or criteria for sodium. <br />WWE has reviewed the salinity (TDS) loading analysis in the most recent version of the North <br />Fork Cumulative Hydrologic Impacts Analysis (CHIA), in the context of MCC's WY98 <br />discharges. In the 1997 CHIA, CDMG calculated the cumulative TDS (salinity} loading to the <br />North Fork from coal mines located in the North Fork valley. The assumptions used for MCC's <br />contribution were a discharge rate of 1,000 gpm (2.23 cfs) and a TDS concentration of 2,500 <br />mg/I,. When assessing WY98, the total volume discharged from ponds MB-1, MB-2R, MB-3, <br />MB-5, SG-1, and Lone Pine pipeline was approximately 627 acre-feet, which translates to an <br />average continuous discharge rate of approximately 394 gpm (0.88 cfs). Based on the 1998 <br />Dischazge Monitoring Reports for the ponds, the flow-weighted, maximum TDS concentrations <br />were as follows: MB-1 = 1,190 mg/L; MB-2R = 1,410 mg/L; MB-3 = 170 mg/L; MB-5 = 2,730 <br />mg/I,; SG-1 = 750 mg/L.; and Lone Pine pipeline = 4470 mg/L. Consequently, the annual <br />salinity loading to the North Fork from the West Elk Mine for WY98 was 2,457 tons, which is <br />well below the value assumed in the CHIA as shown in Table ] 0. <br />Table ]0 <br />WY98 Salinity Loading Relative to 1997 CHIA Analysis <br /> Avg. Coatiauous TDS Anaual Salt <br /> Discharge Rate Conceutratioa Loading Percent of CHIA <br />Scenario (gpm) (mg/L) (tons/year) Loading <br />WY98 394 2,750 2,460 43 percent <br />1997 CHIA ],000 2,500 5,670 -- <br /> <br />831- 2.50 Page rig r aierEngineers <br />