2014-07-11_REPORT - C1980007 - Laserfiche WebLink

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West Elk Mine 2013 Annual Hydrology Report 50 stream flow impacts from mining are expected. Flow at Lower Sylvester Gulch is not measured because of its close proximity to the Middle Sylvester Gulch Flume. Potential impacts to stream flows are based on dramatic decreases or total loss of stream flow due to subsidence. Based on the flow monitoring data through WY 2013 (Appendices A and B), there are no mining- induced impacts to the water quantity of these streams. It is important to note that in previous years (WY 2001 — WY 2006) the data logger flow data from the Upper and Lower Deep Creek (Appendix A -15, 16) stations have been designated as suspect, due to channel variations and the lack of flumes. Current monitoring (including WY 2013) protocols for Upper and Lower Deep Creek specify the collection of instantaneous flow measurements three times per year. 5.1.3 Impacts to the North Fork of the Gunnison River MCC discharges water to the NFGR via sedimentation ponds MB -5E, MB -3, MB -4, RPE, and NSSA and discharges to Sylvester Gulch via pond SG -1 and MWPF (Figure 9). There was no discharge from ponds MB -3, MB -4, MB -5E, the RPE pond or the NSSA pond in WY 2013 (Figure 9) (MCC, 2014). The major cations and anions of the Sylvester Gulch discharge water are sodium and bicarbonate. The discharge from Outfall 014 (Pond SG -1) had a pH value of 7.79 s.u. and a TDS concentration of 210 mg /L in WY 2013. There was no mine water discharged to Sylvester Gulch from Outfalls 011, 017, and 018 in WY 2013 (MCC, 2014). 5.1.3.1 Salinity In compliance with CDPS Permit CO- 0038776, MCC monitors TDS on a quarterly basis at Outfalls 004, 005, 008, 009, 011, 012, 013, 014, 015, 016, 017, 018 and 019. Per the CDPS discharge monitoring reports (DMRs), there was no flow from Outfalls 004, 005, 008, 009, 011, 012, 013, 016, 017, 018 or 019 in WY 2013 (Table 12) (MCC, 2014). A salinity (TDS) loading analysis of the MCC's WY 2013 discharges was completed relative to the current North Fork Cumulative Hydrologic Impact Assessment (CHIA) (CDMG, 2003). The CHIA was conducted to assess the potential cumulative hydrologic impacts of mining and other activities in the North Fork Valley on the water quality and flow of the North Fork of the Gunnison. The CHIA determined that no significant hydrologic impacts were expected as a result of mining activities at the West Elk Mine. The CHIA assumed that MCC's contribution to the NFGR would be a maximum of 5,520 gpm with a TDS concentration of 2,500 mg /L. The total WY 2013 discharge from the mine site to the NFGR was approximately 1.98 gpm or 2.86 x 10 "3 mgd (MCC, 2013). Using this value and TDS values from the WY 2013 CDPS DMRs (210 mg/L), the flow- weighted maximum annual salinity (TDS) load from MCC's mining operations was 0.91 tons. This represents about 0.003 percent of the value used in the CHIA. A comparison of the salinity loading from MCC's mining operations to the CHIA study is shown on Table 13. June 2014 HydroGeo, Inc.