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• facilities, peaked at 3700 mg/1 in June and August. No other notable water quality impacts are evident at any surface water sites monitored during 2002. Recorded 2002 spoil spring discharges remain negligible and, therefore, did not constitute a significant portion of discharge from the TCC mine area with the potential to impact off-site areas. Discharges from sedimentation ponds predominately occurred in conformance with applicable CDPS pemrit limitations and therefore did not constitute significant impacts to receiving waters. Mine water discharge sites 109 (Table 64) and 115 (Table 65) produced little water during the 2002 Water Year. When pumping mine water from the Fish Creek Borehole (mine dischazge site 115) the flow becomes a contributor to sulfate levels in Fish Creek. When pumping mine water from the EMD Dewatering Well (mine dischazge site 109) the flow becomes a contributor to sulfate levels in Foidel Creek. Fish Creek and Foidel Creek, 9n tum, contribute to the sulfate levels in Trout Creek. Trout Creek currently has a secondary drinking water standard limiting sulfate to 250 mg/1. Historic sampling at site 1005 has shown that a sulfate level of 250 mg/I correlates to a conductivity of approximately 750 umhos/cm. In order to quantify the predicted effect of sulfate contributions from sites 115 and 109, TCC in association with a consultant, has developed a computer program -the "FCBH Calculator". In the winter, when stream gauging is difficult, the FCBH Calculator uses the flow and conductivity values from sites 69 (Trout Creek above Fish Creek confluence) and 1005 (Trout Creek below Fish Creek confluence) to estimate • the appropriate discharge for sites 115 and/or 109. These same sites aze also used to estimate appropriate flow for site 109 in the summer. In the summer, the FCBH Calculator uses measured flow and conductivity values from site 16A (upstream of discharge site 115), and conductivity values from site 115 to calculate how much mine water, if any, may be dischazged from site 115. TCC uses these methods to manage controllable dischazge from sites 115 and 109, and avoid contributing to sulfate exceedences downstream in Trout Creek. No unusual occurrences of inflow were noted as a result of the Annual Mine Inflow study. Inflows are within the projected flows presented in the permit. Water quality has not changed significantly and appears to mirror the quality of the adjacent spoil water. Ii appeazs that the elevated EC and iron readings are associated with the water that has pooled in the mine sump, in contact with the overlying Marine Shale. This contact has provided the opportunity for additional salts and iron to be leached from this unit. The pumping of the sump should see a decrease in the elevation of the pool over time, with an anticipated decrease in the EC and concentration of trop in the effluent. During the first half of 2002, subsidence survey data was collected periodically from established monuments on the Union Pacific Railroad and the YVEA power line in azeas underlain by gate roads or panel centers during periods of mining in the 13-Rt longwall panels. This data was presented to DMG in detail in the first of two semiannual subsidence reports for 2002 (First Hnlf 2002 Subsidence Survey Report). Data from this report, as well as earlier historical subsidence information is discussed below. The 13-Rt ]ongwal] panel did not directly undermine the Walcott, Hayden-Gore Pass and Western Area Power Administration power lines, and Foidel • Creek during [he first half of 2002. No significant subsidence ponding, overlying subsurface mined areas along Foidel Creek or Middle Creek was evident in 2002. IS