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Mountain Coal Company 1997 Annual Hydrology Report LVesl Elk A4ine The releases from these ponds did not materially affect the North Fork, with respect to either • quantity or quality. Pond FW-1 During WY97, mine water from the 14 SEHG fault was directly discharged to the North Fork via pond FW-1 spillway. These discharges were made under authorization of the CWQCD. A total volume of approximately 36 acre-feet was discharged over atwelve-day period (January 27 through February 7). As shown in Table 7, these discharges were in compliance with CDPS permit limits. Biomonitoring Testing for Toxicity During WY97, MCC conducted numerous biomonitoring tests for toxicity, utilizing whole effluent toxicity or "WET" tests. Samples were collected on a quarterly basis for ponds MB-1 and MB-2R. Toxicity tests are presented for both acute (48-hour) static tests, and for chronic (96-hour) static tests. The acute test organism was Daphnia magna. The chronic test organism was the fathead minnow (Pimepholes promelas). To ensure that the dilution water itself is not toxic, toxicity tests on dilution water without any effluent (referred to as "controls") were conducted. During WY97, WET tests were conducted at the following locations: MB-1 discharge, MB-2R discharge, direct discharge via FW-I spillway, and North Fork upstream and downstream of the • mine. There were no WET test failures at any of these locations during WY97. In addition to the standard sets of WET tests, MCC contracted Wright Water Engineers, Inc. (WWE) to conduct a biological assessment on the North Fork to assess potential impacts from direct discharge of warm water from the 14 SEHG fault. The initial study was conducted prior to the discharge of the ponds or any direct discharge and then after contributions from the fault inflow had diminished. WWE concluded that temperature increases in the North Fork were restricted to the immediate vicinity of the dischazge point. Furthermore, there were no biological impacts observed. Mine WaterInflows A significant departure from historic observations relative to mine water inflows occurred in WY96 during the development mining of the B East Mains. The unprecedented mine inflows were associated with a fault system that was subsequently given the same name, B East Mains fault. By the end of WY96, the B East Mains were complete and development of the Box Canyon Mains (north of the B East Mains) and the B South Mains (south of the B East Mains) were initiated. In WY97, development mining in the Box Canyon Mains proceeded through the projection of the B East Mains fault system in a northeasterly direction. Observed groundwater inflows in the entries varied from no flow to 5 gpm. The most significant flow in the B East Mains of 5 gpm was observed in Entry #7. As development mining continued to pass through the B East Mains fault projection in a down-dip direction during WY97, capture of the fault inflows occurred, and the previous up-dip inflow from the fault system disappeared. Initial 8.31-031.45 age l Wrig 1 aler Engineers