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Mountain Coa! Company 1999 Annual Hydrology Report West E/k Mine <br />• Ponds MB-3, MB-4 and MB-5 <br />During WY99, ponds MB-4 and MB-5 discharged a total of less than one acre-foot to the North <br />Fork. Pond MB-3 discharged 20.3 acre feet during WY99 as a result of receiving diverted flows <br />from pond MB-2R during sediment removal operations. These discharges were made in <br />accordance with the MCC CDPS permit. Pond MB-5 received exclusively stormwater runoff <br />and ponds MB-3 (under normal operating conditions) and MB-4 received runoff as well as <br />washdown water from conveyors, the silos and the loadout facilities. All relevant numeric <br />discharge limits were met. <br />Pond FW-1 <br />During WY99, there were no discharges from pond FW-1 to the North Fork. Diversions from <br />the North Fork that exceeded the capacity of pond FW-1 were allowed to spill back to the North <br />Fork. <br />Pond FW-1 was lined with a HDPE liner in May 1998. Seepage from FW-1 was also suspected <br />of contributing water to the mine site landslide. Similar to MB-l, the liner has been extremely <br />effective in eliminating seepage to the landslide. Furthermore, the liner has improved the <br />efficiency of using water diverted from the North Fork by not losing water to seepage. <br />Pond SG-1 <br />• During WY99, runoff from disturbed areas and water encountered and used during development <br />of the mine ventilation shafts were collected and discharged from pond SG-] . A total volume of <br />22.7 acre-feet was discharged during WY99. As shown in Table 8, these discharges were in <br />compliance with CDPS permit limits. <br />Biomonitoring Testing for Toxicity <br />During WY99, MCC conducted numerous biomonitoring tests for toxicity, utilizing whole <br />effluent toxicity or "WET" tests. Samples were collected on a quarterly basis for Lone Pine <br />Pipeline (discharge point 013). Toxicity tests were performed for acute 48-hour and 96-hour <br />static tests. The acute test organisms were Daphnia magna for the 48-hour test and fathead <br />minnow (Pimepha/es prome/as) for the 96-hour test. To ensure that the dilution water itself is <br />not toxic, toxicity tests on dilution water without any effluent (referred to as "controls") were <br />conducted. There were no WET test failures during WY99. <br /> <br />Page I S Wright f{'ater Engineers <br />