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West Elk Mine 2004 Mnual Hydrology Report 30 <br />• Pond MB-1 and Pond MB-2R retain water so settling of sediment occurs prior to discharge (batch <br />mode). In WY2004, pond MB-1 had a discharge of 8.0 ac-fr and MB-2R discharged 74.0 ac-fr of <br />water to the North Fork. <br />4.3.2 Ponds MB-3, MB-4, and MB-5 <br />Ponds MB-3 and MB-4 receive storm water runoff and wash down water from the conveyors, silos, <br />and load out facilities. Pond MB-5 collects only storm water runoff. In WY2004 pond MB-4 <br />collected a small amount of water resulting in dischazges of about 1.0 ac-fr. Water was not <br />discharged from ponds MB-3 and MB-5 in WY2004. <br />4.3.3 Pond FW-1 <br />Pond FW-1 is designed to store raw fresh water from the North Fork diversion intake gallery. <br />Pond FW-1 water is pumped to the WWTP and the Project's domestic water system. If the pond <br />overfills, excess water is discharged back to the North Fork. Water was not discharged from pond <br />FW-1 in WY 2004. <br />4.3.4 RPE Pond <br />• The RPE Pond collects runoff from the refuse pile expansion area. In WY 2004 no discharge <br />occurred from the RPE pond. <br />4.3.5 Pond SG-1 <br />Pond SG-1 was built to collect runoff during and afrer construction of the mine ventilation shafts. <br />Discharge from SG-1 is routed to Sylvester Gulch. In WY 2004 pond SG-1 had a discharge of <br />about 1.0 ac-ft. <br />4.4 Biomonitoring Testing for Toxicity <br />During WY 2004, MCC conducted bomoni[orng tests as required by the CPDS permit. <br />Biomonitoring samples were collected quarterly from the West Fork of Sylvester Gulch effluent <br />discharge (outfall 017). Testing included whole effluent toxicity or "WET" tests. Static toxicity <br />tests for acute (48-hour) and chronic (96 hour) were completed in WY 2004. The test organisms <br />included the daphnid (Daphnia magna) and the fathead minnow (Pimephales promelas). The test <br />results indicated that the effluent from outfafl 017 was acutely toxic to daphnid in the 2"a and 3`a <br />quarters of 2004 as detailed in the quarterly Discharge Monitoring Report. (DMR) submittals. <br />• MCC established that high alkalinity is the cause of the Daphnid mortality. <br />August 2005 HydroGeo, Inc. <br />