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West Elk Mine <br />Ponds MB-1 and MB-2R play a pivotal role in water operations at the West Elk Mine. With <br />the exception of mine water that is directly discharged to the MB-1 spillway, such as minor F- <br />Seam colluvial inflow water, most outflows from the mine portals are directed into one of <br />these ponds. The waters are treated and then discharged to the North Fork, in accordance with <br />the NPDES permit that is provided as Exhibit 7. The combined volume of these ponds is 27.9 <br />acre-feet. Because the ponds also intercept stormwater and snowmelt runoff, the optimal mode <br />of pond operations is to keep the pond levels low to maintain the 10-year return frequency, 24- <br />hour duration runoff volume of 6.8 acre-feet for both ponds. One of the major reasons MCC <br />utilized the NW Panels sealed sttmp in late 1996 was to assure that there would be sufficient <br />storage capacity in Ponds MB-1 and MB-2R to treat the necessary stormwater volumes. <br />Mine Water Dischar¢es -MCC has added the capability to discharge water from the NW <br />Panels sealed sump into Lone Pine Gulch. MCC received approval from the CWQCD to add <br />this location as an NPDES discharge point (Outfall i{013). Discharge to Lone Pine Gulch <br />began in late December 1947. <br />Long-term observations of Lone Pine Gulch by MCC staff indicate that it is an ephemeral <br />drainage which flows only in response to snowmelt runoff and intense rainfall runoff events. <br />The maximum flow rate that can be pumped to Lone Pine Gulch is 2,000 gpm, but has <br />typically been approximately 300 gpm. The discharge point is very low in the watershed, <br />Table 48 Estimated Percent Change in North Fork Stream Flows Under <br />Extreme Low Flow Conditions <br />~~ <br /> Diversion Flow Rate <br /> 50 gpm Pump 400 gpm Pump Both Pumps <br />North Fork Streamflow Case River flow <br />(cfs) 0.11 <br />(cfs) 0.89 <br />(cfs) 1.00 <br />(cfs) <br />Historic low flow 17 -0.6 -52 -5.9 <br />7-day, 10-year low flow 32.5 -0.3 -2.7 -3.1 <br />1-day, 10-year low flow 25 -0.4 -3.6 -4.0 <br />1-day,100.yearlowflow 19 -0.6 -4.7 -5.3 <br />Approximate flow rate when <br />Wa[er call begins 300 -0.04 -030 -033 <br />2.05-182 Revised Jun. /995PR06; RevisedNw. 19987880; IN8 PR08 <br />