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• Assistance Program, contracted with Simons, Li & Associates, (Simons Li) <br />to model streamflows for both Magpie and Newlin Creeks. Simons Li <br />utilized the three (3) modeling methods previously noted to calculate peak <br />discharge and total runoff for both the 10-year and 100-year, 24-hour <br />events. <br />Calculated flow values for Magpie Creek are summarized by Table 14, <br />Estimated Peak Flows and Total Runoff For Mine Area Drainages. A detailed <br />explanation of calculation methods, and discussion of relative accuracy <br />of the different modeling approaches is presented in Exhibit 7, Hydrologic <br />Information. For Magpie Creek, peak flows utilizing the MULTSED Method <br />are calculated at approximately 900 cfs for the 10-year, 24-hour storm <br />event and 32,000 cfs for the 100-year event. Similarly, total runoff <br />calculated utilizing the same method is estimated at 50 acre feet for the <br />10-year event and 160 acre feet for the 100-year storm event. Given the <br />lack of historical flows and the relatively low flow volume for the one <br />• recorded occurrence, the peak discharge and total runoff values estimated <br />using modeling are considered to be very conservative. <br />Flows for upper Newlin Creek have been documented indirectly in the form <br />of diversion records for the City of Florence diversion as submitted to <br />and maintained by Water Division 2 of the Colorado State Engineer's <br />Office. Diversion records extending back to 1964 document a peak flow on <br />May 11, 1971 of 21.8 cfs. With initiation of mining operations, <br />Dorchester began, and EFCI continued, flow monitoring on lower Newlin <br />Creek. This more recent site specific information documents the ephemeral <br />flow pattern for lower Newlin Creek and indicates recorded peak discharge <br />rates of approximately 16 cfs as illustrated by Figure 7, Newlin Creek <br />Flow Hydrograph. With the exception of peak discharge resulting from <br />major storm events, ephemeral flows in Newlin Creek have averaged less <br />than 2 cfs. Given the limited flow data for Newlin Creek and the <br />magnitude of storm events to date, peak flows and total runoff were <br />estimated using the modeling techniques previously described for the 10 <br />. and 100-year, 24-hour storm events. Resulting estimated peak discharge <br />and total runoff volumes are summarized by Table 14, Estimated Peak Flows <br />and Total Runoff For Mine Area Drainages. Modeling results utilizing the <br />MULTSED Method indicate peak discharge for the 10 and 100-year events of <br />2.04.7-28 <br />