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15 <br />Schwartzwalder Mine -Hydrologic Evaluation of Mine Closure and Reclamation <br />6). Similarly, the monthly average flow measured by Denver Water from October 1998 to September <br />1999 was less than the long-term average for all months except May. <br />• Flows in Ralston Creek near the mine site are higher than flows measured 1.5 to 2 miles downstream <br />(at the Long Lake Head Gate and Ralston Reservoir.) Ralston Creek must therefore contain losing <br />reaches between the mine and Ralston Reservoir. <br />• The minimum flow in Ralston Creek at nine stations near the mine site occurred during the winter <br />months, and was approximately 3.8 cfs (Table 7). This minimum flow represents base flow equivalent <br />to 1.34 inches per year from the approximately 38 square miles of catchment, or approximately 7% of <br />the average annual precipitation measured at Ralston Reservoir. <br />• The average flow in Ralston Creek at nine stations near the mine site was approximately 9.7 cfs. This <br />average flow represents base flow equivalent to 3.48 inches per year from the approximately 38 square <br />miles of catchment, or approximately 19% of the average annual precipitation measured at Ralston <br />Reservoir. <br />• Peak flows in Ralston Creek near the mine site during the October 1998 -September 1999 monitoring <br />period occurred in May, when the average flow at all nine stations was 32.7 cfs. <br />Peak flows for the 50- and 100-year recurrence interval storms were calculated in a hydrologic analysis of <br />Ralston Creek, which was performed in 1983 as part of the waste rock stability report. The analysis <br />determined that the discharge from the 50-year recurrence interval flood at the mine site is 4,960 cfs <br />(McDermid, 1983a) and the discharge from the 100-year recurrence interval flood is 5,750 cfs (McDermid, <br />1983b). A 100-year peak flow of 119 cfs was used in the waste rock stability analysis. <br />Table 6. Stream Gaging Results for Ralston Creek Near Schwartzwalder Mine <br />N € 10/20/98 ~ 11/19/98 ° 12/17/98 1/19/99 2/15/99 = 3/15/99 4/19/99 5/17/99 :7/19/99 8/2/99 ~ 9/13/99 <br />STATIO <br />SW-UP ~ 74 <br />1 1_70 <br />; 1.64 3.47 3.47 16.70 <br />- 31.47 <br />-- --: 2.89: 16.70 6.34 <br /> <br />SW-UC . <br />33 <br />2 <br />2.23: _ <br />_ <br />2.09 <br />3.20 <br />2.09 <br />3.20 <br />19.72: <br />22.04 <br />8.42 = 16.24: <br />- <br />1 . <br />-- ---- <br />SW-A001 . <br />1.70: 2.96 = 2.96 6.10 12.38 _ 35.09: 1.59 ° 22.44 _ _ __12.38_ <br />SW-BDIS ~ 2.34 ~ 2.22 <br />- 2.32 2.34 2.09 = 4.97 ~ <br />18 <br />3 15.51 <br />45 <br />9 36.00 ~ <br />14 <br />34 8.66 16 56 <br />8.55 17.50 10.24_ <br />8.55 <br />SW-PL 2.08 1.98 ~ __2.53 3.18 1.98 . . , <br />. <br />1 _ <br />_ <br />93 <br />27 <br />. <br />SW-OS , <br />4.37 ~ 6.26. 4.37 ~ 21.27 ~ 5.75 21.27 ~ 34.59 ~ 38.58: <br />---: _ <br />6.32 19.4 . <br />_ <br />SW-BOS 2.03 2.01 _ 1.99: 1.83 1.87: 2.01 3.10: 33.32 = 4.66: 5.81 1.0 <br />SW-GS ~ 2.71: 4.95 3.16 ~ 5.40: 5.04: 5.85 ' 29.40 31.36 6.21:15.70 7.64 <br />SW-BPL ` 2.54 3.99 2.47: 3.99: 3.99 € 5.80: 10.67: 32.95 ~ 6.53: 9.08 <br />AVERAGE 2.43: 3.32: 2.58 5.09 3.60: 6.90 17.39: 32.77: 5.98 16.30 ~ 10.76 <br />RALSTON CR. 1.00 ; 1.00 1.00 2.00: 1.00 2.00 5.00 25.00 2.00: 5.00: 3.00 <br />DAILY ' <br />RALSTON CR 1.06 ; 1.37: 1.13 1.29: 1 04 ` 1.45 11.37 ; 43.23 13.40: 3 45 14.97 <br />MONTHLY ' -- <br />RALSTON CR. <br />LONG-TERM ± 2.24 2.46 1.80 1.55 ~ 1.69: 4.07 14.12 32.41 16.09 3.79 2.90 <br />AVERAGE; - <br />Whetstone Associates <br />4109B.071116 <br />