2010-04-20_REVISION - M1977300 (5)

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Environmental Protection Plan, Schwartzwalder Mine 8-4 • (i) Streams and Reservoirs Three main surface water features are located within two miles of the Schwartzwalder Mine: Ralston Creek, Ralston Reservoir, and Long Lake Ditch (Plate 1, Table 8-1). (i).1 Ralston Creek Ralston Creek is a small stream that drains approximately 41 square miles of mountainous watershed. The creek is intermittent near its headwaters, perennial in the mine area (where it flows from northwest to southeast across Section 25) and intermittent at its mouth on Ralston Reservoir. The canyon is steep and narrow in the vicinity of the mine site (approximately 6,600 feet wide and 1,200 feet deep), where the valley floor ranges from 60 to 300 feet wide. The original valley floor near the mine was covered with waste rock fill to form a pad for mine facilities. Although the creek was rerouted to the north side of the canyon during mine development, it has since developed a series of natural riffles and pools where it flows past the mine site (Shepherd Miller, 1999). Small intermittent tributaries of less than one mile in length enter Ralston Creek from both the north and south directions in the west half of Section 25. In the east half, short, usually dry gulches drain into Ralston Creek from the north (off the west side of Ralston Buttes) while a steep ridge parallels the creek on the south. Flow in Ralston Creek is directly related to precipitation (Table 8-3, Figure 8-1). Table 8-3. Flow Rates in Ralston Creek vs. Monthly Mean Precipitation at Ralston Reservoir • Month Mean Monthly Flow cfs Average Minimum Flow cfs Average Maximum Flow cfs Number of Months Mean Monthly Precipitation in Jan 1.6 1.3 1.8 35 0.61 Feb 1.7 1.2 2.2 35 0.65 Mar 4.1 2.3 9.1 38 1.87 Apr 14.1 4.1 32.4 44 2.41 May 32.4 13.3 57.6 47 2.93 Jun 16.1 4.0 34.5 45 1.96 Jul 3.8 1.4 16.0 40 1.64 Au 2.9 1.1 6.9 39 2.13 Se 2.4 1.1 7.1 37 1.38 Oct 2.2 1.5 6.1 37 1.22 Nov 2.5 1.4 5.8 36 1.13 Dec 1.8 1.4 2.2 35 0.75 Monthly Average 7.1 cfs 1.56 in. Annual Averaize 5160.7 acre-ft 18.68 in NOTES: Flow data obtained from Denver Water, period of record March 1957 through January 2004 Precipitation data from National Climatic Data Center, period of record May 1978 through July 2007 (1) Number of months for which flow data were available • 4109C.100419 Whetstone Associates 6