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9 <br />Schwartzwalder Mine -Hydrologic Evaluation of Mine Closure and Reclamation <br />surface near the Charlie level to the 11 Level. Areas that were not actively worked were typically <br />bulkheaded, to prevent radon gas exposure. <br />During operations, the Schwartzwalder Mine was kept dry by pumping water from the lower levels of the <br />mine. Water was collected in the 19 Level, pumped to the 7 level, and then pumped to the surface where it <br />was sent through the water treatment plant before being discharged to Ralston Creek. <br />The water treatment plant also processed water collected from a series of four sumps in the alluvium and <br />fill. These sumps pumped at a combined average of approximately 100 gpm. The mine operated under <br />Colorado Mining Permit #77-300, Colorado Discharge Permit #CO-0001-244 and Radioactive Materials <br />License number CO-369-03S. <br />3. SURFACE WATER FLOW <br />Ralston Creek is a small, intermittent stream which drains approximately 41 square miles of mountainous <br />watershed. The creek is deeply incised into the surrounding mountains. The canyon is approximately <br />6,600 feet wide and 1,200 feet deep at the mine site, where the valley floor ranges from 60 to 300 feet wide. <br />Near the mine, the original valley floor has been covered with waste rock fill to form a pad for mine <br />facilities. Although the creek was rerouted to the north side of the canyon during mine development, it has <br />since developed a series of natural riffles and pools where it flows past the mine site (Shepherd Miller, <br />1999). <br />3.1 Flow in Ralston Creek at Ralston Reservoir <br />Historical flow data are available for downstream gaging stations on Ralston Creek, for the period from <br />1957 to the present. The information was provided by the Denver Water Board, which measures flow and <br />field parameters at the Long Lake ditch outlet from Ralston Creek (about 1.5 miles downstream from the <br />Cotter property) and at the inlet to Ralston Reservoir. Data from the Ralston Creek and Long Lake Head <br />Gate gaging stations were analyzed for the period from 1956 to January 20042 (Table 4). The flow records <br />were processed3 and evaluated to identify major trends in Ralston Creek. <br />The data indicate that the highest flows in Ralston Creek above Ralston Reservoir occur during the months <br />of April, May, and June. Peak flows occur during the month of May, when the average flow rate is 32.4 <br />cfs. By contrast, the average flow rate from August to February is 2.1 cfs. This relatively stable base flow <br />during the summer, fall, and winter is indicative of steady groundwater flow to the creek. During the <br />spring, runoff and snowmelt add to the groundwater base flow in Ralston Creek. The creek can be prone to <br />flash flooding and significant erosion, due to the narrow channel and large recharge area. <br />Monthly average flow rates in Ralston Creek correlate well with monthly average precipitation, (Figure 6), <br />but have a slightly larger time lag during winter months. Precipitation records for the Ralston Reservoir <br />meteorological station, located about 2 miles east of the mine and 560 ft lower in elevation, are given in <br />Section 2.3. <br />2 Discontinuous records are available from 1953 to 1970. Flow records are fairly complete from 1970 to 2004. <br />s Flow records at Long Lake Feeder Ditch gaging station were added to the flow records for Ralston Creek above Ralston Reservoir <br />gaging station to give the total flow in Ralston Creek. Where data were missing for the Long Lake Headgate flow, it was <br />assumed to be zero. <br />Whetstone Associates <br />4109B.07t116 <br />