2010-06-25_HYDROLOGY - M1977300 - Laserfiche WebLink

Home Browse Search

1q/?77--3 0 49 --- Z S Tawe oeio `i Rationale for Not Conducting Mine Dewatering and Mine Water Treatment at the Schwartzwa er Mine by Susan A. Wyman, P.E., P. G., Whetstone Associates Groundwater levels in the Schwartzwalder Mine have recovered to 6,557 ft above mean sea level (amsl) since the underground pumps were shut off in May, 2000. A May 19, 2010 letter from the Colorado Division of Reclamation, Mining, and Safety (DRMS) contained Corrective Action #2 which said to reinitiate mine dewatering and pump the mine pool down to at least 500 feet below the Steve Level (that is, to approximately 6,102 ft amsl or below) and to treat the water pumped from the mine pool to meet water quality standards prior to discharge into Ralston Creek. Cotter and its technical consultants believe that pumping down the mine pool and treating the water would be ineffective and impractical for the reasons described below. If minor amounts of water from the mine pool are exiting the mine, the water would reach the alluvium and fill where it will be collected at Sump I and treated in the new water treatment system. Cotter and its contractors are working to install pumps, piping, and a new water treatment system to capture and treat groundwater in the alluvium and fill. Groundwater in the alluvium reports to Sump 1, and if not intercepted at the sump, the water reports to the creek. Cotter will begin actively treating groundwater in the alluvium by July 31, 2010, at the latest. All the available groundwater from Sump 1 will be pumped to the water treatment plant where an ion exchange system is being installed by a water treatment contractor. The treatment system is sized for a nominal flow rate of 100 gpm, with a maximum of 150 to 200 gpm, and will be capable of treating all of the water collected from Sump 1. The treatment system can also be expanded. Cotter is committed to this corrective action, which is expensive, and has allocated significant resources and personnel with the intent of starting treatment before July 31, 2010. Corrective action at the site should focus on identified sources of loading to Ralston Creek. There is no direct evidence that the mine pool is contributing uranium to Ralston Creek. In contrast, the alluvium and fill were recognized as a source of loading after the sumps were shut down and before the mine pool rose to an elevation above the creek level. (Note that the "first flush" of uranium from the alluvium and fill was followed by a significant decrease to below drinking water standards. In subsequent years, seasonal spikes in uranium concentrations in Ralston Creek have been followed by steep declines, such as in the most recent (April 2010) sampling results (Table 1, Attachment 1). The initial trend in uranium concentrations was downward after the "first flush". Due to this trend and to seasonality in creek concentrations, the need for water treatment in groundwater from the alluvium and fill was not immediately recognized.) Table 1. Uranium in Ralston Creek, April 2010 Date Sample Station Analyte Result Units 4/14/2010 AWD Uranium, dissolved 0.001 mg/L 4/14/2010 A001 Uranium, dissolved 0.003 mg/L 4/14/2010 BPL Uranium, dissolved 0.034 mg/L 4/14/2010 FBRG Uranium, dissolved 0.034 mg/L 4/14/2010 ARH Uranium, dissolved 0.037 mg/L 4/14/2010 LLHG Uranium, dissolved 0.036 mg/L Source: Energy Laboratories. See attachment 1 for complete analytical results. Whetstone Associates, Inc. 243 N. Main St. ? Gunnison, Colorado 81230 6 Phone 970-641-7471 ? Fax 970-641-7431