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Schwartzwalder Mine -Hydrologic Evaluation of Mine Closure and Reclamation 23 <br />A 72- hour pumping test with a 24-hour recovery period was performed in monitoring well MW9 during <br />the spring of 1999. The objective of the test was to determine the permeability of the alluvium and to <br />evaluate the hydraulic and chemical interaction between the alluvium and the creek. MW9 was pumped at <br />a rate of 30 gpm and water levels were monitored in 7 observation wells and 4 sumps. Pumping from the <br />sumps had been discontinued prior to the start of the test and water levels had recovered to 75% of the pre- <br />pumping condition before starting the pumping test. Flow in Ralston Creek was also monitored during <br />pumping. The methodology, results and analysis of the pumping test are presented in Appendix D. <br />Significant conclusions from the pumping test include: <br />1. The average hydraulic conductivity of alluvium in the vicinity of MW9 is 6.4 x 10.3 cm/sec. <br />2. The specific yield of the alluvium as determined from observation well MW6 is 0.02 <br />3. The distribution of hydraulic conductivity in the alluvium is heterogeneous. The observed <br />resistance to flow was greater upstream of MW9 than it was downstream of the well. <br />4. The test did not appear to influence the chemistry of Ralston Creek or any of the wells or sumps <br />adjacent to the stream. <br />4.2.3 Sump Pumping <br />Groundwater in the alluvium was intercepted and collected by four sumps, which were installed in 19908 <br />and operated until June 2002. The locations of the sump drains are shown in Figure 10. Water drained into <br />each sump by gravity and was pumped to the water treatment plant near the western end of the mine <br />facilities. The water was treated and discharged into Ralston Creek, under Colorado Discharge Permit <br />#CO-0001-244. The last Discharge Monitoring Report (DMR) with discharge indicated was submitted on <br />June 29, 2002. <br />Sump pumping records provide an indication of the interconnection between Ralston Creek and the <br />alluvium and fill material. Flow rates from the sumps were measured or estimated from 1995 to June 2002, <br />when the pumps were shut off. Monthly average pumping rates for the four sumps combined ranged from <br />35 to 404 gpm, with an average of 104 gpm over the period of record (Table 13). A decline in sump <br />pumping rates was observed from 2000 - 2002, which was most likely related to drought conditions. <br />Monthly average sump pumping rates clearly correlated with monthly average precipitation rates (Figure <br />129). A slightly weaker correlation exists between monthly sump pumping rates and monthly average flow <br />rate in Ralston Creek (Figure 13, Figure 14). Although flow rates in the creek peak in May, as did pumping <br />rates from the sumps, the trend between creek flow and pumping rates differed during high flow (spring) <br />months from the trend during low flow months. <br />s Sump #1 went online in August 1990, sump #2 in April 1990, sump #4 in October 1990, and sump #3 went online January1992. <br />v It should be noted that Figure 12 was generated using 26 yeazs of precipitation data (May 1978 -November 2003), while the <br />sump pumping records span only about five years. Some of the sump flow records contain only one or two flow measurements <br />exist for a given month (Jan, Feb, Mar, Sept, Oct, Nov, Dec.) While a longer span of data might make the correlation stronger, <br />the strong relationship between precipitation and sump flow (and the weaker relationship between stream flow and sump flow) is <br />significant. <br />4109B.071116 Whetstone Associates • <br />