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from Sump Number 4 on August 16, 2010, and from Monitor Well 9 ("MW 9") on August 19, <br />2010. Through September 13, 2010, the groundwater extraction and treatment systems at the site <br />have removed approximately 130 pounds of uranium from alluvial groundwater! A significant <br />increase in the rate of uranium removal occurred after the pumping system was expanded to <br />include Sump No. 4 and MW 9. Mass flow calculations of uranium in pounds per day measured <br />at monitoring station SW-BPL [Surface Water - Below Property Line] show the. lowest daily <br />mass flow in Ralston Creek since late 2008. However, during low stream flow conditions, <br />concentrations of uranium at S W-BPL have still exceeded the 0.03 mg/L uranium stream <br />standard. <br />Based on monitoring data and a targeted site inspection, the reason for this result has <br />become clear and has led to a supplemental mitigation strategy. During minimum stream flow <br />conditions, the source of water residing in the Ralston Creek bed just below station SW-BOS <br />comes from alluvial groundwater entering the stream bed just above SW-BOS. If the <br />groundwater entering Ralston Creek near station SW-BOS is intercepted and treated, <br />concentrations in Ralston Creek at downstream locations are expected to be rapidly reduced and <br />are expected to approach or meet the 0.03 standard, even during periods of low or negligible <br />stream flow. In TR-15, Cotter proposed installation of one or more additional sumps and <br />associated French drain systems to intercept all alluvial groundwater in the vicinity of SW-BOS <br />as soon as possible. The additional groundwater captured will be treated at the water treatment <br />facility. Cotter also explained the rationale for this TR-15 in a submission dated September 30, <br />2010 to the Colorado Water Quality Control Division, on which DRMS was copied (Exhibit B). <br />In TR-15, Cotter further requested that a small, temporary pumping system be placed in the <br />1 Through September 27, 2010, 191 pounds of uranium have been removed from alluvial <br />groundwater. <br />4