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In June 2010, routine monitoring of historic "local" sampling stations along Ralston Creek <br />adjacent to the alluvial fill was resumed. Uranium concentration results from local monitoring <br />stations have revealed a clear spatial pattern in uranium loading to the creek. Above station <br />SW-BOS, all monitoring stations consistently demonstrate uranium concentrations well below <br />the 0.03 mg/L standard. However, results for station SW-BOS, particularly during seasonal <br />periods of low or negligible stream flow, show concentrations above this standard. At any given <br />point in time, all monitoring stations below station SW-BOS have uraniwn concentrations that <br />are about the same as that measured at station SW-BOS. <br />In response to these data and observations, Cotter conducted a site investigation on September <br />25, 2010. Several conditions were observed that corroborate postulated mechanisms for the <br />identified spatial patterns in stream water quality, and which specifically pinpoint a relatively <br />short section of stream bank where preferential groundwater inflow pathways appear responsible <br />for uranium loading to the creek. Several conditions suggest further remedial action. Those <br />conditions are: <br />• The creek above sampling location SW-BOS was dry. <br />• The creek immediately above the discharge location of the water treatment system was <br />not dry. <br />• Uranium levels in the water treatment system discharge have been consistently below <br />0.004 rng/L uranium. <br />• Water was observed entering the creek just upstream from SW-BOS. The flow rate of <br />this water, which entered the creek from the bank on the mine side of the creek, appeared <br />to be on the order of a few gallons per minute. <br />Uranium concentrations measured at station SW-BOS during the month of September were <br />consistent with groundwater measured at MW 9, which is immediately adjacent to the <br />groundwater entry point. In other words, during minimum stream flow conditions, the source of <br />all water residing in the creek bed just below station SW-BOS comes from alluvial groundwater <br />entering the stream bed just above station SW-BOS. If all groundwater entering the creek near <br />station SW-BOS can be intercepted and treated, concentrations in the creek at downstream <br />locations should be rapidly reduced and could approach or meet the 0.03 mg/L standard, even <br />during periods of low or negligible stream flow. <br />Proposed Technical Revision <br />At present there is excess treatment capacity at the 100-gpm water treatment facility. The <br />maximum treatment capacity for the current facility is approximately 200 gpm. Cotter proposes <br />installation of one or more additional sumps and associated French drain systems to intercept all <br />alluvial groundwater in the immediate vicinity of SW-BOS as soon as possible. It is possible that <br />additional sump / French drain system locations will be added below the SW-BOS area, but <br />exact locations are yet to be determined pending further site investigation and hydraulic analysis <br />from Whetstone Associates. All additional groundwater captured will be treated at the water <br />treatment facility. <br />The impact of installing a sump and French drain system in the immediate vicinity of station <br />SW-BOS is expected to significantly improve stream water quality at station SW-GS within a