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Daniel Arnold, Esq. January 25, 2011 <br />Denver Water Page 10 of 21 <br />precipitation, timing and intensity of rain storms, timing of snowmelt runoff, and the rate <br />of diversions and timing of diversions of water from Ralston Creek upstream of the mine. <br />These types of data are not contained in the EPP, nor is there an indication that this level <br />of data collection has been performed. <br />EPP Finding: The mine pool is not strongly connected to the alluvium and Ralston <br />Creek. <br />The EPP presents several lines of evidence in an attempt to support this finding. Each line <br />of evidence is questionable and not conclusive. The following discusses these lines of <br />evidence and information is provided that indicates that the mine pool is connected to and <br />affecting the alluvium. <br />A chemical mixing calculation was used to support the minimal connection between mine <br />pool and the alluvium. However, the mixing calculation relies solely on comparison of <br />uranium concentrations in the mine pool and alluvial groundwater. In Table 9 -2 of the <br />EPP it states that 0.8 to 8 percent of alluvial groundwater is sourced from mine pool <br />based on the simple chemical mixing calculations. As an example, in well MW -9 in <br />Table 9 -2, the uranium concentration in the well is 0.308 mg /L, which is divided by the <br />mine pool concentration of 41 mg /L, resulting in the low -end range value of 0.8 percent. <br />This approach does not consider the rate of flow for either the mine pool or alluvial <br />aquifer, which is necessary to estimate the contribution from each. <br />A more appropriate method is to perform the mixing based on loads (concentration times <br />flow rate). This is illustrated in the following example by ARCADIS /Malcolm Pirnie <br />using a conservative mixing equation: <br />where: <br />QmixCmix= Q1C1 + Q2C2 <br />Q = 27 gpm (estimated flow in the alluvial aquifer entering the central mine area <br />from previous Darcy Law calculation) <br />C = 0.4 mg /L (uranium concentration in the alluvial aquifer entering the central <br />mine area based on MW -0, November 9, 2009 sample result) <br />Q2 = 2 gpm (flow rate based on the EPP's estimated upper end of 8 percent of <br />alluvial groundwater that is comprised of mine pool water times the estimated flow <br />in the alluvial aquifer of 27 gpm) <br />C2 = 34 mg/L (uranium concentration in the mine pool December 2010) <br />QMix = 29 gpm (estimated flow in the alluvial aquifer [Q and mine pool, [Q2]) <br />