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Daniel Arnold, Esq. January 25, 2011 Denver Water Page 9 of 21 As described earlier, a significant amount of the water collected in the sumps is from the creek and when the pumping ceased there was less creek water entering the sumps to dilute the groundwater. Shutting down Sump 1 in 2009 allowed the alluvial aquifer to return to higher uranium concentrations because water was not being pulled in from the creek. This resulted in increased dilution at wells MW -06 and MW -07 that are located between the sumps and the creek. Furthermore, the stoppage of pumping at Sump 1 and recirculation would not be expected to affect areas upgradient of the recirculation circuit between Sump 1 and 4. However, MW -3A is 100 feet upgradient of Sump 4 and this recirculation circuit, and uranium concentrations continued to increase through 2009 and into 2010 in that well. This is illustrated on Figure 5 that shows the historical uranium concentrations for well MW -3A. The uranium concentrations in MW -3A increased to a historic high of 0.8 mg /L in January 2010, which is unrelated to the cessation of sump pumping in 2009. EPP Finding: Pumping of Sump 1 continued after June 2002, when the other sumps were shut off, and the untreated water from Sump 1 was recirculated back to Sump 4 and created a hydraulic barrier to protect the creek water quality. The recirculation of water from Sump 1 back to Sump 4 is unlikely to have created a hydraulic barrier as claimed in the EPP. The water that was discharged in Sump 4, which is only 90 feet from the creek, would have created a hydraulic head in the sump that was higher than water levels in the surrounding alluvial aquifer, resulting in radial spreading of the sump water. As discussed previously, the alluvial aquifer is strongly connected to the creek and it is likely that some of this sump water with elevated uranium concentrations flowed toward and discharged to the creek. Instead of protecting the creek water quality, this recirculation of untreated sump water from 2002 through 2009 further degraded the creek water quality. This is evidenced by a noticeable increase in the uranium concentration in the creek in 2002, which corresponds to the beginning of this recirculation of untreated sump water (see Figure 3). Data Adequacy: The necessary data to support that the recirculation created a hydraulic barrier and protected the creek water quality are not contained in the EPP. Groundwater levels around Sump 4 and detailed loading evaluations of the creek along the Sump 4 reach would be needed to support this finding. 3.4 Mine Pool EPP Finding: Shutdown of pumping in the mine had no detectable effect on flow in the creek. Data Adequacy: There are no flow measurements in the EPP to confirm or deny this finding. Detailed stream flow measurements would have to have been made while the mine was dewatered and as it fills to support this finding. Only one stream flow measurement could be found in the EPP (at SW -BPL on November 13, 2008). Further, climatic factors affecting stream flow need to be taken into account such as: changes in