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Daniel Arnold, Esq. January 25, 2011 <br />Denver Water Page 11 of 21 <br />C = ? (uranium concentration resulting from mixing of alluvial groundwater and <br />mine pool water) <br />The resulting uranium concentration of the mixed water (C is 2.8 mg/L, which is <br />within the range of uranium concentrations in the alluvial aquifer of 1.5 to 3.5 mg/L in <br />the last year, as shown on Figure 4 for wells MW -6 and MW -7. This example illustrates <br />that it does not require a substantial amount of mine pool water to further degrade the <br />alluvial groundwater quality, which in turn is hydraulically connected to the creek. Note <br />that this example assumes conservative mixing with no chemical transformations or <br />reactions. <br />The EPP discusses how stable isotopes of hydrogen and oxygen are used to support a <br />weak connection between mine pool and creek. Stable isotope data are said to be <br />contained in Whetstone (2007), but are not provided in the EPP, so this conclusion could <br />not be evaluated. The EPP also discusses the tritium data that have been collected that are <br />used to assess the age of mine pool and creek water. The data indicate that the creek is <br />sourced by water that is younger than 1952 and the mine pool is a mix of pre- and post - <br />1952 water. The tritium data are inconclusive in terms of connection between the creek <br />and mine pool. <br />The EPP states that the mine pool contains elevated molybdenum concentrations of 1.5 <br />mg /L whereas the alluvial groundwater has very low concentrations, and if the mine pool <br />was contributing significant flow to the alluvium then the molybdenum concentrations <br />would be much higher. Conceptually this may appear to be valid, but after closer <br />inspection of the chemical data it is not supported. Molybdenum concentrations are <br />detected in the alluvial groundwater at values that are proportionally similar as uranium <br />in the two waters, as the following explains. Alluvial monitoring wells (MW -1, -4, -6, -7, <br />and -9) have had maximum molybdenum concentrations between 0.1 and 0.24 mg /L, <br />which are approximately one order of magnitude less than values in the mine pool <br />concentration. Uranium concentrations in the mine pool are at 34 mg /L and recent values <br />in the alluvial groundwater are between 1 and 2.7 mg /L, or a similar one order of <br />magnitude less than the mine pool. Consequently, the respective proportions of uranium <br />and molybdenum in mine pool water and alluvial groundwater are actually quite similar, <br />and the low molybdenum concentrations in the alluvial aquifer do not support a lack of <br />connection. <br />Another line of evidence presented in the EPP that is used as a basis for supporting a lack <br />of mine pool water entering the alluvial groundwater is the ratio of uranium to <br />molybdenum in both waters. The EPP states that mine pool water has a ratio of 30:1 <br />uranium to molybdenum and the alluvial groundwater has a ratio of 12:1. Review of <br />recent data from alluvial monitoring wells shows that ratios can be similar to the mine <br />pool ratios. For example, MW -12 has ratios that range from 21:1 to 34:1, which <br />encompass the reported 30:1 ratio for the mine pool. Therefore, ratios of uranium to <br />molybdenum are not a reliable basis upon which to determine a lack of connection <br />