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With respect to minimizing health risks (Criterion 3), even if uranium concentrations in the creek <br />could be reduced in a relatively short time frame due to temporary mine dewatering /active <br />treatment, this measure is unlikely to significantly reduce true risks to human health for a number <br />of reasons. Several incidental anthropogenic and natural controls are present that limit or reduce <br />water concentrations and mitigate pathways for potential human intakes of uranium from this <br />source including: <br />1) Large receiving reservoirs that greatly reduce concentrations by mixing, dilution and <br />natural attenuation processes. <br />2) Municipal water treatment plants that ensure that all drinking water quality standards are <br />met before delivery to the public for domestic uses. <br />3) Institutional controls that restrict public access to the mine site, Ralston Creek and <br />Ralston Reservoir. <br />Cotter does not consider any of these incidental controls to be remedial measures for mitigation <br />of water quality impacts associated with the Schwartzwalder Mine. However, these <br />circumstances are relevant in terms of realistic potential for health risks to members of the public <br />and are thus important to consider in terms of assessing and selecting the most appropriate <br />remedial strategy. <br />From 1994 to 2010, flow from Ralston Creek averaged about 6% of all sources that supply water <br />to Ralston Reservoir (Caine et al., 2011). Quarterly stream monitoring data in 2009 indicated <br />that uranium concentrations in Ralston Creek at the Long Lake Head Gate just above Ralston <br />Reservoir averaged about 250 .tg/L. In late 2009, several individual samples of water from <br />Ralston Reservoir taken at the intake to the Moffat Water Treatment Plant had uranium <br />concentrations in the range of 7 -9 µg/L (Denver Water, 2010). These values are higher than <br />average values measured in previous years (typically ranging from 1 -2 µg/L) but are still less <br />than one third of the drinking water standard (30 µg/L). For comparison, the National Uranium <br />Resource Evaluation (NURE) study found that uranium concentrations in natural waters in the <br />Denver Basin region, including streams, ponds, seeps and wells, average about 14 µg/L (Bolivar <br />et al., 1978). The difference in uranium concentrations in 2009 between water at the Long Lake <br />Head Gate and water at the intake to the Moffat Water Treatment Plant suggests a reduction in <br />uranium concentrations on the order of 96% due to mixing, dilution and attenuation processes <br />occurring in the reservoir. <br />Cotter recognizes that water from Ralston Creek is at times diverted to other reservoirs, yet the <br />same incidental processes of mixing, dilution and attenuation will also occur and any water <br />delivered for direct domestic use by the public is first treated at a municipal water treatment <br />facility. Unrealistic perceptions of actual health risks can be counterproductive in terms of <br />selecting the most effective and sustainable remedial measures for permanent mitigation of the <br />problem as soon as possible. <br />Although mine dewatering /active treatment would not significantly reduce potential risks to <br />human health due to a partial reduction of uranium concentrations in Ralston Creek, it would <br />5 <br />