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July 30, 2010 11 of 24 <br />STEADY-STATE INFLOW TO THE MINE WAS 190 GPM AT FULL DEPTH <br />The Division cites Cotter's mine inflow data to show that transient inflows during mine <br />development were as high as 600 gpm (See Draft Order, paragraph 24). <br />The 600 gpm inflow is not representative of rock transmissivity or steady-state groundwater flow <br />into the mine. Transient initial inflows occur during the development of mines, tunnels, and other <br />construction projects when excavations rapidly enter new ground. If rock is not dewatered in <br />advance, especially in low-permeability rock where fractures are essentially unconnected, the <br />initial inflows to an excavation may be high for several hours, days, or weeks. The inflow is a <br />function of rock storativity, and is a transient effect that does not indicate overall high hydraulic <br />conductivity. In fact, higher permeability materials may be less likely to experience short-term <br />transient high inflows, because the rock is connected and drained in advance of development. Had <br />the mine been developed more slowly or more rapidly, the transient inflow values would have <br />been higher, or lower, respectively. This is not a reflection of the overall permeability of the rock <br />mass. <br />During the last four years of mining, at its total maximum depth of 2,220 feet, groundwater inflow <br />to the Schwartzwalder mine was only 189 gpm. This steady-state flow rate is more representative <br />of the total hydraulic conductivity of rocks surrounding the mine than short-term transient inflows <br />affected by rock storativity and the rate of mine development. <br />Cotter has provided all available hydrogeologic data to assist the Division in understanding this <br />site. The Division has misinterpreted the nature of transient inflows. That said, even if the inflow <br />to the mine had been sustained at 600 gpm, which it was not, the overall hydraulic conductivity of <br />the rock mass would be 9.7 x 10'7 cm/sec or just lower than the recommended upper limit for a <br />Subtitle C landfill liner. <br />RISK-BASED EVALUATION IS VALID <br />DRMS's Technical Adequacy Review (May 19, 2010) states that DBMS will evaluate <br />environmental impacts relative to baseline conditions rather than impacts or perceived risk to <br />human health or aquatic life. <br />Protection of human health and the environment should be implemented using quantifiable, risk- <br />based analysis and decision making. This approach has been widely used for decades by State and <br />Federal regulatory agencies to assess appropriate responses to environmental issues. The <br />protective intent of water quality standards themselves are developed based on concepts of risks to <br />human health or aquatic life. <br />Although the May 19, 2010 Technical Adequacy Review states that "DBMS will evaluate <br />environmental impacts relative to baseline conditions rather than impacts or perceived risk to <br />human health or aquatic life," Mr. Bird's testimony before the MLRB is replete with references to <br />the DRMS's fears and perceived risk of groundwater in the mine pool reaching Ralston Reservoir. <br />DRMS bases most of its arguments for requiring immediate treatment of mine pool water on a <br />premise of serious risks to Denver drinking water supplies and indirectly, on implied health risks <br />to Denver area water users. Meanwhile, DRMS admits that there is no direct evidence that the