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result in a measurable change in flow for low flows with return <br /> periods of about 200 years or greater. Additionally, during the <br /> extreme low flow periods, MCC's water rights would be out of <br /> priority and diversion would not be undertaken. <br /> It is presumed that any change in flow that is less than five percent <br /> and within the measurement error of a stream gauge would not result <br /> in a hydrologic impact. Table 4 of this document shows the estimated <br /> percent changes in North Fork flow volumes due to withdrawals for <br /> projected mine requirements. <br /> The NPDES permit allows for a discharge of 10,000 gpd, based on a <br /> 30-day average, from the sanitary waste water treatment plant. The <br /> potential impact of discharge of waste water effluent would be greatest <br /> when the dilution ratio for effluent is smallest. <br /> Total mine water inflow in the F Seam is estimated to not have <br /> exceeded 15 acre-feet in any one year. The quality of mine water is <br /> considered good and offers no problem for treatment and discharge. <br /> Mine water discharge is treated in sedimentation pond MB-1 and/or <br /> MB-2R. B Seam inflow amounts are expected to be similar to the <br /> mine water inflow amounts of the F Seam. <br /> Overland runoff passes over disturbed areas within the permit area to <br /> one of the five sedimentation ponds, mentioned previously in this <br /> section. This water may be discharged to the North Fork or stored <br /> when water rights are in priority. From previous Annual Hydrology <br /> Reports, it appears that these discharges have had no adverse effect on <br /> the North Fork. In fact, the quality of the discharge usually exceeds <br /> the quality of the North Fork. <br /> i. Refuse Material Disposal Impacts on Surface Water - <br /> Lower Refuse Disposal Area - Runoff from the Lower <br /> Permanent Waste Disposal site will be routed through the <br /> sediment control system and must meet effluent limitations. <br /> Final designs for the waste rock pile, which include surface <br /> and subsurface drainage systems, allow for the collection of <br /> water leachate from the pile. Analysis of sample rock <br /> provided by MCC indicates that potential toxicity levels are <br /> below the Environmental Protection Agency (EPA) standards. <br /> Consequently, it appears that if runoff were to develop from <br /> the waste piles, minimal impact will occur on the North Fork <br /> of the Gunnison River. MCC will be monitoring for both <br /> ground water quality and levels under the piles, leachate <br /> quality and levels from the subdrains, and spring quality from <br /> the base of the pile site. MCC has had leach tests performed <br /> on representative samples of waste rock. Of analyses <br /> 39 <br />