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the head cuts in the stream. This increase in sediment load is anticipated to be no <br /> more than the sediment increase observed during spring runoff and after large <br /> rainstorms. An increased sediment load was not detected during past subsidence <br /> of Fish Creek, Foidel Creek, or Middle Creek. <br /> No impact to groundwater quality is predicted. Ground water could now between <br /> aquifers through subsidence fractures. The Fish Creek alluvium and the <br /> Twentymile Sandstone have the greatest potential for such interstitial flow, but the <br /> stratigraphic separation of several hundred feet between the two units would <br /> prevent any significant amount of flow between them. <br /> Water quality impacts to the stream/alluvial aquifer system of Fish Creek could <br /> result from two additional processes: mine water discharge through the Fish Creek <br /> borehole or Fish Creek Vent Shaft during mining and contamination of tributary <br /> ground water through seepage from the underground workings after mining has <br /> ceased and the workings have flooded. Impacts from mine water discharge during <br /> operation will be discussed first. <br /> Originally, mine water discharge was projected to have an electrical conductivity <br /> of 1 mmhos/cm at a projected discharge rate of 0.41 cfs. Actual data from <br /> numerous years of operation reveal mine water discharge values of approximately <br /> 0.20 cfs but an electrical conductivity of nearly 3 mmhos/cm. Discharge and <br /> conductivity in this range would cause a measurable increase in salinity <br /> downstream on Fish Creek. Stream flow modeling conducted during the CHIA <br /> produced EC values in the area of 0.750 mmhos/cm, given a conservative TDS/EC <br /> ratio of 0.8, for areas downstream of the Fish Creek dewatering borehole. <br /> Electrical conductivity values at this level would not materially damage crop <br /> production from either flood irrigation or sub-irrigation. <br /> As was the case on Trout Creek, the majority of the plant species identified in <br /> surveys conducted by the applicant and summarized in the supplemental package <br /> of September 22, 1986, are rated moderately tolerant to salinity. Only 3.7% of the <br /> relative vegetative cover on Fish Creek was made up of moderately sensitive <br /> species. No production sampling was conducted on Fish Creek, and so a ratio of <br /> 4.5 obtained from sampled fields at the Foidel Creek/Middle Creek confluence was <br /> used to convert relative cover of 3.7%to assumed relative production of 16.6%for <br /> moderately sensitive species. <br /> Cover and productivity data were collected in 1997 in and adjacent to the Fish <br /> Creek AVF. AVF species are dominated by Smooth bromegrass, Kentucky <br /> bluegrass, Common yarrow, sage,Artemesia cana, and Timothy. <br /> Projected Fish Creek water quality for flood irrigation is conservatively estimated <br /> at 0.9 mmhos/cm electrical conductivity. Projected root zone soil salinity would <br /> be less than 1.5 mmhos/cm and therefore no decrease in crop production would <br /> occur. Moderately sensitive species would be expected to exhibit some decline in <br /> productivity if irrigation water conductivity were to exceed 1.0 mmhos/cm. Due to <br /> Foidel Creek Mine 40 August 4,2023 <br />