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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 />the relatively small component of moderately sensitive species, material damage <br />would not occur unless flood irrigation water conductivity were to exceed 2.0 <br />mmhos/cm (which is assumed to correspond to a root zone conductivity of 3.0 <br />mmhos/cm). <br />A 1.5:1 relationship between soil salinity and irrigation water salinity is considered <br />to be a conservative assumption (the actual relationship may be less than 1.5:1). <br />Data collected by the Division on August 15, 1986, showed root zone soil <br />conductivity to be slightly lower than Fish Creek surface water conductivity. <br />The major portion of the Fish Creek Alluvial Valley Floor is not flood irrigated but <br />is assumed to be subirrigated based on vegetation types, alluvial water depths and <br />late growing season color infrared photography. Material damage to subirrigated <br />vegetation would not occur because the majority of discharge to the aquifer occurs <br />during spring and early summer when mine discharge is diluted by high runoff <br />volumes. <br />Foidel Creek Mine 42 August 10, 2018 <br />