2016-05-04_REVISION - C1982056 (12)

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0.20 cfs but an electrical conductivity of nearly 3 mmhos/cm. Discharge and conductivity in this range would cause a measurable increase in salinity downstream on Fish Creek. Stream flow modeling conducted during the CHIA produced EC values in the area of 0.750 mmhos/cm, given a conservative TDS/EC ratio of 0.8, for areas downstream of the Fish Creek dewatering borehole. Electrical conductivity values at this level would not materially damage crop production from either flood irrigation or sub -irrigation. As was the case on Trout Creek, the majority of the plant species identified in surveys conducted by the applicant and summarized in the supplemental package of September 22, 1986, are rated moderately tolerant to salinity. Only 3.7% of the relative vegetative cover on Fish Creek was made up of moderately sensitive species. No production sampling was conducted on Fish Creek, and so a ratio of 4.5 obtained from sampled fields at the Foidel Creek/Middle Creek confluence was used to convert relative cover of 3.7% to assumed relative production of 16.6% for moderately sensitive species. Cover and productivity data were collected in 1997 in and adjacent to the Fish Creek AVF. AVF species are dominated by Smooth bromegrass, Kentucky bluegrass, Common yarrow, sage, Artemesia cana, and Timothy. Projected Fish Creek water quality for flood irrigation is conservatively estimated at 0.9 mmhos/cm electrical conductivity. Projected root zone soil salinity would be less than 1.5 mmhos/cm and therefore no decrease in crop production would occur. Moderately sensitive species would be expected to exhibit some decline in productivity if irrigation water conductivity were to exceed 1.0 mmhos/cm. Due to the relatively small component of moderately sensitive species, material damage would not occur unless flood irrigation water conductivity were to exceed 2.0 mmhos/cm (which is assumed to correspond to a root zone conductivity of 3.0 mmhos/cm). A 1.5:1 relationship between soil salinity and irrigation water salinity is considered to be a conservative assumption (the actual relationship may be less than 1.5:1). Data collected by the Division on August 15, 1986, showed root zone soil conductivity to be slightly lower than Fish Creek surface water conductivity. The major portion of the Fish Creek Alluvial Valley Floor is not flood irrigated but is assumed to be subirrigated based on vegetation types, alluvial water depths and late growing season color infrared photography. Material damage to subirrigated vegetation would not occur because the majority of discharge to the aquifer occurs during spring and early summer when mine discharge is diluted by high runoff volumes. Predicted alluvial water salinity on Fish Creek is approximately 1 mmhos/cm. Well 008 -AU -3 on Fish Creek corresponds more closely with surface water quality and is thought to be a more representative site than 006 -AW -2. Based on 008 -AU - 3, a measurable increase in salinity of alluvial aquifers is projected, but the Page 45 of 52