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1986 aze rated moderately tolerant to salinity. Only 3.7% of the relative vegetative cover on <br />Fish Creek was made up of moderately sensitive species. No production sampling was <br />conducted on Fish Creek, and so a ratio of 4.5 obtained from sampled fields at the Foidel <br />Creek/Middle Creek confluence was used to convert relative cover of 3.7% to assumed <br />relative production of 16.6% for moderately sensitive species. <br />Cover and productivity data were collected in 1997 in and adjacent to the Fish Creek AVF. <br />AVF species aze dominated by Smooth bromegrass, Kentucky bluegrass, Common yarrow, <br />sage, Artemesia cana, and Timothy. <br />Projected Fish Creek water quality for flood irrigation is conservatively estimated at 0.9 <br />mmhos/cm electrical conductivity. Projected root zone soil salinity would be less than 1.5 <br />mmhos/cm and therefore no decrease in crop production would occur. Moderately sensitive <br />species would be expected to exhibit some decline in productivity if irrigation water <br />conductivity were to exceed 1.0 mmhos/cm. Due to the relatively small component of <br />moderately sensitive species, material damage would not occur unless flood irrigation water <br />conductivity were to exceed 2.0 mmhos/cm (which is assumed to correspond to a root zone <br />conductivity of 3.0 mmhos/cm). <br />A 1.5:1 relationship between soil salinity and irrigation water salinity is considered to be a <br />conservative assumption (the actual relationship may be less than 1.5:1). Data collected by <br />the Division on August 15, 1986, showed root zone soil conductivity to be slightly lower <br />than Fish Creek surface water conductivity. <br />The major portion of the Fish Creek Alluvial Valley Floor is not flood irrigated but is <br />assumed to be subirrigated based on vegetation types, alluvial water depths and late growing <br />season color infrared photography. Material damage to subirrigated vegetation would not <br />occur because the majority of dischazge to the aquifer occurs during spring and eazly <br />summer when mine discharge is diluted by high runoff volumes. <br />Predicted alluvial water salinity on Fish Creek is approximately 1 mmhos/cm. Well 008- <br />AU-3 on Fish Creek corresponds more closely with surface water quality and is thought to <br />be a more representative site than 006-AW-2. Based on 008-AU-3, a measurable increase in <br />salinity of alluvial aquifers is projected, but the predicted conductivity would be well below <br />the 3 mmhos/cm material damage suspect level for sub-irrigation. Water quality measured in <br />we11006-AW-2 exceeds the suspect level in both the existing and predicted case, but mine <br />discharge water would actually dilute the salinity of 006-AW-2 water, resulting in an <br />improvement in water quality due to mining. <br />Following mining and reclamation, the mine workings would fill with ground water, and <br />water passing through the mine workings would again discharge to the stream alluvial <br />aquifer system. This water would be expected to have a degraded water quality (3200 mg/1 <br />TDS at the source), but concentrations would decrease as the affected water flows to the <br />dischazge azea. The ground water discharge would be further diluted by flow in the <br />stream/alluvial aquifer system. Because of the low flows involved (0.02 cfs), water quality <br />34 <br />