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<br /> <br />No impact to groundwater quality is predicted. Subsidence could cause inter-communication of <br />aquifers. The two aquifers of significance above the workings are the Fish Creek alluvial aquifer and <br />the Twentymile Sandstone aquifer. No interaction between these aquifers was predicted due to their <br />physical separation. <br />Discharge from the Fish Creek Borehole has not occurred since first quarter 1996. Mine water is <br />recirculated through the Million eallon tank and Site 114 system. <br />Cover and productivity data were collected in 1997 in and adjacent to the Fish Creek AVF. AVF <br />species are dominated by Smooth bromegrass, Kentucky bluegrass, Common yarrow, sage, Artentesia <br />cona,and Timothy. <br />Projected Fish Creek water quality for Flood irrigation is conservatively 0.9 mmhos/cm. Projected root <br />zone soil salinity would 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 productivity if <br />irrigation water 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 quality <br />were to exceed 2.0 mmhos/cm (which is assumed to correspond to a root zone conductivity of 3.0 <br />mmhos/cm). <br />A 1.S:1 relationship between soil salinity and irrigation water salinity is considered to be a conservative <br />assumption (the actual relationship may be less than 1.5:1). Data collected by the Division on August <br />15, 1986, showed root zone soil conductivity to be slightly lower than Fish Creek surface water <br />conductivity. <br />The major portion of the Fish Creek Alluvial Valley Floor is not flood irrigated but is assumed to be <br />subirrigated based on vegetation types, alluvial water depths and late growing season color infrared <br />photography. Material damage to subirrigated vegetation would not occur because the majority of <br />dischazge to the aquifer occurs during spring and early summer when mine dischazge is diluted by high <br />runoff volumes. <br />Predicted alluvial water salinity on Fish Creek is approximately 1 mmhos/cm. Well 008-AU-3 on Fish <br />Creek corresponds more closely with surface water quality and is thought to be a more representative <br />site than 006-AW-2. Based on 008-AU-3, a measurable increase in salinity of alluvial aquifers is <br />projected, but the predicted conductivity would be well below the 3 mmhos/cm material damage <br />suspect level for subirrigation. Water quality measured in well 006-AW-2 exceeds the suspect level in <br />both the existing and predicted case, but mine discharge water would actually dilute the salinity of <br />006-AW-2 water, resulting in an improvement in water quality due to mining. <br />Following mining and reclamation, the mine workings would fill with ground water and water passing <br />through the mine workings would again discharge to the stream/alluvial aquifer system. This water <br />would be expected to have a degraded water quality (3200 mg/I TDS at the source), but concentrations <br />would decrease as the affected water flows to the discharge area. The ground water discharge would be <br />further diluted by flow in the stream/alluvial aquifer system. Because of the low flows involved (O.14 <br />cfs), water quality degradation in the stream/alluvial aquifer system would not be sufficient to cause <br />material damage to the waters which supply the alluvial valley Floor. <br />The proposed operation would preserve,[hroughoutthe mining operation, the essential <br />hydrologic functions of the alluvial valley floor. <br />?~ <br />