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As shown in TABLE 17, projected Fish Creek water quality for flood irrigation is approximately .9 mmhos/cm. 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 quality were to exceed 2.0 mmhos/cm (which is assumed to correspond to a root zone conductivity of 3.0 mmhos/cm). As stated previously in the Trout Creek AVF Findings the 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. TABLE 17 shows a predicted alluvial water quality on Fish Creek of 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 predicted conductivity would be well below the 3 mmhos/cm material damage suspect level for subirrigation. Water quality measured in well 006-AW-2 exceeds the suspect level in both the existing and predicted case, but mine discharge water would actually dilute the salinity of 006-AW-2 water, resulting in an improvement in water quality due to mining. Following mining and reclamation; the mine workings would fill with ground water and water passing through the mine workings would again discharge to the stream/alluvial aquifer system. This water would be expected to have a degraded water quality (3200 mg/1 TDS at the source), but concentrations would decrease as the affected water flows to the discharge area. The ground water discharge would be further diluted by flow in the stream/alluvial aquifer system: Because of the low flows involved (0.14 cfs), water quality degradation in the stream/alluvial aquifer system would not be sufficient to cause material damage to the waters which supply the alluvial valley floor. 3. The proposed operation would preserve, throughout the mining operation, the essential hydrologic functions of the alluvial valley floor. -24-