2016-02-25_GENERAL DOCUMENTS - C1982056

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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 predicted conductivity would be well below the 3 mmhos/cm material damage suspect level for sub -irrigation. 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 (0.02 cfs), water quality degradation in the stream/alluvial aquifer system would not be sufficient to cause material damage to the waters which supply the Fish Creek Alluvial Valley Floor. 3. The proposed operation will preserve, throughout the mining operation, the essential hydrologic functions of the Alluvial Valley Floor. The essential hydrologic functions of the Fish Creek Alluvial Valley Floor have been identified as having the capacity to support subirrigated and flood irrigated agricultural activities. Mining beneath the Fish Creek AVF has occurred in panels 5, 6 and 7 of the Southwest Mining District and did not result in dewatering of the stream/alluvial system. Also, as discussed previously, no material damage would result from changes in the quality of surface and ground water that supply the Fish Creek Alluvial Valley Floor. The essential hydrologic functions of the Fish Creek Foidel Creek Mine 45 February 25, 2016