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<br />As sated previously in the Trout Creek AYF Findi~n; the 1.5:1 relationship <br />between soil salinity and irrigation .vat2r saiinity is considered to be a <br />conservative assumption (the actual relationship may be less than 1.5:1). <br />Data collected by the Division on August 15, 1985, showed root zone soil <br />conductivity to be slightly lower than Fish Creek surface water conductivity. <br />The major portion of the Fish Creek Alluvial Valley Floor is not flood <br />irrigated but is assumed to be sub-irrigated based on vegetation types, <br />alluvial water depths and late growing season color infrared photography. <br />Material damage to sub-irrigated vegetation would not occur because the <br />majority of discharge to the aquifer occurs during spring and early summer <br />when mine discharge is diluted by high runoff volumes. <br />Table 17 shows a predicted alluvial water quality on Fish Creek of <br />approximately 1 mmhos/cm. !dell 008-AU-3 on Fish Creek corresponds more <br />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 <br />alluvial aquifers is projected, but the predicted conductivity would be well <br />below the 3 mmhos/cm material damage suspect level for sub-irrigation. Water <br />quality measured in well 006-AW-2 exceeds the suspect level in both the <br />existing and predicted case, but mine discharge water would actually dilute <br />the salinity of 006-AW-2 water, resulting in an improvement in water quality <br />due to mining. <br />3. The proposed operation would preserve, throughout the mining operation, <br />the essential hydrologic functions of the alluvial valley floor. <br />The essential hydrologic functions of the Fish Creek alluvial valley floor <br />have been identified as the capacity to support sub-irrigated and flood <br />irrigated agricultural activities. <br />The proposed plan would not result in any surface disturbance to the AVF. <br />Also, as discussed previously, no material damage would result from changes in <br />the quality of surface and ground water that supply the alluvial valley <br />floor. Thus, the essential hydrologic functions of the alluvial valley floor <br />would not be affected by the proposed operation. <br />Foidel Creek <br />As discussed previously in the AVF identification section of this document, <br />alluvial bodies on Foidel Creek within the proposed permit area have been <br />determined not to be alluvial valley floors and will not be discussed <br />further. Two alluvial bodies which have been determined to meet the AVF <br />criteria exist downstream from the permit area. The first of these areas is <br />discussed below, the second is at the confluence of Foidel Creek and i4iddle <br />Creek and is discussed separately, in the following section. <br />The first area, a body of alluvium of approximately 100 acres located <br />downstream from the permit area below the water gap in Section 21, 22 and 28 <br />(T5N, R86W) was previously found to be an alluvial valley floor based on an <br />assumed capability to support sub-irrigated agricultural activities. The <br />positive finding was made due to the fact that insufficient hydrologic or <br />vegetative information was provided to detarnine conclusively the presence or <br />absence of sub-irrigation. <br />2C <br />