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The essential hydrologic functions of the Fish Creek alluvial valley <br />floor have been identified as the capacity to support subirrigated and <br />flood irrigated agricultural activities. <br />The proposed plan would not result in any surface disturbance to the <br />AVF. Mining beneath the AVF would be limited to one main and would not <br />result in dewatering of the stream/alluvial system or surface expression <br />of subsidence (as discussed previously in this section). Also, as <br />discussed previously, no material damage would result from changes in the <br />quality of surface and ground water that supply the alluvial valley <br />floor. Thus, the essential hydrologic functions of the alluvial valley <br />floor would not be affected by the proposed operation. <br />Foidel Creek <br />Map 5 (Surface Geology) and supplemental Map No. 1 identify several areas <br />of unconsolidated streamlaid deposits along Foidel Creek. Some of these <br />areas lie upstream of the proposed Foidel Creek Mine and would not be <br />affected by the proposed mining operation. Therefore, no alluvial valley <br />floor determination will be made for those areas that lie upstream of the <br />USGS-WRD gaging station near Pinnacle Peak. Three other areas lie <br />adjacent to or downstream from the proposed mining operation. The first <br />lies in an area immediately adjacent to the proposed operation and the <br />existing surface mining operations. The second area occurs downstream in <br />Sections 21, 22 and 28 and the third area is located at the confluence of <br />Foidel Creek and Middle Creek. (The third area will be discussed in <br />combination with Middle Creek.) <br />As discussed previously in the AVF section of this document, the first <br />area adjacent to the proposed operations has been determined not to be an <br />alluvial valley floor and will not be discussed further. <br />The second 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 <br />28 (T5N, R86W) was previously found to be an alluvial valley floor based <br />on an assumed capability to support subirrigated agricultural <br />activities. The positive finding was made due to the fact that <br />insufficient hydrologic or vegetative information was provided to <br />determine conclusively the presence or absence of subirrigation. <br />Additional data on alluvial ground water depth and quality for the area <br />in question has been provided in Table 67 of the life of mine <br />application. The presence of ground water at depths of 4.3 to 5.7 feet <br />suggests that subirrigation would be possible: Due to relatively high <br />salinities (up to 5.4 mmhos/cm) it is probable that the site would not be <br />particularly productive, however, vegetation information has not been <br />provided. Division staff conducted field visits to the site in May and <br />August, 1986 and it was observed that a silver sage community indicative <br />of subirrigation existed in a relatively narrow belt along the stream. <br />Areas further from the stream appeared to have been treated at some point <br />-25- <br />