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the Trout Creek irrigation diversion (assumed to be subirrigated). The flood irrigated pasture <br />was dominated by pasture grasses while weedy species were visually dominant on the <br />non-irrigated reach (see vegetation data in supplemental Report of 9/22/86). From <br />comparison of the adjacent flood irrigated and non-flood isigated areas, it appears that sub- <br />irrigation has little impact on the agricultural productivity of the confluence AVF, and that <br />flood irrigation is the critical function. <br />Significant increases in the salinity of alluvial ground water in the confluence azea would not <br />be anticipated since the majority of the rechazge to the aquifer occurs during spring and early <br />summer when Middle Creek and Foidel Creek flows aze highest and conductivity levels aze <br />lowest. Further dilution of alluvial waters would be provided by Trout Creek irrigation <br />drainage water. Since Trout Creek irrigation water supports the critical function of the <br />alluvial valley floor and the Trout Creek waters would not be affected by the proposed <br />operations, material damage to the quality of water supplying the AVF would not occur. <br />The proposed operation would preserve, throughout the mining operation, the essential <br />hydrologic functions of the alluvial valley floor. <br />The essential hydrologic functions of the confluence AV F aze flood irrigation primazily and, <br />to a lesser extent, sub-irrigation, and both functions would be preserved. <br />Flood irrigation on the AVF is by diversion of unaffected Trout Creek water. Sub-irrigation <br />does not play a major role in maintaining the agricultural productivity of the AVF, but the <br />quality of alluvial ground water would be maintained above the material damage suspect <br />level of 3 mmhos/cm due to the fact that aquifer rechazge occurs primarily in the spring and <br />eazly summer when stream salinity levels aze lowest, and the alluvial water would be further <br />diluted by the low salinity Trout Creek irrigation drainage water. <br />Alluvial Vallev Floor Monitorine <br />Hydrologic monitoring as discussed in Sections III. A and B of this document will be <br />sufficient to verify projections and monitor effects of mining on the quality and quantity of <br />water supplying the identified alluvial valley floors. Included in this monitoring plan is a <br />monitoring schedule for the Fish Creek AVF to assess for impacts. A surface water and <br />alluvial water site presently exists downstream of all Foidel Creek mining activities on Trout <br />Creek (site 1005 and well 008-AT-1). Surface water monitoring and alluvial monitoring sites <br />aze located along both Foidel and Middle Creeks to assess possible impacts due to the <br />undermining of these perennial streams. <br />The Division finds that activities proposed by the applicant will not interrupt, discontinue, or <br />preclude farming on the alluvial valley floors that are irrigated or naturally subirrigated <br />[4.24.3(1)]. <br />The proposed activities will not materially damage the quantity or quality of water in the <br />surface or ground water system described above [4.24.3(3) and 2.06.8(5)(a)(ii)]. <br />39 <br />