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As discussed in the PHC Section of this document, significant dewatering of the Foidel Creek or Middle Creek stream/alluvial systems due to undermining would be precluded by the low vertical permeabilities between the Wadse seam and the alluvia. Stream flow loss to surficial tensional cracks which may develop is expected to be minimal and the fine-grained nature of the alluvium will rapidly fill any cracks that may develop. Furthermore, surface cracking due to subsidence is typically limited to a maximum of 50 feet in depth and direct connection to the workings is not anticipated due to overburden depths in this area in excess of 600 feet. Also, any stream flow loss will be more than compensated by the projected and existing mine discharge to Foidel Creek averaging over 600 gpm. And lastly, the entire alluvial valley floor is flood irrigated by water diverted from the unaffected segment of Trout Creek above its confluence with Middle Creek, nullifying any temporary, minor impacts which could occur. (See TCC Life of Mine Application Map No. I5). The primary function of the confluence AVF is the support of flood irrigated hayland. As previously noted, the flood irrigation water is not diverted from affected segments of either Foidel Creek or Middle Creek, but is diverted from an unaffected segment of "trout Creek. Afield inspection conducted by the Division in late August of 1986 observed vegetation on the flood irrigated AVF to be more robust than adjacent areas upstream on Foidel Creek above the Trout Creek irrigation diversion (assumed to be subirrigated). The flood irrigated pasture was dominated by pasture grasses while weedy species were visually dominant on the non-irrigated reach (see vegetation data in supplemental Report of 9122/86). From comparison of the adjacent flood irrigated and non-flood irrigated areas, it appears that subirtigation has little impact on the agricultural productivity of the confluence AVF, and that flood irrigation is the critical function. Significant increases in the salinity of alluvial ground water in the confluence area would not be anticipated since the majority of the recharge to the aquifer occurs during spring and early summer when Middle Creek and Foidel Creek flows are highest and conductivity levels are lowest. Further dilution of alluvial waters would be provided by Trout Creek irrigation drainage water. Since Trout Creek irrigation water supports the critical function of the alluvial valley floor and the Trout Creek waters would not be affected by the proposed operations, material damage to the quality of water supplying the AVF would not occur. The proposed operation would preserve, throughout the mining operation, the essential hydrologic functions ofthe alluvial valley floor. The essential hydrologic functions of the confluence AVF are flood irrigation primarily and, to a lesser extent, subircigation, and both functions would be preserved. Flood irrigation on the AVF is by diversion of unaffected Trout Creek water. Subirrigation does not play a major role in maintaining the agricultural productivity of the AVF, but the quality of alluvial ground water would be maintained above the material damage suspect level of 3 mmhos/cm due to the fact that aquifer recharge occurs primarily in the spring and early summer when stream salinity levels are lowest, and the alluvial water would be further diluted by the low salinity Trout Creek irrigation drainage water. Alluvial Valley Floor Monitorin Hydrologic monitoring as discussed in Section III. A and B of this document will be sufficient to verify projections and monitor effects of mining on the quality and quantity of water supplying [he identified alluvial valley Floors. Included in this monitoring plan is a monitoring schedule for the Fish Creek AVF to assess for impacts. A surface water and alluvial water site presently exists downstream of all 27