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Due to the significant expansion of mining operations proposed in the <br />revision application, the potential impacts to identified alluvial valley <br />floors have been reevaluated. Areas previously determined by the <br />Division to not meet alluvial valley floor criteria were not reexamined. <br />Asa result of additional vegetation data and land use information <br />submitted by the applicant and site visits made by Division staff, <br />however, certain lands previously identified as alluvial valley floors <br />have been found not to meet AVF criteria. <br />Based on the limited extent of arable land and relatively high percentage <br />of non-agriculturally useful species as documented by species composition <br />data included in the September 22, 1986 submittal, the Division has <br />concluded that the area of subirrigated alluvium on lower Foidel Creek <br />denoted as "Pasture 19" on supplemental Map No. 1 is not an alluvial <br />valley floor. A negative determination has also been made for <br />sub-irrigated portions of Middle Creek between the Foidel Creek <br />confluence and the first Trout Creek irrigation diversion in Section 12, <br />T5N, R86W due to the limited extent of farmable acreage resulting from <br />the narrow alluvial body (averaging less than 500' in width) which is <br />bisected by the meandering channel of Middle Creek. In both instances <br />the extent of farmable acreage would be 10 acres or less. The areas are <br />not presently and have not historically been farmed and evidence <br />presented indicates that farming is not typically practiced on similar <br />parcels in the region. <br />Effects of Mining on Identified Alluvial Valley Floors <br />Due to elevated levels of salinity documented in current mine discharge <br />water and projected for future mine discharge and potential inhibitory <br />effects of increased soil and alluvial ground water salinity on flood <br />irrigated and subirrigated crops, the potential for material damage <br />caused by salt loading was a major concern which had to be evaluated for <br />each of the alluvial valley floors. <br />Material damage projections were calculated in both a sub-irrigation and <br />a flood irrigation case analysis, using data obtained during <br />low-flow-of-record years (see TABLE 17 contained in Section IX (CRIB) of <br />this Findings Document). The subirrigation scenario assumed that the <br />stream would recharge the alluvial aquifer in the spring during peak <br />flows. The flood irrigation case utilized the period between June 1 and <br />August 31. Assumptions and equations used in projecting water quality <br />impacts are set forth in detail in the CHIS section of this Findings <br />Document. Salt loading projections were arrived at by addition of the <br />projected impacts from spoils aquifers at surface mines in the drainage <br />to predictions of peak discharges from the Foidel Creek Mine. <br />In the supplemental information package dated September 22, 1986, the <br />applicant submitted information on vegetation cover and production by <br />species for flood irrigated and sub-irrigated croplands on the affected <br />alluvial valley floors. Alluvial bodies, irrigated fields and vegetation <br />-19- <br />