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<br />poten*_ially could affect the quality of eater suppl,;inn the AVF. Tn? <br />remaining portions Ufi Ec k1-dn Burk dnd i•li it c' i art wi t~ii:n tic' ..ii u21 ..-22'i <br />watershed, and are not hydrologically connected to the upper i4iddle Creek AVF. <br />Potential impacts to identified alluvial valley floors have been reevaluated <br />by the Division to take into account the recently approved Life-of-Mine <br />revision submitted by Twentymile Coal Company (TCC} for the Foidel Creek <br />Underground Mine, as well as updated hydrologic projections for Eckman Park, <br />Mine 1, Mine 2 and the proposed little iAiddle Creek Tract. The development in <br />recent years of a spoil aquifer discharging as saline springs and seeps along <br />the toe of the regraded surface mine spoils represents a potentially <br />significant impact which was not originally predicted. Since the majority of <br />the alluvial valley floors are potentially affected by both CYCC and TCC <br />operations, certain information submitted by TCC in the Foidel Creek <br />Life-of-Mine Revision is referenced in this document. <br />Areas previously determined by the Division to not meet alluvial valley floor <br />criteria were not reexamined. As a result of additional vegetation data and <br />land use information submitted by the applicant and site visits made by <br />Division staff, however, certain lands previously identified as alluvial <br />valley floors have been found not to meet AVF criteria. <br />Based on the limited extent of arable land and relatively high percentage of <br />non-agricu'i•:~^ally useful species as documented by species composition data <br />included in the Foidel Creek Life-of-Mine Revision, the Division has concluded <br />that the area of sub-irrigated alluvium qn lower Foidel Creek denoted as <br />"Pasture 19" on Map No. 36 is not an alluvial valley floor. A negative <br />determination has also been made for sub-irrigated portions of Middle Creek <br />between the Foidel Creek confluence and the first Trout Creek irrigation <br />diversion in Section 12, TSN, R86W due to the ]invited extent of fannable <br />acreage resulting from the narrow alluvial body (averaging less than 500' in <br />width) which is bisected by the meandering channel of Middle Creek. In both <br />instances the extent of fannable acreage would be 10 acres or less. The areas <br />are not presently and have not historically been farmed and evidence presented <br />indicates that fanning is not typically practiced on similar parcels in the <br />region. <br />Effects of Mining on Identified Alluvial Valley Floors <br />Due to the development of relatively saline (2-4 mmhos/cm) springs along the <br />toe of backfilled spoils at Mine 1, Eckman Park and Mine 2, the potential for <br />material damage caused by salt loading was a major concern which had to be <br />evaluated for each of the alluvial valley floors. The concern was that <br />increased salinity of the receiving streams would lead to elevated soil and <br />alluvial ground water salinity, with resu]ting inhibitory effects on flood <br />irrigated and sub-irrigated crops. <br />iaterial damage projections were calculated in both a sub-irrigation and a <br />flood irrigation case analysis, using data obtained during low-flow-of-record <br />years (see Table 17 contained in Section IX (CRIB) of this Findings <br />Document). The sub-irrigation scenario assumed that the stream would recharge <br />the alluvial aquifer in the spring during peak flows. The flood irrigation <br />case utilized the period between June 1 and August 31. Assumptions and <br />19 <br />