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Information has not been provided concerning the significance of the <br />alluvial valley floor to farming. Consequently, the Division must assume <br />that the Fish Creek alluvial valley floor is significant to farming and <br />make the three required alluvial valley floor findings. <br />1. The proposed mining operations would not interrupt, discontinue or <br />preclude farming on the alluvial valley floor. <br />The only mining activity proposed within the boundaries of the AVF is the <br />2nd west main which would be driven beneath the AVF to access coal <br />reserves to the north of Fish Creek. The crossing would occur at a depth <br />of over 600 feet beneath the alluvium: Aquifer dewatering which might <br />impact farming would be precluded by the low vertical permeabilities of <br />the shales between the alluvium and the Wadge seam. As discussed in the <br />subsidence section of this document, the proposed limited extraction <br />beneath Fish Creek combined with the cover depth and nature of the <br />overburden strata would preclude the surface expression of subsidence <br />which might impact farming activities. <br />2. The proposed mining operations would not cause material damage to the <br />quantity and quality of surface and ground water that supply the <br />alluvial valley floor. <br />For reasons discussed under No. 1, above, neither surface flows nor <br />alluvial ground water would be dewatered directly by undermining. <br />Underground workings would intercept a small component of the ground <br />water currently discharged to the stream (less than 5% of the base flow <br />in Fish Creek) which would not cause material damage to the <br />stream/alluvial aquifer system. Mine discharge of .41 CFS would more <br />than compensate the projected interception related dewatering. <br />Water quality impacts to the stream/alluvial aquifer system of Fish Creek <br />could result from two separate processes, mine water discharge through <br />the Fish Creek borehole/shaft during mining and contamination of <br />tributary ground water through seepage from the underground workings <br />after mining has ceased and the workings have flooded. Impacts from mine <br />water discharge during operation will be discussed first. <br />Discharge of mine water having a projected electrical conductivity of 1 <br />mmhos/cm at a projected discharge rate of .41 cfs would cause a <br />measurable increase in salinity downstream on Fish Creek, but the <br />increased stream salinity would not materially damage crop production <br />when based on irrigation season average flow during low water years. <br />As was the case on Trout Creek, the majority of the plant species <br />identified in surveys conducted by the applicant and summarized in the <br />supplemental package of September 22, 1986 are rated moderately tolerant <br />to salinity. Only 3.7% of the relative vegetative cover on Fish Creek <br />was made up of moderately sensitive species. No production sampling was <br />conducted on Fish Creek, and so a ratio of 4.5 obtained from sampled <br />fields at the Foidel Creek/Middle Creek confluence was used to convert <br />relative cover of 3.7% to assumed relative production of 16.6% for <br />moderately sensitive species. <br />-23- <br />