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water quality changes is projected since only a very small portion of the streamflow <br />comes from adjacent bedrock groundwater dischazge. Surface water quality data <br />collected along Fish Creek, and presented by the applicant in Exhibit Tj, reveal no <br />significant changes in water quality as a result of undermining and subsidence. <br />Some increases in permeability of the aquifer units above the subsided azea was expected <br />up to 600 feet above the Foidel Creek workings. However, after completion of mining, <br />the permeability of the disturbed strata should return to close to pre-mining levels. <br />Review of the data and analysis of Exhibit Tj reveals that shallow bedrock wells <br />completed below the alluvium did show dewatering and casing damage due to <br />subsidence. However, this was likely due to the increased permeability created by tensile <br />stresses within 50 feet of the surface. Water levels showed rapid decline followed by <br />slow recovery and have now recovered to neazly pre-mining levels, as was anticipated. <br />The Fish Creek alluvial aquifer should not be affected due to its fine-grained nature and <br />the neazly 1000 feet of sepazation from the mine workings. Alluvial wells showed slight <br />impacts (see GWAP-7) but it is not clear whether these small water level changes aze <br />due to water loss to the bedrock below or to re-consolidation of the alluvial body. <br />Regazdless, no changes in Fish Creek alluvial water levels in lower Fish Creek have <br />occurred. <br />No impact to groundwater quality is predicted. Subsidence could cause inter- <br />communication of aquifers. The two aquifers of significance above the workings aze the <br />Fish Creek alluvial aquifer and the Twentymile Sandstone aquifer. No interaction <br />between these aquifers was predicted due to their physical separation. <br />As stated previously in the Trout Creek AVF Findings [he 1.5:1 relationship between soil <br />salinity and irrigation water salinity is considered to be a conservative assumption (the <br />actual relationship may be less than 1.5:1). Data collected by the Division on August l5, <br />1986, showed root zone soil conductivity to be slightly lower than Fish Creek surface <br />water conductivity. Additional detail on the projected impacts to the Fish Creek AVF <br />may be found in the Division's May 9, 1996 Findings for Foidel Creek Mine's Permit <br />Revision No. 3. <br />The major portion of the Fish Creek Alluvial Valley Floor is not flood irrigated but is <br />assumed to be sub-irrigated based on vegetation types, alluvial water depths and late <br />growing season color infrared photography. Material damage to sub-irrigated vegetation <br />would not occur because the majority of discharge to the aquifer occurs during spring <br />and eazly summer when mine discharge is diluted by high runoff volumes. <br />Permit Table 17 shows a predicted alluvial water quality on Fish Creek of approximately <br />1000 umhos/cm. Well 008-AU-3 on Fish Creek corresponds more closely with surface <br />water quality and is thought to be a more representative site than 006-AW-2. Based on <br />008-AU-3, a measurable increase in salinity of alluvial aquifers is projected, but the <br />predicted conductivity would be well below the 3000 umhos/cm material damage suspect <br />39 <br />