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3. TEXT CHANGES <br />Therefore, no significant impacts to groundwater quality <br />will occur under this alternative. <br />4.4.5.3 Proposed Acrian <br />The major difference between the alternatives, as they <br />potentially affect groundwater quality, would be the number <br />of cavities constrncted by each alternative. Under this <br />alternative, 330 cavities would be mined. Thus, there would <br />be a greater Dumber of cavities that could fail. <br />ff all of the cavities collapsed, the area at the base of <br />the aquifer in contact with saline minerals would increase <br />up to 20 percent within the leases; however, this would <br />only be about a 1 percent increase over the total area of <br />the base of the groundwater system in the basin that might <br />be in contact with saline minerals. This mold result in an <br />increase in total dissolved solids concentration higher than <br />the state standard in the lower portion of the lower aquifer <br />within the vicinity of the leases. If remedial measures were <br />unsuccessful in mitigating (alleviating) this impact, it would <br />be locally significant and could be regionally sigmificaru. <br />4.4.5.4 SO,000TPYAIrernnrive <br />Under this alternative, 135 cavities would be mined over <br />the project life. If all of the cavities collapsed, the area at <br />the base of the groundwater system in contact with saline <br />minerals would increase by lest than ]0 percent within the <br />leases; however, this would be lest titan .5 percent increase <br />over the total area of the base of the groundwater system <br />in the basin that might be in contact with saline minerals. <br />If remedial measures were unsuccessful in mitigating <br />(alleviating) this impact, it would be locally significant. <br />4.4.5.5 SOO,000TPYA[remative <br />Under this alternative, there would be the greatest risk <br />that am impact to the quality of the groundwater mold occur, <br />because of the larger number of cavities that would be mined <br />(1,320) and because the well field extends to the boundary <br />where the Boies Bed is truncated by the dissolution surface. <br />In this area, which is to the southwest of the plant site, <br />the base of the grotmdwater system intersects the mine zone. <br />This means That any roof collapse, even of a few feet, mold <br />establish a hydraulic connection between the base of the <br />lower aquifer amd the brines of the cavities. <br />)f all of the cavities collapsed, the area at the base of <br />the groundwater system in contact with saline minerals <br />would increase by about 80 percent within the lease <br />boundaries; however, this would be only about a 4 percent <br />increase over the total area of the base of the aquifer in <br />the basin that might be in contact with saline minerals. <br />This could result in an increase of total dissolved solids <br />concentration in the lower portion of the lower aquifer within <br />the vicinity of the leases. If remedial measures were <br />unsuccessful in mitigating (alleviating) this impact, it would <br />be both locally significant and mold be regionally significant. <br />Under this alternative, mat would be used as an energy <br />source. This would generate fly esh, which would require <br />disposal. Two proposals have been made for fly ash <br />disposal: disposal on the surface in clay lined pits or pumping <br />the fly ash into completed mine cavities. <br />The first method would effeMively isolate the fly ash from <br />the hydrologic system. Over the very long-term (5,000 plus <br />years), this material mold be exposed by erosion. The pile <br />mold then cause adverse impacts to the surface water quality. <br />The second method would displace water from the mine <br />cavities, reducing the amount of brine underlying the <br />groundwater system. Generally, either method of fly ash <br />disposal would be unlikely to cause significant environmental <br />impacts; however, disposal of fly ash in abandoned mine <br />cavities could generate some small benefits to the <br />environment. Based on this, subsurface disposal of fly ash <br />would be preferred. <br />4.4.6 Water Uses and Water Rights <br />Because the surface water system in the Piceance Basin <br />is over allocated, any measurable depletion in surface water <br />Bow, as expelled under all commercial-wale alternatives, <br />would be considered significant specially during periods <br />of irrigation and/or low surface flow. <br />Groundwater depletions, from pumping the water supply <br />well(s), may alter the water levels in appropriate stack and <br />domestic wells within the cone of depression. Mining <br />operations may also alter water quality in the aquifer system, <br />thus altering quality levels within the wells. These impacts <br />are considered significant. <br />State law requires that adverse effects to vested water <br />rights holders be mitigated through a water augmentation <br />plan, administered by the State of Colorado. <br />4.4.7 Monitoring Summary <br />The wide range in potential impacts on hydrology, coupled <br />with a high degree of uncertainty as to the magnitude amd <br />significance of these impacts, require that a we0 designed <br />and intensive monitoring system be in place prior to and <br />during operations. This is further supported by the existing <br />sodium lease terms which explicitly require protection of <br />the groundwater resources. <br />The major function of a hydrologic monitoring system <br />is to detect and measure'changes due to mining operations. <br />In order to do so, the monitoring system must be designed <br />to amomplish several objectives, including (1) provide <br />additional needed information on the natural, premining <br />3-20 <br />