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3. TEXT CHANGES to the evaporation ponds. This would effectively contain any spills in the plant. Degradation of surface water quality from brine spills would only take place if the evaporation ponds leaked or overflowed. The evaporation ponds have been designed with dual liners and a leak detection system, and any leaks that are detected will be repaired. During exceptionally wet weather when there is no effective evaporation, the ponds could over top, releasing fluids to ephemeral drainages of Yellow Creek. This potential impact will be mitigated by requiring that the evaporation ponds be maintained with adequate free board. This could be accomplished by hauling waste water to other approved sites, building additional ponds, or using waste heat from the mine to increase the rate of evaporation. In addition, residual solids will be periodically removed from the evaporation ponds and hauled to an approved landfill for disposal. Consideration was given to alternative methods of waste water disposal. Hauling all waste water from the mine site would eliminate the need for evaporation ponds. Disposal of the water hauled from the mine could be accomplished by alternative methods such as deep well injection, evaporation, or cycling through a water treatment facility. All of these alternatives would require more energy than on-site disposal. They cannot be fully analyzed because alternate disposal facilities do not exist; however, [he impacts associated with these alternative methods would be similar to the impacts of the proposed on-site facilities, except that water treatment facilities are generally designed to remove organic pollutants but rarely are designed to remove salts. Based on these concerns, there probably would be no benefit gained from requiring [he of(-site disposal of waste water. There would be a small benefit to allowing the on-site disposal of waste water, because less energy would be used by on-site evaporation, and potential impacts would be localized. In summary, the risk of significant impacts occurring to surface water quality would be very low if the mine is operated as planned. Thu low risk would be further reduced by requiring that the evaporation ponds be maintained with adequate free board. As such, there should be no significant impact to surface water quality from surface operations under any of the alternatives. See the Groundwater Quality section for projected and potential surface water quality impacts from subsurface mining operations. 4.4.3 Groundwater Quantity Groundwater quantity would be directly affected by the pumping of water from the upper aquifer (or project needs. The amount of water removed from the upper aquifer by alternative is shown in Table 4-3. This would be an insignificant percentage on lease and basin wide of the amount of groundwater in storage for all alternatives. However, Gom a water rights standpoint, any measurable depletions would be considered significant (see Section 4.4.6 for a discussion of these impacts). Local effects to vested water right holders would be mitigated by a water augmentation plan administered by the State of Colorado. it may require many years from the end of the projeM life for the aquifer system to recover and to fully replace, through natural recharge, the amount of water removed from storage during sodium mine operations. Subsidence effects on groundwater quantity are expected to be negligible to the hydrologic system and relatively isolated to the base of the lower aquifer. As stated in the draft EIS, Sectiun 4.2.2, Rock Quality, caving of the mined cavities is expected to occur up through the dissolution surface into the base of the lower aquifer under all commercial-scale alternatives. Additional subsidence effects are expected from the downward movement of the overlying formations; the Mahogany Zone (semiconfining layer) would experience some movement, although significant fracturing is not expelled. These subsidence effects could allow some increased communication from the upper aquifer to the lower aquifer, and would establish additional communication between the Saline Zone and the base of the lower aquifer. This would result in small volume changes within the hydrologic system with no expected net loss of water quantity to the system from subsidence; therefore, subsidence impacts to ground- waterquantity are not considered significant. In a report prepared for W RC, Weston (1985) investigated the effects of a high degree of fracturing to the formations overlying the solution cavities due to subsidence from the proposed mining operation. This report projected that the hydraulic head of the perched aquifer within the upper aquifer would drop by 30 feet, and that the hydraulic head of the remaining portion of the upper aquifer and lower aquifer would raise by about 3 feet. These effects would be caused Gom an increase in communication between the aquifers. Although there would be no net loss of water within the system, the strata of the perched aquifer would be dewatered down into the remaining portion of the upper and lower aquifers. Since the recharge rate of the perched aquifer is considered quite low, this zone would be severely reduced or lost as a viable water source for livestock and/ or domestic use. This report assumes the worst case hydraulic effects from subsidence. BLM's analysis predicts that the hydraulic effects from subsidence would probably not be as extensive as portrayed in Wes[on's report; however, monitoring will be utilized to verify predicted impacts to the groundwater system. It is important to note that the extent and rate of subsidence and its resulting effects on groundwater quantity have been analyzed and predicted with the best available information. However, since the predicted impacts of subsidence on the 3-16