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CNAPTERTWO agency PreUi:rred Aiternatiue <br />• Elevations of the monuments would be measured annually during commercial operations and <br />compared to baseline data. <br />• Upon reclamation of a mine panel, monitoring would be continued for 5 }~eazs. If subsidence <br />is detected, monitoring would continue for a period of 5 years following the last detection of <br />movement. <br />Subsun`ace Subsidence Monitoring <br />• A combination of Time Domain Reflectometry (TDR) and borehole geophysics would be <br />used to monitor potential subsurface movement. <br />• TDR, which involves installing coaxial cable along the annulus of a production well to total <br />depth, would be placed in 23 of 26 production wells during the first phase (0 to 5 years) of <br />commercial operations. Crimps, elongations, or faults in the cable would disrupt electrical <br />current passed through the cable and provide an indication of subsurface movement, and the <br />depth of occurrence. TDR data would be collected monthly for each active production well. <br />• The performance of TDR during 0 to 5 yeazs of commercial operations would be evaluated to <br />determine its acceptability for long-term monitoring in future mining panels. <br />• Borehole geophysical (natural gamma) logging would be performed four times over the life <br />of each production well to evaluate potential subsurface movement. <br />American Soda would also evaluate current technologies for characterizing the shape of the <br />solution mining cavities, and present results and recommendations to the BL1~I by the yeaz 2000. <br />Methods to determine cavity configuration would then be mandated and the schedule of <br />implementation stipulated by the BLM. <br />TDR and borehole geophysics would be used to assess the integrity of the solution mining cavity <br />roof. During operations, if greater than 0.5 foot of separation or fracturing is detected within 50 <br />feet of the Dissolution Surface, the mitigation measures provided in the Subsidence Monitoring <br />Plan would be implemented. <br />2.3.3 Groundwater and Surface Water Monitoring Plan <br />The Groundwater and Surface Water Monitoring Plan includes groundwater .and surface water <br />monitoring for the Piceance and Parachute sites for the first phase (0 to 5 years) of commercial <br />operations. The Groundwater and Surface Water Monitoring Plan is provided in Appendix G of <br />this Final EIS. <br />The objective of the Groundwater and Surface Water Monitoring Plan is to supplement existing <br />baseline data and to establish trends in water quality and flow such that any dfeviation from the <br />established characteristics is recognizable. This would be accomplished by monitoring a <br />network of groundwater monitoring wells, surface water monitoring stations, and production <br />facilities. <br />Baseline monitoring would commence by mid-summer to fall of 1999. The baseline monitoring • <br />schedule for groundwater monitoring wells includes montlily water level and water quality <br />monitoring fora 13-month (5 quarters) period. Piceance Creek and Pazachute Creek would be <br />2-8 <br />