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The monitoring well layout for the Yankee Gulch lease site is shown in Appendix I, along <br />with a summary the formations to be monitored at each well completion. <br />(7`'' paragraph, modified 8"' paragraph) If the EPA, using best professional judgement and <br />following standard review practices, determines that the ground water quality in the <br />aquifers overlying the dissolution surface has degraded from the baseline quality the <br />Permittee maybe required to investigate. Methods of investigation may include, but not <br />be limited to, additional monitoring at ground water monitoring wells, mechanical <br />integrity testing of UIC wells, geophysical surveys and review of records. <br />(8`h paragraph, modified 9"'paragraph) In order to establish a clear link between the LTIC <br />Permit and the activities listed in the Subsidence Monitoring Plan (revised as of August <br />2004), EPA has adopted this Plan as Appendix J of this Permit (replacing the original <br />December 23, 1999 document). This subsidence plan maybe changed based on the <br />results of the monitoring data, the results of any required corrective actions that maybe <br />linked to subsidence, and the studies carried out to determine the shape of the cavities. <br />Changes of the Subsidence Monitoring Plan will be made by modifying Appendix J of <br />the Permit. The permittee shall establish surface subsidence monuments, including some <br />located on some wells and well pads, as specified in the Subsidence Monitoring Plan, <br />Appendix J. American Soda shall submit this data in their fourth quarter reports. <br />Solution Mining Well Field Monitoring Program. <br />*~* <br />(f) Cavity development shall be monitored to estimate cavity size. Because <br />the leached solution cavity will be a matrix of oil shale rather than a void, <br />cavity size and shape must be determined by the following indirect <br />methods. Material balances of the volumetric fluid flow rates into and out <br />of the solution mining cavities shall be performed. Continuous monitoring <br />of flow rates, temperature, and fluid densities will monitor ongoing <br />material balance, which will allow the permittee to make calculations of <br />the mass of nahcolite extracted. This information will be submitted <br />quarterly to EPA. A combination of TDR (in test we1120-12) and <br />borehole geophysical techniques shall be employed to evaluate subsurface <br />movement and movement of strata overlying the solution cavities (see <br />Section 3.0, Subsurface Monitoring, Subsidence Monitoring Plan, <br />Appendix J). The performance of the TDR monitoring will determine if <br />TDR is incorporated into the long-range monitoring program. If TDR <br />proves to not be an adequate means of monitoring subsurface movement, <br />EPA may require other instrumentation techniques to be evaluated by the <br />permittee, and if any subsidence changes are significant EPA will be <br />notified as specified by Section III, E.10. TDR will be collected and <br />reported quarterly for we1120-12. <br />FINAL: Modification No. 9, UIC Area Permit No. CO30858-00000 <br />Page 11 of 46 <br />