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<br />Letter to Kurt Nielsen 4 April 13. ! 999 <br />infusion of process solution may be actionable even if ground water quality standards are not exceeded. <br />Likewise, changes in piezome[ric pressure indicating an excursion of fluid from a mining cavity may be <br />actionable even if there is no corresponding impact on water quality. Schedules and methods of <br />reporting data or excursions will also be incorporated into the ongoing plan (Rules 3.1.7(7)(b)(iii) and <br />3.1.7(9)). <br />4. Provide a subsurface subsidence monitoring plan. The focus of the plan should be protection of the <br />Mahogany Zone from adverse impacts that may be caused if subsidence were to fracture or otherwise <br />affect the structural integrity of the zone. Structural damage to the Mahogany Zone may impact future <br />minability of oil shale resources and may increase permeability of the Mahogany Zone and allow for <br />increased flow between the upper and lower aquifers and the potential for adverse water quality <br />impacts. The plan to be provided should include a complete description of Time Domain <br />Reflectometry (TDR) for monitoring subsurface subsidence, and should specify and provide a rationale <br />for actionable levels of subsidence detected by TDR. The plan should further specify the corrective <br />actions to be employed if unacceptable levels of subsurface subsidence are detected and should describe <br />alternative monitoring strategies to be employed if TDR proves to be ineffective. The surface <br />subsidence monitoring plan provided in the existing application is approvable; surface subsidence <br />monitoring information should be included in the annual report for routine data or as soon as possible <br />(within five working days) if surface subsidence is detected. <br />5. A two pass mining strategy is proposed for each of the five-year solution mining panels. It is stated <br />in the permit application that "(w)ell spacing will be at 300-foot centers but will likely be adjusted <br />when cavity growth rate and ultimate cavity diameter have been adequately demonstrated." Prior to <br />solution mining of adjacent wells (i.e., wells on 300-foot as opposed to 600-foot centers) a plan or <br />method for demonstrating ultimate cavity shape and extent must be incorporated into the permit. This <br />plan may be provided subsequent to permit issuance, in which case submittal of the plan would be <br />reviewed as a technical revision (Rules 1.5.2 and 1.9). <br />6. The draft Ground Water and Surface Water Monitoring Plan dated April 1999 includes a <br />completion diagram for American Soda well 20-6, Dissolution Surface Disposal Well. The permit <br />application does not discuss underground injection of any solutions other than the injection fluid for the <br />purpose of solution mining. Please provide a discussion of the purpose and use of American Soda well <br />20-6. <br />7. In the permit application it is stated that residues in the evaporation pond will be tested at the time <br />of final reclamation, and based on the results of that testing the pond liner and pond residues will either <br />be buried and reclaimed in place, or will be removed from the site and disposed of in a landfill. For the <br />purpose of estimating reclamation costs and establishing the amount of reclamation bond to be required, <br />DMG will assume the more expensive reclamation alternative, which is off site disposal. In order to <br />facilitate the estimation of this cost, please provide DMG with an estimated volume of liner and residue <br />to be removed, a description of methods and equipment needed to remove the contaminated material <br />