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<br />2. General Chemical believes that the EPA's Draft Statement of Basis and Draft Area Permit are <br />premised on an inadequate and misleading description of the proposed mining process. <br />3. The solution mining cavity shape must be determined. <br />4. Subsidence is of concern because it could lead to an interchange of water between aquifers or <br />an excursion of mining fluid into the aquifers. The Permit should stipulate a maximum cavity size <br />and maximum lateral dimension. <br />5. The method of identifying the shape of the cavity, which is critical to structural integrity, is not <br />described. Some method of monitoring the migration of the solution front into pillazs via the <br />saline beds is needed. (This is also covered by the response to comment 9.) <br />6. As the application currently is written, the EPA is going to allow American Soda to mine <br />"blind" <br />7. The effects from interconnecting cavities can cause significant problems such as: <br />a. Hydro-fracturing; b. Cavity stability issues; and c. Increased subsidence potential. <br />Each one of these events could cause a release of fluids into the aquifers. None of these <br />problems aze addressed in the Permit application which prevents the EPA from determining how <br />to protect all sources of USDWs. <br />Response: The Draft Permit was written based on the operating results from the test cavities at <br />the Yankee Gulch site and the experience obtained by American Soda from available information <br />developed by Shell doting its oil shale experiments in the vicinity of the site. Solution mining <br />well-operating information was provided to EPA in the Permit Application. As indicated <br />elsewhere in this response to comments, the application included normal values for operating <br />pazameters and described the relationship between operating parameters. These values were <br />based on data collected from the test cavities. The application also presented situations that may <br />be indicative of a cavity leak or an instrumentation failure and provided descriptions of response <br />measures. Additionally, the Water Monitoring Plan and Subsidence Mortitoring Plan, which aze <br />contained in appendices I and J of the Permit, contain monitoring and response information for <br />the process monitoring of the solution mining cavities. These plans aze incorporated in the Final <br />Permit and may be modified as required. <br />The solution mining well-process monitoring is designed to detect a cavity leak virtually <br />immediately. Process monitoring equipment, along with other well field equipment, wiU be within <br />the accuracy range necessary to detect significant changes in operating pressures and volumes. <br />This equipment will be used to measure the following parameters at 10-minute intervals: 1) <br />injection pressure; 2) injection fluid temperature; 3) injection fluid specific gravity; 4) injection <br />fluid flow rate and volume; 5) production pressure; 6) production fluid temperature; 7) production <br />fluid specific gravity; 8) production fluid flow rate; and 9) nitrogen gas cap pressure. Any <br />significant change in these parameters could be an indication of a downhole problem, such as a <br />failure of the well or cavity. The inflow and outflow mass balance is a surrogate measure of the <br />23 <br />