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<br />Comment 25: It is questioned whether the A¢aoito rock mechanics study was conducted using <br />the correct projected average cavity temperature. <br />Response: Even though injection temperatures may be over 400°F and initially (during the start- <br />up phase of the cavity) the cavity temperature could be up to 400°F. It is anticipated that the <br />temperature in the cavity will drop significantly as the volume of the cavity expands. This is due <br />to the thermal properties of the wall rock, the thermal properties of the fluid being circulated, and <br />the limitations on the boiler capacity to heat the injection fluid. EPA agrees with the operators <br />assessment that as the cavity expands the operational constraints, especially the heat loss <br />associated the expansion of the cavity, and will result in an average cavity temperature at maturity <br />that will be close to 300°F. Thus, EPA has concluded that the thermomechnical modeling <br />conducted by Agapito Associates, Inc. using an average cavity temperature of 300°F is <br />appropriate for evaluating stability. <br />As a result of the review of this comment and the associated information, EPA has <br />determined that no changes to the Permit are needed in response to this specific concern. <br />Comment 26: Annular Fluid -the "take" of nitrogen should be monitored, because Qas leakaee <br />may well be the initial fluid loss due to sill pillar caving. <br />Response: The Water Monitoring plan which is incorporated by reference as part of the Permit <br />provides for continuous monitoring devices for the monitoring of cavity pressures including the <br />pressure of the gas cap. Any loss of pressure of the nitrogen gas cap will be recorded and <br />reported to EPA. As part of this monitoring, the operator is also requved to monitor and report <br />the nitrogen consumption on a daily basis (see Table 6 of the Water Monitoring plan). <br />As a result of the review of this comment and the associated information, EPA has <br />determined that no changes to the Permit are needed in response to this specific concern. <br />Comment 27: American Soda has not proven that this project is economically or <br />technologically feasible. Three or four Cavities have: 1. lost circulation: 2. well casing dropped <br />down hole in the well bore: 3. blowout during drilling and high pH completion fluids were <br />released to the environment. <br />Response: The construction and operation of the test mine facility are described in the test mine <br />plan ("Experimental Test Cavity Project", February 1997). This document was reviewed as part <br />of EPA's action for ganting American Soda Class V rule authorization for their test cavities and <br />is part of the administrative record for the Yankee Gulch Class V rule authorization. The existing <br />Class V facilities remain in operation until commercial operations have been fully implemented. <br />The test cavities do not differ significantly from commercial activities covered by this Permit. As <br />part of the program established for monitoring the Class V test operations, EPA received <br />quarterly monitoring reports and reviewed these data. Operational pressures and temperatures <br />commensurate with those proposed for commercial operations have been tested and results were <br />considered acceptable. No unexpected results were obtained. The monitoring reports did not <br />indicate any evidence of cavity blowouts or other problems that would affect USDWs or the <br />40 <br />