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• i <br />the cavity and the need for monitoring the cavities for shape and subsidence. This concern <br />resulted in the incorporation of the Subsidence Monitoring Plan as part of the Permit. As <br />explained in this response, the Final Plan requires that the operator evaluate methods to <br />characterize the caverns. EPA has reviewed all of the comments and does not believe that <br />additional Permit requirements are needed. <br />Comment 10: I am concerned that EPA is authorizine the use often sources of fluids (see <br />oases 17 and I8 of the Statement ofBasis and page 16 ofthe Draft Area Permit) for which it <br />does not have any control over the content of the fluids. No testine of these various fluids is <br />required. so how could anv entity determine whether hazardous waste (as defined in 40 CFR <br />261.31 has been incorporated into the iniection fluid? <br />Response: EPA specifically listed the ten sources of fluid in the Permit as a means of asserting <br />control over their use in the mining fluid stream or their disposal in the cavities. Injection fluid will <br />consist primarily of depleted solution mining production fluid and make-up water. Minor <br />components of the solution mining well injection fluid, such as boiler blowdown and water <br />softener backwash, are common injection streams for UIC Pernuts. It is important to note that <br />American Soda requested authorization to add these nonhazardous fluid waste streams to their <br />injection fluid in order to reduce the necessity for large on-site evaporation ponds. As a result, <br />the project pond requirements have been greatly reduced. This has reduced the potential impacts <br />on wildlife and surface water and will also reduce future reclamation needs. EPA evaluated this <br />request, and does not believe that these fluids will significantly alter the composition of the <br />injection fluid stream. The addition of these fluids to the injection stream also appears to have a <br />significant environmental benefit. It reduces water make-up requirements and avoids the potential <br />problems associated with surface ponds. <br />Eight of the Permitted injection fluid sources are considered minor sources because they <br />do not represent a large portion of the total injection fluid, which, as stated above, consists mostly <br />of the other two sources: Depleted solution mining production fluid and make-up water. For <br />example, the volumetric flow rate of boiler blowdown is expected to be approximately 6 gallons <br />per minute, which is only about 0.2 percent of total volume of the injection fluid. <br />The UIC regulations prohibit the injection of RCRA hazardous wastes, as defined by 40 <br />CFR part 261.3 unless authorized by a Permit. Such injection is restricted to Class I Hazardous <br />waste injection wells that meet specific requvements. At this time, EPA has no reason to <br />conclude, based on the sources of the waste fluids that American Soda's Permitted fluid streams <br />might be RCRA hazardous wastes. The UIC Permit for Yankee Gulch specifically prohibits <br />injection of any hazazdous wastes, as defined by 40 CFR 261.3. The operator has made a <br />preliminary determination as outlined in 40 CFR 262.11 that the various streams aze not <br />hazardous. This included a review of 40 CFR part 261 subpart D to verify that these Permitted <br />streams are not considered to be "listed hazardous wastes." However, these streams will be <br />evaluated during operation as needed per the requirements of 40 CFR 262.11 to confirm that they <br />do not exhibit any of the RCRA "hazardous chazacteristics," which are ignitability, corrosivity, <br />reactivity, and toxicity (as defined in 40 CFR part 261 subpart C). <br />The Final Permit has been modified to require the operator to submit the details of <br />28 <br />