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!' <br />process conditions. Until the Applicant establishes asteady-state operation and has developed <br />supporting data to prove process safety, monitoring must be heavy. <br />SUBSIDENCE MONITORING RECOMMENDATIONS <br />1. The best location to monitor surface subsidence, because it provides the earliest indication of <br />subsidence, is the casing of the well itself. The last cemented casing should be extended <br />above the ground and a fixed point should be welded to the casing to allow a surveyor to <br />measure subsidence off this point. Surface monitoring should be done twice a year instead of <br />the recommended once a year because this is a new undertaking and there is concern that this <br />mining process will result in subsidence. Although it is a good idea to have the subsidence <br />monitors as planned, the monitoring points directly on the well would indicate subsidence <br />much earlier. <br />2. In order to chazacterize cavern development, down hole sonaz's need to be taken on the wells. <br />The technology exists to cleazly show what the cavern is looking like and Time Domain <br />Reflectometry (TDR) will not accomplish this. If the cavern is not collapsing but instead <br />forming a series of arms away from the center sonar may be ineffective and techniques like <br />seismic survey must be used. <br />3. Time Domain Reflectometry will only show stretching and twisting of the cemented casing <br />and will not show subsurface settlement. The wire will show if the casing stretched. The <br />casing and the cement azound it will settle with the ground and will not show it is collapsing <br />into the cavern. Sonaz's (or seismic) are of the utmost importance to show the cavity below <br />the surface and the effects of settlement. These should be done every 6 months during <br />extraction. <br />4. Monitoring subsurface subsidence for five years after well completion is not acceptable. It <br />has been the experience of General Chemical that subsidence occurs below the surface and <br />takes long time to reach the surface unless damage is extensive. General Chemical continues <br />to monitor wells that date back 50 yeazs for subsidence. This is an ongoing process and <br />definitely should not be allowed to stop after 5 years. This will not show damage unless the <br />damage is extensive. <br />We look forwazd to having our concerns addressed and having the appropriate recommendations <br />incorporated into the permit application to ensure the environmental safety of this project. <br />S' erely_ , <br />J n'~v/C/)-E-hm~ann <br />'rector of Operations <br />