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Mr. Ed. Baker <br />April 18, 2003 <br />Page 5 <br />Q7.4: Given the potential for TDR cables to fail, how does Natural Soda, Inc. propose to have a <br />backup plan for the detection of ground movement immediately above the cavity? <br />A: Properly specified and installed TDR cables are not expected to be any less reliable than <br />other dedicated borehole monitoring equipment, such as transducers, extensometers, etc. <br />The cable has been tested to assure that the maximum possible cavern temperatures will <br />not compromise the cable. The cable deployment system has been well thought out to <br />prevent cable damage during installation. For example, no drill steel, tremie lines, or <br />anything else will be permitted to be withdrawn or lowered into the borehole after the <br />TDR cables are installed. This prevents pre-grouting cable damage due to contact <br />between the cables and down-hole tools. AAI designs and oversees manufacture of high- <br />pressure end caps for TDR cables. These end caps are customized to each application. In <br />this particular case, the end caps will be designed to withstand a hydrostatic pressure of <br />700 psi with a safety factor of 2.85. The end caps designed for WRN will also serve as <br />the mechanical connection to the cable delivery system. The caps are precision- <br />machined out of stainless steel and Teflon. <br />The installation of four TDR cables provides backup in the event that one or more TDR <br />cables should fail prematurely. The length of the TDRs have been chosen to provide <br />sequential information, with the expectation that the lowest TDR will fail first as the cave <br />or rock deformation progresses up above the cavern. The TDR cables are designed to <br />"fail" if adjacent rock undergoes localized deformation of between 0.5 inches and <br />0.8 inches. As discussed in response to the first question, failure of the lowest TDR cable <br />would indicate movement between the lowest and second-to-lowest TDR cables, and <br />further deformation would be monitored by the second deepest TDR. <br />Between the point when deformation begins and the point of cable failure, the section of <br />cable that is deforming will return a partial signal when interrogated. The partially <br />reflected signal produces a spike on the TDR plot of reflection coefficient versus time. <br />The reflection coefficient is the quotient of reflected signal and the initial signal. The <br />spike will grow as cable deformation progresses, until the cable is compromised. <br />With regard to the stipulation as proposed by the EPA, we suggest the following: <br />Natural Soda, Inc shall install four TDR cables in the SMW. Three cables shall be <br />installed in the L-5 zone and one shall be installed above the L-5/R-6 contact. The lowest cable <br />should be positioned 55 ft above the Dissolution Surface, and the three additional TDR cables <br />located approximately at 75, 95 and 115 ft above the Dissolution Surface. If the lowest TDR <br />cable fails, Natural Soda, Inc will notify EPABLM/CDMG and implement changes in <br />operations to slow cave development. If the second lowest cable (installed 75 ft above the <br />Dissolution Surface) fails, EPABLM/CDMG will be notified and mining operations will be <br />altered. If the third TDR cable fails, the cavern will be shut-in, EPA/BLMJCDMG will be <br />notified, and Natural Soda will propose more radical means to arrest cave development to the <br />agencies for their approval before continuing operations. Examples of such radical means would <br />be reverse circulation, moving the injection or recovery points and/or altering injection <br />Agapito Associates, Inc. <br />