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previous assumptions. As greater tonnage is recovered from the mine, results of <br />future sonar surveys will reflect how a mature cavity develops at the recovery <br />well. <br />On 2(21(91 a temperature survey was taken of the 88-1 wellbore. The results <br />show no sign of fluid migration behind the 9 5/8" casing. <br />A surface subsidence survey was taken in 1991. Results of the survey show no <br />measurable change in surface elevation and therefore no surface subsidence. <br />The gamma ray iGR) log run in conjunction with the sonar survey showed no <br />subsurface subsidence above the mined zone. The formation GR profile showed 3 <br />well defined radioactive bullets and the fourth not as well defined. The formation <br />• from the top of the Boies Bed was well defined for the 200 feet logged by the <br />gamma ray tool. <br />4.3.5 Lease Modification/Land Exchanr~e <br />On September 5, 1991, NaTec submitted a letter of interest to the BLM regarding <br />Lease modification/land exchange. NaTec is interested in additional BLM lands <br />with mineable Boies Bed nahcolite. A lease modification seems appropriate as <br />requirements can be met for: an existing mine, lands contiguous, limit of 2,560 <br />acres per lease, lands lack sufficient mineral resource for independent development <br />and conservation of natural resources. This action can be authorized by the BLM <br />under Public Law Order No. 4522. Status: pending BLM review, action. <br /> <br />32 <br />