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Apri! !5, 1999 Page 4 4.0 REPORTING A subsidence report will be submitted to the Bureau of Land Management (BLM) annually. The report will contain data from surface monument measurements, TDR data, and borehole geophysical data. The annual subsidence report will include a map of surface monument locations, locations of wells where TDR and borhole geophysics were conducted, a list oi'monument and well coordinates, and a summary of pertinent observations during the reporting period. 5.0 MITIGATION No mitigation is currently planned for surface subsidence. Measurable surface subsidence is not anticipated. Even in the event of the failure of several pillars between mature pillars, long- term subsidence is expected to be less than three feet. A subsidence basin of such small magnitude over the size of a well field will be visually unnoticeable. The TDR and borehole geophysics monitoring will be used for monitoring cavity roof integrity. The thickness of the strata between the cavity roof and the Dissolutiion Surface will vary in thickness from 150 ft up to 300 ft. If one-half foot of separation or fracturing in the cavity roof is detected within a distance of 50 ft of the Dissolution Surface, then the gas c[tp will be lowered so that no fluid is in contact with the cavity roof, and cavern integrity warning systems (process monitoring) will be monitored closely for the life of the well. The process monitoring systems are described in Section 5.0 of the Grotmdwater and Surface Water Monitoring Plan. If cavern integrity is lost as determined by the proces:> monitoring systems outlined in Table 4 of the Groundwater and Surface W ater Monitoring Plan, then corrective action would be initiated according to procedures outlined in Section 6.9.3 of the Grotmdwater and Surface Water Monitoring Plan. 6.0 QUALITY ASSURANCE AND QUALITY CONTROL Procedures for quality assurance and quality control (QAQC) will be developed prior to commencement of commercial operations. The QAQC procedures will address data collection, frequency, accuracy, recording, and reporting. Agapito Associates, Inc.