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Semi-Annual Subsidence Monitorine~pQ <br />Page 2 <br />2. Structures <br />Swctures monitored quarterly for subsidence include the Thompson Ranch buildings, the <br />Florence City water line, and the Newlin Creek point. Summarized survey data for these <br />swctures are shown on accompanying Table 1, Semi-Annual Subsidence Monitoring Data <br />Summary. Location of the structures and monuments with respect to the Mine layout aze shown <br />on Map 17 in the permit application. Discussion of survey monitoring data compared to permit <br />predictions for inventoried swctures follows below. <br />2.1 Thompson Ranch Swctures <br />Consistent with previous subsidence surveys, survey data for the reporting period indicate that no <br />subsidence is occurring. No retreat mining operations occurred in the area of these swctures. <br />2.2 Newlin Creek Point <br />Survey data for the Newlin Creek point shows no additional subsidence during the reporting <br />period. This data agrees with preceding monitoring periods. No mining operations occurred in <br />the area of this survey point; the mining section was closed and sealed in 1982. <br />2.3 Florence Water Line <br />Survey data obtained at the eight monuments along the Florence Water Line indicate subsidence <br />occurring at Monuments C, D, and F during the reporting period. The amount of subsidence <br />occurring ranged from 0.08 to 0.21 feet. The maximum measured subsidence has occurred at <br />Monument I, totalling 3.06 feet as of the most recent survey. This value is between the permit <br />maximum expected and worst-case expected subsidence values of 2.79 and 4.36 feet respectively. <br />The rate of subsidence at Monument I is small, and minimal future subsidence is expected. <br />Minor surface cracks appeared on County Road along a section 500 to 1000 feet west of <br />Monument F. These cracks were first observed in September 1995, during which time retreat <br />mining was occurring directly below the area. The cracks, measuring less than 1/4 inch wide, <br />caused no damage to the road or interruption of its use. Interestingly, the_.crdcks were not <br />appazent in the meadows on eiffier side of the county road. Only the compacted gravel surface of <br />the road was hard enough to exhibit the effects of subsidence strains. in addition, there are no <br />indications that the observed subsidence has adversely affected operation of the Florence Water <br />Line. <br />Subsidence monitoring of swctures indicates that subsidence is occurring only at certain locations <br />along the water line, and that the magnitude of displacement is within predicted values. Only <br />minor additional subsidence is expected to occur at the swcture monitoring locations. <br />