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• The monitoring points, as proposed by the Hucka report for monitoring any subsidence which may occur, <br />have been installed as the underground works were advanced. Since the Eastside Mine has been reclaimed <br />in 1995, no further subsidence monitoring points will be installed. The monitoring stations will be left in <br />place until prior to the preparation of the final bond release application. The monuments will be surveyed <br />to confirm that no subsidence has occurred from the cessation of monitoring in 1996 to the the time that the <br />final bond release application is prepared. If no subsidence has occurred, then the final bond release <br />application will be submitted. If subsidence is found, then Eastside Coal Company will develop and <br />implement a subsidence mitigation program that is acceptable to DMG if needed. <br />Subsidence monitoring points have been constructed as shown in Figure 19: Subsidence Monument <br />Installation, located on page 117A. <br />Baseline monitoring of all monuments has been completed. Due to the cessation of mining and reclamation <br />of the Eastside Mine in 1995, the subsidence monitoring has been suspended per regulatory approval in <br />1996. No significant subsidence movement attributable to mining has been recorded during the monitoring <br />program which began in 1985. The highest subsidence value compared to the original survey is 0.478 feet <br />for Monument 8. The highest a point has risen compared to the original survey is 0.21 feet for Monument <br />2. Monuments 1 and 2 show some wide differences between surveys in the years 1985 to 1990. In 1991, <br />Eastside Coal Company changed surveyors. The data for all monuments shows little, if any, variance <br />between surveys with the range being from 0.11 to -0.12 feet since 1991. This minimal movement between <br />surveys indicates a that the surface is stable and has not subsided. These minimal differences could be <br />related to subsidence, movement from erosion caused by the slope steepness, frost heave, or surveying <br />• error. If subsidence has occurred it has not been significant enough to leave a surficial expression. The <br />subsidence data for each monument and a summary table are included on pages 117 B to 117 G. Charts <br />plotting the subsidence results are included on pages 117 H to 117 L. <br />Subsidence of the recharge zone for the bedrock aquifers will have minimal impact on the ground water in <br />the area. The possible impacts include: 1. interruption of the aquifer; 2. cross contamination of the bedrock <br />aquifer; or 3. dewater the aquifer. <br />The aquifer will not be disrupted or broken. The area to be subsided will be the recharge zone. After mining <br />is completed the recharge capacity of the aquifer will be reestablished. Mining will not stop the recharge of <br />the aquifer down dip of the mine. While mining is occurring, the areas to the east and west of the mine will <br />continue to recharge the aquifer until mining is completed. <br />There will be no more mixing of the aquifer than is occurring now. The only possible affect would be to <br />move the location where the water enters the unbroken aquifer downdip. <br />As mentioned before the aquifers downdip of the subsided area will not be dewatered for two reasons: 1. <br />the subsided area is a recharge zone, and 2. the undisturbed recharge areas to the east and west will <br />continue to provide water to the aquifers. <br />117 Revision 12/94 <br />Technical Revision 3/96 <br />