Laserfiche WebLink
October 11, 2011 Page 19 <br />of the water discharge point may move the discharge point laterally and make the discharged <br />water flow in an unintended direction. <br />4.5.4 Water Pipeline Ancillary Structure Damage Mitigation Plan <br />A damage mitigation plan identical to the water pipeline plan is recommended. <br />4.6 Surface Water Disposal Pit <br />4.61 Surface Water Disposal Pit Subsidence Control Plan <br />Surface water disposal pits, both lined and unlined, are classified as surface water bodies. <br />Since the damage criterion for surface water bodies is horizontal strain of 5 millistrain, no pillar <br />extraction should be performed within a 5° vertical offset angle of the water disposal pits. The <br />vertical offset angle was derived from the subsidence prediction results, which indicated that the <br />furthest a maximum horizontal strain of 5 millistrain is observed on the surface is at a vertical <br />offset angle of 2.5° from the retreat line at the seam level. <br />4.6 2 Surface Water Disposal Pit Monitoring Plan <br />To ensure that the control plan is effective, AAI recommends the following monitoring <br />plan: <br />• Water disposal pit owners should be informed as mining approaches and data generated <br />during monitoring should be shared with them. <br />Visual monitoring of a water disposal pit should be performed monthly as long as the <br />retreat line is within a 10° vertical offset angle of the water disposal pit. Any sudden <br />appearance of cracks within and in the vicinity of the pits, and any sudden drop of water <br />level in the pits should be noted as potential problems. <br />• Structural anomalies reported by the surface owner(s) will be investigated. <br />4.63 Worst Possible Consequences of Damage to Surface Water Disposal Pits <br />Horizontal strains in excess of the allowable strain levels have the potential of <br />cracking /puncturing the bottom lining of a lined water disposal pit. High strains may crack the <br />subsoil of the unlined water disposal pit, allowing water communication with the formations <br />below. In both situations, ground and aquifer contamination may be caused due to seepage of <br />water from the disposal pit. <br />4.64 Surface Water Disposal Pit Damage Mitigation Plan <br />In case monitoring indicates onset of damage or potential for damage to the water <br />disposal pits, the following mitigation plan should be adopted. <br />Agapito Associates, Inc. <br />