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October 11, 2011 <br />Page 17 <br />• Pipeline elevations should be monitored by establishing appropriately located survey <br />points along the segment of a pipeline being undermined, to be spaced at no less than <br />1,000 ft apart. <br />• Monitoring should be performed at least quarterly as long as retreat mining is active <br />within a 40° angle of the pipelines, and annually thereafter, until it is determined that no <br />active subsidence is occurring. <br />• Structural anomalies reported by the surface and/or gas well owner(s) will be <br />investigated. <br />4.2.3 Worst Possible Consequences of Damage to Gas Pipelines <br />In case the gas pipelines experience horizontal strains in excess of the allowable value, <br />the pipes could be damaged, potentially leading to disruption of gas flow and/or product leakage. <br />4.2.4 Gas Pipeline Damage Mitigation Plan <br />In case monitoring data indicate damage or potential for damage to the pipeline, the <br />following mitigation plan should be adopted. <br />• Appropriate personnel at mine and regulatory authorities, as well as the owners of the <br />pipeline and surface owners, should be informed. <br />• The retreat plan should be re- evaluated to ensure that operations will not further damage <br />the pipeline. <br />4.3 Gas Pipeline Ancillary Structures <br />4.3.1 Gas Pipeline Ancillary Structure Subsidence Control Plan <br />This class of structures includes gas valves, gas fuel valves, gas line drips, gas blow -off <br />valves, and gas -line test stations. These installations are found on the gas pipeline network and <br />perform as safety and/or control devices. The retreat mining buffer zone developed around the <br />gas pipeline network should be adequate to protect these structures from damage. <br />4.3.2 Gas Pipeline Ancillary Structure Monitoring Plan <br />A subsidence monitoring plan identical to the gas pipeline monitoring plan is <br />recommended for these structures. <br />4.3.3 Worst Possible Consequences of Damage to Gas Pipeline Ancillary Structures <br />Damage to a gas valve or a gas fuel valve could lead to malfunction of the valves, <br />disruption in gas flow, and leakage of the gaseous products to the atmosphere. Damage to the <br />gas line drip could make it malfunction, possibly resulting in carriage of condensed water into <br />the gas line, and gas flow disruption. Damage to the gas blow -off valve could cause the valve to <br />malfunction, possibly allowing sufficient pressure build -up in the gas line to damage the <br />pipeline, disrupt gas flow, and /or leak gaseous products. Damage to the gas line test station <br />could result in lost access for testing of the gas pipeline. <br />Agapito Associates, Inc. <br />