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October 11, 2011 Page 22 <br />4.9 Structures on Concrete Footings /Skids <br />4.9.1 Subsidence Control Plan for Structures of Concrete Footings /Skids <br />Wellhead equipment such as compressors, pumps, soundproof housing for compressors/ <br />pumps /separators /transformers, and meter houses occasionally have concrete footings or skids. <br />Such footings are typically placed directly on a gravel pad to absorb machine vibrations. No <br />specific subsidence damage criterion was found for such structures during AAI's literature <br />review on the subject. Considering the range of surface deformations predicted by the <br />subsidence analysis, the above - mentioned installations are unlikely to be affected by <br />undermining. Hence, such structures may be fully undermined with appropriate monitoring, as <br />outlined below. <br />4.9.2 Monitoring Plan for Structures of Concrete Footings /Skids <br />plan: <br />To ensure that the control plan is effective, AAI recommends the following monitoring <br />The structure owners should be informed as mining approaches and data generated during <br />monitoring should be shared with them. <br />Visual monitoring should be performed weekly as long as the retreat line is within a 100 <br />vertical offset angle of the structures on concrete footings. Any appearance of tilt or <br />change in elevation in these structures and any large cracks that may destabilize them <br />should be noted. <br />• Structural anomalies reported by the surface owner(s) will be investigated. <br />4.9.3 Worst Possible Consequences of Damage to Structures of Concrete Footings /Skids <br />Horizontal strains in excess of the allowable strain levels have the potential of damaging . <br />gas or water pipes that are connected to compressors and pumps, potentially disrupting <br />production operations and leaking gas or water as the case may be. Damage to the soundproof <br />housings for compressors /pumps /separators could twist or bend the metal panels. High strains <br />may not cause any damage to the meter house since it is constructed with metal panels, but may <br />damage the water pipes connected to it, leading to leakage potential of produced gas and <br />inaccurate production measurements. <br />4.9.4 Structures of Concrete Footings /Skids Damage Mitigation Plan <br />In case monitoring indicates onset of damage or potential for damage to the structures on <br />concrete footings /skids, the following mitigation plan should be adopted: <br />Appropriate personnel at mine and regulatory authorities, as well as the owners of the <br />structure, should be informed in case anomalies are observed that may indicate an <br />affected structure. <br />• The retreat plan should be re- evaluated to ensure that operations will not further damage <br />the structure in question. <br />Agapito Associates, Inc. <br />