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May 11, 2011 Page 13 <br />4.10 Structures on Ground - embedded Metal Columns <br />4.10.1 Subsidence Control Plan for Structures on Ground - Embedded Metal Columns <br />Another class of wellhead structures identified was embedded into the ground using <br />metal columns /poles, e.g., wellhead soundproof walls, electrical panels /meters, and electrical <br />outlets for the well. Since no specific subsidence damage criterion was found for such structures <br />during AAI's literature review on the subject, an allowable horizontal strain of 5 millistrain was <br />deemed appropriate for the purpose, given that these structures are embedded in the ground and <br />are coupled to any potential mining - induced movement. Given no retreat mining is planned <br />under such structures, it is unlikely that horizontal strains in excess of 5 millistrain will occur. <br />4.10.2 Monitoring Plan for Structures on Ground - Embedded Metal Columns <br />plan: <br />To ensure that the control plan is effective, AAI recommends the following monitoring <br />• The structure owner(s) should be informed as mining approaches. <br />• Due to the low probability of perceptible surface deformation, no direct monitoring is <br />required. Structural anomalies reported by the surface owner(s) will be investigated. <br />4.10.3 Worst Possible Consequences of Damage to Structures on Ground - Embedded Metal <br />Columns <br />Horizontal strains in excess of the allowable strain levels experienced by the soundproof <br />enclosures for wellheads could twist or bend the metal panels. High strains may damage the <br />electrical panel/meter house causing loss of power supply and, hence, disruption in well <br />production. Damage to electrical outlets for the wellhead could sever power supply to the well <br />equipment and disrupt production. <br />4.10.4 Structures on Ground- Embedded Metal Columns Damage Mitigation Plan <br />In case monitoring indicates onset of damage or potential for damage to the structures on <br />metal columns /poles, the following mitigation plan should be adopted. <br />Appropriate personnel at mine and regulatory authorities should be informed in case <br />anomalies are observed that may indicate an affected structure. <br />• The mining plan should be re- evaluated to ensure that operations will not further damage <br />the structure in question. <br />4.11 Roads <br />4.11.1 Unpaved Road Subsidence Control Plan <br />The majority of the roads that are likely to be affected by mining - induced subsidence are <br />unpaved. Although no damage criterion could be found for unpaved roads, the allowable levels <br />Agapito Associates, Inc. <br />