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<br />• These stations were installed and surveyed prior to mining, and will be surveyed <br />quarterly as long as evidence of continued subsidence is indicated by survey or <br />observation, and will be discontinued only with the consent of the surface owner and <br />Division approval. <br />Monitoring points were established perpendicular to the third north panel prior to the <br />panel advancing under the Trinidad (formerly Colorado and Wyoming) Railroad trackage <br />and the Purgatoire Rivet. These stations were established in March 1988, and have been <br />surveyed quarterly since mining occurred under the azea. They have shown no <br />discernible movement and Division approval to discontinue surveying these monuments <br />has been granted. <br />Subsidence resulting from longwall mining is considered a form of controlled subsidence. <br />Basin Resources established monitoring stations on each of the longwall panels north of <br />the Purgatoire River to help evaluated the effects of controlled subsidence. Control <br />points were established both parallel and perpendiculaz to the panels. These points were <br />located such that at least one of the stations would be expected to lie outside the <br />anticipated maximum angle of draw typically encountered at mines in the Western United <br />States. These points were surveyed prior to mining, weekly while mining was <br />proceeding under these stations, and quarterly as long as evidence of continued <br />subsidence was indicated by survey or observation. They have shown no discernible <br />movement during the last four quarterly surveys and Division approval to terminate <br />• surveying of these monuments has been granted. <br />Survey stations will also be established at all structures located within the projected <br />longwall subsidence trough to adequately determine the effects of subsidence. In <br />addition, a supplemental quarterly visual inspection of each structure will be completed. <br />This monitoring will be completed quarterly and reported to the Division semi-annually <br />as mining advances. Monitoring of structures will continue as long as subsidence may be <br />expected. With the cessation of mining and no evidence of continuing decemable <br />movement, Division approval to terminate these surveys has been granted. <br />No structures, other than roads, culverts and stock ponds aze located over azeas of <br />projected longwall mining during the next permit term. As mining has ceased, <br />monitoring and control plans will not be required for new structures constructed afrer <br />mining was terminated. <br />2.05-55 ~ (Revised 10/15/98 - TR-48) <br />• <br />