Laserfiche WebLink
For mining under Coal Creek and Jerry Creek in the North Portal mining area, two subsidence <br />monitoring monuments were installed adjacent to Coal Creek and thrive monuments were installed <br />adjacent to Jerry (Creek, in 1997 (see Exhibit 56, Tab 18). ~ <br />The approved subsidence monitoring plan for the entire permit azea is described beginning on page <br />20-8 of the permit application. Because there has been no coal extraction in the permit area since <br />1999, and no future coal extraction is proposed or approved, regular annual subsidence monitoring <br />and reporting is no longer required. Subsidence inspection, documentaation, and evaluation will be <br />triggered only if possible subsidence damage is reported by a surface iwner or otherwise indicated. <br />The regular monitoring program that was conducted through 2001 i:onsisted of a visual surface <br />inspection in spring and fall, to include areas to be mined within the nett year, and areas mined during <br />the previous two years. Coal Creek and Jerry Creek monuments were surveyed immediately prior to <br />undermining and, twice a year for two years subsequent to undermining. Alt monitoring results, <br />including documentation and photographs of subsidence features and structures, were submitted to the <br />Division in an annual subsidence report by December 31, ofeach year. Any new stmctures within the <br />affected area not previously documented will be included in the inspection schedule ifnew mining is <br />projected beneath the structure. Follow-up inspection of structures will be undertaken if possible <br />subsidence damage has been reported by the owner or otherwise indicated. <br />i, <br />The Ute Water Conservancy installed a waterline along the south and west perimeter of the Roadside <br />Refuse Disposal Area in the winter of 1991/1992. Although this pile has remained stable since it was <br />constmcted in 1984, Gaze was taken to protect the pipeline should any subsidence or settling occur. <br />The waterline consists of asix-inch PVC pipe braced inside aten-inch P.I.P. encasement pipe where it <br />crosses the refuse pile. Should a rapture of the PVC pipe occur it would be contained in the P.LP. <br />pipe and directedloffthe pile. , <br />In 1998/99, TransColorado Gas Transmission Company (TGTC) installed a gas transmission line <br />across a portion of the permit area, within a portion of the South Poitals mine area which would <br />possibly be undermined in the future. The operator has committed within the permit application to <br />develop a subsidehce survey or control and mitigation plan, upon resumption of mining via the South <br />Portal. The plan will be approved by TGTC, and will be in place prior to mining within the <br />subsidence angle;of draw of the gas line. An agreement between PCC and TGTC is included as <br />Appendix 20-9, in Volume 6 of the permit application. The agreement includes the provision that <br />Powderhom would notify TGTC six months prior to undermining of the gas transmission line. <br />Because no furthei mining is proposed or approved, it is not likely that this provision will be triggered. <br />Subsidence issues identified in association with PR-02, included updates to the "Man-made Features <br />Map" to include the 345KV Rifle-San Juan transmission line, a house aiid shop building, and an area <br />of "occasionally irrigated pastureland", all within the South Portal miming area. The house and <br />pastureland are on previously undermined areas; the powerline has. not been undermined (August <br />2003). Updated subsidence impact projections were provided in response to Division requests. <br />Projected worst case impact to the occasional{y irrigated pastureland is localized dewatering of ponds <br />or ditches due to subsidence cracks, which the operator has committed'to repairing if they develop. <br />Foundation floor cracking to the dwelling foundation and shop floor as a result of differential settling <br />were projected worst case impacts for these structures, which were constructed over a previously <br />mined out area. i <br />Worst case impacts to the power line are projected to be minor tilting oFtransmission towers which <br />could be repaired by shimming under the legs or replacing deformed rriembers, which the operator <br />i <br />Permit Revision No. 3 ~ ( Permit No. C-1981-041 <br />July 30, 2007 ~ Page 52 <br />