Laserfiche WebLink
2.4 $ybsidence History (RULE 2.05.6(6)(e)(i)(C)) <br />Considerable mining has been conducted in the vicinity of <br />the Dorchester No. 1 Mine. General areas associated with past <br />mining have been identified by the Unites States Geologic Survey <br />and are presented on "Extent of Mining Map for the Rockvale <br />Quadrangle", included in Appendix B. Specific mining conducted <br />within the permit area is represented by mine maps of old <br />"workings", which have been consolidated on a 1' = 200' composite <br />map and is presented in Appendix B. <br />Although there has been considerable mining within the <br />permit boundary, only one subsidence feature has been documented. <br />The feature consists of two subsidence troughs; one trough 25 <br />feet long, 10 feet wide, and 3 feet deep; the second trough is 45 <br />feet long, 5 feet wide, and 2-3 feet deep. This feature is <br />• located approximately 50-60 feet above the Rex Carbon coal seam <br />near the access adit to the Rex Carbon Mine. Additional <br />subsidence features outside the permit boundary have been <br />documented and are shown on the Extent of Mining Map presented in <br />Appendix B. <br />Based on the documented evidence of subsidence and on the <br />extent of mining conducted within the Rex Carbon coal seam, <br />Manley coal seam, Vento coal seam, Red Arrow coal seam and the <br />Dirty Jack coal seam, potential for additional subsidence in <br />these specific areas exists. However, insufficient information <br />is available on old mine wockings to make accurate predictions as <br />to the impacts of these areas on the total expected subsidence <br />• from current and proposed mining. <br />12 <br />