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<br />-16- <br />RVII. Subsidence (2.05.6(6). 4.20) <br /> <br />The application includes the results of the required survey of <br />structures and renewable resource lands within the potentially <br />affected area. The following inadequacies were determined to <br />exist within that survey discussion: <br />1. The applicant observes that a dwelling exists within the <br />potentially affected area, but that this dwelling is owned by <br />Colorado Yampa Coal Company. The location of that dwelling <br />should be clearly delineated upon Map No. 4. Further, on page <br />2.05-62, reference is made to an "unoccupied structure". If <br />these references regard one-in-the-same structure, the <br />applicant should clarify that point. If the structure is <br />inhabitable, then the applicant must discuss "worst case" <br />projected effects of subsidence. In the case of inhabitable <br />dwellings, it has been common to require appropriate <br />precautions be taken, such as a special utility connection <br />modification, in order to eliminate potential hazards to any <br />occupants. <br />2. County Road No. 27 is exposed to potential effects from <br />subsidence and should be monitored to safeguard public health <br />and safety. In connection with the proposed survey <br />monumentation, visual inspection techniques should suffice to <br />safeguard County Road No. 27. <br />3. The Denver, Rio Gcande and Western Railroad Spur is also <br />within the potentially affected area. As in the case of County <br />Road No. 27, periodic visual monitoring of this facility should <br />suffice to protect the public health and safety. <br />4. The applicant projects localized impacts upon both <br />bedrock and surficial aquifers, based upon a specific concept <br />of overburden response which has been insufficiently justified <br />within the application. Recent literature regarding subsidence <br />effects upon ovecbucden above undecground coal woLkings has <br />documented roof caving to heights in excess of 10 times seam <br />height and bed separation to heights in excess of 30 times seam <br />height. On page 2.05.61, among other instances, the applicant <br />refers to overburden caving limitations of 5 times the seam <br />thickness. The mechanical and hydcological implications of <br />such a variance in projected overbucden ceaponse could be <br />significant. The applicant will have to more thoroughly <br />justify the assumptions being made within its projection of <br />subsidence impacts. In addition, the application will have to <br />specifically discuss how the proposed mechanical and <br />hydrological monitoring programs will serve to verify the <br />assumptions made in completing theic projections of impacts. <br /> <br />