Laserfiche WebLink
-5- <br /> longer of the two cracks is shown as continuous for <br /> approximately 3, 500 feet, although it may not be . <br /> Superposition of mine workings should be accurate to within <br /> approximately 50 feet. Coal bed elevation contours are <br /> projected from known points and are also accurate to within <br /> 50 plan feet . Locations of cracks are probably accurate to <br /> only about 100 feet . <br /> Please let us know your ideas concerning renewed subsidence <br /> monitoring . As you know, helicopter-supported surveying is <br /> extremely expensive nd somewhat dangerous, and weather <br /> conditions and monitoring point location in this rugged area <br /> frequently make ground-based surveying an exercise in <br /> frustration . <br /> If you have any questions, or require any further <br /> information, please o advise . <br /> Very truly yours, <br /> Bruce A. Collins, Ph.D. <br /> Assistant to the President <br /> CPG No . 7016 <br /> attachment <br /> cc: J . A. Reeves <br /> J . H . Turner <br /> Diane Delaney <br /> Scott Jones <br />