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C@tt~/ Getty Trading and Transportation Company , P.O. Box 5568 T.A., Denver, CO 80217 iiiiuiiiiuiiuiii 999 • (303) 861-4475 March 2, 1984 REG~?1t~D f114R G 1~d~1 Mr. James A. Pendleton Engineering Geologist Colorado Dept. of Natural Resources Mined Land Reclamation Division Dear Mr. Pendleton, MINED LF,"10 RECU~!+tAT~O"t DIVISION C01o. Dep. u~ Ndlufil neaauices This letter is in response to your letter of January 11, 1984. Getty has performed the attached calculations and modeling for the Dorchester Coal Mine subsidence problem. Getty has determined the following items: 1) The assumption of 10.2 feet of subsidence in a 297.5 foot distance is a worst case analysis. This is based on subsidence profiles which were calculated from the Subsidence Engineers Hand Book, National Coal Board Mining Department, 1975 edition. (See Exhibits I-III) 2) The stress model is based on a beam which is displaced the required subsidence over the appropriate distance. The axial stress was based on a calculated axial strain. The axial strain was calculated according to the Pythagorean theorm. Since the ground follows a longer S type curve, a strain was calculated based on the S curve. A safety factor of 2.75 ie applied to the strain calculated according to the Pythagorean theorm and this brings it in line with the actual S curve strain. Getty proposes to lay pipe commensurate with the above subsidence model,The pipe grades and wall thicknesses that will be used through the Dorchester Coal Miae are shown below. 10.2' SUBSIDENCE MODEL - POSSIBLE PIPE CHOICES 1.) 8.625" O.D., 0.322 W.T., APISLR-42, ERW or Seamless Pipe 2.) 8.625" O.D., 0.250 W.T., APISLR-52, ERW or Seamless Pipe 3.) 8.625" O.D., 0.203 W.T., APISLR-60, ERW or Seamless Pipe 4.) 8.625" O.D., 0.188 W.T., APISLR-65, ERW or Seamless Pipe 5.) 8.625" O.D., 0.172 W.T., APISLx-70, ERW or Seamless Pipe