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~r~mhFrY ~cnb .~s~uri~tr~ <br />CONSULTING GEOTECHNICAL EN(i'i1rcRS AND MATERIAL TESTING <br />August 1, 1996 <br />Goff Engineering <br />555 Camino Del Rio <br />Durango, Colorado 81301 PN: D96046MT <br />Attention: Mr. Harry Goff, P.E. <br />Subject: Oak Ridge Energy <br />Carbon Junction Mine Sandstone Slope <br />Durango, Colorado <br />Mr. Goff, <br />This letter presents our comments based on our July 18 site <br />observations of the sandstone dip slope which is exposed at the <br />Carbon Junction Mine, Durango. <br />We understand that coal was extracted from the dip slope as part <br />of the site mining operation. Remnants of the coal deposits were <br />observed at the lower elevations of the slope. The natural soil <br />mantle is in thin and formational sandstone crops out along the <br />slope surfaces of the hogback ridges in the vicinity of the mined <br />area. The dip of the sandstone surface ranges from about twenty- <br />five (25) to thirty (30) degrees down to the southeast. <br />We understand that the mine reclamation requirements may include <br />placement of soil on the sandstone surface. We anticipate that it <br />will be difficult to place and establish a soil layer on the <br />surface of the sandstone which will return on the slope. Potential <br />difficulties include erosion and slumping of the placed soil <br />materials. <br />Geotechnical engineering analysis of slope stability includes <br />assessment of the soil strength, slope inclination, and the <br />influence of subsurface water. The data is used to evaluate the <br />driving and resisting forces of the soil mass for slope movement. <br />The ratio of resisting forces to driving forces is often called the <br />slope theoretical factor of safety. If the ratio is less than one, <br />the driving forces are greater than the resisting forces and <br />therefore slope movement will occur. Industry and government <br />regulatory standards vary, however generally a ratio of greater <br />than 1.5 is considered an as acceptable ratio for long term <br />stability for slopes. Greater ratios are often desired if the <br />slope area influences a critical structure or environment. <br />P.O. BOX 7996 P.O. BOX 0045 214 Bodo Drive <br />GRAND ,7(JHCT ION, CO MONTROS E, CO. 9140^_ DURANGO, CO. 91701 <br />(9701 245-9605 (970) 249-3154 (570) ]59-5095 <br />