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Slope Stability Analyses - <br />proposed Brighten WON( Storage Project, Adams county, Colorado <br />Job No. 02-0055 <br />May 21, 2002 <br />page 2 of 3 <br />steeper then 1.5:,1 (67 percent gradient or about 33 degrees) which was the maximum <br />slope angle recommended by GROUND. Subsequent measurements obtained by Les <br />Ewegen, LLC, indicated that the project temporary slopes (up to about 45 feet in height) <br />ranged from 1.7:1 to 2.8:1, corresponding to overall slope gradients of about 59 percent, <br />or flatter. These data have been Interpreted by the Division of Mines and Geology to <br />indicate that although the slopes are at angles of 1.71 and flatter overall, they are <br />irregular and exceed-the recommended maximum slope angle locally. <br />Given that the overall slopes reportedly are cut at angles similar to or flatter than <br />recbrnmended in GROUND's May 31, 2002, report, and that drained conditions continue <br />to be maintained, In our opinion the locally over-steep slopes do represent a significantly <br />increased risk of large-scale or deep-seated slope failure. As was noted in the May 31, <br />2002, report regarding the recommended elope angle, "Surficial sloughing and local <br />failures, may. occur on slope faces cut at this angle. , Significant erosion should be <br />anticipated during major rainfall events." These features likely will be observed more <br />frequently in the areas where the local slopes are steeper than 1.5:1 (horizontal <br />vertical). Therefore, the, routine observation of the temporary slopes, and maintenance <br />of areas exhibiting sloughing or erosion, which was necessary for slopes at the <br />recommended angle will be required to a greater extent in the locally ever-steep areas. <br />GROUND recommends that the Contractor pay particular attention to such areas. All <br />eroded or sloughed areas should be re-graded and the slope restored. <br />We also understand that project excavations have, at least locally, reached the permitted <br />limit (10 feet) from the project property line, along the northern and eastern sides of the <br />site. Some of these areas also may be areas where the local slopes are steeper than <br />1.5:1 (horizontal : v®rtical). Our comments above apply to' these areas as well. <br />Maintenance and repair of these slopes by the Contractor is important to protect <br />-improvements on the adjacent land. <br /> <br />Z0 39Vd N393M3 6606PSPOL6T ZZ:ST £00Z/V0190