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Slope StabiliTy Analyses _ <br />Proposed Brighton Water Storage Project. Adams County, Colorado <br />Job No. 02-0065 <br />May 37, 2002 <br />Pegs 2 of 3 <br />steeper than 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 />i"wegen, 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 avera{I 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.T1 and flatter overall, they are <br />irregular and exceed the recommended maximum slaps angle locally. <br />Given that the overall slopes repcrtediy are cut at angles similar to or flatter than <br />recommended 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 slope 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 over-steep area5- <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 :vertical). 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 />