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<br />tants.lnc <br />Geotechnleal I Environmental EnYineerln~ • Materials TestinY <br />December 1, 2003 <br />East Fork Mutual Irrigation Company <br />P.O. Box 38 <br />Hot Sulphur Springs, CO 80451 <br />Job Number: 03-5547 <br />Subject: Additional Remedial Slope <br />Improvements, East Fork Ditch, Grand County, <br />Colorado. <br />~ Gentlemen: <br /> <br />As requested, NWCC, Inc. has prepared this report outlining our recommendations for Additional Remedial <br />Improvements for the failed slope areas and debris flow azeas at the East Fork Ditch located in Grand <br />County, Colorado. Our firm previously evaluated the slope failures and made stabilization <br />recommendations that were summarized in reports dated May 7 and May 17, 2003. <br />Head Scare Face Areas: The slope failure azeas where the failures initiated aze known as the head scarp <br />faces. These azeas were stabilized during this past summer (2003) by the installation of "launched" soil <br />nails, which anchor the exposed soils into deeper, more competent materials behind the face. The slope <br />stabilization design and construction were completed by Soil Nail Launcher, Inc. of Grand Junction, <br />Colorado and the scarp faces currently consist of exposed soil with the reinforcing steel (nails) protruding. <br />Erosion of the exposed soils could result in additional degradation of the slope face, although the <br />design/build contractor has stated that lazger scale slope failures are deemed unlikely. <br />Based on our observations, we believe there are two feasible alternatives for stabilizing the exposed face: <br />(1) Place a minimum 4-inch layer of shotcrete over the exposed scarp faces and underlain by heavy gauge <br />galvanized wire mesh; (2) Place stacked boulders along the exposed scarp faces consisting of minimum two <br />to three foot diameter boulders stacked from the base of the scarp face to the full height of the slope. We <br />~ believe that the shotcrete alternative is probably the most feasible alternative from aconstruct-ability <br />standpoint since the shotcrete can probably be placed with a minimum of difficulty. <br />Debris Flow Areas: The two slope failures produced debris flows that reach several hundred feet below <br />the scarp faces on very steep slopes on the order of 50 percent. These slopes end abruptly at a narrow <br />floodplain along the north side of the East Fork of Troublesome Creek. The failures and debris flows aze <br />located on the Elk Fork Ranch and the property owner has expressed concern over materials from the debris <br />flows reaching the creek with the resulting sedimentation and negative impact on the aquatic habitat <br />conditions. <br />We believe that the debris flows aze mazginally stable at this time and will probably continue to creep <br />(slowly) downslope over time. We do not believe it is likely that the debris flows will reach the road or <br />creek at this time. It is possible that more active mobilization of the debris flow, resulting in material <br />• (970) 879-7888 • Fax (870) 879.7891 • nwccl @mindspring.com <br />2580 Copper Ridge Drive • P.O. Box 775226 • Steamboat Springs, CO 80477 <br />