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Vermillion Ranch Limited Partnership/Surface Water Impoundment 13659-RX <br /> ' 6. Relatively soft soils encountered along Talamantes Creek may present difficulty for <br /> ' vehicle traction and stability. Such areas may also require stabilization before fill can be <br /> successfully compacted in these areas. <br /> 7. The upstream and downstream dam embankments will likely require rock riprap to <br /> protect against erosion and wave action. Depending on haul distance and material <br /> ' availability, riprap may be a significant portion of the dam construction cost and should <br /> be evaluated during the preliminary design phase. <br /> ' Preliminary Recommendations <br /> Earthwork <br /> 1. Prior to construction on the site, all vegetation and organic surface matter should <br /> be removed from the proposed dam foundation area. Based on the test borings, it <br /> appears that stripping depths of approximately 4 to 12 inches may be required. <br /> ' 2. After stripping and excavation to desired site grades, the exposed subgrade in <br /> areas to be filled should be compacted to densify the native subgrade and soils <br /> loosened by excavation. This compaction effort should be performed in the <br /> presence of the Geotechnical Engineer so that soft or loose zones can be <br /> properly identified and improved. If loose or soft zones are encountered that do <br /> ' not improve with repeated compaction, they should be removed and replaced <br /> with properly-compacted fill material, as described in Item 3, below. <br /> Alternatively, soft or loose zones may be stabilized by covering with a woven <br /> geotextile fabric equivalent to Mirafi 500X, Propex Geotex MOST, or <br /> equivalent. Utilization of a geotextile fabric is subject to approval from the <br /> ' Geotechnical Engineer to avoid potential seepage problems beneath the dam. <br /> 3. Fill for the earthen dam may consist of clay material excavated from the <br /> upstream borrow source. The fill should be placed in horizontal lifts not <br /> exceeding 8 inches in loose thickness and compacted to a minimum of <br /> 95 percent of the ASTM D698 (Standard Proctor) maximum dry density at <br /> moisture contents ranging from 2 percent below to 3 percent above the ASTM <br /> ' D698 optimum moisture content. The recommendations presented herein are <br /> based on a homogeneous earthen dam. The contractor's equipment and <br /> ' procedures should produce a uniformly mixed and compacted lift. In-place <br /> density and water content of each lift of fill materials should be tested and <br /> approved. <br /> ' INBERG-MILLER ENGINEERS <br /> 8 February 26,2009 <br />