1915 W MUKILTEO BLVD 2018-01-02 MF Import

Geotechnical Engineering Evaluation and Slide Repairs 1915 Mukilteo Boulevard July 26, 2006 NGA File No. 743206 Page 10 drains typically consist of 4-inch perforated PVC pipes placed in 2- to 3-foot deep trenches filled with pea gravel or washed rock. All excavation spoils should be removed off the slope or placed and compacted in low areas as approved by NGA. The drains would be routed to the bottom of the slope or to an appropriate discharge location. The areas where a wall would not be utilized but still at risk of further movement should be improved by re -grading the over-steepened/loosened areas, removing the vegetative cover, compacting the exposed surface to a non -yielding condition, placing suitable erosion control systems on the prepared areas, and re -vegetating with deep-rooted drought -resistant plants. The actual'mproventent methods for these areas will be highly depended on the conditions encountered during construction. We will work closely with you, contractor to determine the best course of action at the time of construction. Final site grades should allow for drainage ac ,ay from the top of the steep slope and the wall. If possible, the finished ground should be sloped at a gradient of three -percent minimum for a distance of at least 10 feet away from slope. In any case, all runoff generated above the slope, including paved areas, roofs, and yard areas should be collected and routed into a permanent discharge location at the bottom of the slope. A cut-off drain may be installed along the top of the slope to prevent surface and shallow subsurface water from reaching the wall. This cut-off drain is schematically shown on Figure 10. USE OF THIS REPORT NGA has prepared this report for John and Dolores Robinson, and their agents, for use in planning and design of stabilization systems along the top of the steep slope on this site only. The above recommended systems should be considered as an erosion feature intended to slow the rate of slope recession, and should not be considered as a permanent measure of stabilizing the overall slope. The scope of our work does not include services related to construction safety precautions and our recommendations are not intended to direct the contractors' methods, techniques, sequences, or procedures, except as specifically described in our report. There are possible variations in subsurface conditions between the explorations and also with time. Our report, conclusions, and interpretations should not be construed as a warranty of subsurface conditions. A contingency for unanticipated conditions should be included in the budget and schedule. NELSON GEOTECHNICAL ASSOCIATES, INC. iy /�d7