1617 EDGEMOOR LN 2016-11-10 - Laserfiche WebLink

McKinnon Residence Retaining Wall NGA File No 910614 1617 Edgemoor Lane December 2, 2014 Everett, Washington Page 11 northeast of the residence. We anticipated that these pipes likely originated from the roof down spouts and yard drains associated with the residence, but we were unable to confirm this during our site visit. We observed that these pipes were likely daylighting on the steep slopes below the top of slope area. At a minimum, we recommend that all residence downspouts and yard drains along with the proposed retaining wall drain be tightlined and directed to discharge at the bottom of the slope or to a proper location approved by NGA. We recommend that the outfalls of these pipes be armored with rock spall pads to minimize erosion from the outfall of the pipes. USE OF THIS LETTER NGA has prepared this letter for Mr. Bruce McKinnon, and his agents, for use in the planning and design of the retaining wall project on this site only. This letter is a specific evaluation of the existing timber retaining wall and steep slopes and should not be considered an evaluation of the entire site or the existing residence. There is potential for failures to continue to occur on the slope near and below the wall. This potential can be reduced by maintaining the drainage systems and refraining from casting any material what so ever over the slope. Irrigation systems near the new wall should be avoided. 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 letter for consideration in design. There are possible variations in subsurface conditions between the explored and unexplored areas and also with time. Our letter, 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. All people who own or occupy homes on hillsides should realize that landslide movements are always a possibility. The homeowner should periodically inspect the slope, especially after a winter storm. If distress is evident, a geotechnical engineer should be contacted for advice on remedial/preventative measures. The probability that landsliding will occur is substantially reduced by the proper maintenance of drainage control measures at the site (the runoff from the roofs should be led to an approved discharge point). Therefore, the homeowner should take responsibility for performing such maintenance. Consequently, we recommend that a copy of our letter be provided to any future homeowners of the property if the home is sold. We recommend that NGA be retained to review project plans prior to construction and to monitor wall repairs. These additional services are intended to confirm that the conditions encountered are consistent NELSON GEOTECHNICAL ASSOCIATES, INC.