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20150929133442.pdfSeptember 22, 2015 Northwest, Inc. Mr. Leif Bjorback City of Edmonds 121 - 5' Avenue North Edmonds WA, 98020 Geotechnical Engineers, Geologists & Environmental Scientists G-3598 SUBJECT: REQUEST FOR GRADING EXTENSION & WINTERIZATION RECOMMENDATIONS New SFR at 15911 - 74' Place West, Edmonds, WA BLD2014-0317 Ref: City of Edmonds letter dated September 15, 2015, regarding site grading restrictions and winterization. Dear Mr. Bjorback: On behalf of the client, Mr. Leroy Saunders, a grading extension is requested beyond the September 30' winterization ordinance deadline for the site. The majority of the earthwork has been completed, with the following exceptions which will occur after September 30`s : 1. Installation of the storm water detention pipe. The detention pipe has been ordered but has not been delivered due to a back log. 2. Pouring of the house foundation and garage slab (the foundation excavation is complete). 3. Grading of the driveway and use of the driveway material and detention pipe material to backfill around the house foundation. 4. Connecting of the street utilities to the house. Completion Date The anticipated completion date for the above items is November 10, 2015. On November 10', the site will be winterized. Any remaining earthwork will be stayed until after May 1'`, 2016, unless the site is reevaluated by the geotechnical engineer of record to confirm that the site conditions are stable and work may start without creating erosion issues or affecting site stability and the site evaluation is submitted for approval by the City prior to re -commencing work. GEO Group Northwest, Inc. 13240 NE 20th Street, Suite 10 Bellevue, Washington 98005 Phone 425/649-8757 Fax 425/649-8758 September 22, 2015 Grading Extension Request New SFR, 15911 74`h Place W G-3598 Page 2 Site Stability Evaluation The installation of the driveway retaining walls and the mass excavation of the site, including the house foundation excavation, has been completed. The site is currently stable and it is our professional opinion that the remaining earthwork, that will extend beyond September 30th, will not negatively impact on the stability of the site and the earthwork may continue past the ordinance deadline of September 30`x, from a site stability and geotechnical perspective. Erosion Control Winterization Recommendations The following are our winterization recommendations for site. These are in addition to the previously installed TESC measures: A. Cover the exposed bank between the lower west driveway and west side of the home with visqueen plastic and stabilize the plastic with sand bags. B. Extend the silt fence along the east side of the driveway and up the south side of the driveway. The silt fence is be bedded in washed rock on the uphill side of the fence. Water sheeting off the visqueen is to flow into the bedding rock then travel down the rock to the low point of the silt fence. It will then enter and travel through the armored driveway and into the gravel surrounding the catch basin at the southwest corner of the site. C. The foundation excavation for the house has been graded to direct stormwater to it's southwest corner. The foundation excavation is to be covered in visqueen plastic and the plastic secured with sand bags. The southwest corner of the foundation excavation is to be covered with 3 -inches of gravel to slow down the water and protect the subgrade. A filter - fabric wrapped pipe is to be installed to convey the water to the gravel bedding material of the silt fence below. The foundation excavation water will flow down the silt fence bedding rock to the low point of the silt fence where it will enter into the armored driveway and flow to the gravel surrounding the southwest catch basin. D. All exposed or disturbed soils on the site are to be either covered with visqueen plastic or covered with straw mulch. E. Straw waddles are to be installed to slow the velocity of water sheet flowing off the visqueen plastic or other areas of the site. The location of the straw waddles are be determined based on the site conditions. GEO Group Northwest, Inc. September 22, 2015 Grading Extension Request New SFR, 1591174' Place W G-3598 Page 3 F. The west driveway entrance is currently covered in crushed rock quarry spalls. The remainder of the driveway, once graded, shall also be covered with crushed rock quarry spalls. The rock shall be replaced if contaminated with soil. G. All soil stockpiles shall be covered with visqueen plastic and secured with sand bags. H. During storm events, all earthwork activities are to be halted and the site soils protected with visqueen plastic to prevent erosion. 1. All erosion control measures are to be maintained in good condition throughout the project and additional erosion control measures may be required based on the site conditions. J. The geotechnical engineer or designated erosion and sedimentation control supervisor is to monitor the site weekly or after storm events. The weekly monitoring reports are to be submitted to the City inspector upon request. It is our opinion that the above recommended erosion and sediment control methods will be sufficient to mitigate offsite impacts. From an erosion control perspective, it is our opinion that completing the remaining earthwork this fall will be better than waiting until next spring when the site soils will likely be more saturated, be more difficult to work with and have a greater erosion potential. Please let us know if you still need the above winterization recommendations to be provided to the City in a field report, in accordance with your letter. Sincerely GEO GROUP NORTHWEST, INC. Wade J. Lassey, LEG Engineering Geologist William Chang� P.E. Principal GEO Group Northwest, Inc.