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Magic Toyota GT Summary LetterGWENGINEERS 17425 NE Union Hill Road, Suite 250 Redmond, Washington 98052 425.861.6000 September 7, 2018 Magic Toyota 21300 Highway 99 Edmonds, Washington 98026 Attention: David Broadus Subject: Geotechnical Construction Summary Letter Magic Toyota New Dealership Building and Parking Lot Edmonds, Washington File No. 11805-001-05 INTRODUCTION This letter presents a summary of GeoEngineers' construction observation services for the new Magic Toyota dealership facility located at 21300 Highway 99 in Edmonds, Washington. Our services for this project were completed in general accordance with our proposal dated August 3, 2017. The project involved the construction of the new dealership and service building, and associated detention vaults, utilities, retaining walls, and surface parking. During construction, GeoEngineers' observed the over -excavation of unsuitable soils, fill placement and compaction, foundation and pavement subgrade preparation, foundation drain installation, and utility trench backfill. OBSERVATIONS GeoEngineers visited the site on an intermittent basis on 39 occasions between August 15, 2017 and August 9, 2018 to observe over -excavation of unsuitable soils, vault and footing subgrades, fill placement and compaction, footing drain installation and pavement subgrade preparation. Detailed reports of our construction observation services are presented in our daily field reports for the project, Numbers 1through 39 dated August 15, 2017 through August 8, 2018. Copies of these field reports were provided to Magic Toyota, Foushee, and Strotkamp Architects during construction. Large Detention Vault We observed the temporary cut slopes and foundation preparation for the large detention vault located south of the proposed building site. Foushee originally planned on completing the cut slope using a 4-foot-high vertical cut at the base and a 1H:1V (horizontal:vertical) cut slope for the remainder of the Magic Toyota September 7, 2018 Page 2 excavation. The native soils exposed at the base of the excavation did not appear competent enough to stand vertically, and seepage at the face was exposed in the southwest corner of the excavation. Therefore, ecology blocks were used to support the lower vertical face of the cut around most of the excavation. The subgrade forthe vault was prepared by removing loose soil and placing a pad of compacted 11h-inch-minus crushed rock over the exposed native soils. Based on our observations, it is our opinion that the temporary cut and subgrade preparation for the large detention vault were completed in general accordance with our recommendations and the project plans and specifications. Over -excavation of Unsuitable Soils Existing uncontrolled fill was present over much of the southern portion of the building footpring area. The unsuitable fill generally consisted of silty sand with gravel and wood debris and other organic material. The unsuitable fill was overexcavated to depths of 2.5 to 5 feet to expose competent native deposits. Based on our observations, it is our opinion that the over -excavation of unsuitable soils observed during our site visits was completed in general accordance with our recommendations and the project plans and specifications. Foundation Subgrade Evaluation Foundation subgrade conditions for the building and retaining walls were evaluated by a representative from our firm who visited the site intermittently. The north portion of the building and the retaining wall were founded on very dense glacial till while the southern portion of the building was founded on medium dense to dense native deposits. We evaluated the foundation subgrades by means of a 1/2-inch diameter steel probe rod. Subgrade evaluation included confirming adequate bearing soils and recommending over -excavation where unsuitable bearing soils were encountered at the design foundation subgrade elevation. In a few areas, geotextile fabric was placed over the native soil prior to placing and compacting the structural fill. Based on our observations, it is our opinion that foundation subgrades evaluated during our site visits were prepared in general accordance with the project plans and specifications. Fill Placement and Compaction We observed the placement and compaction of fill material within the building footprint to replace unsuitable fill encountered in portions of the building footprint and to raise site grades where necessary, and as backfill for the detention vault, retaining walls, and utility trenches. We observed that structural backfill for the building pad and backfill placed as crushed surfacing base course below pavements was compacted to at least 95 percent of the maximum dry density (MDD) as determined by ASTM D1557. We observed that structural backfill placed for the detention vault, utility trenches and retaining walls was compacted to at least 90 percent of the MDD as determined by ASTM D1557, with the upper two feet compacted to at least 95 percent of the MDD where the backfill was to support pavement or other hardscape features. Based on our observations and testing, it is our opinion thatfill placement and compaction observed during our site visits were completed in general accordance with the project plans and specifications. GMENGINEERS� File No. 11805-001-05 Magic Toyota September 7, 2018 Page 3 Foundation Drain Installation We observed foundation drain installation around the building perimeter. Based on our observations and conversations with the contractors, it is our opinion that footing drains observed during our site visits were installed in general accordance with the project plans and specifications. Pavement Subgrade Evaluation We evaluated the majority of the pavement subgrade. We performed a proof roll with a loaded dump truck and evaluated the pavement subgrade with a 1/2-inch diameter probe rod. In general, we observed that the pavement subgrade was not pumping and minimal deflection was observed under the weight of the loaded dump truck prior to paving. Based upon our observations and evaluations, it is our opinion, that the pavement subgrade was prepared in general accordance with plans specifications and our recommendations. Temporary Erosion Control Temporary erosion control was observed during each site visit by GeoEngineers. The contractor implemented temporary erosion control measures as necessary to reduce the risk of soil and sediment laden runoff from leaving the site. Tank Backfill Three abandoned storage tanks in the northeast corner of the site were left in place and backfilled with CDF. We observed that the tanks had been backfilled as specified by the City of Edmonds. We trust that this summary letter presents the information that you need at this time. We appreciate the opportunity to provide geotechnical services on this project. Please call if you have any questions regarding the information presented in this letter or if you require additional information. Sincerely, GeoEngineers, Inc. Nancy L. Tochko, PE Senior Geotechnical Engineer NLT:DCO:lw cc: Tom Strotka m p, Strotka m p Architects Foushee 29247 "'ON At Debra C. Overbay, PE Associate Disclaimer: Any electronicform, facsimile or hard copy of the original document (email, text, table, and/orfigure), if provided, and any attachments are only a copy of the original document. The original document is stored by GeoEngineers, Inc. and will serve as the official document of record. t.� GWENGIINEEIRS� File No. 11805-001-05