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 2 4. Provide recommendations for improving slope stability, including the use of light retaining structures, erosion control systems, and drainage improvements. 5. Provide recommendations for long-term slope maintenance. 6. Document the results of our explorations, findings, conclusions, and recommendations in a written geotechnical report. SITE CONDITIONS Surface Conditions The site is an irregularly shaped parcel covering, approximately oae-acre. The property is bordered to the north by the Burlington Northern & Santa Fe Railroad, to the south by Mukilteo Boulevard, and to the east and west by residential properties. The property contains a steep north -facing slope overlooking Possession Sound. A single-family residence with a day light basement and a driveway access from Mukilteo Boulevard currently occupy the southwestern portion of the property above the steep slope. A second -story patio and level lawn area enclosed by a stone and glass fence are situated in the backyard behind the existing house. The lot layout and residence location are indicated on the Site Plan in Figure 2. The steep slope located below the residence is approximately 100 feet in height and has an overall inclination of about 34 degrees (68 percent) down to the north and cast, as shown on Cross -Sections A -A' and B-B' in Figures 3 and 4, respectively. The slope is vegetated with alders, blackberry bushes, underbrush and several mature maple trees within the lower portion. A near vertical scarp face approximately 10 feet tall is situated directly below the top of the slope along the northern side of the residence. This scarp along with numerous tension cracks and significant subsidence are the results of the recent slope movement. The steep slope on the eastern side of the residence is approximately 60 feet in height and has an overall inclination of about 40 degrees (84 percent) down to the east, as shown on Cross -Section C-C' in Figure 5. The eastern slope forms part of a ravine that dips moderately towards Possession Sound. The eastern slope is vegetated with similar plant species, as well as two mature fir trees situated near the toe of the slope. We did not observe surface water on site or seepage on the slope during our visits on July 20, and 23, 2006. Tension cracks up to eight inches wide and subsidence of material up to si.c feet deep were NELSON GEOTECHNICAL ASSOCIATES, INC. 64