2202 100TH ST SW Geotech Report 2022-10-25

Subsurface Exploration, Geologic Hazard,and Stephens Everett Property Preliminary Geotechnical Engineering Report Everett, Washington Geologic Hazards and Mitigations 7.0 EROSION CONTROL Review of the City of Everett's "Erosion Hazard Critical Areas Map 3," indicates the site has a "low" risk of erosion. The sediments underlying the site generally contain moderate to high amounts of silt and can be sensitive to erosion. In order to reduce the amount of sediment transported off the site during construction, the following recommendations should be followed. 1. Maintaining cover measures atop disturbed ground provides a significant reduction to the potential generation of turbid runoff and sediment transport. During the local wet season (October 1st through March 31st), exposed soil should not remain uncovered for more than 2 days unless it is actively being worked. Ground-cover measures can include erosion control matting, plastic sheeting, straw or wood mulch, crushed rock or recycled concrete, or mature hydroseed. The contractor must implement and maintain the required measures. 2. All temporary erosion and sediment control (TESC) measures for a given area to be graded or otherwise worked should be installed prior to any construction activity. 3. Construction access points should be surfaced to mitigate sediment track-out onto adjacent streets. Any sediment that is tracked onto adjacent streets should be promptly swept up. 4. Silt fencing should be utilized as buffer protection and not as a flow-control measure. Silt fencing should be placed parallel with topographic contours to prevent sediment-laden runoff from leaving a work area or entering a sensitive area. Silt fences that cross contour lines should have separate flow control in front of the silt fence. A swale/berm combination should be used to provide flow control. 5. During the wetter months of the year, or when large storm events are predicted during the summer months, each work area should be stabilized so that if showers occur, the work area can receive the rainfall without excessive erosion or sediment transport. The required measures will depend on the time of year and the duration the area will be left unworked. During the winter months, areas that are to be left unworked for more than 2 days should be mulched or covered with plastic. During the summer months, stabilization will usually consist of seal-rolling the subgrade. 6. All disturbed areas should be revegetated as soon as possible. If it is outside of the growing season, the disturbed areas should be covered with mulch. Straw mulch provides an effective cover measure and can be made wind-resistant with the application of a tackifier after it is placed. March 29,2019 ASSOCIATED EARTH SCIENCES,INC. TG/ms-180567E001-2-Projects120180567\KEIWP Page 9