4812 HARBOR LN 2018-01-02 MF Import

December 3,1998 Project No. T-4199 Erosion The native soils, combined with the sloping nature of the site, will result in a severe erosion hazard during site grading and excavation activities. To mitigate this hazard, site excavations and grading should only be undertaken during the dry summer months. To prevent or reduce erosion during periods of rain and reduce sediment transport off -site, the following erosion -control practices should be implemented: • Cover all exposed soil conditions, including soil stockpiles, with securely anchored plastic sheeting or erosion -control blankets. • Control surface runoff during and after construction. Runoff should be routed away from the site slopes to a controlled point of collection and discharge. • During construction, contain eroded sediments on -site by erecting silt fencing on the downgradient slopes. The above management practices for erosion prevention and control should be considered minimum. Additional measures may be required by City building codes and may be necessary depending on conditions that develop during construction. Seismic Hazards The Puget Sound area falls within Seismic Zone 3, as classified by the 1997 Uniform Building Code (UBC). Based on the soil conditions encountered and the local geology, a soil profile type of Sc (from Table 16-J of the 1997 UBC) should be used for design purposes in the area to be developed. Generally, seismic hazard areas are defined as lands that, due to a combination of soil and groundwater conditions, are subject to severe risk of Iruond shaking, subsidence, or liquefaction during earthquakes. Based on our subsurface investigation, in our opinion, the risk of site damage due to seismically -induced subsidence is minimal. The medium dense to dense, silty sands and sandy silts encountered are above the water table and arc not susceptible to liquefaction. Some sloughing of the near -surface soils on slopes adjacent to the residence may occur during a major seismic event, particularly if they are in a wet or saturated condition. 4.3 Site Excavation and Grading To prepare the site for construction, all vegetation and organic surface soils and other deleterious materials should be stripped from t',e proposed building and pavement areas. Stripping depths of 12 to 18 inches should be expected to remove the topsoil layer. Following stripping, additional excavation depths of two to four feet will be required in the vicinity of Test Borings B-1 and B-2, respectively, to obtain suitable support for building foundations. Page No. 4