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i .'.. --- — - <br /> � <br /> I <br /> i <br />' DAVID L. NELSON AND ASSOCIATES, INC. <br /> � Consulting Engincering Gculogy <br /> I <br /> la May 31 , 1991 <br /> � Project No. 4791 <br /> Page 4 <br /> I il <br /> � with no apparent signs of instability, sliding or significant erosion within <br /> �$ close proximity to the proposed duplex area. <br />�� � SENSITIVS 11REA EVALUATION <br /> I �� • i � <br />' � <br /> The subject site area was evaluated for sensitive area evaluation, as <br /> E� recommended in the new City of Everett Zoning Code Ordinance Section 37 (1671- <br /> i <br /> 89) . Of the potential reasons tor classificaticn as environmentally sensitive <br />� ,, IY (environmentally sensitive characteristics), the following could occur on <br /> �' ' I <br /> site; unstable soils hazard areas, landslide hazard areas, seismic hazard <br /> �� areas, springs, ground water seepage, and steep slopes associated or in <br /> jM conjunction aith one or more of the environmentally sensitive area elements. <br /> ..r--_, . R,, �� <br /> We will discuss these potential elements below. <br /> i• ,� <br /> Seismic Hazard <br />� '. i The Puget Sound region is classified as a zone 3 by the Uniform Building Code. <br /> " �� Seismic considerations for this type of site include liquefaction potential <br /> � � ; and attenuation of ground motions by soft soil deposits. Typically, seismic <br /> � '� hazards are highest for thick alluvial (organic and/or normally consolidated) <br /> soils. The liquefaction potential is highest for loose sand and silty sand <br />` , � r� deposits with a hiqh ground water table. The thickness of the sand deposit <br />, '. should Ue considered, as liquefaction is dependent on the ability of excess <br /> � pore pressures to dissipate. That is, if the deposit is relatively thin with <br /> 1� <br /> a short drainage path, the pore pressures can dissipate fairly rapidly. <br /> � <br /> t6 We did not encounter alluvial type soils on site which are typically <br /> � liquefaction sensitive. Therefore the potential influence of liquefaction on <br /> � A structures due to these soil types is low�. The same reasoning may be applied <br /> � to the attenuation of ground motion. We did find a minor thickness of fill <br />� . F� on the slope that has some r.isk of slope failure during a seismic event. To <br /> reduce this risk to the structure, foundations should extend through any <br /> I <br /> 1e <br /> i . <br /> F <br />