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Geotechnical Engineering Report SSGC <br /> Hardeson Road Retail <br /> Everett,Washington <br /> SSGC Project No. 18072 <br /> September. 1.8,201.8 <br /> 1 <br /> ' Liquefaction <br /> Soil liquefaction is a condition where loose, typically granular soils located below the <br /> - groundwater surface lose strength during ground shaking, and is often associated with <br /> earthquakes. The risk of liquefaction at this site is considered low as native soils consist of <br /> overall dense glacial till. <br /> ' Infiltration Characteristics <br /> 1111 Infiltration to control stormwater will be difficult at this site due to the presence of glacial till at shallow <br /> depths. Assessment of infiltration was completed per the 2016 King County Surface Water Design <br /> Manual (and 2014 DOE Stormwater Management Manual for Western Washington). Two small-scale <br /> Pilot Infiltration Tests (PIT) were completed in the upper 2 feet of soils on the site. Results of the <br /> infiltration tests are provided in Table 3. <br /> Table 3.Infiltration Rates <br /> «1I ' ��r rre Cot`d, Correction <br /> ' 1111111IIMESWATMINS 111111111Mboommaaght I I�ltr + n tt Infil a on <br /> it Type a;zn }actor `.y Y p ■may. <br /> F �t (1n A F (�; F � �a <br /> Alluvium/weathered <br /> PIT-1,26 in till 3.0 0.70 (0.5/0.5/09) <br /> *Correction Factors from the 2014 DOE Stormwater Management Manual for Western Washington <br /> The field and corrected infiltration rate is considered appropriate for the soil tested based on other test <br /> results in similar soils. However,this rate more likely demonstrates horizontal flow through upper native <br /> soils as denser glacial till below will restrict•vertical infiltration. Conventional infiltration facilities <br /> (trenches or ponds) are not considered feasible at this site. Bioswales, pervious pavements, or other <br /> ' shallow dispersion systems could be considered in the upper native soils where natural grades direct water <br /> to the north,if allowed by the City. A long-term rate of 0.70 inches is recommended for infiltration in the <br /> upper native soils to a depth of 3 feet or shallower. <br /> Cation Exchange Capacity(CEC) and organic content test were completed on a sample from the base of <br /> the PIT sites. Test results are summarized in the table below. <br /> 9 <br />