3210 36TH PL NE 2018-01-02 MF Import

Sand De osits P 'Che compressible fine-grained alluvial and estuanne deposits are underlain at depth by loose [o medium dense, fine to medium sand wi[h variable silt content. The test pits and shallow CPT e;:plorations �acre I generally terniinated in coarscrv6�aincd alluvial sand deposits. The soil boring and deeper CPT esplorations indicate that the sandy soils are located at depths Uehveen about 20 to G� feet beiow existing groand surface and again at depths grcatcr than 35 feet bela�+ ground surface. The sard deposi[s contain interbeds of tine-��rained deposits. IDeeper Fine-grained Soi/s Based on boring B-1 and cone penetration tests CPT-1 through CPT-4, a deeper compressiblc fine-grained alluvial deposit exists betwcen the depths of about 65 and 8.5 Cee! belo�� existing ground surface. 'I�he unit is generally soft to medium stiff, low plasticity silt with variable sand content, �nd contains some interbedded organic soils and sand layers. GROUNDWATER CONDITIONS bloderate to rapid perched groundwater secpage was observed in all of the tes[pits a[depths ranging from about 2'/� to 4 Ccct below thc ground surface. Groundwater secpage was also encountcred at dcpths of 1� and 12 fcet below the ground surface in 'I'P-1 and TP-6, respectively. We anticipate tha� groundwatcr Icvcis at the site will bc in response to water levels in Steamboat Slough and the Snohomish River. We anticipate that the ground��•ater elevation will tluctuate as a function of precipitation, time of year, the tides and surrounding surface water elevations, and other fac[ors. During our ficld work, four groundwater monitoring wclls were abandoned on the project. The wells ��ere located on the north side of the old barn and were completed to depths ranging &om 18'/ to 19 feet belo�v dic ground surface. 'fhe bottum 10 feet of each well was screened and bedded in sand. The wells were abandoned by Holocene Drilling in accordance with the Washington State Department of Lcology j requirements. Prior to abandoning the wefls �ve meaaured the ground�vater Icvcl in each well and found it to be approximatcly 3J fcct bclo�a t{te ground surfacc. SEI.riMICITY General Scismicity in the Puget Sound area is primarily dri�en Uy the Cascadia Subduction Zone, ��hich is the zone where the weshvard advancing Nordi American Plate is ocerriding die subducting Juan de Fuca P(ate. Thrce potential seismic source zuncs are generally ackno��ledged for the Puget Sound area: (1) shallo�v crustal carthquakes associatcd with l:no��n and/or unkno��n faults; (Zj Cascadia Subduction Zone interface carthquakcs, �ehich occur along the boundary located between the Juan de Fuca and North American plates; and (3) Cascadia Subduction Zone intraplate earthquakes, which occur within [he subducting Juan dc Puca Plate. Liquefaction Potential Liquefaction rcCers to the condition where vibration o; shaking of the graund, usually from earthyuake Corces, results in die development of excess pore pressures in saturated soils with subsequent loss of strength in the deposit of soil so affected. In general, soils that are susceptible to liquefaction include very loose to medium dense, dean to silty sands that are situated below the �vater table. I��(c No.899'-00�-00 PQb�J G EOENG IN EE R� U�mGcr 1/,1006