202 ALDER ST Geotech Report 2018-01-02 MF Import

Proposrd Vraw R�dge Subsurface F_cploration, Geofogir Hu:ards, lnfilt�ation Potemial, Elememarv School Replacemem and Preliminnry Geotethnical Engineering Repoit Eve�rtt. W¢shingron Geologic Ha:ards and Mirigations 1613.5.2. The 2009 IBC seismic design parameters Eor short period (Ss) and 1-second period (St) spectral acceleration values were de[ermined by the latitude and longiwde of the project site using the U.S. Geological Survey (USGS) software utility Seismic Hazard Curves ond Uniform Response Specna. The USGS softwaze interpolated ground motions at the project site as follows for periods of 0.2 and 1.0 seconds, respectively, with a 2 percent chance of exceedence in 50 yeus: Ss = 1.212, S�= 0.430. 7.0 EROSION HAZARDS AND MITIGATIONS The following discussion addresses Washington State Department of Ecology (Ecology) erosion control regulations that will be applicable to the project. The Ciry of Everett definition for Erosion Hazazd Areas (Everett Municipal Code Title 19, Chapter 37.080) is linked to published mapping and soil rypes. Although the site does not appear to contain mapped erosion hazard areas, man-made slopes on the south and east parts of the site might meet the intent for management as Erosion Hazard Areas. The following recommendations are related to compliance with Ecology management of erosion on coutitruction sites. The state requirements are detailed, and in our opinion, addressing the state requirements is likety to also comply with City of Everett requirements that migh. be applicable. As of October l, 2008, the Ecology Conswction Storm Water General Permit (also known as the National Pollutant Discharge Elimination System [NPDES] permu) requires weekly Temporary Erosion and Sedimentation Control (TESC? inspections and turbidiry monitoring for all sites 1 or more acres in size that discharge srorm water to surface waters of the state. Because we anticipate that the proposed project will require disturbar.ce of more t6an 1 acre, we anticipate that these inspection and reponing requirements will be triggered. The following recommendations are related to general erosion potential and mitigation. The erosion potential of the site soils is high. The most effective crasion control measure is the maintenance of adequare ground cover. Maintaining cover measures atop disturbed ground provides the greatest reduction to the potential generation of turbid runoff and sediment transport. During the local wet season (October 1" through March 31"), exposed soil should not remain uncovered for more than 2 days unless it is actively being worked. Grou,id-cover measures can include erosion control matting, plastic sheeting, straw mulch, crushed rock or recycled conerete, or mature hydroseed. Some fine-grained surface soils are the result of natural weathering processes that have broken dewn parent materials into their mineral componems. These mineral components can have an inher:nt eiectrical charge. Electrically charged mineral fines will attract oppositely charged particles and can combine (flocculate) to form larger partides that will settle out of suspension. Scptember 22, 10/D ASSOClATFD EARTH SCIENCF,S, INC. ew.;�m-Kr i'rnssFa.v..,�..nimiaizss�KF�wv P2gC 9