10521 19TH AVE SE 2022-05-23 - Laserfiche WebLink

Geotechnical Engineering Report Mixed -Use Everett 10521-1911 Ave. SE Everett, Washington March 23, 2016 RN File No. 3109-001 A Page 3 copy of which is presented as Figure 3. The logs of the test pits are presented in Figures 4 and 5. Subsurface Conditions A brief description of the conditions encountered in our explorations is included below. For a more detailed description of the soils encountered, review the Test Pit Logs in Figures 4 and 5. Our explorations generally encountered a surficial layer of topsoil that was less than 1 foot in thickness. The topsoil consisted of loose, dark brown silty fine sand with roots and organics. Underlying the topsoil we encountered reddish brown to gray -brown medium dense silty sand with varying amounts of gravel interpreted to be highly weathered glacial till. The highly weathered till zone extend to depths ranging from 3 to 3.5 feet below the existing ground surface. Below the highly weathered glacial till we encountered gray to mottled gray dense to very dense silty fine sand with gravel interpreted to be slightly weathered to unweathered glacial till. The glacial till extended to the depths explored in all the test pits. Laboratory Testing We completed moisture content testing on selected samples from our explorations. The moisture contents are shown on the test pit logs. Hydrologic Conditions Shallow groundwater seepage was encountered in Test Pits 2 through 5 approximately at 3.0 to 3.5 feet. We consider this water to be perched. The dense to very dense glacial till interpreted to underlie the site is considered poorly draining. During the wetter times of the year, we expect perched water conditions will occur as pockets of water on top of the till layer. Perched water does not represent a regional groundwater "table" within the upper soil horizons. Volumes of perched groundwater vary depending upon the time of year and the upslope recharge conditions. Moisture content of the on -site weathered till soils was observed to range from 143 to 23.0%. Moisture content of the unweathered till was observed to range from 6.8 to 16.6%. CONCLUSIONS AND RECOMMENDATIONS General It is our opinion that the site is compatible with the planned development. The underlying medium dense to very dense glacial till deposits are capable of supporting the planned structures and pavements. We recommend that the foundations for the structures extend through any fill, topsoil, loose, or disturbed soils, and bear on the underlying medium dense or firmer native glacial till, or on structural fill extending to these soils. Based on our site explorations, we anticipate these soils will generally be encountered at typical footing depths. The site is underlain by dense to very dense glacial till which is considered poorly draining (low permeability). The City of Everett Stormwater Management Manual 2010 Chapter 9 section 3.2 states there must be a minimum 3 feet of separation between the bottom of the infiltration Robinson Noble, Inc