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Geotechnical Engineering Report Mixed -Use Everett 10521-191h Ave. SE Everett, Washington March 23, 2016 RN File No. 3109-001 A Page 8 heavy plastic sheeting, should be placed over the capillary break. An additional 2-inch-thick damp sand blanket can be used to cover the vapor barrier to protect the membrane and to aid in curing the concrete. This will also help prevent cement paste bleeding down into the capillary break through joints or tears in the vapor barrier. The capillary break material should be connected to the footing drains to provide positive drainage. Drainage We recommend that runoff from impervious surfaces, such as roofs, access roadways, and parking, be collected and routed to an appropriate storm water discharge system. The finished ground surface should be sloped at a gradient of 5 percent minimum for a distance of at least 10 feet away from the buildings, or to an approved method of diverting water from the foundation, per IBC Section 1804.3. Surface water should be collected by permanent catch basins and drain lines, and be discharged into a storm drain system. We recommend that footing drains be used around all of the structures where moisture control is important. The underlying till may pond water that could accumulate in crawlspaces. It is good practice to use footing drains installed at least 1 foot below the planned finished floor slab or crawlspace elevation to provide drainage for the crawlspace. At a minimum, crawlspaces should be sloped to drain to an outlet tied to the drainage system. If drains are omitted around slab -on -grade floors where moisture control is important, the slab should be a minimum of 1 foot above surrounding grades. Where used, footing drains should consist of 4-inch-diameter, perforated PVC pipe that is surrounded by free -draining material, such as pea gravel. Footing drains should discharge into tightlines leading to an appropriate collection and discharge point. Crawlspaces should be sloped to drain, and a positive connection should be made into the foundation drainage system. For slabs -on -grade, a drainage path should be provided from the capillary break material to the footing drain system. Roof drains should not be connected to wall or footing drains. Infiltration The City of Everett Stormwater Management Manual 2010 (CESMM) chapter 9 section 3.2 requires 3 feet of separation from the bottom of the infiltration system to hard pan or low permeable soils. Our subsurface explorations encountered very dense hard pan/low permeable soils approximately 3 to 3.5 feet below the ground surface. In our opinion, based on the high silt content of the weathered soils and the shallow depth to the very dense glacial till stormwater infiltration is not feasible for the site. Utilities Our explorations indicate that deep dewatering will not be needed to install standard depth utilities. Anticipated groundwater is expected to be handled with pumps in the trenches. We also expect that some groundwater seepage may develop during and following the wetter times of the year. We expect this seepage to mostly occur in pockets. We do not expect significant volumes of water in these excavations. Robinson Noble, Inc