10721 19TH AVE SE Geotech Report 2023-04-07

Geotechnical Engineering Evaluation NGA File No. 1014317 Zerzura Townhome Development November 9,2017 Everett,Washington Page 12 Site Drainage Surface Drainage: The finished ground surface should be graded such that runoff is directed to an appropriate stormwater collection system. Water should not be allowed to collect in any areas where footings,slabs,or pavements are to be constructed. Final site grades should allow for drainage away from structures. We suggest that the finished ground be sloped at a minimum gradient of three percent, for a distance of at least 10 feet away from structures. Surface water should be collected by permanent catch basins and drain lines,and be routed into an appropriate discharge system. Subsurface Drainage: If groundwater is encountered during construction, we recommend that the contractor slope the bottom of the excavation and collect the water into ditches and small sump pits where the water can be pumped from the excavation and routed to a suitable discharge point. We recommend the use of footing drains around the structures. Footing drains should be installed at least one foot below planned finished floor elevation. The drains should consist of a minimum 4-inch- diameter, rigid, slotted or perforated, PVC pipe surrounded by free-draining material wrapped in a filter fabric. We recommend that the free-draining material consist of an 18-inch-wide zone of clean(less than three-percent fines),granular material placed along the back of walls. Washed rock is an acceptable drain material, or drainage composite may be used instead. The free-draining material or the drainage composite should extend up the wall to one foot below the finished surface. The top foot of backfill should consist of low permeability soil placed over plastic sheeting or building paper to minimize the migration of surface water or silt into the footing drain. Footing drains should discharge into tightlines leading to an appropriate collection and discharge point with convenient cleanouts to prolong the useful life of the drains. Roof drains should not be connected to wall or footing drains. CONSTRUCTION MONITORING We should be retained to provide construction monitoring services during the earthwork phase of the project to evaluate subgrade conditions, temporary cut conditions, fill compaction, and drainage system installation. NELSON GEOTECHNICAL ASSOCIATES, INC.