7007 SEAWAY BLVD 2016-01-01 MF Import

3. SUBSTRATE A. Soil sources The pre-construction soil conditions were characterized by sandy fill soils with some gravels and �obbles from three feet to a maximum of nine feet in depth. The fill layer ' was underlain by native glacial tiil soils and some areas of organic silty sand or peat , layers. Appendix A is the geotechnical report done on the site prior to both design and constructian. Topsoil was imported to the site from nearby land cleared for development. The donor sfte is located approximately 3.6 miles due south of the mitigation area, in the northeast quadrant of the intersection of Admiralty Way and Airport Way in Snohomish County (just south of the Everett City limits). Vegetation cleared from the site consisted of a semi-mature second growth conifer and broadleaf upland forest. The site was not investigated prior to clfaring, though from an inspection of adjacent intact forest, the donor site was apparently free from invasive weeds. The topography was of a moderate, west-facing slope. A complete soils analysis was pertormed on the imported topsoil used on the site. This analysis reports that the imported topsoil is a loamy sand with nutrient levels and an organic content typical of forested upland areas in the northwest. Please refer to the soil report found in Appendix B for a detailed breakdown of ihe textures and nutrient levels. B. Site excavetion The site was worked in manageable units, beginning first with clearing and grubbing, then mass excavation, finish sub-grading and finally topsoil placement and finish grading. Once the pools had filled to capacity, hand raking and minor grading changes were made. Additional minor grade changes may be necessary from time to time over the next few years. Roughly 80,000 cubic yards of soil were removed from 8.5 acres. The average cut across the site was 5.8 feet. With the addition of topsoil, the finish grade averages just over 5 feet lower than the pre-excavation ground surtace. Chipped material from site clearing was stored and later spread across the areas that were excavated. This material consisted of mostly young alder and cottonwood trees. These chippings were spread thinly, at roughly 1-2 inches deep across the site. No additional soil amendments were used on the site except for the potting soil that came with the container and ball-and-burlap plants. C. Soil denth The minimum depth of topsoil is 9 inches. Throughout most of the site, topsoil was placed on an impermeable layer of glacial tili. In some areas the topsoil was placed on peat mixed with blue clay, also impermeable (see A Soil sources, above). 12