9900 19TH AVE SE 2018-01-02 MF Import

5—Alderwood-Urban land complex, 2 to 8 percent slopes. This map unit is on till plains. Areas are irregular in shape and are 100 to 1,000 acres in size. The native vegetation is mainly conifers. Elevation is 50 to 550 feet. The average annual precipitation is about 40 inches, the average annual air temperature is about 50 degrees F, and the average frost -free season is 170 to 190 days. This unit is about 60 percent Alderwood gravelly sandy loam and about 25 percent Urban land. The components of this unit are so intricately intermingled that it was not practical to map them separately at the scale used. Included in this unit are small areas of McKenna and Norma soils and Terric Medisaprists in depressional areas and drainageways on plains. Also included are small areas of soils that are very shallow over a hardpan; small areas of Everett, Indianola, and Ragnar soils on terraces and outwash plains; and soils that have a stony and bouldery surface layer. Included areas make up about 15 percent of the total acreage. The Alderwood soil is moderately deep over a hardpan and is moderately well drained. It formed in glacial till. Typically, the surface layer is very dark grayish brown gravelly sandy loam about 7 inches thick. The upper part of the subsoil is dark yellowish brown and dark brown very gravelly sandy loam about 23 inches thick. The lower part is olive brown very gravelly sandy loam about 5 inches thick. A weakly cemented hardpan is at a depth of about 35 inches. Depth to the hardpan ranges from 20 to 40 inches. Permeability'of the Alderwood soil is moderately rapid above the hardpan and very slow through it. Available water capacity is low. Effective rooting depth is 20 to 40 inches. Runoff is slow, and the hazard of water erosion is slight. A seasonal perched water table is at a depth of 18 to 36 inches from January to March. Urban land is areas that are covered by streets, buildings, parking lots, and other structures that obscure or alter the soils so that identification is not possible. The Alderwood soil in this unit is used mainly for parks, building sites, lawns, gardens, and woodland. The main limitations of the Alderwood soil for homesites and septic tank absorption fields are the depth to the hardpan and the seasonal perched water table. Onsite waste disposal systems often fail or do not function•, properly during periods of high rainfall. Drainage is needed if buildings with basements and crawl spaces are constructed. Topsoil needs to be stockpiled during site preparation and subsequently used to cover the exposed material. Additions of fertilizer and peat are desirable prior to seeding grass for lawns. This map unit is in capability subclass IVe.