6307 36TH AVE W 2021-12-16 - Laserfiche WebLink

Vegetation Criteria The Washington State Wetlands Identification and Delineation Manual, 1997 edition, defines hydrophytic vegetation as "the sum total of macrophytic plant life that occurs in areas where the frequency and duration of inundation or soil saturation produce permanently or periodically saturated soils of sufficient duration to exert a controlling influence on the plant species present." One of the most common indicators for hydrophytic vegetation is when more than 50 percent of a plant community consists of species rated as "Facultative" or wetter. Soils Criteria and Mapped Description The Washington State Wetlands Identification and Delineation Manual, 1997 edition, defines hydric soils as those "that formed under conditions of saturation, flooding,or ponding long enough during the growing season to develop anaerobic conditions in the upper part." Field indicators are used for determining whether a given soil meets the definition and criteria for hydric soils. The soils underlying the site are mapped in the Soil Survey of Snohomish County Area Washington as Alderwood gravelly sandy loam, 2 to 8 percent slopes and Alderwood-Everett gravelly sandy loam, 25 to 70 percent slopes. Alderwood gravelly sandy loam is described as a moderately well drained soil on till plains. It is moderately deep over a hardpan. This soil 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. Included in this unit are small areas of soils that have a stony of bouldery surface layer and areas of McKenna soils, Norma soils, and Terric Medisaprists in drainageways on plains. Also included are small areas of Everett, Indianola, and Ragnar soils on terraces and outwash plains. Included areas make up about 15 percent of the total acreage. Permeability of this soil is moderately rapid above the hardpan and very slow through it. Soils sampled on site appear similar to the description for Alderwood gravelly sandy loam. Although Alderwood gravelly sandy loam is not listed as hydric, the predicted inclusions of Terric Medisaprists, McKenna, and Norma soils are listed as hydric on the Hydric Soils List for Washington State. Alderwood-Everett gravelly sandy loam is on till plains, terraces, and outwash plains. This unit is about 60 percent Alderwood gravelly sandy loam and about 25 percent Everett gravelly sandy loam. Included in this unit are small areas of Ragnar, Indianola, McKenna, and Norma soils and Terric Medisaprists in depressional areas and drainageways on plains. Also included are colluvial soils, slump areas, and escarpments. 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. 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. A seasonal perched water table is at a depth of 18 to 36 inches from January to March. Springs or seep areas are common. Although Alderwood- Everett gravelly sandy loam is not listed as hydric, the predicted inclusions of Terric Critical Area Study and Buffer Mitigation Plan 5 WRI# 09084 lntermec- Lot 2 Revision#2: March 22, 2010