10104 DAKOTA WAY 2022-01-31 - Laserfiche WebLink

5.0 WETLAND AND STREAM DETERMINATION METHODOLOGY The ordinary high water mark (OHWM) of streams was determined using the methodology described in the Washington State Department of Ecology document Determining the Ordinary High Water Mark for Shoreline Management Act Compliance in Washington State (Anderson et. al. 2016). Wetland boundaries in western Washington are determined using the routine methodology described in the Corps of Engineers Wetlands Delineation Manual (Environmental Laboratory 1987) and the Regional Supplement to the Corps of Engineers Wetland Delineation Manua• Western Mountians, Valleys, and Coast Region (Version 2.0) (U.S. Army Corps of Engineers 2010). Under the routine methodology, the process for making a wetland determination is based on three steps: 1.) Examination of the site for hydrophytic vegetation (species present and percent cover); 2.) Examination of the site for hydric soils; 3.) Determining the presence of wetland hydrology The following criteria must be met in order to make a positive wetland determination: Vegetation Criteria The Corps Manual and 2010 Regional Supplement define hydrophytic vegetation as "the assemblage of macrophytes that occurs in areas where inundation or soil saturation is either permanent or of sufficient frequency and duration to influence plant occurrence." Field indicators are used to determine whether the hydrophytic vegetation criteria have been met. Examples of these indicators include, but are not limited to, the rapid test for hydrophytic vegetation, a dominance test result of greater than 50%, and/or a prevalence index score less than or equal to 3.0. Soils Criteria and Mapped Description The 2010 Regional Supplement (per the National Technical Committee for Hydric Soils) defines hydric soils as soils "that formed under conditions of saturation, floodin, or ponding long enough during the growing season to develop anaerobic conditions in the upper part." Field indicators are used to determine whether a given soil meets the definition for hydric soils. Indicators are numerous and include, but are not limited to, presence of a histosol or histic epipedon, a sandy gleyed matrix, depleted matrix, and redoximorphic depressions. According to the NRCS, the soils on the subject site consist of Alderwood-Urban land complex, 2 to 8 percent slopes. This soil map unit is described as moderately well drained. This soil unit contains inclusions of McKenna (5 percent), Norma (5 percent), and Terric Medisaprists (5 percent), which are hydric soil types typically found in depressions. Hydrology Criteria The 2010 Regional Supplement defines wetland hydrology as "areas that are inundated (flooded or ponded) or the water table is less than or equal to 12 inches below the soil surface for 14 or more consecutive days during the growing season at a minimum frequency of 5 years in 10." During the early growing season, wetland hydrology determinations are made based on physical observation of surface water, a high water table, or saturation in the upper 12 inches. Outside of APV Ventures LLC — Dakota Way 4 Critical Area Report, Buffer Mitigation WRI #20015 Plan & Habitat Assessment April27, 2020