1720 121ST ST SE 2016-01-01 MF Import

this soil would be considered a wetland soil by the Corps because: 1) it is supponing a dominance of hydrophytic (wetland) plants (see "Vegetadon' section); and 2) the fill was placed over a silt/organic soil that is rnnsidered a wedand soil. .a►lthough extensive exploradon of the uaderlying soil was not possible due to the depth and density of the fill, the areas invesdgadon revealed soils similar to those found immediately south of the fill. Immediately south of this 611ed area, wetland soils consist of about 1 foot of a dense, saturated silt loam with moderate amounts of organic material. Below the 1 foot layer, the soil consists of at least 4 feet of a saturated mix of silt and organic material. This subsurface soil mix appears to be less dense than the top 1 foot of silG Soils in the wedand in the southeast corner of the site are similar to those in the northern portion of the site. The organic content of the soil is less than that of the northern wedand. Hydrolo� The hydrology of the sites' wetlands is dominated by hig6 groundwater teveis and the inIIuence of Silver Lake Creek. Groundwater levels in the unfilled portian of the wedand are at or above the surface for much of the yeaz. Shallow groundwater displaced from the filled area acrnunts for a significant portion of the water stored in the nnfilled portion of the wedand. It is probable that a direct ground and surface water connection exists between this area and Silver Iake Creek. Reference haz been made to a culvert extending from Silver Lake Creek to the weUand under t6e driveway alignment paraileling the creek. Water exchange between the creek and the wetland may not be rapid due to the relatively dense soil. The density of the fill in the northern portion of the wedand preveats significant upward groundwater movement into the fill. Evidence dces e�dst of surface ponding of precipitation on top of the fill. Water levels in the wetland in the southern pordon of the site aze linked directly with those of the creek and pond. Groundwater levels rise above the surface during periods of heavy precipitadon and probably drop to about 1 to 2 feet below the surface during late summer and early fall. Vegetation T6e vegetation which grows in an area oftea reveals the iong-term condidoas of soils and hydrolo� because the growth requirements of plan species can be very specific. Wetland plants will only grow in areas of saturatcd soils, whereas upland species cannot tolerate s3turated conditions. The USFWS has identified wetland plant species and rated them as to the frequency in which they would be found in wedand situations. Any plant rated FACW (Facuitative, Wetland) or OBL (Obligate) is usually found in wedands with 67% to 99% frequenry.