3620 36TH PL NE 2018-01-02 MF Import

3.2 SURFACE CONDITIONS The site is relatively level with site grades ranging from approximately Elevation 6.5 to Elevation 1,;.5 feet. The high area is located in the north -central portion of the site and extends ; iuth to an existing asphalt pad area. Existing grades descend to about Elevation 6.5 feet to the east, west and south from the north -central high area. The asphalt pad is located in the central portion of the site and measures about 140 feet by 2S0 feet in plan. A small structure ,is located on the north end of the pad. The primary unimproved access road for the site traverses across the site in a roughly east -west direction from the east gate to the future west stormwater pond area. A short spur road extends to the north from the main road to an abandoned ship that is tied up to the levee along Steamboat Slough. The majority of the project area has in the past been used first for agricultural purposes (1960s) and secondly for logging yard operations. Multiple parallel rows of "berms and troughs" have been constructed of native soil and fill, material for the purpose of storing and curing logs. The remnant troughs form low-lying areas throughout the northwest and southwest portions of the project area. This slightly undulating topography and the large amounts of buried fill material found throughout the project area characterize the site. Vegetation, comprised of shrubs and grasses, dominate the majority of the area. Scattered young stands of deciduous trees are located in the south, west and northern parts of the project area. A north -south ditch that forms the eastern boundary of the project area drains seasonal precipitation into the slough. Other drainage ditches that cross the area are remnant of past agricultural use. 3.3 REGIONAL GEOLOGY Geologic information for the project vicinity was obtained from the map prepared by Minard (1.985). All of Smith Island is mapped as being composed of younger alluvial and estuarine deposits. These deposits consist of stratified sediments laid down by the streams and rivers in the area. The sediment deposits consist of silt, sand and clay with organic matter. Peat deposits have also been mapped in the Smith Island area. 3.4 SUBSURFACE CONDITIONS 3.4.1 General The native subsurface conditions encountered in the explorations completed for this study and for previous nearby projects are relatively consistent. In general, topsoil and/or fill (including wood chips) overlie recent alluvial and estuarine deposits consisting of compressible fine-grained soils composed of organic silt, and silt with interbedded sands. The compressible fine-grained alluviai soils are generally underlain at depth by coarser -grained alluvial deposits consisting of sand with variable silt content and occasional silt layers. These units are discussed in more detail below. G e u E n g i n e c r s 4 File To. 10625-00IA2/123003