SOIL EXPOSURE AND AIR PATHWAYS. 5.1 SOIL EXPOSURE PATHWAYS People can be exposed to contaminants in soil either by direct contact with the soil or by breathing contaminant vapors or dust that have migrated from the soil. The soil exposure pathway at this site is likely an incomplete pathway except for excavation workers. This is based on the known contamination at the Xxxxxxx Property, which may be from waste PCE from dry cleaners entering soil on or very close to the source and flowing downward through the vadose zone and then into groundwater. It has likely been 20 years or more since PCE was released at the Xxxxxxx Property, and surface soils likely do not contain high concentrations of VOCs. The extent of soil contamination in the vadose zone is unknown. Much of the surface area surrounding the sources is currently covered with very low permeability (nearly impervious) surfaces such as asphalt and concrete, so direct contact with soil contamination, if present, is greatly reduced. Excavation work in source areas (e.g., utility work at the former dry cleaners) could present a complete exposure pathway if contaminated soils are exposed. It is also likely that people could be exposed to contaminant vapors migrating from contaminated soil under buildings into indoor or outdoor air, especially in buildings closest to the source area. This pathway is likely limited to the buildings closest to the Xxxxxxx Property, which are used for commercial/occupational purposes.
SOIL EXPOSURE AND AIR PATHWAYS. 5.1 REGIONAL AND LOCAL GEOLOGIC SETTING The geological units in the area are divided into two main divisions: the older and generally consolidated rocks that form the higher parts of the area and occur at depth below the valley plain and the unconsolidated materials, mainly sand and gravel of Pleistocene and Holecene age, that compose the valley fill. The older and generally consolidated rocks in the area consist of the Siletz River Volcanics, the marine Tyee and Xxxxxxx Formations, and intrusive igneous rocks. The unconsolidated deposits consist of isolated terrace deposits, older alluvium which underlies the valley plain and younger alluvium which is coextensive with the present flood plain of the Willamette River. (Xxxxx, 1974) According to the boring logs, Site soils consists of silt and clay (Willamette Silt) from the surface to approximately 18 feet bgs, and sand and gravels (Linn Gravels) from approximately 18 to 40 feet bgs. During drilling, water was encountered from 12 to 14 feet bgs.
SOIL EXPOSURE AND AIR PATHWAYS
