Screenings and Preliminary Assessments

PRELIMINARY ASSESSMENT: PATHWAYS OF EXPOSURE

Groundwater

Hydrogeologic Setting

1. Regional geology and hydrology - This description includes the following (if applicable and available): physiographic setting; the general nature of geologic units; controlling regional geologic features; regional aquifers/aquitards; important drinking-water aquifers and/or confining units; regional groundwater depth and flow direction; and unusual and/or important hydrologic features.
2. Site-specific geology and hydrology - This description includes (if applicable and available): geologic units beneath the site and their thicknesses, origin of deposits (channel sand, lake deposits, etc.), and any special features that would affect flow of contaminants through these units; local features that could impact groundwater and/or contaminant flow around site (faults or other controlling structures, confining layers, caliche zones, etc.); well log data; subsurface soil characteristics, including the least permeable continuous subsurface soil layer with a minimum thickness of 15 feet (used to determine subsurface hydraulic conductivity); aquifer/aquitard system beneath and in vicinity of site; important drinking water aquifers; and depth to groundwater at or near the site, if this information is available.
3. Annual net precipitation - from the nearest weather station. This is a measure of total precipitation minus total evapotranspiration. Summed monthly differences between these two are used to calculate this score. (Where monthly net precipitation is less than zero, zero is entered for that month’s total.)

Groundwater Targets

1. Groundwater use - Groundwater use and population over a nine-section area (the USGS section in which the site is located and the eight surrounding sections). If a site is located on or near a section boundary, add any additional sections to the search, as appropriate. Include in the discussion: 1) aquifer(s) of concern - aquifers in use and the types of uses (private or municipal supply, back-up supply, alternate supply, etc.); 2) number of users, with an explanation of how this number is derived; 3) location of and distance to the nearest drinking water well, including well depth and current use; and 4) availability and accessibility of alternate drinking water supplies in the site vicinity.

Groundwater Conclusions

Surface Water

Hydrologic Setting

1. Surface water bodies within 2 miles downgradient of the site – including intermittent streams. Artificial ditches that do not connect to other surface water bodies are not considered surface water. If storm drains and sewers are part of the drainage pattern, include information on the inlet locations, and for storm drains, the outlet locations. The discussion should include distance to surface water - if more than one, include distance for each, name(s) of surface water body, and location in relation to site.
2. Surface soil characteristics – to provide context for runon/runoff potential; this should include a discussion of soil type/constituents and permeability.
3. Maximum 2-year, 24-hour rainfall.
4. Floodplain - Is all or part of the site in a 100-year or 500-year floodplain?
5. Terrain slope - Calculated from the point of contamination to the closest surface water body. Presented as percent slope and determined by the equation (rise/run) x 100, where rise is the change in elevation between the point of contamination and the nearest surface water body, and run is the horizontal distance between the two.

Surface Water Targets

1. Surface water intakes within 2 miles downgradient of hazardous substances that could migrate off-site. List the use(s) of the water and population served, the name of the water district or user(s) accessing the intake, the location of the intake, the distance between the intake and point of contamination, and acres of land irrigated (if applicable).
2. Recreational use of surface water body within 2 miles of the site. For each type of recreational use, describe type, location, and distance from site.
3. Sensitive Environments or fishery resources within 2 miles downgradient. Sensitive Environments are defined in OAR 340-122-115 as: areas of particular environmental value where a hazardous substance could pose a greater threat than in other non-sensitive areas. These include: Critical habitat for federally endangered or threatened species; National Park, Monument, National Marine Sanctuary, National Recreational Area, National Wildlife Refuge, National Forest Campgrounds, recreational areas, game management areas, wildlife management areas; designated federal Wilderness Areas; wetlands (freshwater, estuarine, or coastal); wild and scenic rivers; state parks; state wildlife refuges; habitat designated for state endangered species; fishery resources; state designated natural areas; county or municipal parks; and other significant open spaces and natural resources protected under Goal 5 of Oregon's Statewide Planning Goals. The presence or nesting place of an endangered species is not a Sensitive Environment; the area in question must be designated critical habitat to be considered a Sensitive Environment. This is a federal designation - not all areas where endangered species are found are critical habitats.

A fisheries resource is as an area necessary for the maintenance of spawning or migratory pathways for anadromous or resident fish species. Anadromous fish return upstream from the ocean to their place of spawning. Resident fish live and breed in the same area.

Surface Water Conclusions

Air

Physical Conditions

1. Sources available to the air pathway and the quantity associated with each. Review each hazardous substance associated with these sources to determine whether air transport is gaseous or via particulates.
2. Containment of sources of hazardous substances available to the air pathway.
3. Predominant soil textural class of surface soils observed at the site.

Air Pathway Targets

1. Distance from source of contamination to nearest population - Nearest population is considered the nearest dwelling, public building, park, or other area outside the facility boundary where people may be exposed to hazardous substances daily or seasonally. Include a description of the population type considered. If the nearest population is a dwelling, use a descriptive label such as "Smith residence."
2. Population within a 0.5-mile radius of the source - measured from any on-site emission sources, this can consist of private residences, schools, businesses, rural residences, cities, towns, etc. A population can consist of one residence. Explain how this population was determined.
3. Distance to nearest Sensitive Environment – See Surface Water Targets section for definition of Sensitive Environment.

Air Pathway Conclusions

Direct Contact

Physical Conditions

1. Sources available for direct contact and the quantity associated with each.
2. Hazardous substances associated with sources available for direct contact.
3. Accessibility - Could humans enter the site and contact hazardous substances directly rather than through air or water? Are there barriers that limit accessibility, such as fencing or security?

Direct Contact Targets

1. Nearby residences - those residences with property lines within 1,000 feet of the contaminated area, whether on- or off-site. Specify distance from source of contamination and number of residents within 1,000 feet.
2. Other structures or activities with property lines within 1,000 feet of a contaminated area. This would apply to on-site or adjacent property, and include parks, schools, day care facilities, playgrounds, and fairgrounds. Include the distance of each (as applicable) from the point of contamination.
3. Is site located in a Sensitive Environment? See Surface Water Targets section for definition of Sensitive Environment.

Direct Contact Conclusions

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