3.3.4.5 Example exposure area decision units

Figure 3-4 depicts the investigation of an older, residential home that is suspected to have been built on top of a former pesticide mixing area. The objective of the investigation is to determine whether pesticides and lead in the soil pose a direct-exposure hazard to the residents. Contaminants include arsenic and dioxins as well as pesticides.

Exposure area DUs designated for a residential house lot.

Figure 3-4. Exposure area DUs designated for a residential house lot.

The back yard was designated as a separate DU from the front and side yards based on anticipated use patterns due to higher frequency of exposure in backyard.




The majority of the yard is included in DU-1 because the exposure scenario consists of the assumption that an equal amount of time will be spent in all parts of the back yard over the assumed exposure duration. Lead-based paint is suspected to have been used on the house; therefore, DU-2 consists of the drip-line of the house, which is suspected to contain elevated levels of lead in the soil. DU-2 can be considered both an exposure-area DU and a source-area DU because it represents the exposure to chips of lead-based paint, which may be of concern for acute or subchronic exposure and is a potential source of lead. Exposure patterns in the front and side yard are different than in the backyard, therefore; DU-3 is designated as the front and side yards. ISM samples consisting of the specified number of increments would be collected from each of the DUs.