3.3.4.1 Residential exposure area decision units

Exposure areas for residential use can vary in size depending on the location of the site and local regulatory requirements. Consideration of lot-size exposure areas is generally adequate to evaluate long-term, chronic health risks. When exposure can be assumed to be relatively consistent across the lot, it is not necessary to investigate concentration trends at a property below the scale of the residential lot. If there are specific areas that receive higher use in an exposure area, such as a play area, that area should be evaluated as a smaller and separate DU (see Section 3.3.4.4).