RISK-BASED BTEX SCREENING CRITERIA FOR A GROUNDWATER IRRIGATION SCENARIO

A human exposure activity for which risk-based cleanup goals are typic ally not defined is the 'irrigation' scenario. This refers to resident ial use of contaminated well water for watering lawns or gardens at ho mes having potable water supplied by their community. Exposures from i ngestion, dermal contact or vapor inhalation by a child playing under the sprinkler, from vapor inhalation by an adult gardening downwind of the sprinkler, and from adult/child ingestion of vegetables grown in a garden irrigated by the sprinkler have been modeled. Screening level target values for BTEX compounds in the groundwater have been derived for reasonable exposure assumptions associated with a child receptor, an adult receptor, and a receptor living as both a child and adult in the house over a 30-year duration. Due to existing legislative preced ents and growing regulatory acceptance worldwide, a target cancer risk level of 1 x 10(-5) is adopted. At this level, the cleanup target for benzene is 1.1 mg/l for the child and 3.2 mg/l for the adult. For the combined child/adult case, the target is 0.85 mg/l. Based on a hazard index of one, the TEX compounds have target levels ranging from 9.5 t o 1090 mg/l for the three receptor scenarios. Note that these numeric values are considered appropriate for screening purposes to determine whether or not an irrigation risk may be present. While shown to be co nservative, they are only applicable if the assumptions used are perti nent to the site-specific situation being evaluated.