T. Walden et L. Spence, RISK-BASED BTEX SCREENING CRITERIA FOR A GROUNDWATER IRRIGATION SCENARIO, Human and ecological risk assessment, 3(4), 1997, pp. 699-722
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.