A baseline risk assessment (RA), was conducted for a Superfund site in the Southeast. The site is a former landfill, with associated localized soil and groundwater contamination. There was concern for the potential for the landfill to contaminate groundwater which is used as the regional drinking water supply source.
During the baseline RA, 95 percent upper confidence limits (UCLs) on the arithmetic mean were calculated for groundwater assuming both a normal and lognormal distribution. The UCLs were then used to estimate potential risks associated with the worst-case exposure scenario.
The purpose of this paper is to illustrate how the assumption of the data distribution can influence the results of the calculation of statistics of measured concentrations, and subsequently, associated risk estimates. Groundwater was the medium which was evaluated for this study, however, the process and results could be applicable to any environmental medium.