Cost-Effective Risk Assessment of Multiple off-Site Receptors

SRS professionals have completed a risk assessment for a site in Pennsylvania that was formerly an automotive service station but was later used for residential purposes (i.e. apartment building).  The site had a unique hydrogeologic condition in which the groundwater flow exhibited a radial flow pattern.  The site was surrounded by other residential properties.  This unique groundwater condition and potential for site-related constituents to migrate in multiple directions resulted in an extensive receptor and exposure pathway analysis which included both on-site receptors and off-site receptors in every direction surrounding the site.  However, a detailed comparative analysis of each receptor on each property was completed which entailed an assessment of the number of constituents of interest (COI) retained, concentration of COI, and similarity in exposure scenarios.  Calculated upper confidence levels (UCLs) of mean concentrations that were used in quantitative risk analyses for certain receptors were compared to maximum concentrations of soil and groundwater datasets used to evaluate other receptors in order to ensure that the quantitative assessments of risks and hazards estimated for select receptors are a conservative analysis that is protective of other off-site receptors surrounding the site.  This type of comparative analysis saved significant effort and cost in performing additional quantitative assessments of risks and hazards that would not have been necessary to complete.