Exposure Point Concentrations (EPCs)
As you develop your EPCs for a site, remember to evaluate your data to see if there are hotspots present in any of your media. A hotspot is a location which has a Contaminant of Concern concentration > 100x higher than surrounding locations. Hotspots are considered distinct EPCs and must be separately evaluated in the risk characterization. Typically, at least five sampling points are necessary to have insight into the variability of a data set.

Consistent with the Guidance for Disposal Site Characterization (MassDEP, July 1995) and 310 CMR 40.0926, an EPC  should be a “conservative estimate of the average concentration” to which a receptor may be exposed over the applicable exposure period and at the exposure point. Caveats or exceptions to the use of the average concentration as the EPC include:

• Acute exposure evaluations – typically the maximum concentration is recommended;         
• Screening/streamlined assessments - typically maximum or other upper bound concentrations are recommended; and
• When data are limited/insufficient to characterize the “temporal variability or the spatial distribution of Site concentrations.”