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Estimating Exposure Point Concentrations (EPCs) Overview
ATSDR has developed specific guidance that teaches health assessors how to estimate EPCs for either discrete sampling or non-discrete sampling data (see text box below).
This primer will provide general information on how to estimate EPCs for some example scenarios. However, the calculations you do will depend on your specific data set (such as the number of samples or the amount of non-detect data). When it comes time to do your health effects evaluations, always refer to “ATSDR’s Exposure Point Concentration Guidance for Discrete Sampling” and “ATSDR’s Exposure Point Concentration Guidance for Non-Discrete Sampling.” You can find final guidance on the PHAGM Resources page.
These guidance documents will outline how to calculate EPCs for your specific scenarios. The Associate Director for Science (ADS) group is a good source of information if you have questions about EPC estimates.
Remember:
A discrete sample is an individual environmental sample from a given point and time that is independent of other samples.
ATSDR’s guidance on non-discrete sampling refers to composite sampling and the incremental sampling methodology (ISM). Composite sampling involves combining multiple discrete environmental samples for analysis. ISM is a structured form of composite sampling, designed to characterize the overall contamination level within an area of interest. Numerous incremental soil samples (typically 30 or more) are collected and combined to form a single ISM sample for laboratory processing and analysis.
Go to the next section to learn about the statistics that ATSDR recommends for EPCs.