Using PCB Congener Data to Assess Compliance with NPDES Permit Limits Based on Aroclors

Ensuring Reliable Data
Oral Presentation

Prepared by H. McCarty
General Dynamics Information Technology, 3170 Fairview Park Drive, Falls Church, VA, 22042, United States


Contact Information: [email protected]; 703-254-0093

ABSTRACT

The EPA Office of Water validated Method 1628, a low-resolution GC/MS procedure for the analysis of polychlorinated biphenyl (PCB) congeners, and published the method in January 2024. The EPA’s goals for developing the method were to have a sufficiently sensitive method for congeners that can be implemented in typical commercial environmental laboratories. Three of the four currently approved methods for PCB analyses for NPDES permits are GC/MS methods for the seven Aroclor mixtures that were included on the Priority Pollutant List in 1976 but those methods lack the sensitivity to meet many common NPDES permit limits for the Aroclors. The fourth method, 608.3, is a GC/ECD procedure with better sensitivity, but that relies on identification of the Arolcors by pattern matching. The analysis of all 209 PCB congeners by Method 1628 provides a much more accurate picture of PCB releases than is possible with Aroclor analysis, in part because there are other environmental sources of PCBs beyond the Aroclor mixtures that have not been manufactured since 1978. Using 1996 published data from Frame et al., we have developed an approach to assist dischargers and regulators in utilizing results from PCB congener analyses with existing Aroclor regulatory limits. We identified nine “cut-off points” in Frame’s data on the cumulative weight percent of the congeners that are characteristic of those seven Aroclors. Using Method 1628 congener results, one can calculate the sum of the congener concentrations for each cut-off point and divide those sums by the total PCB concentration for the sample, to yield the percentage of the total concentration for each cut-off point. Those percentages are compared to the data from Frame et al. to identify the likely Aroclor present. We also discuss how the congener results can be used to assess compliance with various other PCB permitting scenarios.