Guidance on Method 23 and EMPCs

Per direction from EPA's Emission Measurement Center, if Method 23 test results contain a congener value labeled as the "Estimated Maximum Possible Concentration" (EMPC), then it must be added to the total dioxins/furans catch, as reported. It is never permissible to report an EMPC as zero.

If the Source (facility) includes EMPCs in the total reported for dioxins/furans and is still in compliance with the emission limit, then the results can be accepted. If the Source includes EMPCs in the total reported for dioxins/furans and is above the emission limit for total dioxins/furans, it may be because of a positive interference. However, the interference cannot be quantified and the interference will prevent the lab results from meeting the quality assurance requirements for identifying and quantifying their results. In this case, the only options are for the laboratory to re-analyze the sample if they archived a sample fraction, or for the Source to repeat the test. The re-analysis would involve re-cleaning the sample to remove the interfering substances.