VOC Emissions from Sewer Junction Boxes and Drop Structures: Estimation Methods and Experimental Results

New federal and state regulations have placed increased scrutiny on sources of hazardous air pollutants (HAPs), including many volatile organic compounds (VOCs).The U.S. Environmental Protection Agency will continue to develop National Emission Standards for HAPs (NESHAPs) and subsequent Maximum Achievable Control Technology (MACT) implementation requirements for industrial source categories over the next several years.To a great degree, industryspecific NESHAPs will be developed based on estimates of VOC emissions from specific process streams.These estimates may be in the form of (1) extrapolations from VOC emissions measurements at a limited number of similar processes, and/or (2) empirical emission models.This paper focuses on VOC emissions from junction boxes and drop structures.It is based on the results of 17 pilot experiments designed to illustrate the effects of entry pipe location, liquid flow rate, headspace ventilation rate, and drop height on VOC stripping efficiency.Experimental results are compared to predictions based on standard estimation procedures as outlined in AP-42.Experimental stripping efficiencies were observed to be highly sensitive to VOC physicochemical properties, drop height and liquid flow rate.Except at very low liquid flow rates, experimental stripping efficiencies were lower than those estimated using AP-42 estimation methods.Finally, it was observed that passive modifications to existing junction boxes or drop structures can lead to significant reductions in VOC stripping efficiency. IMPLICATIONSSignificant uncertainties in VOC emissions estimates for on-site industrial sewers exist.This paper involves a comparison of AP-42 emissions estimates and experimental data associated with a pilot junction box and drop structure.Limitations of AP-42 emissions estimates are identified, as are the relative effects of several system operating conditions and chemical properties on VOC stripping efficiencies.Results should be of value to those interested in improving VOC emissions estimates or employing passive control measures to suppress VOC emissions.