The United States Environmental Protection Agency (USEPA) is finalizing its vapor intrusion guidelines. One of the important issues related to vapor intrusion is background concentrations of volatile organic chemicals (VOCs) in indoor air, typically attributed to consumer products and building materials. Background concentrations can exist even in the absence of vapor intrusion and are an important consideration when conducting site assessments. In addition, the development of accurate conceptual models that depict pathways for vapor entry into buildings is important during vapor intrusion site assessments. Sewer gas, either as a contributor to background concentrations or as part of the site conceptual model, is not routinely evaluated during vapor intrusion site assessments. The research described herein identifies an instance where vapors emanating directly from a sanitary sewer pipe within a residence were determined to be a source of tetrachloroethylene (PCE) detected in indoor air. Concentrations of PCE in the bathroom range from 2.1 to 190 ug/m3 and exceed typical indoor air concentrations by orders of magnitude resulting in human health risk classified as an "Imminent Hazard" condition. The results suggest that infiltration of sewer gas resulted in PCE concentrations in indoor air that were nearly two-orders of magnitude higher as compared to when infiltration of sewer gas was not known to be occurring. This previously understudied pathway whereby sewers serve as sources of PCE (and potentially other VOC) vapors is highlighted. Implications for vapor intrusion investigations are also discussed.

中文翻译：

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下水道气体：蒸汽侵入调查期间要考虑的 PCE 室内空气源。

美国环境保护署 (USEPA) 正在最终确定其蒸气侵入准则。与蒸汽侵入相关的重要问题之一是室内空气中挥发性有机化学物质 (VOC) 的背景浓度，通常归因于消费品和建筑材料。即使没有蒸汽侵入，背景浓度也可能存在，这是进行现场评估时的一个重要考虑因素。此外，在蒸汽侵入现场评估期间，开发描述蒸汽进入建筑物的路径的准确概念模型很重要。下水道气体，无论是作为背景浓度的贡献者还是作为场地概念模型的一部分，在蒸汽侵入场地评估期间都不会进行常规评估。此处描述的研究确定了一个实例，其中直接从住宅内的卫生下水道管道散发出的蒸汽被确定为在室内空气中检测到的四氯乙烯 (PCE) 的来源。浴室中 PCE 的浓度范围从 2.1 到 190 ug/m3，超过典型的室内空气浓度几个数量级，导致人类健康风险被归类为“迫在眉睫的危险”状况。结果表明，与不知道下水道气体渗入发生时相比，下水道气体渗入导致室内空气中的 PCE 浓度高出近两个数量级。强调了以前未充分研究的下水道作为 PCE（以及潜在的其他 VOC）蒸气来源的途径。还讨论了对蒸汽侵入调查的影响。