A conceptual model for vapor intrusion from groundwater through sewer lines

The role of sewer lines as preferential pathways for vapor intrusion is poorly understood. As a result, these pathways are often not considered when developing vapor intrusion investigation or mitigation plans. Neglecting this pathway can complicate data interpretation, which can result in repeated, and potentially unnecessary, rounds of sampling. Although a number of recent studies have highlighted the importance of sewers as preferential pathways at individual buildings, there is currently little specific technical or regulatory guidance on how to address it. The purpose of our study, therefore, was to conduct systematic testing to better understand the sewer vapor intrusion conceptual model. Through sampling at >30 different sites, the degree of interaction between impacted groundwater and the sewer lines were identified as the main factor when determining the degree of risk for sewer vapor intrusion at a given site. Higher risk sites are those with direct interaction between the subsurface volatile organic compound (VOC) source, such as groundwater, and the sewer line itself. This information can be used to prioritize sites and buildings to test for this particular exposure pathway.