Theme: 09. Vapor Intrusion

Topic Area: 9c. Vapor Intrusion Preferential Pathways

Formatted Title:

Implementation of Wisconsin’s Preferential Pathway and Conduit Vapor Intrusion Guidance, RR-649

Background/Objectives:

Prior to 2021, vapor samples from within conduits were rarely collected in Wisconsin. In June 2021, the Wisconsin Department of Natural Resources (WDNR) published a major revision of our preferential pathway and utility corridor guidance, RR-649. We included an extensive section on conduit vapor intrusion (VI). In the period since, collection of samples from within conduits has become standard practice for many Wisconsin vapor investigations. Although most samples have been collected using evacuated canisters, beginning in late 2022, WDNR began recommending the use of passive sorbent samplers in sanitary sewer manhole sampling. In 2023 WDNR began using passive sorbent samplers in sanitary sewer manholes and other conduits at state-funded investigations. In 2024, WDNR will be finalizing revisions to our VI guidance, RR-800, which will include additional recommendations related to conduit VI. The importance of conduit VI has only been recognized within the past decade. The objective of WDNR guidance is to promote consistent evaluation of this pathway at contaminated site investigations. This presentation will share information from a significant number of such assessments.

Approach/Activities:

Sampling of contaminant vapor in conduits at more than 50 remedial sites has been submitted to WDNR or collected by WDNR contractors. This includes sampling within indoor plumbing systems (sealed sumps, floor drains, below p-traps, clean-outs, plumbing stack vents, mitigation system vents) in both source buildings and off-site impacted buildings, and sanitary and storm sewer main manholes. At most sites, chlorinated solvents, primarily tetrachloroethene (PCE) or trichloroethene (TCE), are the contaminants of concern resulting from dry cleaning or metal degreasing. However, concentrations of a longer list of compounds are often measured. Although most results are from canister or passive sorbent samplers, a gas chromatograph with an electron capture detector (GC/ECD) was used on some projects. Additional results from conduit sampling are being submitted to WDNR on a routine basis and will be incorporated into the presentation.

Results/Lessons Learned:

Although concentrations have been low in many locations, conduit concentrations have been significant at some sites. High detects include PCE concentrations of over 7,000,000 micrograms per cubic meter (µg/m³) from within a floor drain, and ¾ mile of sanitary sewer mains with TCE vapor concentrations above regulatory screening levels of 70 µg/m³and as high as 7,660 µg/m³. Mitigation, including depressurization of sanitary sewer mains, has begun at some sites. The recommendations in RR-649 and RR-800 related to conduit sampling will be briefly reviewed to provide context for the remainder of the presentation. Overall results will be summarized (sources, concentration data in various settings, sampling methods used, comparison between sampling methods where available, etc.). Results from a few specific buildings or sanitary sewers that provide interesting examples will be highlighted. Major lessons and remaining challenges will be discussed, including sampling method selection and sampler placement best practices, attenuation of vapor concentrations along conduit flow paths, criteria for mitigating the conduit VI pathway, mitigation options, communicating results with building occupants and municipalities, and placement of institutional controls related to contaminated conduits.

Menu

Jennifer Borski