Connections and Networking in Unusual Places: Awareness of Sewer Air and Vapor Intrusion
James A. Jacobs, CPG-7760
In a very unsettling way, we are more connected than we think. Although these connections may not be well documented or until recently, even widely acknowl- edged, some subsurface conduits such as our sewer pipes may provide a pathway for toxic chemicals to enter into our work and living spaces. Earth scientists have long been involved with developing site conceptual models for releases of haz- ardous compounds and in assessing and determining the fate and transport in the subsurface and associated exposure pathways. In some cases, geologists and other professionals evaluate human exposure pathways and, specifically, indoor air quality in relation to ground- water plumes containing volatile organic compounds (VOCs).
Up to now, one human exposure path- way from subsurface VOC plumes has not received evaluation. Recent studies document that legacy sewer-plumbing systems, land drains and subsurface utility conduits/lines/trenches are expo- sure pathways for VOCs in the shallow subsurface to migrate into indoor air. The term legacy sewer refers to a sewer which through time allows leakage into and also out of the pipes and components. Sewer air (the air space above the tran- siting sewer wastes in the pipes) in leak- ing sewer systems that intercept VOC contaminated groundwater or vapor are predicted to contain VOCs. By design, sewer-plumbing systems inside build- ings completely vent sewer air gases to prevent them from entering the living spaces. Several decades or even centu- ries after installation, many components of sewer systems in the subsurface and in buildings leak, and some vapor seals designed to protect against sewer air intrusion into structures become com- promised (pipes crack, fittings loosen, wax seals degrade and crack and P-traps dry out).
Plumbing venting was not designed to contain VOCs, which are excellent at diffusing through very small apertures.
When compromised, sewer and plumb- ing systems intercept groundwater con- taining VOCs, the VOCs partition into sewer air, the indoor air becomes con- nected to sewer air, and then the indoor air can contain VOCs. The nationwide result is that legacy sewer lines are unin- tended conveyance systems for VOCs. VOCs that might be found in sewer air might include industrial chemicals such as petroleum hydrocarbons and chlorinated solvents, household clean- ers and maintenance compounds, and even wastes associated with illegal drug manufacturing and medicine disposal. These compounds could be sourced from the disposal act itself, or by infiltration of the contaminants into the leaking sewer lines.
Are these abstract worries? Migrating VOCs in sewer air have not been carefully evaluated for human exposure potential. Many sewer-plumbing systems were not designed to be liquid and vapor tight, resulting in the diffusion and fugitive release of VOCs. Recent vapor intrusion studies in Denmark and Massachusetts have shown unhealthy indoor levels of tetrachloroethyene (PCE) vapors air in buildings when vapor seals (p-traps, wax toilet rings, etc.) have failed in areas with nearby PCE-containing groundwa- ter plumes.
How many vapor seals leak? If you have ever smelled a moldy or sulfur smell in a bathroom near a low-use sink or tub or in the basement, it is possible a p-trap may have dried out. A wobble on a toilet can indicate wood rot and a damaged wax seal ring (leaking vapor seal). Based on six smoke testing projects in northern California, about 10% of the sewer lat- erals leak, and about five laterals out of 1,250 houses (0.4%) leak within 2 feet of the building, under the building or in the building vents. Certainly more research is needed to study VOC migration in active and abandoned sewer lines, land drains, and other systems which are
some of the largest known connected pore spaces in the subsurface.
References
Abbreviated references for this piece include: California Department of Toxic Substances Control (DTSC), 2014; J.A., Jacobs, O.P., and K.G. Pennell, 2014 and 2015; Johnson, P. C, and R. A. Ettinger, 1991; Massachusetts DEP, 2011; Pennell, K.G., et al., 2013: Riis, C.E., et al., 2010; Sewerage Agency of Southern Marin (SASM), 2010; San Francisco Bay Regional Water Quality Control Board (RWQCB), 2013; USEPA, 2002 and 2011.
Please contact author James A. Jacobs at his email address below for a complete list of references and the entire article from which this was based; “PCE Vapors within Sewer Air in Legacy Sewer Systems Outside of Plume Areas,” by James A. Jacobs and Olivia P. Jacobs.
The author thanks the following col- leagues who worked on the original arti- cles and presentations: Olivia Jacobs, C.E.M., is a Thomas J. Watson Fellow. She brings experience with I&I model- ing to decades of environmental sci- ence experience. President of Clearwater Group, she can be reached at oj@clear-
watergroup.com. Kelly G. Pennell, PhD, PE, is an Assistant Professor in the Department of Civil Engineering at the University of Kentucky. She has over 15 years combined environmental engineering experience as a consultant, governmental liaison and faculty mem- ber. She can be reached at kellypennell@
uky.edu.
James A. Jacobs is a geologist with over three decades of experience. He is a Fulbright Scholar and co-authored four books. Since 2002, he is an elected sewer board director. He can be reached at
jjacobs@clearwatergroup.com.
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