One Alternative Exposure Pathway of Volatile Organic Compound (VOC) Vapors from Contaminated Subsurface Environments into Indoor Air - Legacy Sewer- Plumbing Systems
Editor’s Note: this article is abridged and republished by permission of Groundwater Resources of California from an article in Hydrovisions, Spring 2015. The original citation is: Jacobs, J.A., Jacobs, O.P. and K.G. Pennell, 2015. One Alternate Exposure Pathway of VOC Vapors from Contaminated Subsurface Environments into Indoor Air - Legacy Sewer-Plumbing Systems. Hydrovisions, Groundwater Association of California, Spring 2015 issue, p.20-24. We thought the topic of the article important enough to bring to the attention of our readers, and we thank the authors and Hydrovisions for giving us permission to do so. – JLB/JMP
James A. Jacobs, Olivia P. Jacobs, and Kelly G. Pennell
Abstract
Sewer-plumbing systems, land drains and subsurface utility conduits/lines/ trenches are ‘alternative exposure path- ways’ (i.e. indirect pathways) for vola- tile organic compounds (VOCs) in the shallow subsurface to migrate into the indoor air. The term ‘legacy sewer’ refers to a sewer which, through time, allows leakage in and out of the pipes. Legacy sewers that intercept VOC contaminated groundwater or vapor likely contain VOCs in the sewer air (that air space above the transiting sewer wastes). This article discusses and highlights an often overlooked implication of legacy sewers and their interception of VOC plumes- -the potential for VOC-impacted sewer air to enter indoor air spaces.
Introduction
Sewer systems were designed to deliv- er residential, commercial, and indus- trial liquid wastes to treatment plants, without their loss of the wastes in transit. Sewer-plumbing systems inside buildings were designed to properly vent sewer gases to prevent sewer gases from entering the inhabited space inside a structure. Several decades or even
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centuries after the installation of sewer collection systems under the streets and the construction of vented plumbing in buildings, many components of sewer systems 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). When compromised sewer and plumbing systems intercept contami- nated groundwater plumes, indoor air becomes directly connected to sewer air which can contain VOCs.
Nationwide, legacy sewer lines are unintended conveyance systems for VOCs in sewer air. VOC-impacted groundwater (and vapor) infiltrates cracked and leaky sewer trunk lines and sewer laterals. The VOCs volatil- ize from the sewer/groundwater liquids into sewer air and, once in the sewer air, migrate throughout the sewer system into the indoor air in those buildings which have failed vapor seals in their plumbing system.
This paper presents (1) currently used vapor intrusion conceptual models, (2) leakage and pipe damage as docu- mented in a northern California sewage conveyance system, (3) the indoor air
presence of VOCs as a result of breached sewer systems with failed plumbing seals intersecting PCE plumes in three case studies, and (4) recommendations.
Indoor Air Quality Studies
There are many sources of indoor air pollution, but one that has captured the attention of regulators and hazardous waste site managers is the transport of subsurface vapors into indoor air spaces (i.e. vapor intrusion). U.S. EPA (2002) developed a series of models for estimating indoor air concentrations of VOCs and the associated health risks from subsurface vapor intrusion into buildings. These vapor intrusion models were based on the analytical solutions of Johnson and Ettinger (1991) for contam- inant partitioning and subsurface vapor transport into buildings. Figure 1 shows a common site conceptual model for the mitigation of VOC vapor intrusion, based on US EPA (2002) and modified by oth- ers. Since that time, several revisions to the vapor intrusion model have been made and a series of new models has been developed.
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