Sewer system pipes are a potential alternate exposure pathway for toxic sewer gases and volatile organic compounds (VOCs) like benzene in gasoline, and tetrachloroethylene (PCE), a common dry cleaning solvent, to migrate into indoor air.
Figures are included in the Photo Gallery (above)
A common US EPA (2002) vapor intrusion model (Figure 1) needs to be re-evaluated and updated to include this important exposure pathway, especially in buildings located upgradient and outside of mapped groundwater contaminant plumes containing VOCs. The US EPA (2002) and other regulatory agencies use various vapor intrusion prediction models to make risk-based environmental decisions, including the commonly used model by Johnson and Ettinger (1991). VOC-impacted groundwater can infiltrate into cracked and leaking sewer trunk lines. The VOC volatilizes into sewer air and migrates through the sewer system into the indoor air in houses which have inadequate vapor seals (Figure 2). There are hundreds of thousands of shallow groundwater plumes containing VOC in urban areas in North America. There are also countless urban sewer systems which leak significantly during strong rain events. The research is focused on studying the migration of VOCs into indoor air through legacy sewer-plumbing systems and ineffective vapor seals and are planning to document the extent to which VOC vapors migrate within sewer pipes located upgradient and outside of delineated VOC groundwater plume areas.
Figure 1: A common VOC vapor model (modified after others, original from US EPA, 2002).
Figure 2: An example of an alternate exposure pathway model showing sewer gases and VOCs entering indoor air through ineffective plumbing vapor seals. Note: VOCs are released to the indoor air and through the vent line on roof.
VOC data ( Riis et al., 2010; and Pennell et al., 2013) support this alternate VOC exposure pathway into indoor air. Conditions in the houses reflect exposure pathways. (See Figure 2, right side of diagram): A: Intact vapor seals and not over VOC plume (exposure pathway not completed); B: Leaky vapor seals and not over VOC plume (exposure pathway completed); C: Intact vapor seals and working SSD over VOC plume (exposure pathway not completed); and D: Leaking vapor seals and working SSDs over VOC plume (exposure pathway completed).
Legacy Sewer and Plumbing Systems: Many urban sewer systems in North America are more than 100 years old and are well past their design life. The legacy sewer mains and associated laterals and components frequently subside, fail, and develop cracks or separations over time. These are evidenced as breaches in the concrete, clay or transite pipes or corrosion in cast iron pipes. Tree and plant roots commonly damage sewer pipe integrity.
Legacy sewer system pipes experience infiltration of groundwater during the rainy season. Inflow and infiltration (I&I) during significant rain events (Figure 3) in a northern California collection system was shown to contribute 8 to 33 times the amount of daily sewer flow shortly after a downpour (SASM, 2010). The conceptualized diagram showing the wastewater flow components of rainfall-dependent infiltration/inflow (RDI/I) into sewer pipes (Figure 4) illustrates the lag between the timing of rainfall and infiltration into sewer pipes. Diurnal base wastewater flow (BWF) shows increased flow in the early morning hours and during dinner through evening hours. Groundwater infiltration (GWI) into sewer pipes is relatively constant during a 24-hour period in an area with no tidal influences.
Figure 3: Variations in wastewater flow within a sewer pipeline (modified after SASM, 2010; from Jacobs et al., 2014).
Figure 4: Conceptual diagram showing wastewater flow components ((modified after SASM, 2010; from Jacobs et al., 2014).
Within structures, ineffective vapor seals in plumbing systems in buildings (dry P-Traps, breached toilet wax rings, cracked plumbing drain pipes, loose fittings and gaskets, for example) are common (Figures 5, 6, and 7).
Figure 5: Anatomy of a P-Trap vapor seal. If water evaporates or is siphoned to below the trap dip (upper dip) sewer air can be released into indoor air.
Figures 6a and 6b: Examples of vapor leak locations.
Figure 7: Potential sewer gas and VOC can migrate into buildings. (Figures 5-7; modified after base diagram, US Dept. of Army, 2001).
Breached Sewer Lines
When breached sewer collection pipes intersect contaminated soil and groundwater containing VOCs, for example, the potential for VOC-containing water and VOC-containing vapor to infiltrate into breached sewer pipes is high. While VOC-containing fluids are conveyed downgradient in the sewer pipes toward the wastewater treatment plant, the VOCs in groundwater, pipe debris/solids and soil vapor naturally volatilizes and migrates in the sewer pipes. VOCs in vapor form (sewer air) migrates without specific regard to gravity.
Sewer air, which migrates throughout the system, frequently contains sewer gases such as methane, ammonia, hydrogen sulfide, and low levels of carbon dioxide and any other volatile compounds. Some sewer gases, such as hydrogen sulfide or ammonia, are odoriferous and are recognizable. Depending on concentrations, commonly detected VOCs such as PCE, trichloroethene (TCE), benzene, and other chemicals as well as sewer gases mentioned above, can migrate by diffusion or other methods throughout the main sewer lines, the attached sewer laterals and plumbing pipes in each structure on the wastewater system.
Indoor Air Quality
Indoor air quality degradation caused by vapor intrusion of VOCs into structures has been a health concern of the US EPA and other agencies for three decades. Sewers and plumbing systems have not been generally included as potential vapor conduits in the standard site conceptual models for indoor air quality developed by US EPA (2002) and others.
Two recent PCE-specific vapor intrusion studies documented significant indoor air contributions of PCE from the plumbing-sewer systems located within PCE groundwater plume areas; the PCE groundwater plumes studied were in Skuldelev, Denmark (Riis et al., 2010) and in Boston, Massachusetts (Pennell et al., 2013). In both studies, PCE vapors were found in indoor air and were tracked back to sewer-plumbing systems which intersected a delineated PCE groundwater plume. In both cases, the concentrations of PCE detected inside the buildings were orders of magnitude higher than the levels generally considered safe for long-term indoor air exposure.
In the Denmark study (Riis et al., 2010), PCE was reported in indoor air near the drain under a kitchen sink as high as 810 µg/m3. In the Boston study, concentrations of PCE in isolated bathroom air was 2.1 µg/m3. When the sewer connection for the toilet in the bathroom was open to indoor air, the inside air had a PCE concentration of 62 µg/m3 to 190 µg/m3.
For the Massachusetts Department of Environmental Protection (MassDEP), the threshold value for PCE is 1.4 μg/m3. The two studies described above (Riis et al., 2010 and Pennell et al., 2013), although not in California, represent residential exposures. Using the California Department of Toxic Substances Control (DTSC, 2014) Human and Ecological Risk (HERO) recommended values for PCE concentrations for residential air screening levels calculated using the Regional Screening Level (RSLs) calculator are 0.41μg/m3 for cancer and 37μg/m3 for non-cancer risk. San Francisco Bay Regional Water Quality Control Board (RWQCB, 2013) Environmental Screening Levels (ESLs) for PCE in indoor air (residential) is 0.41 μg/m3. Clearly, the indoor air concentrations in both studies indicate the PCE concentrations in indoor air are at levels worthy of concern and additional study and a need for mitigation.
Regardless of the regulatory level used for environmental guidance or action levels, the hazard communication about the potential for vapor exposure of toxic compounds to unsuspecting building occupants is needed. The levels of PCE detected in indoor air (Riis et al., 2010 and Pennell et al., 2013) are small compared to the immediately dangerous to life and health (IDLH) for an instantaneous exposure of PCE. However, the concern is regarding low level of exposure of possibly multiple volatile compounds over decades to building occupants who are unaware they are being exposed, especially because they may be located far away from the release of the volatile compounds.
Many urban PCE plumes intersect breached sewer systems. Due to the potential for migration of toxic vapors within the breached sewer-plumbing system, this study sets out to evaluate the pattern of PCE migration into upgradient buildings connected by the sewer-plumbing systems but which are clearly outside of the known impacted soil or groundwater plume area. The significance of the research is that unsuspecting, upgradient occupants in buildings which have vapor seal leaks and which are connected to failed sewer trunk lines which have infiltration of PCE-impacted groundwater may have long-term exposure to toxic vapors. A second significance is that the scientific and regulatory community has not generally included this exposure pathway in regulatory decision making. The vapor exposure potential for residents or workers outside of the impacted soil and groundwater plume is not part of the standard indoor air exposure model.
The objective of the type of projects described above is to provide the following:
1) Working with the local sewer agency, to document the presence of PCE outside the groundwater plume area and to verify the exposure vulnerability of upgradient occupants. The study will start with screening and sampling iteratively in sewer manholes and cleanouts for sewer gases and PCE in a system which intercepts a known groundwater PCE plume. The next phase will follow up in buildings sharing a compromised sewer trunk line within and upgradient of a documented PCE release.
2) Once detected in outside manholes and cleanouts, indoor air will be sampled within accessible buildings in basements or crawl spaces, at each floor, and near vapor seals such as in bathrooms and kitchens. The project will include the inspection and documentation of plumbing fixtures and the condition of vapor seals in buildings where PCE detections are observed. Methodology: Perform vapor screening using hand-held digital vapor meters (photoionization detectors [PIDs] calibrated for PCE), and confirm PID detections with discrete air samples using SUMMA canisters analyzed by gas chromatography methods (6L; 24 hrs, EPA Method SIM TO-15);
3) Develop sewer system inspection documentation protocols for sewer agencies;
4) Based on field observations, develop consistent, simple, low-cost and effective building inspection protocols for vapor seal evaluations in buildings where sewer gases or PCE are detected. Improve sewer gas and PCE sampling protocols and methods for low-cost and simple vapor intrusion evaluations of the sewer-plumbing system. Determine radius of influence for indoor air exposures from initial source of air contaminants for the study area based on field data and observations;
5) Develop simple process and low-cost mitigation measures in buildings for vapor seal repair or replacement; and
6) Develop a ranking method for sewer replacement and vapor mitigation measures. Prepare a guidance document to share the findings with sewer and regulatory agencies, building owners and environmental professionals.
California Department of Toxic Substances Control (DTSC). 2010. Human Health Risk (HERO), Office of Human and Ecological Risk Overview; Retrieved January 20, 2014; https://www.dtsc.ca.gov/assessingrisk/humanrisk2.cfm
Gorder, K. and Dettenmaier, E. 2011. Portable GC/MS Methods to Evaluate Sources of cVOC Contamination in Indoor Air. Groundwater Monitoring & Remediation, National Groundwater Association, Fall, Vol. 31, Issue 4, p. 113-119.
Jacobs, J.A., Jacobs, O.P., and K.G. Pennell. 2014. Geologists and Site Conceptual Models: VOCs and Sewer Gas in Indoor Air Resulting from Migration from Breached Sewer Conveyance Systems, American Institute of Professional Geologists National Meeting, Abstracts, p. 73-74.
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, Groundwater Resources Association of California, Spring 2015, p. 20-24.
Johnson, P. C, and R. A. Ettinger. 1991. Heuristic model for predicting the intrusion rate of contaminant vapors in buildings. Environ. Sci. Technol. 25: 1445-1452.
Johnson, P. C. 2014. Vapor Intrusion: Lessons-Learned from Four Years of Intensive Monitoring of a House Over a Dilute Chlorinated Solvent Plume, GRACast Web Seminar
Series on Vapor Intrusion, Part 2, Groundwater Resources Association of California, Sacramento, California, June 25.
Massachusetts Department of Environmental Protection (MassDEP). 2011. Interim final vapor intrusion guidance, WSC#11-435. Boston, Massachusetts: MassDEP.
Pennell, K.G., Scammell, M.K., McClean, M.D., Arnes, J., Weldon, B., Friguglietti, L., Suuberg, E.M., Shen, R., Indeglia, P.A., and W.J. Heiger-Bernays. 2013. Sewer Gas: An Indoor Air Source of PCE to Consider During Vapor Intrusion Investigations, Groundwater Monitoring & Remediation; Volume 33, Issue 3, Summer 2013, p. 119–126.
Riis, C.E., A.G. Christensen, M.H. Hansen, and H. Husum. 2010. Vapor Intrusion through sewer systems: Migration pathways of chlorinated solvents from groundwater to indoor air. Presented at the Seventh Battelle International Conference on Remediation of Chlorinated and Recalcitrant Compounds, Monterey. http://indoorairproject.files.wordpress.com/2011/03/ sgs-attachment-1.pdf (accessed August 1, 2014).
San Francisco Bay Regional Water Quality Control Board (RWQCB). 2013. 2013 Tier 1 ESLs, Summary Table F, December, 19 p.
Sewerage Agency of Southern Marin (SASM), 2010, Sewage Spill Reduction Action Plan; Annual Report on Flow Monitoring, Prepared by RMC, October, Mill Valley, CA, 31 p.
United States Department of the Army. 2001. Plumbing, Pipe Fitting, and Sewerage, Field Manual FM 3-34.471 (FM 5-420), Headquarters, Washington, D.C., August 31, 276 p.
United States Environmental Protection Agency (US EPA). 2011. Background indoor air concentrations of volatile organic compounds in north American residences (1990–2005): A compilation of statistics for assessing vapor intrusion. EPA 530-R-10-001. Washington, DC: Office of Solid Waste and Emergency Response (OSWER). United States Environmental Protection Agency (US EPA). 2002. OSWER Draft Guidance for Evaluating the Vapor Intrusion to Indoor Air Pathway from Groundwater and Soils (Subsurface Vapor Intrusion Guidance), November 2002.
Other Suggested Readings
Agency for Toxic Substances and Disease Registry (ATSDR). 2004. Health Consultation. Mountain View Sewer Gas Investigation, Scottsdale, Maricopa Country, Arizona, 16 p.
American Society for Testing and Materials (ASTM) International. 2003. "Standard Practice for Installing Radon Mitigation Systems in Existing Low-rise Residential Buildings" (ASTM E-2121-03, February 10, 2003).
Brown, S.K., M.R. Sim, M.J. Abramson, and C.N. Gray. 1994. Concentrations of volatile organic compounds in indoor air — A review. Indoor Air 4:123–124.
Bylin, C. 2009. New Measurement Data has Implications for Quantifying Natural Gas Losses from Cast Iron Distribution Mains: Pipeline and Gas Journal, September, 2009.Federal Register. 2011. Public comment on the development of final guidance for evaluating the vapor intrusion to indoor air pathway from contaminated groundwater and soils (subsurface vapor intrusion guidance).
California Department of Toxic Substances Control (DTSC). 2014. Human Health Risk Assessment (HHRA) Note, Office of Human and Ecological Risk (HERO), Table 3, Page 1, Alternate air screening levels currently recommended in lieu of the Spring 2013 RSLs, July 14, 27 p.
Federal Register 76, no. 52: 14660-14661.
Hartman, B., and J. Jacobs. 2000. Soil Vapor Principles, Standard Encyclopedia of Environmental Science and Technology, J. Lehr, ed., McGraw Hill, New York, NY; p. 11.87 -11.95.
Hartman, B., and J. Jacobs. 2000. Applications and Interpretation of Soil Vapor Data to Volatile Organic Compound Contamination, Standard Encyclopedia of Environmental Science and Technology, J. Lehr, ed., McGraw Hill, New York, NY; p. 11.96 – 11.112.
Hawkins, J. 2008. Vapor Intrusion in Texas: Evaluating the indoor air pathway. Presentation to the Society of Texas Environmental Professionals, Texas.
www.txstep.org/presentations/vapor_intrusion_mar_08.pdf (accessed January 13, 2013).
Hodgson, A.T., and H. Levin. 2003. Volatile organic compounds in indoor air: A review of concentrations measured in North America since 1990. Report LBNL-51715. Berkeley, California: Lawrence Berkeley National Laboratory.
Holcomb, L.C., and B.S. Seabrook. 1995. Indoor concentrations of volatile organic compounds: Implications for comfort, health, and regulation. Indoor Environment 4:7–26.
Interstate Technology and Regulatory Council (ITRC). 2007. Vapor intrusion pathway: A practical guideline. VI-1. Washington, DC: ITRC.
Kladder, D. L, Burkhart, J.F., Jelinek, S.R. 1993. "Protecting Your Home from Radon: A Step-by-step Manual for Radon Reduction."Massachusetts Department of Environmental Protection (MassDEP). 2011. Interim final vapor intrusion guidance, WSC#11-435. Boston, Massachusetts: MassDEP.
Massachusetts Department of Environmental Protection (MassDEP). 2008. Residential typical indoor air concentrations. Technical Update. Boston, Massachusetts: MassDEP.
McAlary, T., and P.C. Johnson. 2009. Editorial: GWMR focus issue on vapor intrusion. Ground Water Monitoring and Remediation 29 1: 40-41.
New York State Department of Environmental Conservation. 2002. "Draft DER-10 Technical Guidance for Site Investigation and Remediation." Division of Environmental Remediation. December 2002.
New York State Department of Health (NYDOH). 2006. Final guidance for evaluating soil vapor intrusion in the state of New York, October, Troy, NY, 82 p.
Office of Hazard Evaluation and Emergency Response (HEER). 2014. State of Hawaii Office Technical Guidance Manual (TGM), Section 7 Soil Vapor and Indoor Air Sampling Guidance, Soil Vapor and Indoor Air Sample Analysis; Interim Final; p. 118-132.; Retrieved June 4, 2014; http://www.hawaiidoh.org/tgm-pdfs/HTGM%20Section%2007-13.pdf
Shah, J.J., and H.B. Singh. 1988. Distribution of volatile organic chemicals in outdoor and indoor air. Environmental Science & Technology 22, no. 12:1381–1388.
Stolwijk, J.A.J. 1990. Assessment of population exposure and carcinogenic risk posed by volatile organic chemicals in indoor air. Risk Analysis 10, no. 1:4 9–57.
United States Environmental Protection Agency (US EPA). 2012. US EPA’s Vapor Intrusion Database: Evaluation and characterization of attenuation factors for chlorinated volatile organic compounds and residential buildings. EPA 530-R-10-001. Washington, DC: Office of Solid Waste and Emergency Response (OSWER).
United States Environmental Protection Agency (US EPA). 2011. Background indoor air concentrations of volatile organic compounds in North American residences (1990–2005): A compilation of statistics for assessing vapor intrusion. EPA 530-R-10-001. Washington, DC: Office of Solid Waste and Emergency Response (OSWER).
United States Environmental Protection Agency (US EPA). 2010. Review of the draft 2002 subsurface vapor intrusion guidance.
http://www.epa.gov/oswer/vaporintrusion/documents/review_of_2002_draft_vi_guidance_final.pdf. Washington, DC: Office of Solid Waste and Emergency Response (OSWER).
United States Environmental Protection Agency (US EPA). 2008a. Draft US EPA’s vapor intrusion database: Preliminary evaluation of attenuation factors. Washington, DC: USEPA.
United States Environmental Protection Agency (US EPA). 2008b. Brownfields Technology Primer: Vapor Intrusion Considerations for Redevelopment; EPA-542-R-08-001, March, 44 p.
United States Environmental Protection Agency (US EPA). 2003. Toxicological review of hydrogen sulfide (CAS No. 7783-06-4). EPA/635/R-03/005. Washington, DC: USEPA.
United States Environmental Protection Agency (US EPA). 2003. "Consumer's Guide to Radon Reduction" (EPA 402-K-03-002; revised February 2003).
United States Environmental Protection Agency (US EPA). 2002. Draft guidance for evaluating the vapor intrusion to indoor air pathway from groundwater and soils, EPA 530-D-02-004. Washington, DC: USEPA.
United States Environmental Protection Agency. 2001. "Building Radon Out: A Step-by-Step Guide on How to Build Radon-Resistant Homes" (EPA 402-K-01-002, April 2001).
United States Environmental Protection Agency. 1999a. "Compendium of Methods for the Determination of Toxic Organic Compounds in Ambient Air, Second Edition. Compendium Method TO-15; Determination of Volatile Organic Compounds (VOCs) in Air Collected in Specially-Prepared Canisters and Analyzed by Gas Chromatography/Mass Spectrometry (GC/MS), Center for Environmental Research, Office of Research and Development, Cincinnati, OH, January, 52 p.
United States Environmental Protection Agency. 1999b. "Compendium of Methods for the Determination of Toxic Organic Compounds in Ambient Air, Second Edition. Compendium Method TO-13; Determination of Polycyclic Aromatic Hydrocarbons (PAHs) in Ambient Air using Gas Chromatography/Mass Spectrometry (GC/MS), Center for Environmental Research, Office of Research and Development, Cincinnati, OH, January, 84 p.
United States Environmental Protection Agency (USEPA). 1998. A comparison of indoor and outdoor concentrations of hazardous air pollutants. Inside IAQ EPA/600/N-98/002 Spring/Summer. Washington, DC: USEPA.
Vroblesky, D.A., M.D. Petkewich, M.A. Lowery, J.E. Landmeyer. 2011. Sewers as a source and sink of chlorinated-solvent groundwater contamination, Marine Corps Recruit Depot, Parris Island, South Carolina. Ground Water Monitoring and Remediation, 31, no. 4: 63–69.