Skip to main content


Buy Article:

$9.50 plus tax (Refund Policy)

Or sign up for a free trial

A subsurface plume of non-aqueous phase liquid (NAPL) in contact with the side wall of a large combined sanitary and storm water trunk sewer was suspected as a source of toxic and odorous vapors in ambient air in the vicinity of the sewer manholes and catch basins and in residences serviced by the sewer. An evaluation involving vapor transport modeling was conducted to assess the potential for vapor release through untrapped storm water catch basin openings to outdoor air and through faulty residential traps to indoor air. The results were used to assess the potential for human exposure and associated health risks.

The NAPL, characterized as a light petroleum naphtha with traces of gasoline, was discovered floating on the groundwater surface, and chemical components of the NAPL were detected in the underlying groundwater. Chemicals of potential concern for the evaluation included benzene, ethylbenzene, naphthalene, toluene, xylenes.

Two time frames were evaluated. In the first, the pre-remediation phase, the potential for human exposure due to NAPL infiltrating the sewer and floating on the wastewater surface was predicted. An oil film model was used to estimate emissions from the NAPL layer on top of the in-sewer wastewater surface. In the second, a post-remediation phase (i.e., following recovery of the NAPL), the residual contaminated groundwater infiltrating the sewer reach was assumed to have mixed with the wastewater, resulting in volatilization from the water surface into the sewer air. Emissions to the air from the contaminated wastewater were estimated using the ToxChem+ model (Enviromega, Inc.). In both time frames, the estimated chemical-specific emission rates were then partitioned between sewer air and the service connections (i.e., a catch basin and sewer lateral/faulty residential sewer trap). The estimated emission rates from the service connections were input to a computerized atmospheric dispersion model and a household air-exchange model to estimate chemical concentrations in ambient outdoor and indoor air, respectively.

Two potential human exposure scenarios were developed for each time frame based on likely indoor and outdoor activity patterns and representative exposure parameters. In the first, contaminated air from the sewer was assumed to escape by way of catch basin openings, dispersing downwind in the direction of nearby residences. In the second, contaminated air from the sewer was assumed to enter a residence by way of a faulty sewer trap. The estimated exposure levels were coupled with appropriate toxicological criteria to characterize pre-remediation health risks and predict post-remediation health risks associated with post- NAPL removal residuals.

This paper presents the conceptual models for the chemical migration and exposure scenarios, the development of emission rates and dispersion model inputs and outputs, and the potential risks estimated using these techniques.
No Reference information available - sign in for access.
No Citation information available - sign in for access.
No Supplementary Data.
No Article Media
No Metrics

Document Type: Research Article

Publication date: 2000-01-01

More about this publication?
  • Proceedings of the Water Environment Federation is an archive of papers published in the proceedings of the annual Water Environment Federation® Technical Exhibition and Conference (WEFTEC® ) and specialty conferences held since the year 2000. These proceedings are not peer reviewed.

    A subscription to the Proceedings of the Water Environment Federation includes access to most papers presented at the annual WEF Technical Exhibition and Conference (WEFTEC) and other conferences held since 2000. Subscription access begins 12 months after the event and is valid for 12 months from month of purchase. A subscription to the Proceedings of the Water Environment Federation is included in Water Environment Federation (WEF) membership.

    WEF Members: Sign in (right panel) with your IngentaConnect user name and password to receive complimentary access. Access begins 12 months after the conference or event
  • Subscribe to this Title
  • Membership Information
  • About WEF Proceedings
  • WEFTEC Conference Information
  • Learn about the many other WEF member benefits and join today
  • Ingenta Connect is not responsible for the content or availability of external websites
  • Access Key
  • Free content
  • Partial Free content
  • New content
  • Open access content
  • Partial Open access content
  • Subscribed content
  • Partial Subscribed content
  • Free trial content
Cookie Policy
Cookie Policy
Ingenta Connect website makes use of cookies so as to keep track of data that you have filled in. I am Happy with this Find out more