The objective of this project was to demonstrate and validate a suite of tools that can improve the ability to more accurately, cost-effectively, and confidently assess vapor intrusion (VI) impacts and, if necessary, select appropriate remedies in neighborhoods and industrial buildings overlying dilute chlorinated solvent plumes.
This suite of tools is referred to as the “VI Diagnosis Toolkit.” This project recognized that there can be multiple VI pathways, including the traditional “soil VI” conceptualization (source through soil through foundation to indoor air), “pipe flow VI” from sources like land drains to sub-foundation regions, and “sewer VI” where vapors originate from sewers and travel to indoor air through sewer piping. VI impacts might extend beyond dissolved plume boundaries due to impacted water distribution by sewers and other subsurface infrastructure, and VI pathways may be present but not discernible by traditional site characterization.
The project focused on advancing the acceptance and use of a suite of tools referred to as the VI Diagnosis Toolkit, which includes:
- External VI source screening for at-risk building identification (e.g., use of groundwater, soil gas, and subsurface piping vapor concentration data).
- Building-specific controlled pressurization method (CPM) testing to quickly measure worst-case VI indoor air impacts in at-risk buildings.
- Indoor vapor source identification through use of portable analytical tools.
- Passive samplers for longer-term (week to month duration), time-weighted indoor air concentration measurement.
- Use of the data from all tools to construct comprehensive VI pathway conceptual models that can be used to select appropriate mitigation strategies, if needed.
Overall, this project met its performance objectives. The CPM protocol (Task 2) and the use of passive samplers (Task 3) were validated and demonstrated in both residential and industrial scale buildings. The effectiveness of a sub-slab depressurization system (Task 4) was evaluated in a study house with a known pipe-flow VI pathway through the land drain system.
Relative to current regulatory approaches for VI pathway assessment - which incorporate some, but not all of its components - use of the VI toolkit components offers the potential for greater confidence, speed, and cost-efficiency in pathway assessment and decision-making. In particular, this project focused on advancing the following tools as their use for VI pathway assessment is relatively new: vapor sampling in subsurface piping (e.g., sewers and land drains), building-specific controlled pressure method testing, use of passive samplers for longer-term monitoring and validation, and use of data to identify likely VI pathways and appropriate mitigation strategies. Protocols and guidance for use of these tools were developed, demonstrated and validated in residential and industrial buildings as part of this work.
The toolkit incorporates fairly standard hardware and practices. For example, data needs for External VI Source Strength Screening involve soils and/or groundwater data and vapor data from manholes, and CPM testing utilizes readily available blower door equipment from the heating, ventilation, air conditioning industry. The adoption of passive samplers is growing, but standardized approaches for their validation and calibration are needed as discussed above, particular for use in time-varying concentration environments.
The VI Diagnosis Toolkit can be applied under current regulatory guidance and does not require any additional approvals, licenses, etc. beyond those normally associated with site investigations. No barriers to the collection of the necessary data are anticipated other than those presented by unique site conditions. For manhole sampling, however, it is recommended that manhole access approval is obtained from local governmental engineering departments and those entities are aware of sampling dates to avoid any issues with local law enforcement.
Guo, Y., P. Dahlen, and P.C. Johnson. 2020. Development and Validation of a Controlled Pressure Method Test Protocol for Vapor Intrusion Pathway Assessment. Environmental Science & Technology, 54(12):7117-7125.
Guo, Y., P. Dahlen, and P. Johnson. 2020. Temporal Variability of Chlorinated Volatile Organic Compound Vapor Concentrations in a Residential Sewer and Land Drain System Overlying a Dilute Groundwater Plume. Science of the Total Environment, 702:134756.