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.
An addendum to the original project was conducted to validate the use of passive samplers for accurate, long-term, time-weighted volatile organic air concentration measurements in manhole environments. Studies conducted under this project as well as ESTCP project ER-201505 identified sewers and/or land drains as alternative pathways for VI and suggested manhole air sampling be part of VI assessment. Additionally, it was found that manhole concentrations can be temporally variable and suggested long-term sampling of that environment was important. Passive samplers offer a cost-effective method for collecting samples. ESTCP ER-200830 showed that the passive sampler is an effective long-term sampling tool and ER-201501 indicated the passive sampler can provide accurate, long-term, time-weighted concentrations for indoor air environments with time-variable concentrations for up to three weeks with calibration and validation of the sampler used.
Passive samplers, however, have not been validated for manhole environments where relative humidity and volatile organic vapor concentrations could be elevated and vapor concentrations, temperature, and relative humidity could each be variable over both the short and long term. Under the study addendum, performance of passive samplers was tested against the traditional TO-17 type thermal desorption tube (TD tube) active sampler.
The project focused on advancing the acceptance and use of a suite of tools referred to as the VI Diagnosis Toolkit, which includes:
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.
Passive sampler performance in manhole environments was tested against the traditional TO-17 type TD tube active sampler. The demonstration included two, back-to-back, eight-day sampling events in which samplers (passive and active TD tube) were deployed in triplicate in five manholes. Passive sampler validation was based on a comparison of passive vs active sampler concentrations using both linear regression and an assessment of comparability using a method developed by Bland and Altman (1986). Bland and Altman used plots of difference in concentration vs mean concentration for data pairs to evaluate the magnitude of variation. Testing indicated that the passive sampler could be an effective sampling tool in manhole environments with proper calibration and validation. Results of the passive sampler performance in manhole environments is available in the Final Report Addendum.
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.
Cost assessment for passive sampler use in manhole environments was based on a per sample assessment or multiples thereof, since it is not possible to estimate how many samplers might be used in manhole deployments across a neighborhood. Cost focused on deployment/retrieval and analytical costs, but did not include preparation, travel, or reporting time. The per sample cost estimate for deployment/retrieval was based on $100/hr for a total of one hour and analytical costs of $200, for a total of $300/sample. (Project Completion - 2021; Addendum Completion - 2023)
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.