The VI Diagnosis Toolkit for Assessing Vapor Intrusion Pathways and Impacts in Neighborhoods Overlying Dissolved Chlorinated Solvent Plumes

Dr. Paul Johnson | Arizona State University

ER-201501

Objective

The objective of this project is to demonstrate and validate a suite of tools that can improve our ability to more accurately, cost-effectively, and confidently assess vapor intrusion (VI) impacts and, if necessary, select appropriate remedies in neighborhoods and industrial areas overlying dilute chlorinated solvent plumes. This suite of tools is referred to as the “VI Diagnosis Toolkit.” This project recognizes 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. This project will demonstrate and validate that use of the VI Diagnosis Toolkit is practicable and leads to correct outcomes under scenarios relevant to the Department of Defense (DoD). The outcomes using the VI Diagnosis Toolkit will be compared to outcomes from the conventional multiple lines of evidence (MLE) paradigm and used to assess if conventional mitigation systems are less effective or possibly even amplifiers of VI impacts when alternate VI pathways are present.

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Technology Description

The primary components of the VI Diagnosis Toolkit include:

  • Neighborhood-Scale Vapor Source Characterization
  • External VI Source Mass Flux Screening - identify buildings and neighborhood sub-areas most likely to be impacted by VI and needing building-specific testing
  • Indoor Air Source Screening - identify and remove indoor air sources prior to indoor air testing under natural or depressurized conditions.
  • Controlled Pressurization Tests - verify VI impacts from sources other than indoor sources, identify VI source types, and estimate potential maximum indoor air impact under natural conditions.
  • Passive Long-Term Monitoring - longer-term confirmation monitoring in low risk cases and validation of mitigation system performance.
  • New Comprehensive VI Pathway Conceptual Models - used as framework to interpret data collected from the components above.

These are at different levels of technical maturity. For example, the indoor air source screening, controlled pressurization tests, and passive long-term monitoring are the most advanced, having been components of recent SERDP and ESTCP projects ER-1686, ER-200707, ER-201119, and ER-200830. Implementation questions still exist however. For example, results from ER-1686 show lingering contaminant memory after indoor source removal, so it is important to determine sufficient waiting periods before testing after source removal. ER-1686 results also illustrate that forced depressurization tests can amplify the contributions of some VI sources and pathways over others; thus, it is important to conduct the test in a way that provides results that are accurately informative of behavior under natural conditions. 

Components of the VI Diagnosis Toolkit will be validated under a range of controlled conditions at a well-instrumented facility and then demonstrated at other residential and industrial buildings having a range of conditions of interest.

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Benefits

Knowledge gained from this project has the potential to be incorporated in regulatory guidance for VI pathway assessment. It would be beneficial to DoD to have a replacement or alternative for the conventional MLE paradigm. That would change the way that VI assessments are conducted and lead to quicker, better, and more cost-effective outcomes. It should also reduce the frequency of false positive and negative conclusions from VI assessments, and the risk of installation of remedies that unintentionally amplify VI impacts. (Anticipated Project Completion - 2020)

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Points of Contact

Principal Investigator

Dr. Paul Johnson

Colorado School of Mines

Phone: 303-273-3280

Program Manager

Environmental Restoration

SERDP and ESTCP

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