Tools for Understanding Transients in Vapor Intrusion

Dr. Eric Suuberg | Brown University

ER-201502

Objective

Many present and former Department of Defense (DoD) facilities are impacted by vapor intrusion (VI). The contaminants of concern are volatile organic compounds (VOCs) including chlorinated solvents, such as trichloroethene (TCE) and perchloroethene (PCE), as well as petroleum derived compounds such as benzene. There is still considerable uncertainty as to how to best manage VI sites. Recent field data have contributed to the uncertainty regarding proper management, because they have shown even greater variation in indoor air contaminant concentrations than had been earlier recognized. This project is specifically aimed at providing a general tool for better assessing and managing sites impacted by VI. The advances in three-dimensional (3-D) engineering modeling of complex phenomena, such as VI, have not been fully brought to bear on management of the problem, either during site investigation or during remediation. This project will provide a software tool that is designed to improve both aspects.

 

ER-201502 Graphic

An Example of Transients – Sampling of PCE following a Rainfall Event.

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Technology Description

Brown University has, with support from the National Institute of Environmental Health Sciences, developed a steady state 3-D model of the VI process, which it has applied to describing many aspects of the process. What is now needed is a significant extension of this model to describe the all-important transient aspects of the VI process, for which no mathematical model exists. The extended model will focus on diffusional-advective transport of contaminant vapors in the subsurface, as well as their entry into structures built atop the contamination. It will incorporate new terms describing the variation in subsurface conditions (e.g., moisture content, temperature) as well as indoor conditions (e.g., air exchange rates), and take into account equilibrium partitioning in both the indoor environment as well as in the subsurface (to soil organics and moisture). The model will be developed so that it can be run on desktop computing equipment, using standard finite element solvers (e.g., COMSOL), to make it maximally accessible to those in the field. The project team will perform the additional model development in close collaboration with those managing and studying actual DoD VI sites.

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Benefits

A reliable, easily implementable model of a site of VI concern will help guide field investigations. Right now, many investigations are conservative, and by their nature, intrusive to potentially impacted residents. Any tool that will allow more targeted investigation of a more limited scope would be beneficial. In addition, at the present time, regulators do not have a good sense of how large the variations in contaminant vapor exposure concentrations might be, and cannot develop health-protective guidelines based upon predictions of such variation. This model would provide such information. Once a good site model is developed, it will be available for guiding design of mitigation systems (e.g., subslab depressurization). (Anticipated Project Completion - 2018)

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Points of Contact

Principal Investigator

Dr. Eric Suuberg

Brown University

Phone: 401-863-1420

Fax: 401-863-9120

Program Manager

Environmental Restoration

SERDP and ESTCP

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