[CPEO-BIF] "A Stakeholder’s Guide to Long-Term Management at Vapor Intrusion Sites"

[Lenny Siegel <lsiegel@cpeo.org>]

A Stakeholder’s Guide to Long-Term Management at Vapor Intrusion Sites[1]
By Lenny Siegel
April, 2016

Vapor intrusion occurs when toxic volatile substances are pulled into overlying buildings from the subsurface. The contamination that causes vapor intrusion, typically chlorinated volatile organic compounds (VOCs) such as TCE (trichloroethylene) and PCE (tetrachloroethylene), tends to persist in the subsurface. In most cases where there have been significant releases, neither natural biological degradation nor conventional treatment reduces contaminant concentrations to acceptable levels in a reasonable amount of time. Therefore, long-term management is necessary to protect the people who might be exposed. This is true, whether a decision is made to mitigate—that is, interrupt the vapor intrusion pathway—or not, and whether an effort is made to accelerate the removal or degradation of the subsurface contamination. 

Long-term management may include: 

• monitoring of subsurface contamination, in the form of groundwater or soil gas;

• inspecting possible pathways from the subsurface to indoors;

• operation, maintenance, monitoring, and inspection of mitigation systems;

• training building maintenance personnel;

• controlling and monitoring of mitigation system emissions;

• monitoring  indoor and outdoor air;

• being prepared to implement contingency plans should indoor air concentrations exceed or even approach target levels;

• establishing institutional controls to limit activities and uses at the site and to ensure continuation of the steps above;

• periodic review of the protectiveness and/or efficiency of the response;

• notifying building occupants and public at large, including prospective purchasers, of site conditions and the current status of the environmental response;

• developing a decision-making process for turning off active mitigation when the vapor intrusion threat has receded;

• preparing reports documenting all of the above.

Particularly at high-profile sites with robust regulatory oversight, best practices have emerged. They are described in U.S. EPA’s June, 2015 vapor intrusion Technical Guide, as well as numerous guidance documents produced by the states. But at many sites, especially new developments with little of no regulatory oversight, site management activities end after early rounds of sampling or soon after the installation of mitigation systems. To this day, there is no national accounting of the number of buildings that have been evaluated for vapor intrusion, let alone the number of sites subject to future investigation or mitigation.

This guide is designed to help stakeholders, particularly the people who live, work, study, pray, and recreate in buildings potentially susceptible to vapor intrusion, ensure that their sites receive proper long-term attention. And if there is no entity taking long-term responsibility, it provides a template for insisting that an agency or private entity take that responsibility. As with subsurface remediation, public oversight is the central element in making sure things are done right.


[1] This is a supplement to Lenny Siegel, “A Stakeholder’s Guide to Vapor Intrusion: Update,” Center for Public Environmental Oversight (CPEO), November 2015, http://www.cpeo.org/pubs/SGVIU.html


To download the 6 MB, 20-page report, go to
http://www.cpeo.org/pubs/VILTM.pdf

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Lenny Siegel
Executive Director, Center for Public Environmental Oversight
a project of the Pacific Studies Center
278-A Hope St., Mountain View, CA 94041
Voice: 650/961-8918 or 650/969-1545
Fax: 650/961-8918
<lsiegel@cpeo.org>
http://www.cpeo.org

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