U.S. EPA Contaminated Site Cleanup Information (CLU-IN)


U.S. Environmental Protection Agency
U.S. EPA Technology Innovation and Field Services Division

For more information on Vapor Intrusion, please contact:

Michael Adam
Technology Integration and Information Branch

PH: (703) 603-9915 | Email: adam.michael@epa.gov



Vapor Intrusion

Mitigation


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Passive Mitigation | Active Mitigation | Operation and Maintenance | New Buildings

Mitigation of vapor intrusion comprises the many approaches to lessen the severity of of vapor entry into buildings. One of the ways to mitigate vapor intrusion into buildings is to remediate the underlying sources of contaminants in soil or groundwater. However, this can take considerable time, so other mitigation methods to prevent human exposure may be needed. These methods involve eliminating the entry routes to the building, removing or reversing the force that drives the contaminants into the building, or providing a preferential pathway to divert contaminants away from the building (EPA, 2008). The following sections discuss the various types of mitigation methods.

A Citizen's Guide to Vapor Intrusion Mitigation Adobe PDF Logo
EPA 542-F-12-021, 2012.

The Citizen's Guide series summarize cleanup methods used at Superfund and other sites. Each two-page fact sheet answers six questions about the cleanup method: 1) What is it? 2) How does it work? 3) How long will it take? 4) Is it safe? 5) How might it affect me? and 6) Why use it?

Vapor Intrusion Mitigation in Existing Buildings Fact Sheet Adobe PDF Logo
Navy Alternative Restoration Technology Team, NFESC, 6 pp, 2011.

This fact sheet provides a brief overview of methods that can be used to mitigate VI in existing buildings along with important considerations for selecting and designing an appropriate mitigation system for your site. The methods discussed include sub-slab depressurization, submembrane depressurization, building pressurization, and indoor air treatment. More detailed information on VI mitigation systems for existing buildings can be found in the resources listed at the end of this fact sheet.

Passive Mitigation

Passive mitigation methods to vapor intrusion prevent vapor intrusion by blocking entry of vapors
through the building foundation.

Sealing Cracks and Openings in the Building Foundation

Cracks and openings in the building foundation are the primary routes of vapor entry. Sealing cracks in the floors and walls as well as gaps around utility conduits, sumps, and elevator shafts is an important first step in preventing vapor intrusion. Sealing cracks and gaps may also be necessary when used with other mitigation strategies, such as sub-slab depressurization to ensure system efficiency.

Indoor Air Vapor Intrusion Mitigation Approaches Adobe PDF Logo
EPA/600/R-08-115, U.S. Environmental Protection Agency, 49 pp, October 2008.

Engineering Issue Paper explains the range of vapor intrusion mitigation technologies available. It also provides information on selecting appropriate technologies in consultation with qualified engineering and risk management professionals. It provides information for making appropriate selections and evaluating the recommendations of mitigation contractors and engineers.

Vapor Intrusion Pathway: A Practical GuideAdobe PDF Logo
Interstate Technology & Regulatory Council, 172 pp, January 2007.

Step 13 of ITRC’s 13-step approach to evaluating vapor intrusion is deciding whether or not mitigation is warranted. The
guidance goes on to provide summarizes several approaches including passive barriers, passive venting, sub-slab and
sub-membrane depressurization, sub-slab and building pressurization, indoor air treatment, and sealing the building envelope.


Liquid Bood Vapor Barrier
Zoom In

Installation of geomembrane
(Liquid Boot®) as a vapor barrier

Passive Barriers

Passive barriers are materials or structures (commonly a sheet of geomembrane or polyethylene plastic) installed below a building to block the entry of vapors. Barriers are usually installed during construction, but they can be installed in existing buildings with a crawl space, if needed.

Indoor Air Vapor Intrusion Mitigation Approaches Adobe PDF Logo
EPA/600/R-08-115, U.S. Environmental Protection Agency, 49 pp, October 2008.

Engineering Issue Paper explains the range of vapor intrusion mitigation technologies available. It also provides information on selecting appropriate technologies in consultation with qualified engineering and risk management professionals. It provides information for making appropriate selections and evaluating the recommendations of mitigation contractors and engineers.

Vapor Intrusion Pathway: A Practical Guide Adobe PDF Logo
Interstate Technology & Regulatory Council, 172 pp, January 2007.

Step 13 of ITRC’s 13-step approach to evaluating vapor intrusion is deciding whether or not mitigation is warranted. The guidance goes on to provide summarizes several approaches including passive barriers, passive venting, sub-slab and sub-membrane depressurization, sub-slab and building pressurization, indoor air treatment, and sealing the building envelope.

Adobe PDF LogoAccelerating the Redevelopment of a Vapor-Impacted Property Based On Data-Informed Verification of Vapor Barrier Technology
Lowe, John, Jessica Raphael, Loren Lund, and Robert Casselberry, in Proceedings of the Air & Waste Management Association’s Vapor Intrusion 2009 Conference
11 pp, 2009.

Describes a cold-spray applied vapor barrier equipped with an overlying monitoring layer that was installed as part of an
integrated commercial redevelopment, demonstrating protection of human health without the need for indoor air sampling.

ASTM E2435 - 05(2010)e1 Standard Guide for Application of Engineering Controls to Facilitate Use or Redevelopment of Chemical-Affected Properties

Provides a general overview of the procedures for evaluating and selecting engineering controls for use in property development or reuse. Intended for use at properties that are presently developed or proposed for development but have contaminated soil, groundwater, air, or other environmental media, that may pose a risk to human health.

Adobe PDF LogoVapor Intrusion/Indoor Air Guidance Survey
Massachusetts Department of Environmental Protection, 215 pp, July 2010.

Presents the results of a survey of state and agency guidance and of vapor barrier research.

Sustainable Vapor Intrusion Controls - Designing an Effective Passive SystemAdobe PDF Logo
Ash, James, Mark Ensign, and William Simons, in Proceedings of the Air & Waste Management Association’s Vapor Intrusion 2010 Conference, 8 pp, 2010.

Describes some of the conditions and design requirements for implementing successful passive vapor intrusion control systems (generally consisting of vapor barrier membranes combined with ventilation piping) at both residential and commercial buildings.Also presents monitoring data collected at residential properties and an office building where passive systems were successfully implemented.


Gravel Base and Passive Ventilation Pipes
Zoom In

Gravel Base and Passive Ventilation Pipes

Passive Venting

Passive venting systems are often combined with passive barriers to safeguard against vapor intrusion. Typically, perforated collection pipes are installed in a layer of permeable sand or gravel to direct vapors to the edges of the foundation. Passive systems rely on wind currents to induce vapor flow through the pipes, so they can be ineffective at removing vapors on days that aren’t windy.

Indoor Air Vapor Intrusion Mitigation Approaches Adobe PDF Logo
EPA/600/R-08-115, U.S. Environmental Protection Agency, 49 pp, October 2008.

Engineering Issue Paper explains the range of vapor intrusion mitigation technologies available. It also provides information on selecting appropriate technologies in consultation with qualified engineering and risk management professionals. It provides information for making appropriate selections and evaluating the recommendations of mitigation contractors and engineers.

Vapor Intrusion Pathway: A Practical Guide Adobe PDF Logo
Interstate Technology & Regulatory Council, 172 pp, January 2007.

Step 13 of ITRC’s 13-step approach to evaluating vapor intrusion is deciding whether or not mitigation is warranted. The guidance goes on to provide summarizes several approaches including passive barriers, passive venting, sub-slab and sub-membrane depressurization, sub-slab and building pressurization, indoor air treatment, and sealing the building envelope.

Sustainable Vapor Intrusion Controls - Designing an Effective Passive System Adobe PDF Logo
Ash, James, Mark Ensign, and William Simons, in Proceedings of the Air & Waste Management Association’s Vapor Intrusion 2010 Conference, 8 pp, 2010.

Describes some of the conditions and design requirements for implementing successful passive vapor intrusion control systems (generally consisting of vapor barrier membranes combined with ventilation piping) at both residential and commercial buildings.Also presents monitoring data collected at residential properties and an office building where passive systems were successfully implemented.

ASTM E2435 - 05(2010)e1 Standard Guide for Application of Engineering Controls to Facilitate Use
or Redevelopment of Chemical-Affected Properties

Provides a general overview of the procedures for evaluating and selecting engineering controls for use in property development or reuse. Intended for use at properties that are currently developed or proposed for development but have contaminated soil, groundwater, air, or other environmental media, that may pose a risk to human health.

Active Mitigation

Active approaches to mitigating vapor intrusion remove the driving force behind vapor migration, which is the higher pressure that exists in the sub-slab area relative to indoors. By lowering the pressure beneath the sub-slab or passive barrier or inducing a higher pressure in the building, vapor flow is neutralized or reversed.

Exhaust Pipe and Fan for Active Mitigation
Zoom In

Exhaust Pipe and Fan for Active Mitigation

Depressurization

There are several types of depressurization systems, including sub-slab depressurization and sub-membrane depressurization systems. In most instances, mitigation of residential structures requires a sub-slab depressurization system (Mosley, 2005), which can be installed in houses with basements or slab-on-grade construction. They are similar to passive venting systems, except that they include a fan to induce a level of sub-slab depressurization that compensates for the depressurization of the building.

Indoor Air Vapor Intrusion Mitigation Approaches Adobe PDF Logo
EPA/600/R-08-115, U.S. Environmental Protection Agency, 49 pp, October 2008

Engineering Issue Paper explains the range of vapor intrusion mitigation technologies available. It also provides information on selecting appropriate technologies in consultation with qualified engineering and risk management professionals. It provides information for making appropriate selections and evaluating the recommendations of mitigation contractors and engineers.

Vapor Intrusion Pathway: A Practical Guide Adobe PDF Logo
Interstate Technology & Regulatory Council, 172 pp, January 2007.

Step 13 of ITRC’s 13-step approach to evaluating vapor intrusion is deciding whether or not mitigation is warranted. The guidance goes on to provide summarizes several approaches including passive barriers, passive venting, sub-slab and sub-membrane depressurization, sub-slab and building pressurization, indoor air treatment, and sealing the building envelope.

Assessment of Mitigation Systems on Vapor Intrusion: Temporal Trends, Attenuation Factors, and Contaminant Migration Routes under Mitigated and Non-Mitigated ConditionsAdobe PDF Logo
Truesdale, R., C. Lutes, B. Cosky, B. Munoz, R. Norberg, H. Hayes, and B. Hartman.
EPA 600-R-13-241, 608 pp, 2015

In 2011, researchers began an investigation into the general principles of how vapors enter into a single residence study site, a highly instrumented pre-1920 residential duplex located in Indianapolis, Indiana. This report, the second in a series of reports based on that research, examines the efficiency of a subslab depressurization system to prevent and remove radon and VOCs with reference to (a) subsurface conditions that influence the movement of VOCs and radon into the home; (b) system effects on VOC and radon concentrations; and (c) the influence of a winter capping event on vapor movement into the home.

Subsurface Depressurization Systems, New Jersey Department of Environmental ProtectionAdobe PDF Logo
1 p, June 2005.

Fact sheet describes the two most common subsurface depressurization systems: the sub-slab depressurization system and the sub-membrane depressurization system.

Important Information about Vapor Mitigation Systems and Power Outages, New Jersey Department of Environmental ProtectionAdobe PDF Logo
1 p, November 2012.

Fact sheet describes actions to reduce exposure to organic vapors during a power outage for property owners with subsurface depressurization systems.

Adobe PDF LogoDesign, Effectiveness, and Reliability of Sub-Slab Depressurization Systems for Mitigation of Chlorinated Solvent Vapor Intrusion
Davild Folkes, presented in a series of EPA seminars on vapor intrusion at the roll-out of the 2002 draft OSWER guidance, 5 pp, 2002 and 2003.

Describes the design, installation, and performance of the Redfield Site sub-slab depressurization and sub-membrane depressurization systems, the modifications required in approximately 30% of the homes to achieve the State of Colorado interim action level for 1, 1-dichloroethene, and factors that may affect long-term system reliability.

Designing Commercial Sub-Slab Depressurization Systems Adobe PDF Logo
in 2002 International Radon Symposium Proceedings, March 2002, 9 pp.

Describes the design of a sub-slab depressurization system for an 18,000 square-foot school building in New Jersey and a classical
three-story, stone-faced building at Lehigh University in Pennsylvania.

Adobe PDF LogoOverview of Two Large-Scale Residential Sub-Slab Depressurization System Installation Programs
Lucas Hellerich, et al., in Proceedings of the Annual International Conference on Soils, Sediments, Water and Energy, 11(1), 21 pp, January 11, 2010.

Describes case studies of two large-scale residential sub-slab depressurization systems designed and installed to mitigate intrusion of soil gas that contained low levels of volatile organic compounds, into over 100 houses and several buildings in a multi-structure condominium complex.

Adobe PDF LogoPneumatic Testing, Mathematical Modeling and Flux Monitoring to Assess and Optimize the Performance and Establish Termination Criteria for Sub-Slab Depressurization Systems (PowerPoint presentation),
Todd McAlary, David Bertrand, Paul Nicholson, Sharon Wadley, Danielle Rowlands, Gordon Thrupp and Robert Ettinger, Geosyntec Consultants, Inc., Presented at the U.S. EPA workshop, "Addressing Regulatory Challenges in Vapor Intrusion: A State-of-the-Science Update Focusing on Chlorinated VOCs," held at the Association for Environmental Health and Sciences 21st Annual Meeting and West Coast Conference on Soils, Sediments, and Water - Workshop: Addressing Regulatory Challenges in Vapor Intrusion, San Diego, California, March 15, 2011

Adobe PDF LogoHigh Vacuum, High Airflow Blower Testing and Design for Soil Vapor Intrusion Mitigation in Commercial Buildings
Brodhead, William and Thomas Hatton in Proceedings of the Air & Waste Management Association’ Vapor Intrusion 2010 Conference, 22 pp, 2010.

Describes method used to design and optimize a soil vapor intrusion mitigation system for a medical center that
is heavily contaminated by benzene and chlorinated solvents. The system uses high-output radial blowers.

ASTM E2435 - 05(2010)e1 Standard Guide for Application of Engineering Controls to Facilitate Use or
Redevelopment of Chemical-Affected Properties

Provides a general overview of the procedures for evaluating and selecting engineering controls for use in property
development or reuse. Intended for use at properties that are presently developed or proposed for development but
have contaminated soil, groundwater, air, or other environmental media, that may pose a risk to human health.

Cupolex® Under-Slab Network
Zoom In

Installation of under-slab void network
for application of a sub-slab
depressurization system (Cupolex®)

The Cupolex® Vapor Intrusion SolutionAdobe PDF Logo
9 pp.

Describes a proprietary flooring system developed to provide an efficient under-slab void network for application of sub-slab depressurization to facilitate the dilution and dispersal of Vapors from beneath buildings. Demonstration Video

ASTM E1465 - 08a Standard Practice for Radon Control Options for the Design and Construction of New Low-Rise Residential Buildings

Lays out design details and construction methods for two depressurization radon control and reduction systems appropriate for use in new low-rise residential buildings.

Long Term Performance of Radon Mitigation SystemsAdobe PDF Logo
Prill, R. and W.J. Fisk, 7 pp, March 2002.

Examines the performance of 12 residential radon mitigation systems comprising active sub-slab ventilation,
basement over-pressurization, and crawlspace isolation and ventilation systems over a ten-year period.

Building Pressurization

Building pressurization involves adjusting the building’s heating, ventilation, and air-conditioning (HVAC) system or installing a new system to maintain a positive pressure indoors relative to the sub-slab area. This approach is more common for large commercial buildings and can be the most cost effective if the existing HVAC system already maintains a positive pressure (ITRC, 2007).

Vapor Intrusion Pathway: A Practical Guide Adobe PDF Logo
Interstate Technology & Regulatory Council, 172 pp, January 2007.

Step 13 of ITRC’s 13-step approach to evaluating vapor intrusion is deciding whether or not mitigation is warranted. The guidance goes on to provide summarizes several approaches including passive barriers, passive venting, sub-slab and sub-membrane depressurization, sub-slab and building pressurization, indoor air treatment, and sealing the building envelope.

HVAC Influence on Vapor Intrusion in Commercial and Industrial BuildingsAdobe PDF Logo
Shea, David, Claire Lund, and  Bradley Green, in Proceedings of the Air & Waste Management Association’s Vapor Intrusion 2010 Conference, 12 pp, 2010.

Presents an overview of common HVAC components and how they influence indoor air quality. Several case studies are presented describing the role of HVAC operations in vapor intrusion assessment and mitigation. Favorable and unfavorable effects of HVAC operations on vapor intrusion also are given.


Adobe PDF LogoVerification of Building Pressure Control as Conducted by GSI Environmental, Inc. for the Assessment of Vapor Intrusion: Environmental Technology Verification Report
MacGregor, I., M. Prier, D. Rhoda, A. Dindal, and J. McKernan.
ETV Advanced Monitoring Systems Center, 148 pp, Dec 2011

The building pressure-control technique was implemented in autumn 2010 at each of two buildings over the course of 3.5 days. The effectiveness of the method to support decision-making was evaluated through three different metrics. 1) Can building pressure be decreased, controlled, and subsequently elevated and controlled at each of the two buildings under induced negative and positive pressure (NP and PP) conditions, respectively? 2) Does inspection of the mass discharge of radon from subsurface sources show whether VI was enhanced under NP and reduced (or stopped) under PP? 3) How well does the technique allow calculation of the fractional contribution of VI for different concentrations of indoor COCs? While pressure control was achieved at both buildings, the magnitude of the induced pressure gradients varied, likely due to differences in building characteristics, such as HVAC systems.


Operation and Maintenance

Over time, breakdowns in the mitigation system can occur. Fans may need to be serviced, leaks may develop, or exhaust stacks may be damaged. When a system is installed, it should be understood by all stakeholders who will be responsible for operation and maintenance (O&M): e.g., the building owner or lessee, developer, or overseeing regulatory agency. Also, it is a good idea to determine how long the system may need to operate to meet treatment objectives: e.g., until the groundwater plume is treated, until contaminant concentrations are no longer detected in indoor air, or as long as the building is occupied.

Long Term Performance of Radon Mitigation Systems Adobe PDF Logo
Prill, R. and W.J. Fisk, 7 pp, March 2002.

Examines the performance of 12 residential radon mitigation systems comprising active sub-slab ventilation, basement
over-pressurization, and crawlspace isolation and ventilation systems over a ten-year period.

Vapor Intrusion Pathway: A Practical GuideAdobe PDF Logo
Interstate Technology & Regulatory Council, 172 pp, January 2007.

Step 13 of ITRC’s 13-step approach to evaluating vapor intrusion is deciding whether or not mitigation is warranted. The guidance goes on to provide summarizes several approaches including passive barriers, passive venting, sub-slab and sub-membrane depressurization, sub-slab and building pressurization, indoor air treatment, and sealing the building envelope.

New Buildings

Adobe PDF LogoVapor Intrusion Mitigation in Construction of New Buildings Fact Sheet
Navy Alternative Restoration Technology Team, NFESC, 8 pp, Aug 2011

VI mitigation systems integrated during construction of new buildings are more cost effective, function better, and are less obtrusive than mitigation systems retrofitted into existing buildings. VI mitigation in new construction can include passive methods (e.g., vapor barriers, natural venting), active systems (e.g., sub-slab depressurization), or a combination of passive and active methods. A case study describes the VI mitigation features incorporated in the construction of a new supermarket-style building.

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