Using a Weight of Evidence Approach to Show on Indoor Air Impacts at Homes Located at a Site Impacted with Chlorinated VOCs
Raymond J. Cadorette, Shaw Environmental, Inc., Hopkinton, MA

Vapor Intrusion Attenuation Factors Based on Long-term Data
David J. Folkes, EnviroGroup Limited, Centennial, CO

The Use of Tracer Gas in Soil Vapor Intrusion Studies
Peter Reynolds, URS Corporation, Wayne, NJ

Emerging Approaches for Weighing the Significance of the Vapor Intrusion Pathway at Petroleum Hydrocarbon Sites  
Harley Hopkins, American Petroleum Institute (API), Washington, DC

A Practical Guideline to Vapor Intrusion: ITRC’s Perspective  
John Boyer, ITRC/NJDEP, Trenton, NJ  

Near-Building and Structure Sampling Results from Vapor Intrusion Sites in New York, Implications for Site Screening Approaches

William E. Wertz, New York State Department of Environmental Conservation, 625 Broadway, Albany NY 12233-7017, Tel: 518-402-9814, Email: wewertz@gw.dec.state.ny.us

Over the past several years, the New York State Department of Environmental Conservation, in partnership with the New York State Department of Health, have undertaken a comprehensive evaluation of the vapor intrusion pathway at remedial sites throughout the state. Investigations have taken place or are underway at more than 250 sites, and more than 70 sites have required installation of mitigation systems to address exposures associated with vapor intrusion.  Based on the information obtained from these sites, it is clear that spatial, and to a lesser degree temporal, variability in soil gas contaminant concentrations are significant factors that must be addressed in the site screening process.  At many sites, there are significant differences between the soil gas concentrations of samples obtained from probes near (< 100 feet) structures and from the neighboring sub-slab probes. Near-structure soil gas probe data often under-represent the concentrations of soil gas obtained from sub-slab structures at nearby structures.  Accordingly, New York State routinely includes structure sampling programs into almost all vapor intrusion investigations where even low-level (5 Fg/m³) concentrations of chlorinated VOCs are observed in soil gas samples. 

Vapor Intrusion Attenuation Factors Based on Long-term Data 

David J. Folkes, EnviroGroup Limited, 7009 S. Potomac Street, Suite 300,Centennial, CO 80112, Tel: 303-790-1340, Fax: 303-790-1347, Email: dfolkes@envirogroup.com
Eric J. Wannamaker, EnviroGroup Limited, 7009 S. Potomac Street, Suite 300,Centennial, CO 80112, Tel: 303-790-1340, Fax: 303-790-1347, Email: ewannamaker@envirogroup.com
Jeffrey P. Kurtz, EnviroGroup Limited, 7009 S. Potomac Street, Suite 300,Centennial, CO 80112, Tel: 303-790-1340, Fax: 303-790-1347, Email: jkurtz@envirogroup.com

Screening for vapor intrusion potential is likely to be required at a large number of sites in the future, due to federal or state requirements, real estate transactions, or voluntary cleanups.  At many sites, only groundwater data will be available in sufficient quantity to conduct initial screening.  Therefore, groundwater data will tend to drive the need for additional vapor intrusion investigations.  The current EPA subsurface vapor intrusion screening guidance (EPA 2002) assumes that soil vapor concentrations immediately above the water table are at equilibrium with groundwater concentrations and that indoor air concentrations in overlying buildings are 1000 times lower (an attenuation factor of 10-3), due to attenuation through the soil column and building shell.  According to EPA (2002), attenuation factors based on groundwater and indoor air measurements are less than 10-3 approximately 95% of the time.  Unfortunately, the resultant groundwater screening levels are often at or below federal drinking water standards (MCLs).  In most cases however, the data used to develop this attenuation factor were based on measurements of groundwater and indoor air at one point in time.  Groundwater and indoor air monitoring at a number of houses in Colorado over the past eight years has allowed comparison of attenuation factors based on 1,1-DCE at single points in time and on long-term averages.  These data indicate that single point measurements can significantly differ from long term average attenuation factors.  The upper bound attenuation factor based on short-term tests at several hundred homes was about 10-3, similar to the findings of the EPA studies.  However, short-term attenuation factors were observed to vary by one-half to one order of magnitude over time in homes where long-term monitoring was conducted.  Long-term attenuation factors were in the 10-5 to 10-7 range, with a 95 percentile of approximately 10-5.  Vapor intrusion screening levels based on long term average attenuation factors and groundwater concentrations may provide a more realistic approach to vapor intrusion screening in the future.  

Using a Weight of Evidence Approach to Show no Indoor Air Impacts at Homes Located at a Site Impacted with Chlorinated VOCs

Raymond J. Cadorette, BS in Bio-Resource Engineering, Shaw Environmental, Inc., 88C Elm Street, Hopkinton, MA  01748, Tel: 508-497-6102, Fax: 508-435-9641, Email: Raymond.Cadorette@shawgrp.com
Lawrence Nesbitt, PE, BS in Civil Engineering, MS Water Resources, MBA, Shaw Environmental, Inc., 88C Elm Street, Hopkinton, MA  01748, Tel: 508-497-6125, Fax: 508-435-9641, Email: Larry.Nesbitt@shawgrp.com

Although the risk assessment for the site showed there is no significant risk posed by chemicals from the site, a residential indoor air-testing program was completed at the request of local officials and residents.  The objectives of the sampling program were to determine if the site groundwater plume is a source of VOCs detected in indoor air samples, and if so, to (1) assess if the levels of VOCs present in indoor air were above published background concentrations and, (2) assess whether those VOCs pose a potential significant risk of harm to human health.

Shaw sampled indoor air in approximately 30 homes during the summer and again during the winter.  Using a weight of evidence approach, Shaw was able to show that the VOCs in indoor air had not come from the site, nor is there any significant risk to residents from the site.  Sampling and data evaluation in this indoor residential air assessment was completed in accordance with recently published state guidance.

The Use of Tracer Gas in Soil Vapor Intrusion Studies

Peter Reynolds, URS Corporation, 201 Willowbrook Boulevard, Wayne, NJ  07474-0290, Tel: 973-812-6834, Fax: 973-785-0023, Email: peter_reynolds@urscorp.com

There has been a rapid rise in the need for soil vapor intrusion (SVI) assessments to meet environmental compliance requirements regarding brownfields development and asset improvement. 

Our approach to SVI sub-slab testing for existing structure interiors incorporates a tracer gas monitoring technique that has proven to be very cost effective. This method allows for verification that the sample collected from beneath an impervious surface is truly isolated from the ambient air inside the building. Implementation of this method has met with the approval of New York regulators and is consistent with their Soil Vapor Intrusion Guidance, which was published in 2005.

An inert tracer gas is used to first blanket the surface of the slab and a gas tight seal is formed between atmosphere and the sub-slab sample targeting point, sometimes just inches below the ambient space. The sample point is isolated with a small enclosure that is then charged with the tracer gas until the concentration exceeds 90%. The isolated sampling point below grade is then purged and tested for the same tracer gas to measure the potential for sampling influence (or bias) from the overlying ambient space. Once it has been determined that the target sample is relatively free from bias (by a measured tracer gas concentration of 10% or less), sampling proceeds. The tracer gas blanket and sampling space are monitored throughout the sampling period to ensure that the potential for ambient air to migrate into the sampling zone is minimized. 

For sample collection, the events targeted VOCs by Method EPA TO-15. However, other data collection efforts using calibrated pumps and sampling media, such as EPA TO-11A for the measurement of Formaldehyde, also were used.

The reduced time and effort associated with these sampling techniques allow for expedited assessment of analytical data and early recognition of potential environmental risks associated with the purchase and improvement of real property.

Emerging Approaches for Weighing the Significance of the Vapor Intrusion Pathway at Petroleum Hydrocarbon Sites

Harley H. Hopkins, API, 1220 L Street NW, Washington, D.C. 20005, Tel: 202-682-8318, Email: hopkins@api.org

While it is increasingly recognized that the potential for subsurface petroleum vapors to migrate inside buildings is less for than chlorinated solvents, developing reliable site screening approaches remains a challenge.  The complexity arises from the difficulty in quantifying the significance of biodegradation and background sources of petroleum-derived compounds in indoor air.  Improving our understanding of which combinations of site characteristics are significant for petroleum vapor intrusion (e.g., foundation type, source strength, vertical and horizontal source location relative to a building, and petroleum type), may lead to a more useful screening approach.   Our goal is to identify the types of sites that truly need additional site-specific data collection before a decision can be made about the significance of the pathway.  Several promising approaches are emerging that should improve our ability to screen petroleum sites including:  3D vapor and oxygen transport modeling, vertical profiling of unsaturated zone hydrocarbon and oxygen soil gas concentrations, and the use of tracers and pressure measurements for assessing transport and attenuation across the foundation.  

A Practical Guideline to Vapor Intrusion: ITRC’s Perspective

John E. Boyer, New Jersey Department of Environmental Protection, 401 East State Street, P.O. Box 413, Trenton, New Jersey 08625-0413 Tel: 609-984-9751, Fax: 609-292-0848, Email:  john.boyer@dep.state.nj.us
Bill Morris, Kansas Department of Health and Environment, Bureau of Environmental Remediation, 1000 SW Jackson, Suite 410, Topeka, KS  66612-1367, Tel: 785-296-8425, Email: bmorris@kdhe.state.ks.us

The Interstate Technology & Regulatory Council (ITRC) formed a Vapor Intrusion Team in January 2004 to prepare guidance that would present a comprehensive national approach to the evaluation, investigation and remediation of VI sites. Once completed, the goal of the team is to reach concurrence with all 50 state environmental agencies and provide Internet and classroom training to state regulators, consultants and interested parties.

Working with a diverse group of state and federal regulators, environmental consultants, Department of Defense personnel, industry representatives, and community stakeholders, ITRC’s VI Team has conducted two regulatory surveys and prepared a series of guidance documents to meet that goal.

The ITRC approach is outlined in the companion documents, Vapor Intrusion Pathway: A Practical Guide and Vapor Intrusion Pathway: Investigative Approaches for Typical Scenarios.  Both guidance documents have recently completed external review and should be released by December 2006.

An overview of the vapor transport mechanisms involved in the VI pathway, as well as the complicating factors that influence the collection and interpretation of analytical data are discussed in the documents.  A basic framework for the preliminary assessment, investigation and mitigation of the VI pathway at a contaminated site is provided.  The investigation of six typical scenarios (e.g., gas station, dry cleaners, Brownfields) are presented with detailed discussions on workplan development, sampling, data interpretation, and technical rationale.

Since various states express a wide range of comfort about the data types that are acceptable for assessing a site, the ITRC approach is not prescriptive as to the specific investigative tools or technical methodology appropriate.  Rather, it is intended to assist the investigator in understanding the factors and techniques that may be used to assess the vapor intrusion pathway.  A comprehensive directory of mitigation methods is included with detailed information on passive and active building control remedies, institutional controls, ongoing monitoring and maintenance, sitewide approaches and closure.

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