Vapor Intrusion

Sample collection for chemical analysis is the primary way in which a CSM is augmented and refined with site-specific data. Sampling may be needed to refine the understanding of the source and extent of contamination, as well as possible receptors and risk levels. The use of real-time analysis can expedite the investigation of vapor intrusion at a site. Figure 2 shows EPA's Trace Atmospheric Gas Analyzer (TAGA) mobile lab deployed in the field. Other commercial available portable gas chromatographs/mass spectrometers also provide the same capabilities (EPA Region V, 2020). Sampling may also help evaluate the amount of contamination present beneath the floor or foundation or inside a particular building. Table G-5 of ITRC's 2014 Petroleum Vapor Intrusion guide provides a matrix of measurement approaches and their appropriateness for evaluating vapor intrusion in different circumstances. The investigation toolbox in Appendix G was developed for both petroleum and non-petroleum vapor intrusion assessments. Table G-6 evaluates the advantages/disadvantages of investigative strategies. The strategies discussed here include:

• Groundwater Sampling
• Soil Gas Sampling
• Bulk Soil Sampling
• Sub-Slab Sampling
• Conduit/Utilities Sampling
• Air Sampling
• Analytical Methods

Groundwater Sampling

Contaminated groundwater may serve as a source for vapor intrusion into commercial and residential buildings. It is important to identify which groundwater contaminants are most likely to partition into a vapor phase that could potentially migrate into overlying structures. Section 6.3.1 of the EPA's 2015 Vapor Intrusion Technical Guide contains recommendations for characterizing groundwater plumes so that representative vapor source concentrations can be determined. Characterizing water table concentrations is key. To that end, the EPA recommends that groundwater samples be obtained from wells with short, screened intervals that span the water table. For additional information on various groundwater sampling methods and their associated pros and cons, see the Interstate Technology & Regulatory Council (ITRC) 's 2014 Petroleum Vapor Intrusion: Fundamentals of Screening, Investigation and Mitigation, Table G-1 Groundwater Sampling Methods for Vapor Intrusion Investigations.

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Soil Gas Sampling

Soil gas samples are collected in the area of concern to determine the nature and extent of vapor contamination in the vadose zone. Figure 3 shows a soil gas probe being used to collect data near the foundation of a structure. Soil gas data can also help in the design and performance monitoring of soil vapor extraction systems. Soil gas surveys can employ either active2 or passive3 soil gas sampling techniques. Soil gas sampling methods are available from a variety of sources (e.g., EPA Region 5, 2020, ITRC 2014, and state-specific guidance). If vapor contamination is present, further characterization of nearby buildings might be warranted using approaches such as sub-slab soil gas and indoor air sampling.

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Bulk Soil Sampling

Bulk soil sampling is useful in delineating source areas of VOC contamination (nature and extent) and determining the gross mass of contamination present in a source area. However, it is problematic to use bulk soil sampling to assess the potential for vapor intrusion exposure from VOCs in undisturbed soil or residual soil contamination left in an excavation following a removal action. As described in EPA's Challenges in Bulk Soil Sampling and Analysis for Vapor Intrusion Screening of Soil, (2014), the challenges in using bulk soil samples for vapor intrusion exposure calculations include:

• Volatilization and degradation losses - Significant losses of VOCs can occur during collection of the bulk samples. Samples must be prepared and preserved quickly in the field to limit losses of VOCs. Preservatives, such as methanol, used to prevent volatilization and degradation of the sample are flammable and can be dangerous to transport. A non-field-preservation method uses sampling devices that minimize VOC loss by containing the soil sample in a sealed zero headspace chamber. The sample can be stored up to 48 hours before analysis.
• Sensitivity of analytical methods - The method detection limits (MDLs) for bulk soil analytical methods when methanol is used as a preservative are typically higher than the calculated soil screening levels for vapor intrusion. In addition, for some VOCs such as trichloroethylene (TCE) and tetrachloroethylene (PCE), which are common vapor intrusion concerns, the non-methanol preservative method still has MDLs above the screening levels for vapor intrusion.
• Heterogeneity of soil and contaminant distribution - Soil properties such as fraction of organic carbon, porosity and moisture content can exhibit significant heterogeneities (i.e., vary considerably both laterally and with depth at a site). The scale of the heterogeneities may also vary. Additionally, soil moisture may exhibit temporal variability. These variabilities pose challenges when trying to use VOC vapor concentrations from discrete soil samples to estimate large-scale average VOC concentrations.

Bulk sampling is useful for determining the nature and extent of contamination. Field headspace techniques can be employed on bulk soil samples to rapidly determine the presence and concentrations of VOCs with enough precision to identify areas for excavation/removal. Remaining contamination can then be addressed by subsurface remedies that will achieve concentrations below vapor intrusion concentrations of concern. Bulk sampling is unreliable for predicting whether VOC concentrations detected in the soil or groundwater will migrate as vapor into structures (EPA, 2014).

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Sub-Slab Sampling

In addition to collecting soil gas data from a potential vapor intrusion source, the investigator may want to assess the soil vapor directly beneath a building where there is a concern about indoor air quality. This is done by collecting sub-slab soil vapor samples. Sub-slab sampling is the collection of a soil vapor sample from beneath a building's slab foundation. Sub-slab sampling is typically employed when the CSM and existing data (e.g., groundwater or soil vapor) suggest that vapor intrusion through the foundation may be a concern. A sub-slab soil gas sample is obtained by coring or drilling through the slab to insert a probe (Figure 4). Placement of the probe is targeted to air spaces that have formed beneath the concrete over time or the pore space within the granular material placed below the slab during construction. Sub-slab data may be useful in determining whether the subsurface vapor migration pathway is complete and poses a potential health concern. Additional considerations regarding sub-slab soil gas sampling can be found in EPA's 2015 Vapor Intrusion Technical Guidance.

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Conduit/Utilities Sampling

As part of the vapor intrusion investigation, the site should be evaluated to identify the presence of utilities or conduits that may facilitate vapor transport across the site and potentially into buildings or structures that are serviced by the utilities. A search of public and facility records for as-built diagrams, construction specifications and/or locations of the utilities may be warranted (EPA, 2015).

As in the ESTCP Project ER-201505 report, the following sampling methods may be used to assess the contribution to vapor intrusion in buildings/structures via conduits and utility tunnels:

• Collect vapor samples from sewer or conduit - If the conduit or sewer has liquid in it, collect a vapor sample by lowering the collection device to within 1 foot of the bottom or the liquid in the conduit, whichever is shallower. Connect a small-diameter nylon tubing to a three-way valve to allow purging of the line and sample collection. After at least three line volumes of vapor are purged, a sample container can be attached for collection of a sample.
• Collect liquid samples from sewer or conduit - Liquid samples should be collected in the appropriate VOA vials provided by the analytical lab. The same sample protocols for handling groundwater samples apply to liquid samples from the sewer or conduit.
• Tracer Testing - Research conducted by McHugh, T., et al. (2017) at the EPA vapor intrusion research duplex in Indianapolis, Indiana, demonstrated that tracer testing could be used as a tool to determine whether conduits such as sewer lines are contributing to vapor intrusion into a structure.

Tracers such as perfluorocarbon4 tracers (PFTs) are deployed within the sewer or conduit as sources. Each source emits a different perfluorocarbon compound. Passive samplers are stationed within various locations of the structure to collect data for assessing if and when a particular perfluorocarbon compound (tracer) reaches the sampler. In this way, the vapor intrusion contribution can be "mapped" from different sources such as sewer lines, utility conduits, etc. Data from the tracer test, used in conjunction with sewer liquid and vapor samples, sub-slab vapor samples, indoor air samples and soil gas samples can determine whether sewer lines or other utilities act as conduits for intrusion of contaminant vapors into structures.

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Air Sampling

Air samples are collected to assess whether vapors are present in the building at levels that pose a health risk. Indoor air data can also be used to evaluate the performance of vapor mitigation systems. Interpreting indoor air sampling results can be complicated by indoor and outdoor air sources of VOCs unrelated to the subsurface contaminant source (see EPA, 2015 and EPA, 2011).

Sample collection methods include pressurized (active) and unpressurized (passive) evacuated canisters and active and passive sorbent samplers. Canisters provide the benefit of "whole air" samples (i.e., collection of the vapor phase itself), allowing multiple sub-samples and the ability to analyze for a wide variety of compounds. The canisters are typically left in place for a period of 8 hours in commercial settings and 24 hours in residences (EPA, 2015). Passive sorbent samplers provide the ability to collect time-integrated samples over longer periods, as recommended in EPA's Vapor Intrusion Technical Guidance, in part to reduce the likelihood of obtaining false-negative results (Nocetti, D., et al., 2019). Disadvantages of sorbent samplers include the need to pair the sorbent material with the chemicals of interest, and potentially being limited to only one analysis for each individual device. Additional information regarding indoor air sampling can be found in EPA's Vapor Intrusion Technical Guidance.

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Analytical Methods

Analytical methods used in vapor intrusion site assessment should be capable of achieving detection limits below applicable screening criteria such as the levels identified by EPA's Vapor Intrusion Screening Level Calculator. The calculator provides general risk-based target concentrations for groundwater, near source soil gas and sub-slab soil gas, and indoor air. Table G-5 of ITRC's 2014 Petroleum Vapor Intrusion guide provides a list of parameters and the appropriate associated analytical methods.

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Building design will impact the potential for vapor intrusion to be a complete pathway for human exposure and should be considered in developing and refining the CSM. Appendix C of ITRC's 2007 Vapor Intrusion Pathway: A Practical Guide provides a more detailed discussion of the various factors in building design that can affect the potential for vapor intrusion into buildings. These factors include but are not limited to:

• Building air exchange.
• The presence or absence of cracks, seams, gaps in basement floors, walls, or foundations.
• The presence or absence of openings for utilities in basement floors, walls, or foundations.
• Whether the building is constructed with a crawl space, basement or is built on a slab on grade.

In addition to building factors, recent research has shown that sanitary sewers, land drains, and utility tunnels can act as preferential pathways for vapor intrusion (e.g., Guo et al 2015, McHugh and Beckley 2018). Sites are typically at higher risk for sewer vapor intrusion if the sewer lines directly intersect subsurface VOC sources. Thus, sewer preferential pathways should be considered during development of the CSM and the investigation program.

Vapor intrusion investigation approaches continue to be developed. Ma et al (2020) summarizes a variety of conventional and innovative methods currently in use. These methods include the following:

High Purge Volume Sub-slab Sampling/Pneumatic Conductivity Testing

Sub-slab soil gas sampling is a common line of evidence in vapor intrusion investigations. However, spatial variability is common and can increase the risk of failing to identify elevated chemical concentrations beneath the building. To overcome this problem, high purge volume sampling can be done to spatially average the sub-slab concentrations and obtain an improved understanding of conditions beneath a given building(McAlary, et al., 2010).

This method can also be applied to support design of mitigation systems. It is analogous to pneumatic testing for soil vapor extraction system pilot tests. Application of suction and measuring the vacuum can be used for pneumatic conductivity testing of subsurface geologic layers. Data from pneumatic testing may be used to determine whether a laterally continuous soil layer acts as a barrier to upward soil vapor transport, or of a building's floor slab to optimize the design of sub-slab depressurization or venting systems.

Meteorological Monitoring

Weather conditions can influence both soil gas and indoor air concentrations of contaminants. Meteorological parameters that may affect soil gas and indoor air concentrations include (ITRC, 2007):

• Rainfall events - Vapor intrusion rates and concentrations of soil gas can be affected by precipitation. Significant rainfall events may skew data collected during or immediately after the event and, therefore, may not be representative of long-term conditions.
• High wind speed - Pressure differentials can be created around a structure during high wind events. This can cause an advective flow in shallow soil gas around and beneath the structure.
• Frozen ground or permafrost - When the ground is frozen, the flow of air into the vadose zone and/or the flow of soil gas out of the vadose zone may be restricted.
• Major storm events - A process known as barometric pumping can occur due to changes in barometric pressure creating movement in the near surface vadose zone.

Because weather can affect soil gas and indoor air concentrations, meteorological monitoring (and monitoring of building differential pressure) during sample collection can provide another line of evidence for interpretation of vapor intrusion investigation data.

Forensic Approaches

Because indoor sources of VOCs are ubiquitous, it can be difficult to distinguish whether VOCs found in indoor air samples are from indoor sources or the subsurface (i.e., vapor intrusion). Several innovative methods are now available to help differentiate the chemical profiles of subsurface sources (i.e., groundwater, soil gas) and indoor air samples. Forensic approaches include hydrocarbon fingerprinting and forensic analysis, CSIA (compound-specific isotope analysis), on-site chemical analysis, and the use of radon as a tracer (NAVFAC, 2013; Ma et al 2020).

Guo, Y., et al., 2015. Identification of Alternative Vapor Intrusion Pathways Using Controlled Pressure Testing, Soil Gas Monitoring, and Screening Model Calculations. Environmental Science & Technology, 49:22, p. 13472-13482, October 12.

Interstate Technology Regulatory Council (ITRC), 2014. Petroleum Vapor Intrusion: Fundamentals of Screening, Investigation, and Management. 388 pp, October.

Interstate Technology Regulatory Council (ITRC), 2007. Vapor Intrusion Pathway: A Practical Guideline. 172 pp, January.

Ma, J., et al., 2020. Vapor Intrusion Investigations and Decision-Making: A Critical Review. Environmental Science & Technology, 54:12, p. 7050-7069, May 8.

McAlary, T., et al., 2010. High Purge Volume Sampling-A New Paradigm for Subslab Soil Gas Monitoring. Groundwater Monitoring & Remediation, 30:2, p. 73-85, May 12.

McHugh, T. et al., 2017. Evidence of a Sewer Vapor Transport Pathway at the USEPA Vapor Intrusion Research Duplex. BLN-113837-2017-JA. 18 pp, April.

McHugh, T. and L. Beckley, 2018. Sewers and Utility Tunnels as Preferential Pathways for Volatile Organic Compound Migration into Buildings: Risk Factors and Investigation Protocol. ESTCP Project ER-201505. 791 pp, November.

Naval Facilities Engineering Command (NAVFAC), 2013. Innovative Vapor Intrusion Site Characterization Methods. 8 pp, February.

Nocetti, D., et al., 2019. Sampling Strategies in the Assessment of Long-term Exposures to Toxic Substances in Air. Remediation Journal, 30:1, p. 5-13, December.

U.S. EPA Region V, 2020. Vapor Intrusion Handbook. Superfund and Emergency Management Division. 150 pp, March.

U.S. EPA, 2015. OSWER Technical Guide for Assessing and Mitigating the Vapor Intrusion Pathway from Subsurface Vapor Sources to Indoor Air. OSWER Publication 9200.2-154. 267 pp, June.

U.S. EPA, 2014. Challenges in Bulk Soil Sampling and Analysis for Vapor Intrusion Screening of Soil. Office of Research and Development. EPA/600/R-14-277. 14 pp, December.

U.S. EPA, 2011. Background Indoor Air Concentrations of Volatile Organic Compounds in North American Residences (1990-2005): A Compilation of Statistics for Assessing Vapor Intrusion. EPA 530-R-10-001. EPA, 67 pp, June 2011.

Search:

Filter Resources By: All Groundwater Sampling Soil Gas Sampling (Passive/Active) Sub-Slab Soil Gas Sampling Indoor Air Sampling Analytical Methods Predictive Modeling Building Design High Purge Volume Sub-slab Sampling/Pneumatic Conductivity Testing Meteorological Monitoring Forensic Approaches

Title	Date	Authors/Sources	Description	Groundwater Sampling Soil Gas Sampling (Passive/Active) Sub-Slab Soil Gas Sampling Indoor Air Sampling Analytical Methods Predictive Modeling Building Design High Purge Volume Sub-slab Sampling/Pneumatic Conductivity Testing Meteorological Monitoring Forensic Approaches
Underground Storage Tanks (USTs) Petroleum Vapor Intrusion	2021	U.S. Environmental Protection Agency, February 1, 2021.	EPA website provides an overview of petroleum vapor intrusion sampling and characterization, modeling, mitigation and remediation, and guidance.	Groundwater Sampling Soil Gas Sampling (Passive/Active) Sub-Slab Soil Gas Sampling Indoor Air Sampling Analytical Methods Predictive Modeling Building Design Meteorological Monitoring Forensic Approaches
Vapor Intrusion Investigations and Decision-Making: A Critical Review	2020	Jie Ma, Thomas McHugh, Lila Beckley, Matthew Lahvis, George DeVaull, and Lin Jiang, Environmental Science & Technology 2020 54 (12), 7050-7069, DOI: 10.1021/acs.est.0c00225.	Paper provides a detailed review of the vapor intrusion conceptual site model including biological and hydrogeologic factors that may affect the potential for vapor intrusion. Key elements to vapor intrusion characterization are summarized and a review of innovative investigation tools is provided.	Soil Gas Sampling (Passive/Active) Sub-Slab Soil Gas Sampling Indoor Air Sampling Analytical Methods Predictive Modeling Building Design High Purge Volume Sub-slab Sampling/Pneumatic Conductivity Testing Meteorological Monitoring Forensic Approaches
Passive Sampling for Vapor Intrusion: Let Diffusion Do the Work for You!	2020	Pautler, B., H. Hayes, and T. McAlary. Midwestern States Environmental Consultants Association Virtual Environmental Conference, 2-3 and 9-10 December, 68 minutes, 2020.	Webinar discusses passive sampling for soil vapor, indoor air, and outdoor air to support subsurface vapor intrusion to indoor air assessments. The presentation includes theoretical considerations for sampler selection, sorbent selection, sample duration, and uptake rate verification; laboratory considerations for high-quality data; a patented method to quantify soil vapor concentration using the Waterloo Membrane Samplerâ„¢; and benefits relative to conventional summa canister/TO-15 methods of sampling and analysis.	Soil Gas Sampling (Passive/Active) Indoor Air Sampling Analytical Methods
Vapor Intrusion Handbook	2020	U.S. Environmental Protection Agency, 150 pp. March 2020.	This handbook was developed for On-Scene Coordinators and Remedial Project Managers in the EPA's Superfund and Emergency Management Division. The document focuses on hazardous substances other than petroleum hydrocarbons. It provides an overview of vapor intrusion, development of a conceptual site model, sampling strategies and data quality objectives and mitigation. It includes a discussion regarding community engagement in the assessment and remedial decision-making process.	Groundwater Sampling Soil Gas Sampling (Passive/Active) Sub-Slab Soil Gas Sampling Indoor Air Sampling Analytical Methods Building Design
Vapor Intrusion Mitigation Model: VIM Model V2.2	2020	McAlary, T., ESTCP Project ER-201322, Model/Software, 2020.	This spreadsheet tool was developed to help users: 1) interpret the results of sub-slab venting pilot tests, 2) calculate building-specific attenuation factors from flow and vacuum data, 3) assess the mass removal rate of a vapor mitigation system, and 4) interpret high volume sampling testing programs. Stepwise instructions to use the spreadsheet are provided.	Predictive Modeling
Demonstration Of A Long-Term Sampling And Novel Analysis Approach For Distinguishing Sources Of Volatile Organic Compounds In Indoor Air	2020	Rossner, A., ESTCP Project ER-201504, 16 pp, 2020.	The recently commercialized Aura™ capillary canister sampling method captures both canisters and sorbent samplers' advantages without their limitation by allowing for longer-term (1-3 weeks) sample collection and characterization of average VOCs in buildings at risk for vapor intrusion. The approach is robust, comparable in cost or is less expensive than current methods, allows for long-term sample collection, and requires one sample to capture the full range of analytes and concentrations of interest. Sampling does not require a power source, and analysis does not require solvent desorption.	Indoor Air Sampling
Vapor Intrusion: Modeling Tools and Cost Effective Mitigation	2019	Suuberg, E. and T. McAlary. | SERDP & ESTCP Webinar Series, Webinar #93, July 2019.	SERDP and ESTCP sponsored two presentations on new vapor intrusion modeling projects. The first examined the factors responsible for reports of large, several-order-of-magnitude variations in indoor air contaminant concentrations resulting from vapor intrusion processes. A case study of the Arizona State University site adjacent to Hill AFB was presented where modeling was used to characterize VI preferential pathways. The second presentation demonstrated new tools to reduce the cost of mitigating VOC vapor and radon intrusion to buildings. This research demonstrated several new ways to assess the radius of influence of soil gas extraction wells, including vacuum, velocity, travel time, vertical flow across the floor slab, and mass removal rates to design, operate and maintain optimal systems. A summary of the testing methods and four case studies were provided.	Predictive Modeling
Key Design Elements of Building Pressure Cycling for Evaluating Vapor Intrusion - A Literature Review	2019	Schumacher, B., John H Zimmerman, C. Lutes, R. Truesdale, AND C. Holton. Key Design Elements of Building Pressure Cycling for Evaluating Vapor Intrusion—A Literature Review. Groundwater Monitoring & Remediation. Wiley-Blackwell Publishing, Hoboken, NJ, 39(1):66-72, (2019).	Building pressure cycling is a tool used to distinguish between the contribution of subslab vapor and indoor sources of vapor intrusion. Protocols and outcomes from applications of the technology are reviewed in this paper. Lessons learned, testing protocols and research gaps are discussed.	Building Design
Sewer and Utility Tunnels as Preferential Pathways for Volatile Organic Compound Migration into Buildings: Risk Factors and Investigation Protocol	2018	McHugh, T., L. Beckley. ESTCP Project ER-201505, 793 pp, November 2018.	Report on investigation of sewer/utility tunnel vapor intrusion as a pathway in the conceptual site model for vapor intrusion. Risk factors and investigation protocols were identified. The project was divided into three tasks: Task 1 included field demonstrations of investigation protocols, Task 2 refined and validated the protocols based on the results of Task 1, Task 3 incorporated the results of Task 1 and 2 into the development of the conceptual site model and evaluation of risk factors.	Sub-Slab Soil Gas Sampling
Use of Tracers, Surrogates, and Indicator Parameters in Vapor Intrusion Assessment, Fact Sheet Update No. 005	2017	Tri-Service Environmental Risk Assessment Workgroup. 13 pp. September 2017.	Fact sheet suggests that VI assessments can be improved using tracers, surrogates, and indicator parameters. Tracers are substances that migrate similarly to the VOCs of interest for VI. Indicators are parameters or variables that are associated with the potential for VOC exposures through VI. Surrogates are variables with a quantitative relationship to the target VOCs for a VI study, sufficient to be useful as a substitute for directly measuring the target compounds.	Sub-Slab Soil Gas Sampling
EPA Spreadsheet for Modeling Subsurface Vapor Intrusion	2017	U.S. Environmental Protection Agency, September 2017.	Spreadsheet tool that implements the steady-state solution to vapor transport described by Johnson and Ettinger in 1991.	Predictive Modeling
Use of Building Pressure Cycling in Vapor Intrusion Assessment	2017	Department of Defense, Vapor Intrusion Handbook Fact Sheet Update No:004, August 2017.	Building pressure cycling (BPC) offers an alternative approach to the methods for indoor air sampling and determining the influence of background sources described in the Handbook.	Building Design
High Volume Soil Gas Sampling for Vapor Intrusion Assessment, Fact Sheet Update No. 003	2017	Tri-Service Environmental Risk Assessment Workgroup. 14 pp. February 2017.	This fact sheet summarizes high volume sampling as a method for assessing vapor concentrations and distributions in the subsurface, and is particularly well suited to sub-slab soil vapor sampling as part of a VI assessment.	Sub-Slab Soil Gas Sampling
Passive Sampling for Vapor Intrusion Assessment, Fact Sheet Update No. 001	2017	Tri-Service Environmental Risk Assessment Workgroup. 7 pp. Revised February 2017.	This fact sheet is intended to provide a high level overview and offer reference to resources that detail the application and analysis of passive sampling for VI.	Soil Gas Sampling (Passive/Active) Sub-Slab Soil Gas Sampling Indoor Air Sampling
Real-Time Monitoring for Vapor Intrusion Assessment, Fact Sheet Update No. 002	2017	Tri-Service Environmental Risk Assessment Workgroup. 9 pp. February 2017.	This fact sheet summarizes the rationale for using real-time monitoring in VI investigations as well as potential advantages and limitations.	Soil Gas Sampling (Passive/Active) Sub-Slab Soil Gas Sampling Indoor Air Sampling
Petroleum Vapor Intrusion Modeling Assessment with PVIScreen	2016	U.S. EPA, National Risk Management Research Laboratory, Ada, OK. EPA 600-R-16-175, 53 pp, August 2016.	To better understand the behavior of petroleum compounds, the PVIScreen model was developed that applies the theory developed for the BioVapor model to a lens of petroleum hydrocarbons in the subsurface that is capable of acting as a source of petroleum vapors. The PVIScreen model automatically conducts an uncertainty analysis using Monte Carlo simulations and is intended to make uncertainty analysis practical for application at petroleum vapor intrusion sites. The model can be run in either a batch mode, using Microsoft Excel files for both input and model outputs, and an interactive mode using a graphical user interface. Each of these is described, along with required inputs, example problems and the theoretical background of the model. Model simulations agree with an EPA-sponsored analysis of field data that illustrate and document the attenuation of concentrations of petroleum compounds in soil gas with distance above the source of the vapors.	Predictive Modeling
Integrated Field-Scale, Lab-Scale, and Modeling Studies for Improving Our Ability to Assess the Groundwater to Indoor Air Pathway at Chlorinated Solvent-Impacted Groundwater Sites	2016	Johnson, P.C., C. Holton, Y. Guo, P. Dahlen, H. Luo, K. Gorder, E. Dettenmaier, and R.E. Hinchee. SERDP Project ER-1686, 248 pp, 2016.	This project was conducted mainly at a house overlying a dilute chlorinated hydrocarbon (TCE) groundwater plume. The house was outfitted with sensors and automated systems to facilitate monitoring of indoor air and ambient and building conditions as well as groundwater and soil gas. Monitoring was conducted under both natural and controlled building conditions for about 2.5 yr, and both TCE and radon were quantified in indoor air and soil gas. Two recurring behaviors were observed with the indoor air data. The temporal behavior prevalent in fall, winter, and spring involved time-varying impacts intermixed with sporadic periods of inactivity. In summer, VI showed long periods of inactivity with sporadic VI impacts.	Predictive Modeling
Vapor Intrusion Estimation Tool for Unsaturated-Zone Contaminant Sources: User's Guide	2016	Johnson, C.D., M.J. Truex, M. Oostrom, K.C. Carroll, and A.K. Rice. ESTCP Project ER-201125, 50 pp, 2016	This guide presents a tool for estimating vapor intrusion into buildings from unsaturated (vadose) zone contaminant sources. The tool builds on and is related to guidance for evaluation of SVE performance relative to the impact of a vadose zone source on groundwater concentrations. This user guide is available with several tools for estimating vapor intrusion at the bottom of the project web page.	Predictive Modeling
Vapor Intrusion Screening Level (VISL) Calculator	2015	U.S. EPA Office of Superfund Remediation and Technology Innovation (OSRTI).	The U.S. EPA Office of Superfund Remediation and Technology Innovation developed a tool that: (1) lists chemicals considered to be volatile and sufficiently toxic through the inhalation pathway; and (2) provides VISLs for groundwater, soil gas and indoor air, which are generally recommended, media-specific, risk-based screening-level concentrations. The primary purpose of the VISL calculator is to assist Superfund site managers and risk assessors in determining, based on an initial comparison of site data against the VISLs, whether chemicals found in groundwater or soil gas can pose a significant risk through vapor intrusion and, if so, whether a site-specific vapor intrusion investigation is warranted. Other Agency cleanup programs may also find it helpful to consider the VISLs for their own specific needs.	Predictive Modeling
Identification of Alternative Vapor Intrusion Pathways Using Controlled Pressure Testing, Soil Gas Monitoring, and Screening Model Calculations	2015	Yuanming Guo, Chase Holton, Hong Luo, Paul Dahlen, Kyle Gorder, Erik Dettenmaier, and Paul C. Johnson, Environmental Science & Technology 2015 49 (22), 13472-13482, DOI: 10.1021/acs.est.5b03564.	Alternative vapor intrusion pathways such as neighborhood sewers, land drains, and other major underground piping can be significant contributors to vapor intrusion into buildings, even those beyond the footprint of the soil and groundwater contamination. Controlled-pressure-method testing (CPM), soil gas sampling and screening level emissions calculations were used to identify alternate vapor intrusion pathways that might have been overlooked using conventional sampling methods.	Groundwater Sampling Soil Gas Sampling (Passive/Active) Indoor Air Sampling Analytical Methods
NAVFAC Technical Memorandum on Vapor Intrusion Passive Sampling	2015	Dawson, H., T. McAlary, and H. Groenevelt. NAVFAC Technical Memorandum TM-NAVFAC EXWC-EV-1503, 20 pp, 2015.	This technical memorandum describes the basics of passive sampler theory and design, available types of passive samplers, advantages and limitations of passive samplers, and important considerations when implementing a passive sampling program. Results from two vapor intrusion case studies at DoD sites are highlighted.	Soil Gas Sampling (Passive/Active) Sub-Slab Soil Gas Sampling Indoor Air Sampling
OSWER Technical Guide for Assessing and Mitigating the Vapor Intrusion Pathway from Subsurface Vapor Sources to Indoor Air	2015	U.S. Environmental Protection Agency, 214 pp, June 2015.	This Technical Guidance presents current technical recommendations of the EPA based on our current understanding of vapor intrusion into indoor air from subsurface vapor sources. One of its main purposes is to promote national consistency in assessing the vapor intrusion pathway. At the same time, it provides a flexible science-based approach to assessment that accommodates the different circumstances (e.g., stage of the cleanup process) in which vapor intrusion is first considered at a site and differences among pertinent EPA programs.	Groundwater Sampling, Soil Gas Sampling (Passive/Active), Sub-Slab Soil Gas Sampling, Indoor Air Sampling, Analytical Methods, Predictive Modeling, Building Design, Meteorological Monitoring, Forensic Approaches,
Petroleum Vapor Intrusion: Fundamentals of Screening, Investigation and Management	2014	Interstate Technology & Regulatory Council, 388 pp, October 2014.	A reference document designed to support the screening, investigation, and management of petroleum vapor intrusion (PVI) sites that is protective of human health. The document builds off of the 2007 Vapor Intrusion Pathway: A Practical Guideline (VI-1) which addressed both PVI sites and sites with chlorinated volatile organic compounds.	Groundwater Sampling Soil Gas Sampling (Passive/Active) Sub-Slab Soil Gas Sampling Indoor Air Sampling Analytical Methods Predictive Modeling Building Design High Purge Volume Sub-slab Sampling/Pneumatic Conductivity Testing Meteorological Monitoring Forensic Approaches
Development of More Cost-Effective Methods for Long-Term Monitoring of Soil Vapor Intrusion to Indoor Air Using Quantitative Passive Diffusive-Adsorptive Sampling	2014	T. McAlary, 358 pp, July 2014.	Five passive samplers — the SKC Ultra and Ultra II, Radiello®, Waterloo Membrane Sampler, Automated Thermal Desorption tubes, and 3M OVM 3500 — were tested in lab and field conditions for VOCs (e.g., chlorinated ethenes, ethanes, and methanes, and aromatic and aliphatic hydrocarbons). All provided data that met the success criteria under some or most conditions, and most provided highly reproducible results throughout the demonstrations at costs comparable to or lower than monitoring with conventional methods.	Soil Gas Sampling (Passive/Active) Indoor Air Sampling
Vapor Intrusion from Entrapped NAPL Sources and Groundwater Plumes: Process Understanding and Improved Modeling Tools for Pathway Assessment	2014	Illangasekare, T., B. Petri, R. Fucik, C. Sauck, L. Shannon, T. Sakaki, K. Smits, A. Cihan, J. Christ, P. Schulte, B. Putman, and Y. Li. SERDP Project ER-1687, 206 pp, 2014.	Mechanisms controlling vapor generation and subsequent migration through the subsurface in naturally heterogeneous subsurface under different physical and climatic conditions were investigated using lab and modeling studies alongside the development of improved modeling tools. Dynamic and complex subsurface vapor pathways sometimes contribute to counterintuitive cause-effect relationships. Infiltration affects vapor signals in indoor air, with the time scales and the strength of the vapor signals depending on the interplay of the intensity, duration of rainfall, and subsurface heterogeneity. Water table fluctuation imparts very complex transport behavior within the capillary fringe, which has significant effects on vapor loading from the groundwater plumes. Trapped sources in the unsaturated zone are capable of loading significant mass into the unsaturated zone, but the loading rate is a strong function of the moisture distribution in the vicinity of the source. Indoor sampling strategies need to factor in the transients associated with climate and weather.	Predictive Modeling
User's Guide for CSIA Protocol	2014	Beckley, L., T. McHugh, T. Kuder, and P. Philip. ESTCP Project ER-201025, 16 pp, 2014.	This document i) describes the applicability of CSIA for vapor intrusion investigations (Section 2.0), ii) provides a step-by-step procedure for sample collection (Section 3.0), and iii) includes guidelines for data interpretation (Section 4.0). Additional background information on this investigation approach is available in the ESTCP Project ER-201025 Final Report (GSI, 2013a).	Forensic Approaches
Passive Samplers for Investigations of Air Quality: Method Description, Implementation, and Comparison to Alternative Sampling Methods	2014	U.S. EPA, Engineering Technical Support Center. EPA 600-R-14-434, 44 pp, 2014.	This paper covers the basics of passive sampler design and compares passive samplers to conventional methods of air sampling; discusses considerations for implementing a passive sampling program; and addresses field sampling and sample analysis considerations to ensure adequate data quality and supportable interpretations of the passive sample data. The reader is expected to have a basic technical background on the VI exposure pathway and the use and interpretation of indoor air sampling data.	Soil Gas Sampling (Passive/Active) Sub-Slab Soil Gas Sampling Indoor Air Sampling
Innovative Vapor Intrusion Site Characterization Methods	2013	TDS-NAVFAC EXWC-EV-1301, 8 pp, 2013.	This fact sheet provides an overview of the following emerging and innovative methods for the characterization of indoor air at potential vapor intrusion sites: passive sampling, use of a portable gas chromatography/mass spectrometry instrument, use of building pressure control techniques, hydrocarbon fingerprinting, compound-specific isotope analysis, and radon sampling. Three brief case studies are included.	Sub-Slab Soil Gas Sampling Indoor Air Sampling Analytical Methods Building Design
Conceptual Model Scenarios for the Vapor Intrusion Pathway	2012	Abreu, L. and H. Schuver. EPA 530-R-10-003, 154 pp, 2012.	The simulation results presented in this document illustrate how different site and building conditions may influence both the distribution of VOCs in the subsurface and the indoor air quality of the structures in the vicinity of a soil or groundwater VOC source. This information can help practitioners develop more accurate conceptual site models about soil and vapor intrusion, design better sampling plans, and better interpret the results of site investigations.	Predictive Modeling Building Design
Vapor Intrusion Database: Evaluation and Characterization of Attenuation Factors for Chlorinated Volatile Organic Compounds and Residential Buildings	2012	Dawson, H.E. and R.B. Kapuscinski. EPA 530-R-10-002, 188 pp, 2012.	This report provides updated information about the design, structure, and content of EPA's vapor intrusion databases, which supersedes EPA's 2008 preliminary report on the database. Technical information is presented about sites in the United States that have been investigated for vapor intrusion. The primary focus is the evaluation of concentrations of chlorinated VOC's in and beneath residential buildings based on EPA's vapor intrusion data as of 2010. This report was peer reviewed under a different working title: U.S. EPA's Vapor Intrusion Database: Preliminary Evaluation of Attenuation Factors.	Building Design
Simulation Program i-SVOC User's Guide	2012	Guo, Z. EPA 600-R-13-212, 92 pp, 2013 .	The i-SVOC simulation program estimates the emissions, transport, and sorption of semivolatile organic compounds in the indoor environment as functions of time when a series of initial conditions is given. This program implements a framework for dynamic modeling of indoor SVOCs and covers six types of indoor compartments: air (gas phase), air (particle phase), sources, sinks (i.e., sorption by interior surfaces), contaminant barriers, and settled dust. Potential applications of this program include (1) use as a stand-alone simulation program to obtain information that the current equilibrium models cannot provide, including evaluation of the effectiveness of pollution mitigation methods such as variable ventilation rates, source removal, and source encapsulation; (2) reducing the uncertainties in the existing multimedia models; and (3) use as a front-end component for stochastic exposure models to provide information about the SVOC distribution in indoor media in the absence of experimental data. This program is intended for advanced users who are involved in and familiar with indoor environmental quality modeling or indoor exposure assessment. i-SVOC model setup.	Predictive Modeling
Ground Water Issue: An Approach for Developing Site-Specific Lateral and Vertical Inclusion Zones within Which Structures Should Be Evaluated for Petroleum Vapor Intrusion Due to Releases of Motor Fuel from Underground Storage Tanks	2012	Wilson , J.T., J.W. Weaver, and H. White. EPA 600-R-13-047, 35 pp, 2012.	Definition of subsurface lateral and vertical inclusion zones in combination makes the best use of site characterization data for assessing the risk of PVI to structures at a leaking underground storage tank site. The procedures outlined in this issue paper provide a realistic data-driven approach to screen buildings for vulnerability to PVI .	Predictive Modeling
Use of Compound Specific Stable Isotope Analysis to Distinguish Between Vapor Intrusion and Indoor Sources of VOCs: Laboratory Validation Report	2012	McHugh, T., T. Kuder, M. Klisch, and R.P. Philp. ESTCP Project ER-201025, 59 pp, 2012.	The objective of this study was an empirical validation of selected adsorbents for preconcentration of TCE, PCE, and benzene in air samples containing low concentrations of these VOCs. For validation of adsorbent tube performance, the investigators selected adsorbent-analyte pairings likely to offer good quantitative recovery of the target VOCs. Results demonstrate fractionation-free performance for Carboxen 1016, which allows precise isotope ratio analysis into vapor intrusion site assessment protocols and other applications where VOCs of interest are present at low microgram-per-cubic-meter concentrations.	Forensic Approaches
Guidance for Environmental Background Analysis, Volume IV: Vapor Intrusion Pathway	2011	Naval Facilities Engineering Command (NAVFAC), UG-2091-ENV, 153 pp, April 2011.	This guidance document provides instructions for evaluating background conditions in vapor intrusion investigations. The background analysis techniques presented in this document are based on exploratory, forensic, and statistical methods. The guidance recognizes the unique features of vapor intrusion investigations and treats the recommended methods as "multiple lines of evidence" that should be considered when determining whether volatile chemicals measured in indoor air should be attributed to subsurface releases, indoor air background, or possibly both.	Soil Gas Sampling (Passive/Active) Sub-Slab Soil Gas Sampling Indoor Air Sampling Analytical Methods Forensic Approaches
Pneumatic Testing, Mathematical Modeling and Flux Monitoring to Assess and Optimize the Performance and Establish Termination Criteria for Sub-Slab Depressurization Systems (PowerPoint presentation)	2011	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.	Presentation slides include explanation of how to calculate the pneumatic conductivity of a building’s floor slab.	High Purge Volume Sub-slab Sampling/Pneumatic Conductivity Testing
Vapor Intrusion in Urban Settings: Effect of Foundation Features and Source Location	2011	Yijun Yao, Kelly G. Pennell, Eric Suuberg, in Procedia Environmental Sciences, Vol. 4, pp 245–250, 2011.	A 3-D computational fluid dynamics model is used to investigate how the presence of impervious surfaces affects vapor intrusion rates. To complement modeling efforts, the investigators are in the initial stages of conducting a field study in a neighborhood where vapor intrusion is occurring.	Predictive Modeling Building Design
Temporal Variation of VOCs in Soils from Groundwater to the Surface/Subslab: APM 349	2010	Elliot, J., G. Swanson, and B. Hartman. EPA 600-R-10-118, 143 pp, October 2010.	This report presents the activities, results, findings, and recommendations associated with monitoring the variations in active soil vapor sample results near and under a slab adjacent to Building 170 at Naval Air Station Lemoore from November 2008 through October 2009. The work described in this report follows up on EPA's 2009 report, Vertical Distribution of VOCs in Soils from Groundwater to the Surface/Subslab.	Groundwater Sampling Soil Gas Sampling (Passive/Active) Sub-Slab Soil Gas Sampling
Household Products Database	2010	U.S. National Library of Medicine.	Determine what's in consumer products before sampling indoor air.	Indoor Air Sampling
The Use of Tracer Gas in Soil Vapor Intrusion Studies	2010	Peter Reynolds, in Proceedings of the Annual International Conference on Soils, Sediments, Water, and Energy, Vol. 12, Issue 1, Article 39, 7 pp, January 15, 2010.	Discusses the use of tracer gas to verify that sub-slab samples do not contain ambient air.	Sub-Slab Soil Gas Sampling
HVAC Influence on Vapor Intrusion in Commercial and Industrial Buildings	2010	David Shea, Claire Lund, and Bradley Green, in Proceedings of the Air & Waste Management Association’s Vapor Intrusion 2010 Conference, 12 pp, 2010.	This paper 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 provided.	Sub-Slab Soil Gas Sampling Building Design
Vertical Distribution of VOCs in Soils from Groundwater to the Surface/Subslab	2009	U.S. Environmental Protection Agency, 326 pp, August 2009.	Field study conducted at Installation Restoration Program Site 14 on Naval Air Station Lemoore, California to assess the vertical and horizontal distribution of volatile organic compounds in the subsurface and to develop a database of paired macro-purge and micro-purge soil gas sample measurements. In addition, sampling was conducted to evaluate the performance of a variety of soil gas probe construction materials (tubing types) and to test passive diffusion samplers.	Soil Gas Sampling (Passive/Active)
Review of Best Practices, Knowledge and Data Gaps, and Research Opportunities, for the U.S. Department of Navy Vapor Intrusion Focus Areas	2009	T. McAlary et al, 86 pp, May 2009.	Provides a review by a team of subject-matter experts of current best practices, opinions on the current state of knowledge and data gaps, and offers suggestions for research directions for the following three Navy-identified VI focus areas: Sub-surface sampling for complete determination of VI pathway to minimize the need for intrusive sub-slab sampling; Passive indoor air sampling methods to improve VI exposure estimates; and Indoor air source separation to determine if indoor air contamination is from VI or indoor sources.	Soil Gas Sampling (Passive/Active) Sub-Slab Soil Gas Sampling Indoor Air Sampling Predictive Modeling
DOD Vapor Intrusion Handbook, The Tri-Service Environmental Risk Assessment Workgroup	2009	Department of Defense, 172 pp, January 2009.	Guidance from the Department of Defense includes discussion of sampling soil, groundwater, soil gas, sub-slab, and indoor air for vapor intrusion sites as well as the influence of building design parameters.	Groundwater Sampling Soil Gas Sampling (Passive/Active) Sub-Slab Soil Gas Sampling Indoor Air Sampling Analytical Methods Predictive Modeling Building Design
Vapor Intrusion Sampling Options: Performance Data for Canisters, Badges, and Sorbent Tubes for VOCs	2009	Linda S. Coyne, George Havalias, and Maria C. Echarte, in Proceedings of the Air & Waste Management Association’s Vapor Intrusion 2009 Conference, 9 pp, San Diego, California, January 27-30, 2009.	Discusses results of two field studies comparing Summa canisters, passive sampling badges, and sorbent tubes. The study found good correlation between the canisters and the other two methods and concluded that sorbent-based sampling devices can be used effectively in vapor intrusion studies as a reliable alternative to canister sampling.	Indoor Air Sampling
A Guide for Assessing Biodegradation and Source Identification of Organic Ground Water Contaminants Using Compound Specific Isotopes Analysis (CSIA)	2008	EPA 600/R-08/148, U.S. Environmental Protection Agency, 82 pp, December 2008.	Intended for managers of hazardous waste sites who design sampling plans that will include CSIA and specify data quality objectives for CSIA analyses, for analytical chemists who carry out the analyses, and for staff of regulatory agencies who review and approve the sampling plans and data quality objectives, and review the data provided from the analyses.	Forensic Approaches
Canisters v. Sorbent Tubes: Vapor Intrusion Test Method Comparison	2008	Joseph Odencrantz, Harry O`Neill, and James Kirkland, in Proceedings of the Sixth International Battelle Conference: Remediation of Chlorinated and Recalcitrant Compounds, 7 pp, May 2008.	The results from each method revealed a linear relationship between molecular weight and the difference in concentration between the two methods. The TO-17 results were generally lower than the TO-15 results for PCE.	Sub-Slab Soil Gas Sampling
Recommendations for the Investigation of Vapor Intrusion (ESTCP Project ER-0423)	2008	Thomas McHugh, 23 pp, April 2008.	Recommends approaches to collecting groundwater and soil gas samples to generate data suitable for pathway screening and a field investigation program to provide a cost-effective and timely evaluation of the presence or absence of vapor intrusion impacts.	Groundwater Sampling Soil Gas Sampling (Passive/Active) Sub-Slab Soil Gas Sampling Indoor Air Sampling
Evaluation of Spatial and Temporal Variability in VOC Concentrations at Vapor Intrusion Investigation Sites	2007	Thomas McHugh, Tim Nickels, and Samuel Brock, in Proceedings of Air & Waste Management Association’s Vapor Intrusion: Learning from the Challenges, 14 pp, September 2007.	Discusses the representativeness of sub-slab samples given temporal and spatial concentration variability.	Sub-Slab Soil Gas Sampling
Vapor Intrusion Pathway: A Practical Guide (VI-1)	2007	Interstate Technology & Regulatory Council, 172 pp, January 2007.	A reference document that provides a flexible framework for developing an investigative strategy at vapor intrusion sites. Various tools for investigation, data evaluation and mitigation are described.	Groundwater Sampling Soil Gas Sampling (Passive/Active) Sub-Slab Soil Gas Sampling Indoor Air Sampling Analytical Methods Predictive Modeling Building Design High Purge Volume Sub-slab Sampling/Pneumatic Conductivity Testing Meteorological Monitoring Forensic Approaches
Vapor Intrusion Pathway: A Practical Guide, Interstate Technology & Regulatory Council	2007	ITRC, 72 pp, January 2007.	Includes discussion of the utility of and how to conduct pneumatic tests for the investigation of vapor intrusion.	Groundwater Sampling Soil Gas Sampling (Passive/Active) Sub-Slab Soil Gas Sampling Indoor Air Sampling Analytical Methods Predictive Modeling Building Design High Purge Volume Sub-slab Sampling/Pneumatic Conductivity Testing
Comparison of Geoprobe® PRT and AMS GVP Soil-Gas Sampling Systems with Dedicated Vapor Probes in Sandy Soils at the Raymark Superfund Site	2006	EPA/600/R-06/111, U.S. Environmental Protection Agency, 79 pp, November 2006.	Documents study conducted near the Raymark Superfund Site in Stratford, Connecticut to compare results of soil-gas sampling using dedicated vapor probes, a truck-mounted direct-push technique - the Geoprobe Post-Run-Tubing (PRT) system, and a hand-held rotary hammer technique - the AMS Gas Vapor Probe kit.	Soil Gas Sampling (Passive/Active)
Groundwater Sampling and Monitoring Using Direct Push Technologies	2005	U.S. Environmental Protection Agency, 78 pp, August 2005.	Explains groundwater sampling issues related to use of direct push technology, in particular those regarding the quality and usability of the groundwater data.	Groundwater Sampling Indoor Air Sampling
A Review Of Recent Vapor Intrusion Modeling Work	2021	Verginelli, I. and Y. Yao. | Groundwater Monitoring & Remediation 41(2):138-144(2021)	This paper reviews vapor intrusion modeling studies published from 2010-2020.	Predictive Modeling
Modeling Fate and Transport of Volatile Organic Compounds (VOCs) Inside Sewer Systems	2021	Verginelli, I. and Y. Yao. | Groundwater Monitoring & Remediation 41(2):138-144(2021)	A new numerical model simulates the VOC concentrations in sewer gas in different stages throughout the sewer lines. The model considers temperature, sewer liquid depth, groundwater depth, and sewer construction characteristics to incorporate local and operational conditions. The output was verified using field data from a sewer system constructed near a Superfund site. A sensitivity analysis was conducted to evaluate the model's response to variation of the external input parameters. The model can be used as a numerical tool to support the development of sewer assessment guidelines, risk assessment studies, and mitigation strategies.	Predictive Modeling
The VI Diagnosis Toolkit for Assessing Vapor Intrusion Pathways and Impacts in Neighborhoods Overlying Dissolved Chlorinated Solvent Plumes	2021	Johnson, P.C., Y. Guo, and P. Dahlen. ESTCP Project ER-201501, 525 pp, 2020	The objective of this project was to develop, demonstrate and validate a suite of tools to more accurately, cost-effectively, and confidently assess VI impacts in residential and industrial buildings overlying dilute chlorinated solvent plumes. The project focused on advancing the VI Diagnosis Toolkit, which includes: external VI source screening for at-risk building identification; building-specific controlled pressurization method testing to measure worst-case VI indoor air impacts in at-risk buildings quickly; identification of indoor vapor sources through the use of portable analytical tools; passive samplers for longer-term (week to month duration), time-weighted indoor air concentration measurements; and using the collected data to select appropriate mitigation strategies if needed.	Analytical Methods Indoor Air Sampling
Evaluation of Passive Diffusive-Adsorptive Samplers for Use in Assessing Time-Varying Indoor Air Impacts Resulting from Vapor Intrusion	2021	Guo, Y., H. O'Neill, P. Dahlen, and P.C. Johnson. Groundwater Monitoring & Remediation [Published online 15 September 2021 prior to print]	Passive sampler performance for VI pathway assessment was examined in settings with time-varying indoor air concentrations by comparing passive sampler results to concentrations determined by 24-hr active sorbent tube sampling in a series of multi-week deployments. Sampling was performed in a residential building and industrial buildings for one to seven weeks. Strong linear correlations were noted between passive and active sampling concentration results for some passive samplers, with passive sampling results being similar to or lower than measured active sampling results by ~50% in the residential study and ~25% higher in the industrial study. Other samplers produced a poor correlation. Results indicated that passive samplers may have potential for use in multi-week indoor air quality monitoring, though accepted procedures to validate and calibrate passive samplers for use in the field are needed.	Indoor Air Sampling
Field Study of Vertical Screening Distance Criteria for Vapor Intrusion of Ethylene Dibromide	2021	Hers, I., J.T. Wilson, R.V. Kolhatkar, M.A. Lahvis, E. Luo,and P. Jourabchi. Groundwater Monitoring & Remediation	Depth-discrete soil-gas samples were collected at a site in Sobieski, Minnesota, contaminated with leaded gasoline containing EDB, to study an appropriate vertical screening distance to address EDB attenuation in the vadose zone. The maximum EDB concentration in groundwater was 175 µg/L. Soil gas was analyzed for EDB using modified EPA Method TO-14A and achieved analytical detection limits below the EPA Vapor Intrusion Screening Level for EDB based on a 10-6 cancer risk (<.16 µg/m3). Concentrations of EDB in soil gas above LNAPL reached as high as 960 µg/m3 and decreased below the VISL within a source-separation distance of 7 ft. This result, coupled with BioVapor model predictions of EDB concentrations, indicates that vertical screening distances recommended by regulatory agencies at PVI sites are generally applicable for EDB over the range of source concentrations and soil types encountered at most sites.	Soil Gas Sampling (Passive/Active)
Modeling Vapor Migration for Estimating the Time to Reach Steady State Conditions	2021	Jourabchi, P. and G.K.-C. Lin. ǀ Groundwater Monitoring & Remediation 41(4):25-32(2021)	The model derivation, analytical solutions, and the assumptions and limitations of a one-dimensional VOC vapor transport model, based on diffusion in porous media and equilibrium partitioning of VOCs in solid, aqueous, and vapor phases, are presented. The model assumes a finite domain with boundary conditions that represent vapor migration scenarios in the environment. The upper (or exit) boundary conditions and the distance between the source and the applicable boundary, rather than the distance from the source to the measurement point, are critical in the time estimates as compared to an expression typically used and cited in guidance documents. The study reveals the importance of defining a conceptual model and relevant boundaries in assessing near steady-state conditions and suggests a tiered approach in refining the estimate with increasing level of effort for practical applications in vapor assessment.	Soil Gas Sampling (Passive/Active)
Fate & Transport of Vinyl Chloride in Soil Vapor	2022	Eklund, B., R. Rago, G. Plantz, E. Haddad, M. Miesfeldt, and R. Volpi. Remediation 32(4):273-279(2022)	This paper sets forth a conceptual model for understanding vapor intrusion results for VC and summarizes data from several field sites to illustrate the concepts. Data from multiple field sites are presented to illustrate the fate and transport of VC. At sites drawn from various regions of the U.S. covering a range of conditions, VC was detected at relatively high concentrations in groundwater. It may also have been detected in deeper soil gas but generally was fully attenuated before reaching shallow soil depths. Indoor air results were consistently non-detect. VC behavior is also discussed for sites with very shallow groundwater, where VC was found in some sub-slab soil gas samples but not in the overlying indoor air.	Soil Gas Sampling (Passive/Active) Indoor Air Sampling
Flux Equations for Gas Diffusion in Porous Media	2021	McWhorter, David B., 2021. The Groundwater Project, Guelph, Ontario, Canada.	This book is an introduction to the fundamental processes governing the movement of gases in the vadose zone. These processes are key to understanding important topics such as the fate of petroleum products that leak into the subsurface and how harmful vapors from toxic chemicals move through the vadose zone to cause deterioration of indoor air. Moreover, this book examines how the movement of gases in the vadose zone came to be correctly understood in the context of both Fick's law of diffusion and Graham's law of gas diffusion.	Soil Gas Sampling
High-Volume Sampling for Vapor Intrusion Assessments Fact Sheet	2023	Naval Facilities Engineering Command, 4 pp, 2023	This fact sheet covers the high-volume sampling (HVS) method to characterize the nature and extent of VOC vapor distributions beneath large buildings. Case studies at NAS Corpus Christi and NS Norfolk are presented in addition to a summary of the advantages and limitations before selecting and applying HVS.	Sub-Slab Soil Gas Sampling