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Vapor Intrusion

Geosyntec is innovating how the industry collects meaningful data, here using quantitative passive samplers such as the pictured Waterloo Membrane Sampler™.
Geosyntec is innovating how the industry collects meaningful data, here using quantitative passive samplers such as the pictured Waterloo Membrane Sampler™.

Geosyntec approaches problems using sound science and engineering such as on-site, real-time monitoring and data analysis during High Volume Purge sub-slab testing.
Geosyntec approaches problems using sound science and engineering such as on-site, real-time monitoring and data analysis during High Volume Purge sub-slab testing.

Geosyntec designs and installs a wide array of customized mitigation solutions such as this aerated flooring design using Cupolex® technology.
Geosyntec designs and installs a wide array of customized mitigation solutions such as this aerated flooring design using Cupolex® technology.

Geosyntec Consultants maintains an international reputation as one of the preeminent firms for the assessment and management of subsurface vapor intrusion to indoor air. We earned our reputation by providing 25 years of innovation in applied research and practical project experience.

Clients seek us out for customized solutions founded in an understanding of physical, chemical, and biological processes. We design our solutions to add value and address risk by targeting corrective actions where they are warranted.

Our practitioners are noted contributors to technical guidance documents published by regulatory agencies and industry associations and regularly contribute to the body of published vapor intrusion literature.

Practice Specialties

  • Regulatory Negotiation: Geosyntec practitioners have long-established credibility and expertise in the negotiation of regulatory approvals for our clients’ vapor intrusion solutions. Our engineers and scientists participated in the development of more than a dozen regulatory guidance documents on vapor intrusion during the past two decades. Clients rely upon this depth of knowledge and experience to negotiate sensible and cost-effective scopes of work among local, state, federal officials.
  • Litigation Support: Geosyntec’s legal clients represent some of the world’s largest corporations. Our practitioners have extensive experience in providing litigation support in cases involving dozens of sites where vapor intrusion or subsurface gas migration have resulted in claims. These include cases touching on issues of human health impacts, medical monitoring, and property devaluation. We also specialize in management and access to large, complex databases for joint-defense groups.
  • Cutting-Edge Soil Gas Sampling: Geosyntec’s soil gas surveys include the use of pioneering approaches in mobile gas chromatography, pneumatic testing, High Volume Purge sub-slab soil gas sampling (McAlary et al., 2010), tracer testing, sampling in low permeability materials (McAlary et al., 2009), and multi-phase partitioning assessments. Our practitioners developed sampling protocols for the Electric Power Research Institute (EPRI, 2005) and the United Kingdom Energy Institute (in press) and have conducted extensive applied research and development of passive quantitative samplers for use in soil gas, indoor, and outdoor air sampling.
  • Indoor Air Quality (IAQ) Monitoring: Our professionals have assessed indoor air quality as part of vapor intrusion investigations since 1992. We provide technical direction for one of the largest vapor intrusion investigations in the world, which required us to develop a new method of sampling and laboratory analysis to achieve reporting limits as low as three parts-per-trillion. We have established long-term relationships with the world's leading laboratories and research institutes and have extensive experience with both traditional and emerging methods for sampling volatile organic compounds (VOCs), semi-volatile compounds, polychlorinated biphenyls, polycyclic aromatic hydrocarbons, and other, less common compounds.
  • Mathematical Modeling: Geosyntec offers clients world-class experience in the application of vapor transport models. Our professionals co-developed the most widely used mathematical model for vapor intrusion to indoor air and use modeling to assist with targeted investigation design (Johnson and Ettinger, 1991) . We study large-scale, long-term vapor transport modeling and develop models with non-equilibrium phase partitioning for transient analysis of mass removal during soil vapor extraction.  Our professionals established several forensic methods for discriminating indoor and outdoor sources of common VOCs from subsurface sources of VOCs to indoor air.
  • Customized Mitigation System Design and Optimization: We provide engineering services for vapor intrusion mitigation system design, construction, operation, trouble-shooting, and repair for both passive and active systems, including real-time control and monitoring services. We are pioneers in the use of aerated flooring in the United States as a cost-effective way to manage risk, particularly in new construction. Our patented sub-slab venting system is in use at brownfield sites found throughout the country. Our current research explores the use of wind- and solar-powered systems for sub-slab ventilation.
  • Ventilation Assessment: Geosyntec practitioners apply heating, ventilating, and air-conditioning (HVAC) system manipulation to assess points of soil gas entry. This allows us to establish target locations for sealants or other barriers, assess the sources of VOCs to indoor air, and implement means to mitigate the VI pathway.  In some cases, minor modifications to an HVAC design or operations are sufficient to eliminate the vapor intrusion pathway while reducing or eliminating otherwise costly disruptions of manufacturing or retail operations.

Advancing the State of the Practice

Geosyntec engineers and scientists are co-authors or contributing editors of guidance and regulatory documents that outline and advocate the latest advancements and research related to the remediation of vapor intrusion around the world. These include standards, information supplements, and handbooks issued by the U.S. EPA, the EPRI, the Interstate Technology and Regulatory Council, and ASTM International, formerly known as the American Society for Testing and Materials. The efforts associated with this public involvement represent significant steps forward in the evolution of vapor intrusion assessment and control technology.

In recent years, Geosyntec was retained by the U.S. Department of Defense to compare four quantitative passive samplers to the conventional Summa canister method of sampling and analysis and has performed applied research with the University of Waterloo to develop another quantitative passive sampler, the Waterloo Membrane Sampler (WMS)™, and commercialize it for use in vapor intrusion assessments. Quantitative passive samplers provide long-term average concentrations, which are more relevant for assessing human health risks. Quantitative passive samplers like the WMS have several advantages over conventional sampling, including simplicity of use, low cost, and small size, making them discrete, easy to ship, and useful in vent pipes. 

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Mitigation of the Vapor Intrusion Pathway at Four Chlorinated Solvent Sites
Risk Management Approaches at Vapor Intrusion Sites - Chlorinated Solvents Case Studies
Recommended Soil Gas Sampling Techniques for Vapor Intrusion Investigations
Soil Gas Sampling Methods
Modeling the Vapor Intrusion Pathway
Sub-Slab Soil Gas Monitoring for Assessing Subsurface Vapor Intrusion to Indoor Air
Spatial and Temporal Variability in Hydrocarbon and Oxygen Concentrations Beneath a Building Above a Shallow NAPL Source
The Effects of Purge Rate and Volume on Sub-slab Soil Gas Samples
Beyond Screening – The Site Characterization Process
Regulatory Perspectives on Vapor Intrusion
Practical Considerations for Vapor Intrusion Investigations
A Practitioner’s Perspective on Vapor Intrusion
Key Considerations for Vapor Intrusion Evaluations
Reference Handbook for Site-Specific Assessment of Subsurface Vapor Intrusion to Indoor Air
Strategy for Assessment, Data Analysis, and Interpretation of Subsurface Vapor Intrusion
Examples of Data Collection Strategies and Methods
How to Determine, Interpret, and Resolve Background Contributions from Indoor Air Data
Future Directions for Assessing Vapor Intrusion
Approaches and Methods Influencing Observational Data
Vapor Intrusion: Regulatory Drivers and Technical Challenges
Presentation of the First Draft Best Practices Manual for Site-Specific Assessments of Subsurface Vapor Intrusion to Indoor Air
Subsurface Vapor Intrusion, Challenges and Future Directions
Vapor Intrusion at a Former Manufactured Gas Plant Site – Assessing Background Contributions to Indoor Air Quality
Measured Attenuation Coefficients for Soil Gas to Indoor Air, Runcorn, Cheshire, UK
The Fresh Water Lens and its Effects on Groundwater to Indoor Air Attenuation Coefficients
Empirical Alpha Factors at ‘Wet Basement’ Sites
Vapor Intrusion: Regulatory Drivers, Challenges, and Management Issues
Federal Guidance on Vapor Intrusion, History and Status
Conceptual Site Models of Vapor Intrusion
Vapor Intrusion into Indoor Air, with a focus on New Jersey
Empirical Experience Gathering Data to Assess Vapor Intrusion
Strategies for the Site-Specific Assessment: How to Protect Yourself from the Hidden Traps
Key Considerations for Evaluating the Vapor Intrusion Pathway
Assessment of Subsurface Vapour Transport Through Triassic Sandstone and Quarry Fill into Indoor Air in Weston Village
Characterization of Vapour Transport in Fractured Rock
Management Decisions for Assessing Subsurface Vapor Intrusion into Indoor Air
Intrusion of Subsurface Vapors into Buildings - Chlorinated Solvents Case Studies
Alpha Factors, Measured and Modeled: A Case Study
Characterization of Subsurface Vapour Transport in Triassic Sandstone
Vapor Intrusion Modeling for Contaminated Properties
The Impact of Background Concentration on Vapor Intrusion Assessment
Key Modeling Considerations For Subsurface Vapor Intrusion Evaluation
Identifying Key Factors and Preferred Lines of Evidence
Chemical Vapor Intrusion from Soil or Groundwater to Indoor Air: Significance of Unsaturated Zone Biodegradation of Aromatic Hydrocarbons
Migration of Soil Gas Vapors to Indoor Air: An Empirical Assessment of Subsurface Vapor-to-Indoor-Air Attenuation Factors Using Data from the CDOT-MTL Denver, Colorado Site
Vapor Intrusion Modeling: Theory and Implications
Vapor Migration to Indoor Air Fate and Transport Considerations
Practical Considerations for the Assessment of the Vapor Migration to Indoor Air Pathway
Effects of Diffusion-Coefficient Heterogeneity and Biodegradation on Vapor Transport to Indoor Air at Gasoline Spill Sites
How Does Ethanol In Gasoline Change Things?
Options for Mitigation of Vapor Intrusion
Sources of Groundwater Impacts at Landfills, Is it Landfill Gas or Leachate?
Vapor Control Issues and Considerations for Development of Brownfields Sites
Use of Innovative Technologies in Developing Brownfields Sites: Case Studies Involving Engineering Controls to Mitigate Vapor Intrusion
San Diego County Site Assessment and Mitigation Manual Vapor Sampling and Risk Assessment Guidance Update
Urban Infrastructure and the Challenges Posed for Assessing and Mitigating Vapor Intrusion Adjacent to a Former Dry Cleaner: A Case Study.
High Purge Volume Sampling - A New Paradigm for Sub-Slab Soil Gas Monitoring