Vapor Intrusion Exposure: Long-Term Evidence-Based Protection & Sustainability in Residential, Commercial, and Industrial Buildings The 25th Annual AEHS International Conference on Soil, Water, Energy, and Air—March 23-24, 2015, San Diego, CA Abstracts (in order of presentation)
Monday Afternoon, March 23, 2015 – 1:00–5:00 PM PDT
Introduction, Welcome, Overview, and Overarching Context Dr. Henry Schuver, U.S. EPA ORCR; Doug Grosse, U.S. EPA NRRML (ret.); John Zimmerman, U.S. EPA NERL
Since 2004, the USEPA has sponsored annual Vapor Intrusion (VI) Workshops at the AEHS Foundation’s Annual International West Coast Conference in San Diego, CA. This years’ technical workshop, which will be held over two successive half-day sessions, is focused on the latest scientific observations and evidence regarding the efficacy of various management approaches for providing long-term (sustainable) evidence-based protection. Commonly VI risks are presented by contaminated groundwater sources, and the long-term evidence-based approaches and degree of certainty expected for groundwater ingestion exposures (e.g., NRC 2012 1) will be compared with those currently typical for the VI pathway’s inhalation exposures. The evidence and scenarios considered will range from the simplest pre-construction and existing (single family) residential settings, to more complicated residential scenarios and the typically even-more variable non-residential “large building” scenarios.
Residential scenarios will include the latest data from two of the world’s most thoroughly studied VI-research houses (and consideration of their representativeness) along with studies that illustrate the building-specific complexities that are often only observable after applying physical intrusion controls/ diagnostics to a given building. Finally, because “there are two choices for dealing with a possible vapor intrusion pathway at a given site: (1) invest in sampling and analyses to confirm whether or not the potential exposure is of concern, or (2) install a vapor mitigation system,”* this workshop will continue the discussion from our 2014 workshop by presenting the latest scientific and economic evidence for informing such a decision, likely made more efficient by an earlier awareness of the long-term stewardship obligations that can become more obvious with time. Also note that in response to numerous ‘too much information in too little time to discuss’ comments from our previous workshops, this split-day format will allow an optional informal evening discussion session that is being planned for all technical topics, including impacted-community stakeholder groups’ comments and perspectives.
1 Alternatives for Managing the Nation’s Complex Contaminated Groundwater Sites, NRC 2012. http://www.nap.edu/catalog/14668/alternatives-for-managing-the-nations-complexcontaminated-groundwater-sites
EPA/AEHS 2015 Vapor Intrusion Workshop Abstracts 1 Passive Samplers for the Investigations of Air Quality
Heidi Hayes, Eurofins Air Toxics; Dr. Helen Dawson, Geosyntec Consultants; Robert Truesdale, RTI International; Chris Lutes, CH2MHill; Dr. Todd McAlary, Geosyntec Consultants
Passive air samplers are gaining increased interest as a means to investigate subsurface vapor intrusion to indoor air. In response to this interest, the U.S. EPA Engineering Technical Support Center has developed an Engineering Issue Paper (EIP) that compiles and summarizes the available information on the advantages and proper use of passive samplers in indoor air investigations of volatile organic compounds (VOCs) at vapor intrusion and other sites where VOCs are of concern. The EIP covers passive sampler basics (theory, design and operation), sampling program design and implementation, data quality objectives, how to interpret results, and current challenges, limitations, and research needs.
As compared to conventional indoor air sampling techniques using evacuated canisters or pumped tubes, passive samplers are simple to deploy, require no mechanical equipment to operate, and can be used to obtain long-term integrated VOC measurements. A successful passive sampling program requires careful planning to ensure reliable results are achieved and data quality objectives are met. The available passive sampler configurations and considerations for sampler selection are discussed, including targeted compound list, reporting limit requirements, and desired sampling duration. Field and laboratory protocols relevant to passive air samplers are presented along with approaches to verify passive sampler field performance. Additional research is needed to evaluate the performance of passive samplers over longer-term sample durations and to determine the applicability of passive samplers for a wide range of VOCs including challenging compounds such as low molecular weight chemicals and those with relatively low risk-based screening levels.
EPA/AEHS 2015 Vapor Intrusion Workshop Abstracts 2 Vapor Intrusion Pathway Screening for Soil Excavation Remedies
Dr. Helen Dawson, Geosyntec Consultants; Chris Lutes, CH2MHill; Dan Carr Sanborn|Head Associates; Dr. Todd McAlary, Geosyntec Consultants; Robert Truesdale, RTI International
Soil excavation often is a component of site remedies for subsurface volatile organic compound (VOC) contamination. Bulk soil sampling and analysis is a conventional method for assessing the completeness of soil excavation remedies, but information is lacking on how to use soil sampling and analysis results to determine whether a soil excavation remedy for VOC contamination has been completed to a degree that is protective of the vapor intrusion (VI) pathway. To address this issue, the U.S. EPA Engineering Technical Support Center has developed an Engineering Issue Paper (EIP) that discusses the benefits and limitations of bulk soil sampling for assessing VI risks from contaminated soil and describes alternatives for monitoring and enhancing soil remedies at sites where soil excavation is being considered or used as a remedy for VOC-contaminated soils.
The information and analysis presented in the EIP indicates that bulk soil sampling is useful for identifying and delineating source areas with high concentrations of VOCs, such as where NAPL is present, and for estimating the total VOC mass that may be present in soils at a site. However, available analysis methods are not sufficiently sensitive to detect VOCs in bulk soil concentrations corresponding to typical VI screening levels and, consequently, bulk soil sampling alone may not to provide adequate information to fully assess potential VI exposures after a soil excavation. Other technical challenges with bulk soil sampling and analysis include the potential for low bias (underestimation) of VOC levels from VOC loss during sampling and analysis, and the difficulty in characterizing the heterogeneity in VOC concentration distributions in the bulk soil mass of interest.
Soil excavation can be an appropriate part of a VOC contamination remedy if focused on shallow accessible source materials with relatively high concentrations of VOCs, which are readily measured with bulk soil samples. However, because of the limitations described above, other polishing remedies are likely to be needed to augment soil excavation. Polishing options include SVE, bioventing, and natural attenuation (for PHCs); enhanced/accelerated bioattenuation (for chlorinated hydrocarbons); building structure mitigation; institutional controls; and/or backfilling of the excavated areas with low-permeability barrier materials that will reduce the concentrations reaching the surface. The time frame other remedies would need to be applied depends on the total mass of VOCs remaining in the soil after excavation and the rate of mass depletion through either natural or engineered means.
EPA/AEHS 2015 Vapor Intrusion Workshop Abstracts 3 Soil Vapor Extraction: Mitigation of Vapor Intrusion from Subsurface Sources over Large Areas
Dr. Lloyd “Bo” Stewart, P.E., Praxis Environmental Technologies, Inc.
Decades of soil vapor extraction to remediate sources of contamination in the vadose zone illustrate the dominance of soil heterogeneity and mass transfer limitations on the migration of volatile contaminants in the subsurface. Almost all applications of SVE experience an exponential-like decay in the initial extracted vapor concentration followed by a slow, asymptotic decay that can persist for many years. The initial decay represents the sweep of a permeable soil volume and generally indicates an area of influence that largely exceeds that indicated by traditional vacuum responses. The subsequent slow, persistent decay is associated with the mass transfer limited migration of contaminants from low permeability soils (e.g., clay), soils with high water contents, and contaminated groundwater. These mass transfer limitations can be quantified by well-established techniques (e.g., concentration rebound during a suspension of extraction). The site-specific mass transfer rates are then applied to other site concerns such as groundwater impact and vapor intrusion into buildings. Two example sites are presented where SVE data are utilized to characterize the mass transfer of contaminants in the subsurface and the results used to predict the impact on underlying groundwater and overlying vapor intrusion. The results also illustrate the large area over which SVE can be protective against vapor intrusion, dependent upon the depth of application, subsurface geology, surface conditions, etc. In one example site, a single SVE well below a fine-grained soil interval is shown to capture vapors volatilizing from contaminated groundwater over an area of approximately five acres.
EPA/AEHS 2015 Vapor Intrusion Workshop Abstracts 4 A Case for Profiling of Soil and Rock at VI Sites: Total Mass and Mass Flux as Metrics
Daniel B. Carr, P.E., P.G., and David Shea, P.E., Sanborn, Head & Associates, Inc.; Dr. Helen Dawson, Geosyntec Consultants
Based on field experience over the last decade it is increasing evident that the total mass of VOCs in the subsurface coupled with the rate of mass depletion or transfer through either natural or engineered means are important metrics for assessing the potential risks posed by vapor intrusion. These parameters are relevant both to assessing the potential risk under present conditions and assessing the length of time the pathway may pose a risk. This presentation makes the case that detailed profiling of relevant soil or rock properties and VOC mass distribution at a few locations can dramatically improve site conceptual models and better inform risk management decisions about the vapor intrusion pathway.
We will introduce approaches for estimating VOC mass flux and total mass from soil data and demonstrate how these estimates can be used to evaluate the vapor intrusion pathway. We will present examples illustrating the application of these approaches and discuss considerations and methodologies for developing and executing this characterization work. Finally, we will discuss potential applications of these concepts in the context of the life cycle of a vapor intrusion site from assessing future building scenarios to development of criteria for shutdown/termination of mitigation system operation.
EPA/AEHS 2015 Vapor Intrusion Workshop Abstracts 5 Mass Transfer Concepts in Predicting VI: Large Building Examples
David Shea, P.E., Brad Green, P.G., and Daniel Carr, P.E., P.G., Sanborn, Head & Associates, Inc.
Recent experience with vapor intrusion (VI) characterization and mitigation of large buildings supports that data collection oriented toward estimating mass transfer rates can be particularly useful for predicting long-term VI exposures, establishing mitigation performance goals, and criteria for termination/exit of VI mitigation. A site conceptual model for VI prediction built on mass balance and mass flux principles is more robust than the conventional approach that relies mainly on concentration data from short-term, relatively small volume samples, which are typically subject to a high degree of variability that makes assessing long-term chronic exposure problematic. Since structures act as macro-scale flux chambers, certain types of data collection in support of assessing VI data in terms of mass flux can be used to estimate potential short- and long-term indoor air exposure conditions. We will present and discuss how data such as VOC gross mass estimates in groundwater and the soil column, mass transfer mechanisms including volatilization, partitioning, and diffusion rates, and building air exchange rates may influence mass loading to a building. Performance data from subslab depressurization mitigation of large buildings suggests that long-term VI potential is diffusion-limited and may be readily predictable based on subsurface profiling. In the short term, VI potential may be greater due to advective transfer of mass from storage in the vadose zone. By investing in data collection that will support mass transfer estimates, better predictions of long-term VI potential and mitigation performance are achievable.
EPA/AEHS 2015 Vapor Intrusion Workshop Abstracts 6 ORD VI-Research Duplex and Wheeler Building, Indianapolis- Summary of Evidence to Date: Temporal Variability in Long-term Mitigation Performance and Before Mitigation: What Causes It?
Dr. Brian Schumacher and John Zimmerman, U.S. EPA/ORD/NERL; Christopher C. Lutes, CH2M HILL; Brian Cosky, ARCADIS U.S., Inc. (ARCADIS); Robert Truesdale and Robert Norberg, RTI International
We will present observations and statistical analysis on indoor air and soil gas data, collected over four years (including parts of five winter seasons) along with data on meteorological and hydrological variations at an unoccupied pre-1920 duplex. The monitoring program has now included a set of mitigation on/off tests as well as a year-long period of continuous post mitigation monitoring. Extensive time series statistical analyses were completed to examine the causes of temporal variability with and without the mitigation system operation. This presentation will address some of the frequently asked questions about this study, such as: What is the role of preferential pathways, including sewer lines, in this data set? To what extent are the features of this duplex and other well studied cases “typical” of the US housing inventory? Is the VOC mass observed entering the duplex primarily from groundwater or vadose zone sources? Why do chloroform and PCE differ at this site, in terms of sources and VI behavior? What is the spatial and temporal variability of the observed attenuation factors?
Additionally, new data will be presented from the 100,000 square-foot Wheeler Arts Building, which was an industrial facility from 1911 until 1995. Subsequent renovations converted the building into live-work lofts, office space and a theater. In this presentation we will present temporal variability data collected pre and post installation of a mitigation system was installed in 2010. Indoor VOCs include a mix of constituents dominated by vapor intrusion sources and those dominated by indoor sources. This presentation will focus on the performance of the mitigation system during a 6 month VOC monitoring period over the winter of 2013-2014. This case study will demonstrate relatively low post mitigation variability in a commercial building.
EPA/AEHS 2015 Vapor Intrusion Workshop Abstracts 7 Diagnosing Vapor Intrusion Occurrence, Impact, and Contributing Pathways
Dr. Paul C. Johnson, Ira A. Fulton Schools of Engineering, Arizona State University, with contributions from: C. Holton, Y. Guo, P. Dahlen, H. Luo, K. Gorder, E. Dettenmaier, and R. Hinchee, Arizona State University, Hill AFB ERB, Chevron Energy Technology Company, IST
Regulatory guidance for assessing the vapor intrusion (VI) pathway varies from the federal to the state and local levels, but most utilize sparse point-in-time multiple-lines-of-evidence data sets. When interpreting the data and making decisions, indoor air data are weighted heavily and data interpretation, decision-making, and mitigation schemes are founded on a simplistic conceptual model of the vapor intrusion pathway.
Recent publications from focused VI studies suggest that the conventional approach is neither robust nor timely, and that we need to develop assessment approaches that are practicable and reliable, provide timely answers, and that work in a range of scenarios (e.g., multi-zone residences, office and industrial buildings).
This presentation will summarize key lessons-learned from five years of study at a house overlying a dilute chlorinated solvent plume and implications of these results for more rapid and robust VI pathway assessment. Particular emphasis will be placed on recently published results from long-term controlled pressure tests and the combined use of controlled pressure testing, soil gas monitoring, and screening-level modeling to identify pathways contributing to vapor intrusion impacts. The need to re-conceptual the vapor intrusion pathway will also be discussed as well as future plans for a new study recently funded by the Environmental Security Technology Certification Program (ESTCP).
EPA/AEHS 2015 Vapor Intrusion Workshop Abstracts 8 Tuesday Morning, March 24, 2015 – 8:30 AM–12:00 PM PDT
The value of proper diagnostics and pathway identification for radon mitigation systems—commercial and residential examples
Tony McDonald, A-Z Systems
Choosing the correct SSD System technology based on complete diagnostic data ensures a successful mitigation system. Scenarios discussed include identifying multiple or disconnected preferential VI/RN pathways, overcoming temperature driven radon spikes in homes, the limitations of horizontal remediation wells, and utilizing suction trenches as a force multiplier
EPA/AEHS 2015 Vapor Intrusion Workshop Abstracts 9 Soil Vapor Extraction and Subslab Depressurization Work Together for Successful Mitigation of a Series of Commercial Buildings
Dr. Loren Lund, Christopher Lutes, Kim Stokes, Michael Niemet, and Scott McKinley, CH2M HILL; Michael Torres, USEPA – Region 6, Dallas, Texas
The McGaffey and Main Ground Water Plume Superfund Site in Roswell, New Mexico has been the focus of remediation efforts as a result of historical releases of tetrachloroethylene (PCE) from multiple dry cleaner facilities. PCE concentrations up to 11,900,000 μg/m3 have been detected in shallow soil vapor samples, which have contributed to vapor intrusion to indoor air at several buildings. The site’s source area setting consists of mixed residential and commercial buildings. The Record of Decision for the site specified that a vapor intrusion mitigation system (VIMS) be installed and operated to protect indoor air until remediation of vadose zone soil is completed using an enhanced soil vapor extraction (SVE) system. The USEPA implemented a vadose zone remedy for the site’s source area that utilizes a holistic approach with centralized blowers, underground piping, and a vapor phase treatment system that services several sub-slab depressurization (SSD) systems and SVE wells and trenches. After the first several months of operation, the combined VIMS and SVE remedies have removed over 450 pounds of PCE from the subsurface. A VIMS pilot study, conducted at one of the buildings, indicated that traditional SSD systems were not appropriate at the site because high PCE concentrations in the untreated exhaust vapors were ultimately re- entrained into the building. As a result, centralized blowers and a granular activated carbon based treatment system were designed to treat exhaust vapors from both the VIMS and SVE system. The full-scale VIMS remedy consists of SSD systems in six buildings with a combined flow of approximately 1,000 standard cubic feet per minute (scfm). The SVE remedy consists of nine relatively deep SVE extraction wells and two shallow SVE trenches with a combined flow of approximately 250 scfm. A HAPSITE portable gas chromatograph/mass spectrometer (GC/MS) was used to assess real-time changes in PCE concentrations in the indoor air and sub-slab exhaust vapors during VIMS startup. PCE concentrations in the VIMS exhaust averaged approximately 72,400 μg/m³ immediately following startup. Within 24 hours, indoor air PCE concentrations were reduced by approximately one order of magnitude at most buildings as measured by the HAPSITE. After one month of operation, indoor air PCE concentrations had dropped by up to 99 percent, while the extracted sub-slab vapor PCE concentrations were virtually unchanged. The SVE system was brought online two months after VIMS startup. During SVE startup, PCE concentrations in the SVE exhaust averaged 210,000 μg/m³. The average PCE concentration in the SVE exhaust declined to 8,900 μg/m³ after 5 months of SVE operation. After 7 months of VIMS operation, both indoor air and sub-slab vapor PCE concentrations were reduced to near or below the USEPA regional screening level. The results suggest that the SVE system is remediating deep vadose zone soil while limiting transport of the high concentration PCE vapors to shallow soil underlying the building slabs. Rebound pilot testing at one building after taking the VIMS offline showed a small increase in PCE indoor concentrations after 30 days with subslab levels remaining below detection limits, which indicated SVE is likely sufficient to mitigate vapor intrusion while remediating the vadose zone source. Additional long-term monitoring and system optimization are planned as part of future operations and maintenance activities.
EPA/AEHS 2015 Vapor Intrusion Workshop Abstracts 10 ESTCP Research on Optimization of Vapor Intrusion Mitigation Systems in Large Military Buildings
Todd McAlary, Geosyntec Consultants; Dr. Paul Johnson, Arizona State University; Bill Angell, University of Minnesota; Bill Brodhead, WPB Enterprises, Inc.; Bill Wertz, NYSDEC; Henry Schuver, U.S. EPA ORCR; Robert Ettinger, Paul Nicholson, Geosyntec Consultants
Mitigation systems for radon and VOC vapor intrusion mitigation have traditionally been designed to induce a vacuum below the floor (sub-slab depressurization). There are challenges with this concept: 1) the range of pressure differential across the floor depends on the building design, wind and weather conditions, floor slab integrity and operation of mechanical fans, 2) measuring an induced vacuum that is clearly resolved from ambient cross-floor pressure fluctuations requires a certain “signal to noise” ratio that is not consistent from building to building, 3) the permeability of materials below the floor and leakage of air across the floor have a significant influence, but are not typically quantified. New methods for measuring design parameters and monitoring the performance of mitigation systems are being tested to assess whether mitigation can be achieved more cost-effectively, especially for large buildings.
Results of testing at a 64,000 ft2 building will be presented, including mass flux monitoring, transient and steady-state pneumatic testing, sub-floor helium testing (inter-well and flood designs), radon monitoring and mathematical modeling to quantify the permeability of the materials below the floor and the leakance across the floor slab. These new lines of evidence provide insight into the performance of the system, and provide strong scientific evidence for system optimization. The study shows the system can be operated with about 10- fold reduction in cost and may result in a reduction in health risks with minimal modification.
EPA/AEHS 2015 Vapor Intrusion Workshop Abstracts 11 Survey of LTS programs (State & Federal)
David Gillay, Barnes & Thornburg LLP
This presentation will highlight the results of a survey of representative state and federal Long Term Stewardship (LTS) programs. The highlights will focus on key benchmarks that are essential for a viable LTS program, including but not limited to regulatory, legal, and practical mechanisms used to track, enforce, maintain, and manage LTS obligations. The federal LTS program springs from US EPA’s new IC policy which is set forth in two guides: Institutional Controls: A Guide to Planning, Implementing, Maintaining, and Enforcing Institutional Controls at Contaminated Sites, EPA-540-R-09-001 (Dec. 2012) [referred to as “IC Guidance”] and Institutional Control: A Guide to Preparing Institutional Control Implementation and Assurance Plans at Contaminated Sites, EPA-540-R-09-002 (Dec. 2012) [referred to as “ICIAP Guidance”]. The IC Guides are relevant to cleanup actions taken at Comprehensive Environmental Response, Compensation and Liability Act (CERCLA, or Superfund), Brownfields, federal facility, underground storage tank (UST), and/or Resource Conservation and Recovery Act (RCRA) sites. EPA’s IC Guidance clarifies how to plan, implement, maintain, and enforce ICs at contaminated sites. The IC Guidance was designed to help promote consistent national policy on these prevalent issues. The ICIAP Guidance is the companion document to the IC Guidance and offers a template to develop IC plans at contaminated sites where the response action includes ICs. EPA describes an ICIAP as a “document designed to systematically: (a) establish and document the activities associated with implementing and ensuring the long- term stewardship of ICs: and (b) specify the persons and/or entities that will be responsible for conducting these activities.” If a responsible party plans to leave residual contamination in place as part of a remedial action, then these IC Guides will help identify the long-term care, stewardship obligations, and costs for such risk-based remedies.
EPA/AEHS 2015 Vapor Intrusion Workshop Abstracts 12 Example application of LTS for the CVI pathway (and VOC sources)
Megan Hamilton, Environmental Forensic Investigations, Inc. (EnviroForensics)
Long Term Stewardship (LTS) is a topic that is currently at the forefront of the Environmental Field, as it is a pivotal component of site closure. In 2014, U.S. EPA and the Indiana Department of Environmental Management (IDEM) clarified and refined guidance that significantly affects how contaminated sites are investigated, remediated, and closed. Some of these clarifications involve the potential LTS obligations related to residual contamination remaining after remedial activities have been completed. Long-term management is necessary in these situations to protect human health and the environment. This presentation will outline an example application of how the emerging concepts of LTS can be practically applied to a site with chlorinated volatile organic compounds (VOCs) and a completed chlorinated vapor intrusion (CVI) pathway. The presentation will outline three site remediation strategies with LTS components included, along with associated conceptual costs for each.
EPA/AEHS 2015 Vapor Intrusion Workshop Abstracts 13 Residential Building Vapor Intrusion Lifecycle Cost Evaluation for Natural and Controlled Conditions
Dr. Ian Hers, Golder Associates Ltd.; Robert Truesdale, RTI International; Dr. Henry Schuver, U.S. EPA ORCR; Chris Lutes, CH2MHill; David Folkes, Geosyntec Consultants
The long-term evidence-based protection and sustainability of approaches to evaluate and mitigate pathway completeness and potential risk is an emerging topic of interest to vapor intrusion practitioners. This presentation develops a lifecycle cost evaluation for residential buildings by comparing a strategy involving monitoring only to one where a building is mitigated early in the process followed by a limited monitoring program to verify that mitigation is effective. For monitoring programs, the concept of equivalent protection is introduced to enable the efficacy of different monitoring frequencies to be compared in the context of both acute and chronic toxicological concerns. Indoor concentration variability plays a role in the design of monitoring programs and data interpretation. Data from four case studies are summarized to provide insight on this issue.
A comprehensive monitoring and mitigation design basis is established to support the lifecycle cost analysis and a detailed cost breakdown is provided for monitoring only and mitigation scenarios based on typical cost ranges for residential houses. Preliminary results of the lifecycle analysis indicate that for an acute concern with a monitoring frequency that is equally protective to mitigation (i.e., sampling on a monthly or bi-monthly basis), lower costs are associated with the mitigation option when compared to the monitoring only scenario, with a breakeven point of less than 2 years. For monitoring appropriate to characterize a chronic concern, the lifecycle analysis does not indicate a clear difference with respect to costs for monitoring only versus mitigation, assuming that less frequent monitoring is appropriate for the mitigation scenario.
EPA/AEHS 2015 Vapor Intrusion Workshop Abstracts 14 Non-residential Building Vapor Intrusion Lifecycle Cost
Chris Lutes, CH2MHILL; Dr. Ian Hers, Golder Associates Ltd.; David Folkes, Geosyntec Consultants; Dr. Henry Schuver, U.S. EPA ORCR; Robert Truesdale, RTI International
In this presentation we will compare the economics for two basic scenarios that could be chosen at a building with one round of indoor air data already in hand: 1) mitigation early vs.
2) extensive investigation
The context for the analysis will be a hypothetical industrial/commercial building with conditions that make this decision “in the grey area”. The goal will be to compare costs to deliver an equivalent level of protectiveness with either approach. Cumulative cost curves over 30 years will be presented. A sensitivity analysis will explore the impact of: Building size
Building Complexity
Mitigation difficulty (soil type)
Sampling frequency requirements and
Reporting requirements
Remediation that reduces the operational time on these costs.
EPA/AEHS 2015 Vapor Intrusion Workshop Abstracts 15 Community perspective on non-quantitative aspects of assessment/mitigation decisions, including a recent school case and the need for early risk communication
Lenny Siegel, Center for Public Environmental Oversight (CPEO); Nate Burden, FICS (Fidelity Inspections)
Public stakeholders at vapor intrusion study sites, if properly informed about investigations in a timely fashion, can be constructive partners in developing suitable, protective environmental responses. Using recent experience at Moffett Military Housing (California), former Ft. Gillem (Georgia), and above all the Hanes- Lowrance Middle School Complex in Winston-Salem, North Carolina, Lenny Siegel will describe how trust remains the key foundation of any community engagement strategy. If people feel they have been denied information, or if agencies fail to work with community-based organizations, then community members may assume the worse.
EPA/AEHS 2015 Vapor Intrusion Workshop Abstracts 16 Update on Soil Gas Mitigator’s Standard and Credential
Kyle Hoylman, Protech Environmental; Tony McDonald, AZ Solutions, Inc.
A review of the progress toward finalizing the AARST/ ANSI Standard for Residential Radon/ VI Mitigation Systems will be presented. Current committee discussions include decision making based on site specific contamination levels, the relationship between sub-slab contaminate strength and discharge requirements, and designing low maintenance systems. A preview of how to get involved in the upcoming public comment period on the standard and credential will also be discussed.
EPA/AEHS 2015 Vapor Intrusion Workshop Abstracts 17 Poster Abstracts
Monday Evening, March 23, 2015 – 7:00–9:00 PM PDT
Estimating Mass Flux to Groundwater & Vapor Intrusion from SVE Data and High Resolution Measures of Permeability and Concentration
Dr. Lloyd Stewart, Praxis Environmental Technologies, Inc., Burlingame, California, USA
Background/Objectives. Techniques to estimate accurately the long-term contaminant mass loading to underlying ground water or overlying buildings from persistent contaminant sources in the vadose zone have been studied for more than two decades. The results are commonly used for assessing closure of SVE systems. Guidance is provided by EPA, Army Corps of Engineers, and Department of Energy. Benchmarks for ceasing soil vapor extraction (SVE) are usually based on mass flux predictions from simplistic transport models such as VLEACH that assume one-dimensional vertical transport through uniform soil with a constant infiltration rate. The boundary condition at the water table ignores any interaction with the ground water. The results from such modeling are very often unrealistic as dominant transport features are marginalized or lost. The presented work describes a robust framework for predicting the impact to vapor intrusion or ground water of residual vadose zone contamination. The approach overcomes the deficiencies of assuming a uniform vadose zone while maintaining a simplicity of calculation and a connection to actual conditions. An example site in Southern California with a highly stratified, TCE-contaminated vadose zone where SVE had operated for five years illustrates the approach.
Approach/Activities. The evaluation of the residual TCE mass in the vadose zone of the example site was initiated by reviewing the extraction and rebound data measured during SVE. The SVE data yielded estimates of diffusion-limited mass transfer constraints calculated as described in USACE (2002). The mass transfer constraints observed during SVE are often ignored but are the same as those that dominate post-SVE transport. The SVE values provide a basis for estimating contaminant diffusion rates. Concurrent with the SVE data evaluation, a field effort employed pneumatic logging to provide high resolution measures (i.e., 2-cm vertical intervals) of vapor permeability and TCE concentration along SVE well screens located among the centroid of the residual mass. With these profiles, a layered model of the vadose zone with variable diffusion coefficients was readily constructed and the high resolution vapor concentration profile provided the initial condition for modeling. The modeling was performed with a modified VLEACH code that included variable soil properties and more realistic boundary conditions at the water table and ground surface. A boundary condition representing the resistance of ground water to the entry of contaminants was employed and is described.
Results/Lessons Learned. The model diffusion coefficients based on the logged profiles were found to be consistent with those estimated from the SVE data, providing independent support for the model validity. The calculation of mass flux into groundwater and its mixing were consistent with historical ground water concentrations measured in monitoring wells adjacent to the site. The initial rate of TCE mass entering ground water was almost an order-of-magnitude less than the end of SVE, as expected. A comparison calculation with VLEACH and a uniform vadose zone revealed that property averaging eliminated the dominant transport process at the site yielding unrealistic results.
EPA/AEHS 2015 Vapor Intrusion Workshop Abstracts 18 Remote monitoring and management of vapor intrusion systems supporting structured OM&M and efficient long term stewardship
Tom Hatton and Daniel Nuzzetti, Clean Vapor, LLC
For the past 25 years technical advancements in soil depressurization systems and the application of allied technologies to better manage vapor intrusion sites have been at a virtual standstill. Post mitigation Operations and Maintenance programs are typically proposed as part of commissioning reports but only occasionally do they advance to the next stage of field application. Advancements in telemetry and an increased awareness in the importance of delivering an extended standard of care have ushered in a new era of vapor intrusion Operations Maintenance, Monitoring and Management.
With a greater need for continued care, consultants have been able to integrate telemetric monitoring and active management into the sites long term stewardship agreement. The poster will graphically illustrate how integrating dynamic controls and telemetric surveillance at a subject site has facilitated real time active offsite management and yielded significant energy savings. The poster will also illustrate how the application of telematics can achieve a component of regulatory compliance; provide a greater level of care through real time performance monitoring, fault notification and active management. Telemetrically managed systems can deliver automated regulatory and client reports all within the umbrella of energy savings, reducing operational costs and limiting liability.
Building a Vapor Intrusion Case: Use of Multiple Lines of Evidence to Support a Site Conceptual Model for TCE Migration Under a Residential Neighborhood
Nadine Weinberg, Katherine Eyre, Darren Scillieri, ARCADIS U.S., Inc. (ARCADIS)
Draft guidance released by U.S. Environmental Protection Agency (USEPA) has the potential to extend vapor intrusion (VI) investigations indefinitely due to perceived uncertainties in the data sets generated to evaluate this exposure pathway. At this site, a multiple lines of evidence (MLE) approach was used to evaluate VI from a large trichloroethylene (TCE) plume. TCE concentrations were historically up to 15 milligrams per liter (mg/L) in groundwater on the source property and determined to be present under several residential and commercial buildings. An initial, local Agency investigation of VI did not identify any immediate concern.
TCE concentrations in shallow groundwater were later determined to be significantly lower (< 0.050 mg/L but still exceeding USEPA VI screening levels) than concentrations at deeper depths. Thus, additional VI investigation was requested, in part due to vadose zone lithology of well-sorted fine to medium grained sand. A MLE was developed to focus the data collection and analysis, and obtain USEPA approval on the scope. The MLE started with nested soil gas samples from 17 locations downgradient from the source area. These data confirmed that TCE was not present in the vadose zone above reporting limits, providing clear evidence that TCE was not migrating into residential homes.
Per the MLE and agreement with USEPA, direct measurements (i.e., sub-slab soil gas and indoor air) were required because the Agency continued to express concern that the VI pathway was complete for residences overlying the TCE plume. With regulatory concurrence on the MLE work plan, data were collected from 21 residences and a commercial building that demonstrated that TCE was not present in sub-slab soil gas or indoor air above conservative screening levels. Thus, the data confirmed the findings of the comprehensive soil gas study in which data were collected over and close to the TCE groundwater plume.
EPA/AEHS 2015 Vapor Intrusion Workshop Abstracts 19 A Life Cycle and Cost Analysis of Preemptive Mitigation, Site Characterization, and/or Vapor Source Reduction Strategies at Industrial VI Sites with Multiple Buildings
Dr. Loren Lund, Christopher Lutes, and John Lowe, CH2M HILL
Preemptive vapor intrusion (VI) mitigation is the phrase used for implementing controls to prevent potential VI from occurring prior to having fully demonstrated the pathway is complete and significant in a building. Preemptive VI mitigation has been proposed in the U.S. Environmental Protection Agency (EPA) 2013 External Review Draft VI guidance as a management strategy that is more timely, more cost effective, less disruptive, and that is preferable to communities and building occupants. However, it is important to consider the practical aspects of its implementation and whether this is the case at all buildings/sites. A decision analysis approach is presented in this poster that allows multiple factors to be considered, such as human health protection, occupant disruption, time to protection and time to closure. The performance of each mitigation alternative is scored based on expert judgment and weighted to reflect the priorities of stakeholders in order to calculate an overall value. These overall values can then be compared with cost.
This poster summarizes several of the above issues and risk management factors, including the basis of design for preemptive VI mitigation systems, performance monitoring, long-term stewardship, demonstration of risk reduction, and VI site exit strategies/closure. Examination of different VI site conditions using scenario analysis, alternatives analysis, and lifecycle assessment indicates that preemptive VI mitigation may only be preferable for a limited subset of buildings/sites. This is particularly true when considering preemptive VI mitigation at a large group of non-residential structures. These analyses were also used to systematically evaluate the other proposed benefits of preemptive mitigation, particularly cost-effectiveness and health risk reduction. A particular concern identified in these analyses is that preemptive mitigation has the potential to adversely impact closure of VI sites by averting or deferring the characterization of the nature and extent of subsurface VOC impacts, as is required under the (National Contingency Plan) NCP. The pros and cons of preemptive VI mitigation under different scenarios and site/building conditions will be summarized in order to facilitate data- driven risk management decisions.
A Survey of Vapor Intrusion Characteristics of Nonresidential Buildings—are Industrial Buildings Different?
Christopher Lutes, Keri Hallberg, John Lowe, Dr. Loren Lund, Mike Novak, CH2MHill; Patricia Venable, Tanwir Chaudhry, and Tara Meyers, EXWC; Ignacio Rivera, SPARWAR; Donna Caldwell, NAVFAC-LANT
Background/Objectives: Most vapor intrusion (VI) policy in the US is informed primarily by studies conducted in residential structures of volatile organic compounds (VOCs) in groundwater, located away from the primary contaminant release. For example the default attenuation factors used routinely are derived from the EPA database analysis of residential structures. It has been frequently suggested that nonresidential buildings vary significantly in their resistance to VI due to foundation and ventilation characteristics, but few datasets are available to support that hypothesis. In addition, when faced with large populations of buildings within screening distances of volatile subsurface contaminants, innovative methods are needed to:1) prioritize those buildings in an area most likely to be effected by VI, and 2) make decisions concerning investigation and mitigation strategies based on subslab and groundwater data sets.
Approach/Activities: We assembled a relational database containing information on 150 sampling zones in 49 military structures at 12 different installations where measurements of chlorinated VOCs were available in indoor air, subslab soil gas and/or groundwater. The relational database contains chemical measurements, multiple observations characterizing the buildings, and descriptions of specific locations within a building where
EPA/AEHS 2015 Vapor Intrusion Workshop Abstracts 20 the chemical measurements were made. Building characteristics analyzed include dimensions, use, and construction date, HVAC type, flooring types, subgrade structures and atypical preferential pathways. Subsurface characteristics analyzed include soil type, depth to groundwater and distance to location of primary release. Exploratory data analysis was conducted using graphical presentations and descriptive statistics. Frequency of detection and issues regarding data censoring were assessed. Screening to minimize the impacts of indoor sources on the analysis was performed. Buildings influenced by atypical preferential pathways were analyzed separately.
Results/Lessons Learned: PCE and TCE show a correlation between sub-slab soil gas and indoor air concentrations as expected; however, only very high sub-slab soil gas concentrations (relative to USEPA [2014] defaults, which are based primarily on residential buildings) result in indoor air concentrations in excess of conservative indoor air screening levels. For example, PCE concentrations in sub-slab soil gas in excess of 100,000 µg/m3 were necessary before concentrations in indoor air exceeded the USEPA (2014) indoor air screening level of 47 µg/m3. TCE concentrations in excess of 2,000 µg/m3 were required in sub-slab soil gas before indoor concentrations exceeded 3.0 µg/m3.
The correlation between groundwater vapor concentration and sub-slab soil gas concentration for PCE appears approximately linear on a log-log plot, suggesting a power law relationship between the two variables. A similar but weaker relationship was observed for TCE. Analysis of the relationship between groundwater vapor concentration (calculated through Henry’s Law) and indoor air suggests that exceedances of indoor air screening levels should only be expected when the groundwater vapor concentration exceeds 10,000x the indoor air screening level in DoD buildings.
Increasing sample zone area was significantly associated with decreasing indoor concentration on a log-log plot. Higher sub-slab soil gas concentrations were associated with fine (i.e., silt or clay) soil types for PCE; TCE; trans- 1,2-DCE; cis 1,2-DCE; 1,1,1-TCA; and 1,1-DCE. The single strongest predictor variable for high indoor concentrations, in many of the multiple regressions performed was winter sampling.
A Real-Time VOC Sensor for VI Investigations: Recent Research, Planned Field Tests, and Potential Future Applications
Robert Truesdale, Li Han, David Ensor, RTI International; Chris Lutes, CH2MHill
RTI has developed an innovative real- time sensor capable of detecting volatile organic compounds (VOCs) at low levels in indoor and outdoor air. RTI’s patented sensor operates on the principle of conductivity changes of composite polymer nanofibers (containing carbon nanotubes) when exposed to sub-ppbv levels of VOCs. It was developed and tuned to target classes of priority VOCs by selecting polymers with appropriate moieties. Prototype monitors have been constructed for laboratory feasibility tests where proof of concept has been demonstrated, including sensitivity to common contaminants of concern for the vapor intrusion (VI) pathway (i.e., trichloroethylene [TCE]; tetrachloroethylene [PCE]). These contaminants are often of concern at VI sites because they are resistant to biodegradation (leading to long groundwater plumes under many buildings), have significant cancer risks, and, for TCE, have short term developmental health effects (i.e., birth defects). These concerns, along with recent studies suggesting that short term concentration spikes can contribute significantly to long term VI exposure have created a need for cost-effective “real-time” monitoring of VOCs in indoor and outdoor air at VI sites. Traditional methods (e.g., TO-15 Summa canisters, passive samplers) do not provide the temporal resolution for short-term monitoring, have relatively high costs, and do not provide real-time signaling when VOC levels rise indoors or outdoors. Field deployable GCs can give the real-time, short-interval sampling,
EPA/AEHS 2015 Vapor Intrusion Workshop Abstracts 21 but are expensive to buy and require significant maintenance and a trained operator to operate successfully in the field.
RTI’s sensor device is small and inexpensive even in the prototype stage; the potential for widespread adoption is great if certain development challenges can be overcome. It has been demonstrated to be sensitive to both TCE and PCE down to sub-ppb levels (e.g., 0.03 ppbv TCE) and has a fast response time (< 7 minutes) for both compounds. The relatively low cost of current prototype sensor (<$500 for the parts) and small size of the device (cell phone size; < 50g) makes it attractive and potentially suitable for large field applications at VI sites or for other environmental problems where air VOC concentrations are of concern. Because it works through conductivity changes, it produces an electrical signal that is ready for telemetric networking through smart phone apps and other wireless communication technologies.
Side by side studies with TO-15 and passive samplers will be described as a next step for testing of this novel sensor, including tests against long-term Summa canister devices as well as side by side testing against passive samplers. Although challenges remain (e.g., compound specificity; interferents [moisture]; unknown lifetime), approaches to solve these problems have been developed and will be underway soon to provide more robust, second-generation devices for testing in calendar year 2015-2016.
EPA/AEHS 2015 Vapor Intrusion Workshop Abstracts 22