Presented January 14, 2016- Presentation Slides
Impact of EPA’s Final Vapor Intrusion Guidance on the Regulated Community by Dr. Helen Dawson
EPA’s publication of its June 2015 “Technical Guide for Assessing and Mitigating the Vapor Intrusion Pathway from Subsurface Vapor Sources to Indoor Air” represents a major update in EPA’s recommendations for addressing the vapor intrusion (VI) pathway. The Guide reaffirms many prior EPA VI policies, modifies some, and adds a few new policies and recommendations. This presentation will focus on EPA’s modified or new recommendations that have significant impact on the regulated community.
The cumulative impact of EPA’s final VI technical guide is to require more comprehensive characterization, i.e., greater numbers of samples over space and time, and more frequent remediation. As a result, assessment and, potentially, mitigation have become more costly. These impacts are due to concerns over: (1) the magnitude of spatial and temporal variability exhibited by VI pathway media concentrations; and (2) adverse health effects from short-duration exposures to trichloroethylene.
In 2015, ESTCP began funding a VI research project (ER-201503) that aims to demonstrate mass flux characterization as an alternative means of VI assessment capable of reducing the uncertainty associated with spatial and temporal variability. If successful, the methodology will allow more representative and timely estimates of the potential indoor air concentrations associated with VI, as well as provide a metric for terminating mitigation. The result will be more efficient and less expensive characterization and mitigation at VI sites. This presentation will also include a brief introduction to the mass flux characterization approach utilized in ER-201503.
Demonstration/Validation of Passive Samplers for Vapor Intrusion Assessment by Dr. Todd Alary
Vapor intrusion risks depend on the concentrations which building occupants are exposed to, and this can vary over time due to changes in the weather, building pressure and ventilation rate, and other factors. Temporal variability can be managed by collecting time-weighted average (TWA) samples to provide an average concentration over a representative interval. Conventional methods for volatile organic compound (VOC) sampling (EPA Method TO-15 and TO-17) are unfortunately limited to sample durations of about 24 hours. By contrast, radon guidance documents refer to 90-day long samples as “short-term” samples. Passive samplers for VOC monitoring are capable of longer samples than methods TO-15 or TO-17, so a comprehensive research program was conducted by ESTCP to demonstrate and validate their performance. The approach included laboratory testing at low concentrations typical of indoor air with a range of compounds, temperature, humidity, velocity and durations, as well as high concentrations typical of soil gas. The field testing included five DoD sites with indoor air, outdoor air, and soil gas. Five different passive samplers were tested with several different sorbents, durations of 10 minutes to 12 days, and concentrations from 0.1 to >100,000 µg/m3. Mathematical modeling was also performed to assess the rate of diffusion of VOC vapors to passive soil vapor samplers.
Results showed that passive samplers have good precision and accuracy for a given set of conditions. This is dependent on the calibration of the uptake rate for a particular compound/sampler/sorbent combination and conditions such as temperature, humidity, sample duration, and concentration. The commercially-available samplers tested are well-calibrated for many of the compounds of interest for vapor intrusion assessments, and can be field-calibrated if needed for other compounds or atypical conditions. Care is needed to avoid blank contamination and oversaturation of the sorbent by relying on QA/QC procedures similar to the ones used with EPA Method TO-17. This research also demonstrated for the first time the ability of low-uptake rate passive samplers to provide quantitative soil vapor concentration data.
Dr. Helen Dawson is a senior consultant for Geosyntec Consultants with more than 30 years of experience in private practice, academia, and public service. Her practice spans a wide range of technical disciplines including vapor intrusion, groundwater characterization, and contaminant fate and transport modeling related to the spread of dense non-aqueous phase liquids, chlorinated solvents, and metals in the environment. Dr. Dawson is a recognized leader in vapor intrusion. She was the primary author of the U.S. EPA’s Office of Solid Waste Emergency Response (OSWER) draft guidance for evaluating the vapor intrusion to indoor air pathways from groundwater and soils in 2002. She also was the primary investigator and author of two key technical documents that support vapor intrusion assessment, one on background indoor air concentrations in residences and another on the subsurface-to-indoor air attenuation at vapor intrusion sites. Dr. Dawson received her Bachelor’s degree from Stanford University in Geology, her Master’s degree in Geochemistry from the Colorado School of Mines, and her doctorate from Stanford University in Civil and Environmental Engineering.
Dr. Todd McAlary is a principal engineer at Geosyntec Consultants with more than 25 years of international consulting experience focused on the evaluation of contaminant fate and transport in soil and groundwater. At Geosyntec, Dr. McAlary has served as the Practice Leader for Vapor Intrusion Services for 17 years where he coordinates company-wide training, protocol development, marketing, and recruiting related to these services. Dr. McAlary has also served as a member of EPA’s Expert Panel on Vapor Intrusion for 16 years, and has authored or co-authored a dozen guidance documents on vapor intrusion. He is an Adjunct Professor in Chemical Engineering at the University of Toronto. Dr. McAlary received his Bachelor’s degree in Geological Engineering, Master’s degree in Hydrogeology, and doctorate in Chemistry, all from the University of Waterloo.