INVESTIGATION OF VOLATILE ORGANIC COMPOUNDS (VOCs) DETECTED AT VAPOR INTRUSION SITES

This dissertation investigates unexplained vapor intrusion field data sets that have been observed at hazardous waste sites, including: 1) non-linear soil gas concentration trends between the VOC source (i.e. contaminated groundwater plume) and the ground surface; and, 2) alternative pathways that serve as entry points for vapors to infiltrate into buildings and serve to increase VOC exposure risks as compared to the classic vapor intrusion model, which primarily considered foundation cracks as the route for vapor entry. The overall hypothesis of this research is that theoretical knowledge of fate and transport processes can be systematically applied to vapor intrusion field data using a multiple lines of evidence approach to improve the science-based understanding of how and when vapor intrusion exposure risks will pose increased exposure risk; and, ultimately this knowledge can be used to develop policies that reduce exposure risks. The first objective of this research involved numerical modeling, field sampling and laboratory tests to investigate which factors influence soil gas transport within the subsurface. Combining results of all of these studies provide improved understanding of which factors influence VOC fate and transport within the subsurface. Importantly, the results demonstrate a non-linear trend between the VOC source concentration in the subsurface and the ground surface concentration at the study site, which disagrees with many vapor intrusion conceptual models. Ultimately, the source concentration may not be a good predictor of shallow soil gas concentrations. Laboratory tests described the effect of soil characteristics such as the soil water content on VOC vapor diffusion. The numerical model was able to explain specific conditions that could not be described by the field and laboratory data alone. A paper was published that summarizes the major outcomes from this objective (Pennell et al, 2016). The second objective of this research investigated preferential pathways for VOC vapor migration into buildings. Sewer systems can act as important pathways for vapor intrusion. The research objective is to evaluate conditions that increase the potential for inhalation exposure risks via vapor intrusion thorough sewer systems into indoor spaces. A field study was conducted in California over a 4-year period to investigate the spatial and temporal variability of alternative pathways (e.g. aging infrastructure piping systems) within the context of vapor intrusion exposure risks. A paper was published that summarizes the major outcomes from the field study (Roghani et al. 2018). The final research objective involved the development of a numerical model to describe VOC fate and transport within a sewer system. The numerical model predicts VOC mass transport. The model results were compared to the field data and provides insight about the role preferential pathways play in increasing VOC exposure risks

INVESTIGATION OF ATMOSPHERIC EFFECTS ON VAPOR INTRUSION PROCESSES USING MODELLING APPROACHES

Most people in the United States (US) spend considerable amount of time indoors—about 90% of their time as compared to outdoors, which makes the US population vulnerable to adverse health effects of indoor air contaminants. Volatile organic compound (VOC) concentrations are well-known to be higher in indoor air than outdoor air. One source of VOC concentrations in indoor air that has gained considerable attention in public health and environmental regulatory communities is vapor intrusion. Vapor intrusion is the process by which subsurface vapors enter indoor spaces from contaminated soil and groundwater. It has been documented to cause indoor air contamination within hundreds of thousands of communities across the US. Vapor intrusion is well-known to be difficult to characterize because indoor air concentrations exhibit considerable temporal and spatial variability in homes throughout impacted communities. Unexplained variations in field data have not been systematically investigated using theoretical fate and transport processes. This study incorporates the use of numerical models to better understand processes that influence spatial and temporal variability in field data. The overall research hypothesis is that variability in indoor air VOC concentrations can be (partially) explained by variations in building air exchange rate (AER) and pressure differentials between indoor spaces and outdoor spaces. Neither AER nor pressure differentials are currently calculated by existing vapor intrusion numerical models. To date, most vapor intrusion models have focused on subsurface fate and transport processes; however, there is a need to understand the role of aboveground processes in the context of vapor intrusion exposure risks, which are commonly measured as indoor air VOC concentrations. Recent field studies identify these parameters as potentially important and their important role within the broader field of indoor air quality sciences has been well-documented, but more research is needed to investigate these parameters within the specific context of vapor intrusion. To test the overall hypothesis, the dissertation research developed a new vapor intrusion modeling technique that combines subsurface fate and transport modeling with building science approaches for modeling driving forces, such as wind and stack effects. The modeling results are compared with field data measurements from actual vapor intrusion sites and confirms that the research is relevant to not only academic researchers, but also policy decision makers

Demonstration and Validation of the Use of Passive Samplers for Monitoring Soil Vapor Intrusion to Indoor Air

This thesis documents a demonstration/validation of passive diffusive samplers for assessing soil vapor, indoor air and outdoor air concentrations of volatile organic compounds (VOCs) at sites with potential human health risks attributable to subsurface vapor intrusion to indoor air. The study was funded by the United States (U.S.) Department of Defense (DoD) and the U.S. Department of the Navy (DoN). The passive samplers tested included: SKC Ultra and Ultra II, Radiello®, Waterloo Membrane Sampler (WMS), Automated Thermal Desorption (ATD) tubes, and 3M OVM 3500. The program included laboratory testing under controlled conditions for 10 VOCs (including chlorinated ethenes, ethanes, and methanes, as well as aromatic and aliphatic hydrocarbons), spanning a range of properties and including some compounds expected to pose challenges (naphthalene, methyl ethyl ketone). Laboratory tests were performed under conditions of different temperature (17 to 30 oC), relative humidity (30 to 90 % RH), face velocity (0.014 to 0.41 m/s), concentration (1 to 100 parts per billion by volume [ppbv]) and sample duration (1 to 7 days). These conditions were selected to challenge the samplers across a range of conditions likely to be encountered in indoor and outdoor air field sampling programs. A second set of laboratory tests were also conducted at 1, 10 and 100 parts per million by volume (ppmv) to evaluate concentrations of interest for soil vapor monitoring using the same 10 VOCs and constant conditions (80% RH, 30 min exposure, 22 oC). Inter-laboratory testing was performed to assess the variability attributable to the differences between several laboratories used in this study. The program also included field testing of indoor air, outdoor air, sub-slab vapor and deeper soil vapor at several DoD facilities. Indoor and outdoor air samples were collected over durations of 3 to 7 days, and Summa canister samples were collected over the same durations as the passive samples for comparison. Subslab and soil vapor samples were collected with durations ranging from 10 min to 12 days, at depths of about 15 cm (immediately below floor slabs), 1.2 m and 3.7 m. Passive samplers were employed with uptake rates ranging from about 0.05 to almost 100 mL/min and analysis by both thermal desorption and solvent extraction. Mathematical modeling was performed to provide theoretical insight into the potential behavior of passive samplers in the subsurface, and to help select those with uptake rates that would minimize the risk of a negative bias from the starvation effect (which occurs when a passive sampler with a high uptake rate removes VOC vapors from the surroundings faster than they are replenished, resulting in biased concentrations). A flow-through cell apparatus was tested as an option for sampling existing sub-surface probes that are too small to accommodate a passive sampler or sampling a slip-stream of a high-velocity gas (e.g., vent-pipes of mitigation systems). The results of this demonstration show that all of the passive samplers provided data that met the performance criteria for accuracy and precision (relative percent difference less than 45 % for indoor air or 50% for soil vapor compared to conventional active samples and a coefficient of variation less than 30%) under some or most conditions. Exceptions were generally attributable to one or more of five possible causes: poor retention of analytes by the sorbent in the sampler; poor recovery of the analytes from the sorbent; starvation effects, uncertainty in the uptake rate for the specific combination of sampler/compound/conditions, or blank contamination. High (or positive) biases were less common than low biases, and attributed either to blank contamination, or to uncertainty in the uptake rates. Most of the passive samplers provided highly reproducible results throughout the demonstrations. This is encouraging because the accuracy can be established using occasional inter-method verification samples (e.g., conventional samples collected beside the passive samples for the same duration), and the field-calibrated uptake rates will be appropriate for other passive samples collected under similar conditions. Furthermore, this research demonstrated for the first time that passive samplers can be used to quantify soil vapor concentrations with accuracy and precision comparable to conventional methods. Passive samplers are generally easier to use than conventional methods (Summa canisters and active ATD tubes) and minimal training is required for most applications. A modest increase in effort is needed to select the appropriate sampler, sorbent and sample duration for the site-specific chemicals of concern and desired reporting limits compared to Summa canisters and EPA Method TO-15. As the number of samples in a given program increases, the initial cost of sampling design becomes a smaller fraction of the overall total cost, and the passive samplers gain a significant cost advantage because of the simplicity of the sampling protocols and reduced shipping charges

The 23rd Annual International Conference on Soils, Sediments and Water

Conference at a Glance Monday, October 15, 2007 (workshop #1-2: 9:00am – 5:00pm, workshop #3: 10am – 5:00pm, workshop #3, 10:00am – 5:00pm, workshops #4, 5, & 6, 1:00pm – 5:00pm, workshop #7 & 8, 2-5pm) 1) Compliant Analysis of Water, Wastes and Related Solid Environmental Samples Using Inductively Coupled Plasma Atomic Emission and Mass Spectrometry 2) In-Situ Chemical Oxidation Workshop 3) Theory and Use of Field Portable X-ray Fluorescence for Soil Analysis 4) The 2007 MCP Audit – A Case Study Approach 5) “Lies, Damned Lies, and Statistics”: Avoiding Pitfalls in Environmental Sampling 6) Evaluating Monitored Natural Attenuation of MTBE and TBA 7) Environmental Forensic Techniques for Classic and Emerging Contaminants 8) Environmental Fate of Hydrocarbons in Soils and Groundwater Tuesday, October 17, 2007 Morning 8:30am – 9:00am Conference Welcome and Overview 9:00am – Noon, Sessions are concurrent Session 1: Ethics in Environmental Practice: Responsibilities, Benefits & Case Examples Session 2a: Pesticides Session 2b: Vapor Intrusion Session 3a: Brownfields Session 3b: Fisherville Mill - Assessment and Cleanup of a Brownfields Site on the Blackstone River Session 4a: Environmental Fate Session 4b: Sediments Afternoon 1:30 to 5:30pm, Sessions are concurrent Session 1: Phytoremediation Session 2: Biotechnology Session 3: Tungsten Session 4: Combining Chemical and Biological Technologies for Soil and Groundwater Remediation Session 5: Environmental Forensics Poster Sessions 4:00 – 6:00pm Arsenic Environmental Fate Environmental Forensics Pesticides Phytoremediation Remediation Sediments Tungsten Vapor Instrusion Social 4:30 – 6:00pm, exhibit area, 1st floor Workshops (Evening, 7:00 – 10:00pm) 9) In-Situ Thermal Remediation 10) Applied Chemical Fingerprinting in Environmental Forensics 11) Utilization of Stable Isotopes in Environmental and Forensic Geochemistry Studies 12) Professional Ethics, Professional Conduct, and Environmental Professionals Wednesday, October 17, 2007 Morning 8:30am – Noon, Sessions are concurrent Session 1: Gasoline Oxygenates I Session 2: Remediation I Session 3: Regulatory Session 4: Coated and Uncoated Microbubble Ozone Remediation Projects Afternoon 1:30 – 5:30pm, Sessions are concurrent Session 1: Gasoline Oxygenates II Session 2: Perchlorate/MECs Session 3: Analysis Session 4: Chemical Oxidation Poster Sessions 4:00 – 6:00pm Acid Mine Drainage Analysis Bioremediation Brownfields Chemical Oxidation Emerging Issues with Energy in the Environment Heavy Metals MECs Miscellaneous MTBE Radionuclides Site Assessment Social 4:30 – 6:00pm, exhibit area, 1st floor Workshops (Evening, 7:00 – 10:00pm) 13) Critical Exposure Pathways 14) Characterizing PAH Bioavailability in Sediments for Remedial Decision-Making 15) Theory and Application of Molecular Biological Tools (“MBTs”) and Biogeochemistry to Bioremediation Process Monitoring and Monitored Natural Attenuation Programs 16) Geochemical Evaluations of Metals in Environmental Media: How to Distinguish Naturally Elevated Metals Concentrations from Site-Related Contamination Thursday, October 18, 2007 Morning 8:30am – Noon Sessions are concurrent Session 1: Bioremediation Session 2: Remediation II Session 3: Modeling Session 4: Risk Assessment Afternoon 1:30pm – 5:00pm Sessions are concurrent Session 1: Heavy Metals Session 2: Innovative Technologies Session 3: Site Assessmen

Transport and biodegradation of volatile organic compounds : influence on vapor intrusion into buildings

Vapor intrusion occurs when volatile subsurface contaminants, migrating from the saturated zone through the unsaturated zone, accumulate in buildings. It is often the most relevant pathway for human health risks at contaminated sites, especially in urban areas; yet its assessment is controversial. Field assessment of vapor intrusion risk is complicated by two interrelated main factors that are controlled by the contaminant’s properties: transport processes in the unsaturated zone and biodegradation in the unsaturated zone. Commonly available vapor intrusion models either overlook significant properties at the field scale or, conversely, are too complex to be applicable at this scale. Specifically, moisture variation, liquid diffusion, dynamic processes such as water table variations, and biodegradation are not adequately accounted for. As a result, the soil gas and indoor air concentrations predicted by existing models frequently overestimate measured concentrations by several orders of magnitude. This thesis addressed transport and biodegradation processes of volatile organic compounds, focusing on aerobic unsaturated zones. The main aims were to i) characterize significant transport processes influencing vapor intrusion and ii) quantify and mechanistically describe biodegradation in unsaturated soils. Field experience, numerical modeling and laboratory experiments with toluene and vinyl chloride as reference compounds were combined to separate out the relevant processes influencing vapor intrusion. The main conclusions from this thesis indicate that soil moisture variations and aerobic biodegradation are crucial aspects to be jointly considered for the assessment of vapor intrusion. These may contribute to a significant reduction in the risk associated with dissolved volatile organic contaminants. Specific and relevant implications for modeling and monitoring vapor intrusion can be derived. With respect to vapor intrusion modeling, when including unsaturated zone biodegradation, the use of liquid phase biodegradation rates as derived from liquid mixed batches may underestimate by several orders of magnitude the liquid degradation rates in the unsaturated system. Therefore, biodegradation rates derived from unsaturated system appear more appropriate. With respect to monitoring, vertical soil moisture variations and contaminant/oxygen concentration profiles need to be measured in the field, in order to account for the above processes. </p