Dajun DaiRadon is a colorless, odorless, naturally occurring gas. It is currently the second leading cause of lung cancer and the number one cause of lung cancer to non-smokers in the United States. DeKalb County offers free screening for radon for residents. However, screening rates vary across the county. This pilot study focused on 14 selected tracts within DeKalb County with relatively low levels of radon screening. Over 200 households were recruited and homes were tested for indoor radon concentrations on the lowest livable floor over an 8-week period from March – May 2016. Tract-level characteristics were examined to understand the varitations of race, income, education, and poverty status between the 14 selected tracts and all of DeKalb County. The 14 selected tracts were comparable to all of DeKalb County in most factors besides race. Radon was detected in 73% of the homes sample and 4% had levels above the EPA guideline of 4 pCi/L. Multi-variate linear regression was used to compare all housing construction characteristics with radon concentrations and suggested that having a basement was the strongest predictive factor for detectable and/or hazardous levels of radon. Radon screening can identify problems and spur home owners to remediate but low screening rates may impact the potential health impact of free screening programs. More research should be done to identify why screening rates vary in order to identify ways to enhance screening and reduce radon exposure in DeKalb County.

The migration of contaminants from the subsurface into the indoor air environment, in a process described as soil vapor intrusion, is gaining attention as a potential pathway for exposure to contaminated soil and water. Indoor, outdoor and soil air samples were collected from forty homes in North Texas to investigate the attenuation of trichloroethylene (TCE) from contaminated groundwater into residential buildings. The mean and standard deviation of the soil and indoor air attenuation factors (ratio of indoor air concentration to soil vapor concentration) were 0.14 and 0.17, respectively. Five of the 40 values were greater than 0.1 which is the suggested upper-bound by the U.S. EPA (2002). Statistical tools were used to draw correlative relationships between contaminant groundwater, soil air and indoor air concentrations. The VolaSoil model described by Waitz et al. (1996), was modified for use as a screening tool for future investigations of indoor TCE concentration. Using measured soil vapor data, the model under predicted indoor air TCE concentrations likely due to heterogeneities in the unsaturated subsurface. Inputting groundwater TCE concentrations, the model was able to capture the contaminant migration processes and produce results consistent with measured indoor TCE concentrations. Therefore, the model described in this paper maybe appropriate to be use as a screening tool in future investigations in the contamination area. / text

Volatile chlorinated solvents such as trichloroethylene (TCE), 1,2 dichloroethane (1,2 DCA), and perchloroethylene (PCE) have been identified in the indoor air of residences located near Hill Air Force Base (AFB), Utah. These vapors can originate from either volatilization of contaminates from shallow contaminated groundwater and transport into residences or from sources within the residence. The focus of the thesis was the development of a testing strategy for determining sources of TCE, 1,2 DCA, and PCE in the indoor air of residences near Hill AFB. Eight residences were selected for this study by Hill AFB based on prior detections of TCE, 1,2 DCA, and PCE in indoor air. Residents were asked to turn off the heating, ventilation, and air conditioning (HVAC) system and keep windows and doors closed for at least 3 hours prior to the sampling visit to reduce mixing of residence air. Indoor air samples were collected on Tenax© sorbent tubes from various locations within the residences to determine the location of the potential source(s). Sampling tubes were analyzed by thermal desorption gas chromatography/mass spectrometry (GC/MS). Results from a tracer experiment using sulfur hexafluoride gas confirmed the effectiveness of sampling approach. In cases where elevated levels of chlorinated solvents were found, the suspected source materials(s) were removed and the room air was re-sampled. If removal of the materials reduced or eliminated indoor air contamination, an emission chamber was used to determine contaminant emission from the materials. Sources were identified in three of the sampled residences. Sampling in two of the residences was discontinued due to scheduling problems. Sources were not located in the remaining residences. The emission of contaminants from items identified as sources in two of the residences was measured using an emission chamber developed for this project. An ornament from residence U8-8452 emitted 36.4 ng/min/cm2 of 1,2 DCA. The emission of 1,2 DCA from a wedding dress located at residence U8-8211 was below the method detection limit of 1.99 pg/min/cm2 but the emission of PCE was 18.9 ng/min/cm2 and decreased by a factor of 7 during repeated measurements.

abstract: In this work, the vapor transport and aerobic bio-attenuation of compounds from a multi-component petroleum vapor mixture were studied for six idealized lithologies in 1.8-m tall laboratory soil columns. Columns representing different geological settings were prepared using 20-40 mesh sand (medium-grained) and 16-minus mesh crushed granite (fine-grained). The contaminant vapor source was a liquid composed of twelve petroleum hydrocarbons common in weathered gasoline. It was placed in a chamber at the bottom of each column and the vapors diffused upward through the soil to the top where they were swept away with humidified gas. The experiment was conducted in three phases: i) nitrogen sweep gas; ii) air sweep gas; iii) vapor source concentrations decreased by ten times from the original concentrations and under air sweep gas. Oxygen, carbon dioxide and hydrocarbon concentrations were monitored over time. The data allowed determination of times to reach steady conditions, effluent mass emissions and concentration profiles. Times to reach near-steady conditions were consistent with theory and chemical-specific properties. First-order degradation rates were highest for straight-chain alkanes and aromatic hydrocarbons. Normalized effluent mass emissions were lower for lower source concentration and aerobic conditions. At the end of the study, soil core samples were taken every 6 in. Soil moisture content analyses showed that water had redistributed in the soil during the experiment. The soil at the bottom of the columns generally had higher moisture contents than initial values, and soil at the top had lower moisture contents. Profiles of the number of colony forming units of hydrocarbon-utilizing bacteria/g-soil indicated that the highest concentrations of degraders were located at the vertical intervals where maximum degradation activity was suggested by CO2 profiles. Finally, the near-steady conditions of each phase of the study were simulated using a three-dimensional transient numerical model. The model was fit to the Phase I data by adjusting soil properties, and then fit to Phase III data to obtain compound-specific first-order biodegradation rate constants ranging from 0.0 to 5.7x103 d-1. / Dissertation/Thesis / Ph.D. Civil and Environmental Engineering 2012

abstract: Vapor intrusion (VI) pathway assessment often involves the collection and analysis of groundwater, soil gas, and indoor air data. There is temporal variability in these data, but little is understood about the characteristics of that variability and how it influences pathway assessment decision-making. This research included the first-ever collection of a long-term high-frequency indoor air data set at a house with VI impacts overlying a dilute chlorinated solvent groundwater plume. It also included periodic synoptic snapshots of groundwater and soil gas data and high-frequency monitoring of building conditions and environmental factors. Indoor air trichloroethylene (TCE) concentrations varied over three orders-of-magnitude under natural conditions, with the highest daily VI activity during fall, winter, and spring months. These data were used to simulate outcomes from common sampling strategies, with the result being that there was a high probability (up to 100%) of false-negative decisions and poor characterization of long-term exposure. Temporal and spatial variability in subsurface data were shown to increase as the sampling point moves from source depth to ground surface, with variability of an order-of-magnitude or more for sub-slab soil gas. It was observed that indoor vapor sources can cause subsurface vapor clouds and that it can take days to weeks for soil gas plumes created by indoor sources to dissipate following indoor source removal. A long-term controlled pressure method (CPM) test was conducted to assess its utility as an alternate approach for VI pathway assessment. Indoor air concentrations were similar to maximum concentrations under natural conditions (9.3 μg/m3 average vs. 13 μg/m3 for 24 h TCE data) with little temporal variability. A key outcome was that there were no occurrences of false-negative results. Results suggest that CPM tests can produce worst-case exposure conditions at any time of the year. The results of these studies highlight the limitations of current VI pathway assessment approaches and demonstrate the need for robust alternate diagnostic tools, such as CPM, that lead to greater confidence in data interpretation and decision-making. / Dissertation/Thesis / Doctoral Dissertation Civil and Environmental Engineering 2015

Regulatory agencies have recently focused on assessing the potential for soil vapor intrusion (SVI) and risk posed to occupants of residential and commercial properties overlying and surrounding former Manufactured Gas Plants (MGPs). This study evaluated the potential for SVI at 10 commercial buildings and 26 single family and multi-family residential properties overlying and/or adjacent to three former MGPs. The potential for SVI exposure was categorized into three groupings according to thickness of the vadose zones: no vadose zone; 0 - 6 feet thick, and 6 to 25 feet thick. Indoor and outdoor air and soil vapor samples were collected and analyzed for VOCs by the USEPA Method TO-15. These findings were compared to federal and state regulatory background data sets. The results did not identify evidence of MGP-related soil vapor intrusion from any of the 36 sites regardless of depth to water table or proximity to MGP source tar or dissolved phase plumes. In addition, comparative risks were calculated based on maximum and mean concentrations for benzene, toluene, ethylbenzene, and xylenes measured in ambient air samples, soil vapor, and indoor air. These chemicals were selected based on frequency of detection within the data sets. Hazard Indexes were calculated using the study results and the mean, maximum and 95th percentile concentrations from regulatory data bases. Carcinogenic risks associated with benzene were calculated using both the measured mean and maximum study results and the mean, maximum and 95th percentile concentrations from state and federal data bases. The calculated Hazard Indexes were less than 1 or were comparable to the regulatory mean and maximum background levels. Calculated cancer risks for residential and occupational exposures ranged from 9.75x10-6 to 4.52x10-4. However background benzene exposure not related to former MGP sites ranged from 9.9x10-6 to 3.59x10-3. Cancer risk and exposures to indoor air, soil vapor or ambient air concentrations were equivalent or less than a normal resident in the northeast United States. No increased public health risks were associated with occupied residential or commercial properties overlying or surrounding MGPs.

Over the course of the past several decades the benefits of redeveloping brownfields have been widely recognized. Actions have been taken to foster sustainable redevelopment of brownfields by government, policy makers and stakeholders across the world. However, redevelopments encounter great challenges and risks related to environmental and non-environmental issues. In this work, we intend to build a comprehensive and practical framework to evaluate the hydrogeological and financial risks involved during redevelopment and to ensure developers reserve sufficient capital to cover unexpected future costs within the guarantee period. Punitive damages, which contribute to these costs, are in this thesis solely associated with the cost of repossessing a house within a development should the indoor air concentration of TCE exceed the regulatory limit at a later time. The uncertainties associated with brownfield remediation have been among the barriers to brownfield redevelopment. This is mainly caused by the lack of knowledge about a site’s environmental condition. In order to alleviate uncertainties and to better understand the contaminant transport process in the subsurface, numerical simulations have been conducted to investigate the role of controlling parameters in determining the fate and transport of volatile organic compounds originating from a NAPL source zone located below the water table in the subsurface. In the first part of this thesis, the numerical model CompFlow Bio is used on a hypothesized three-dimensional problem geometry where multiple residential dwellings are built. The simulations indicate that uncertainty in the simulated indoor air concentration is sensitive to heterogeneity in the permeability structure of a stratigraphically continuous aquifer with uncertainty defined as the probability of exceeding a regulatory limit. Houses which are laterally offset from the groundwater plume are less affected by vapour intrusion due to limited transverse horizontal flux of TCE within the groundwater plume in agreement with the ASTM (2008) guidance. Within this uncertainty framework, we show that the Johnson and Ettinger (1991) model generates overly-conservative results and contributes to the exclusion zone being much further away from the groundwater plume relative to either CompFlow Bio or ASTM (2008). The probability of failure (or the probability of exceedence of the regulatory limit) is defined and calculated for further study. Due to uncertainties resulting from parameter estimation and model prediction, a methodology is introduced to incorporate field measurements into the initial estimates from the numerical model in order to improve prediction accuracy. The principle idea of this methodology is to combine the geostatistical tool kriging with the statistical data assimilation method Kalman filter to evaluate the worth and effectiveness of data in a quantitative way in order to select an optimal sampling scenario. This methodology is also used to infer whether one of the houses located adjacent to affected houses has indoor air problems based on the measurements subject to the observation that the affected house is monitored and has problems and developers have liability if a problem occurs. In this part of the study, different sampling scenarios are set up in terms of permeability (1 – 80 boreholes) and soil gas concentration (2, 4 and 7 samples) and three metrics are defined and computed as a criterion for comparison. Financing brownfield redevelopment is often viewed as a major barrier to the development process mainly due to risks and liabilities associated with brownfields. The common way of managing the risk is to transfer it to insurers by purchasing insurance coverage. This work provides two different strategies to price the risk, which is equivalent to an insurance premium. It is intended to give an instructive insight into project planning and feasibility studies during the decision-making process of a brownfield project. The two strategies of risk capital valuation are an actuarial premium calculation principle and a martingale premium calculation principle accounting for the hydrogeological and financial uncertainties faced in a project. The data used for valuation are the posterior estimates of data assimilation obtained from the results of different sampling scenarios. The cost-benefit-risk analysis is employed as a basis to construct the objective function in order to find the least cost among sampling scenarios for the project. As a result, it shows that drilling seven boreholes to extract permeability data and taking soil gas samplings in four locations or seven locations alternatively give the minimum total cost. Sensitivity analysis of some influential parameters (the safety loading factors and the possible methods to calculate the probability of failure) is performed to determine their roles of importance in the risk capital valuation. This framework can be applied to provide guidance for other risk-based environmental projects.

Over the course of the past several decades the benefits of redeveloping brownfields have been widely recognized. Actions have been taken to foster sustainable redevelopment of brownfields by government, policy makers and stakeholders across the world. However, redevelopments encounter great challenges and risks related to environmental and non-environmental issues. In this work, we intend to build a comprehensive and practical framework to evaluate the hydrogeological and financial risks involved during redevelopment and to ensure developers reserve sufficient capital to cover unexpected future costs within the guarantee period. Punitive damages, which contribute to these costs, are in this thesis solely associated with the cost of repossessing a house within a development should the indoor air concentration of TCE exceed the regulatory limit at a later time. The uncertainties associated with brownfield remediation have been among the barriers to brownfield redevelopment. This is mainly caused by the lack of knowledge about a site’s environmental condition. In order to alleviate uncertainties and to better understand the contaminant transport process in the subsurface, numerical simulations have been conducted to investigate the role of controlling parameters in determining the fate and transport of volatile organic compounds originating from a NAPL source zone located below the water table in the subsurface. In the first part of this thesis, the numerical model CompFlow Bio is used on a hypothesized three-dimensional problem geometry where multiple residential dwellings are built. The simulations indicate that uncertainty in the simulated indoor air concentration is sensitive to heterogeneity in the permeability structure of a stratigraphically continuous aquifer with uncertainty defined as the probability of exceeding a regulatory limit. Houses which are laterally offset from the groundwater plume are less affected by vapour intrusion due to limited transverse horizontal flux of TCE within the groundwater plume in agreement with the ASTM (2008) guidance. Within this uncertainty framework, we show that the Johnson and Ettinger (1991) model generates overly-conservative results and contributes to the exclusion zone being much further away from the groundwater plume relative to either CompFlow Bio or ASTM (2008). The probability of failure (or the probability of exceedence of the regulatory limit) is defined and calculated for further study. Due to uncertainties resulting from parameter estimation and model prediction, a methodology is introduced to incorporate field measurements into the initial estimates from the numerical model in order to improve prediction accuracy. The principle idea of this methodology is to combine the geostatistical tool kriging with the statistical data assimilation method Kalman filter to evaluate the worth and effectiveness of data in a quantitative way in order to select an optimal sampling scenario. This methodology is also used to infer whether one of the houses located adjacent to affected houses has indoor air problems based on the measurements subject to the observation that the affected house is monitored and has problems and developers have liability if a problem occurs. In this part of the study, different sampling scenarios are set up in terms of permeability (1 – 80 boreholes) and soil gas concentration (2, 4 and 7 samples) and three metrics are defined and computed as a criterion for comparison. Financing brownfield redevelopment is often viewed as a major barrier to the development process mainly due to risks and liabilities associated with brownfields. The common way of managing the risk is to transfer it to insurers by purchasing insurance coverage. This work provides two different strategies to price the risk, which is equivalent to an insurance premium. It is intended to give an instructive insight into project planning and feasibility studies during the decision-making process of a brownfield project. The two strategies of risk capital valuation are an actuarial premium calculation principle and a martingale premium calculation principle accounting for the hydrogeological and financial uncertainties faced in a project. The data used for valuation are the posterior estimates of data assimilation obtained from the results of different sampling scenarios. The cost-benefit-risk analysis is employed as a basis to construct the objective function in order to find the least cost among sampling scenarios for the project. As a result, it shows that drilling seven boreholes to extract permeability data and taking soil gas samplings in four locations or seven locations alternatively give the minimum total cost. Sensitivity analysis of some influential parameters (the safety loading factors and the possible methods to calculate the probability of failure) is performed to determine their roles of importance in the risk capital valuation. This framework can be applied to provide guidance for other risk-based environmental projects.

abstract: Vapor intrusion (VI), can pose health risks to building occupants. Assessment and mitigation at VI impacted sites have been guided by a site conceptual model (SCM) in which vapors originate from subsurface sources, diffuse through soil matrix and enter into a building by gas flow across foundation cracks. Alternative VI pathways and groundwater table fluctuations are not often considered. Alternative VI pathways, involving vapor transport along sewer lines and other subsurface infrastructure, have recently been found to be significant contributors to VI impacts at some sites. This study evaluated approaches for identifying and characterizing the significance of alternative VI pathways and assessed the effectiveness of conventional mitigation at a site with an alternative VI pathway that can be manipulated to be on or off. The alternative pathway could not be identified using conventional pathway assessment procedures and can only be discovered under controlled pressure method (CPM) conditions. Measured emission rates were two orders of magnitude greater than screening model estimates and sub-foundation vertical soil gas profiles changed and were no longer consistent with the conventional VI conceptual model when the CPM test was conducted. The pipe flow VI pathway reduced the vacuum performance of the sub-slab depressurization (SSD) VI mitigation system, but the SSD system still provided sufficient protection to the house. The relationship between groundwater table fluctuations and subsurface vapor emissions and transport is examined using multi-year data from the field site, and is studied in the laboratory. In addition, a broader range of conditions is examined through use of modeling validated with the experimental data. The results indicate that fluctuating groundwater tables will lead to amplified volatile organic chemical (VOC) emissions from groundwater to soil surface relative to steady water table elevation, however, the magnitude of this amplification is less concerned when long-term water fluctuation present. No clear correlations were found between VOC emissions and water table changes at the study site where annual water table fluctuations of about 0.3 m existed. Significant VOC emission amplifications by water table fluctuation would be expected under shallow groundwater conditions according to model analysis results. / Dissertation/Thesis / Doctoral Dissertation Civil and Environmental Engineering 2015

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