Environmental Forensic Investigation of Historical Air Dispersion Modeling, Sensitivity Analysis, and Community Exposure Assessment
Project Overview
Air dispersion modeling plays a central role in modern environmental forensic investigations because it provides a scientifically accepted method for reconstructing historical airborne contaminant concentrations when direct environmental measurements are unavailable or incomplete. By integrating engineering source characterization, meteorological observations, terrain data, atmospheric physics, emission inventories, and computational modeling, investigators can estimate historical community exposures over periods spanning years or even decades. These evaluations are frequently performed during environmental investigations, regulatory reviews, remediation projects, and complex litigation involving hazardous air pollutants. Developing technically defensible exposure reconstructions requires expertise in atmospheric science, environmental engineering, industrial processes, meteorology, toxicology, and quantitative risk assessment working together within an integrated scientific framework (U.S. EPA, 2017; ASTM International, 2021).
RoseyFields conducted a comprehensive environmental forensic investigation involving historical air dispersion modeling and quantitative exposure assessment for a hazardous airborne contaminant emitted from an industrial facility. The investigation extended beyond the preparation of a conventional regulatory air model by evaluating the robustness of model predictions through multiple independent sensitivity analyses. The primary objectives were to reconstruct historical airborne concentrations, evaluate the influence of alternative modeling assumptions, characterize uncertainty associated with model inputs, and determine whether predicted community exposures remained scientifically consistent under a range of technically reasonable scenarios. This approach provided a substantially more rigorous evaluation than reliance upon a single deterministic model run and strengthened confidence in the resulting exposure assessment.
A major focus of the investigation involved evaluating the sensitivity of predicted concentrations to several key modeling assumptions commonly encountered in environmental forensic analyses. Multiple representative meteorological datasets were independently processed to evaluate interannual variability in prevailing weather conditions. Additional sensitivity analyses examined alternative source representations, including elevated point releases, building downwash effects, distributed volume sources, and area-source release scenarios representing potential fugitive emissions across the facility footprint. These analyses demonstrated the extent to which engineering assumptions regarding source configuration influence predicted ground-level concentrations and provided important context for interpreting model uncertainty. The investigation further incorporated accepted atmospheric dispersion principles to evaluate how building-induced turbulence, local meteorology, and source geometry collectively influence contaminant transport and dilution under representative operating conditions. These independent evaluations strengthened the technical defensibility of the exposure reconstruction by demonstrating that conclusions were not dependent upon a single modeling assumption but instead reflected a comprehensive assessment of plausible environmental conditions (U.S. EPA, 2017; American Meteorological Society & U.S. EPA, 2019).
The investigation also included a detailed review of engineering reports, environmental analyses, industrial hygiene evaluations, atmospheric modeling methodologies, and technical opinions prepared by multiple independent experts. Rather than relying solely on computational modeling, each technical opinion was evaluated within the broader context of environmental regulations, engineering practice, emissions characterization, exposure science, toxicology, and accepted atmospheric modeling guidance. Integrating engineering analyses with sensitivity testing, quantitative exposure assessment, and critical review of independent technical evaluations produced a scientifically rigorous environmental forensic investigation suitable for environmental consulting, regulatory investigations, remediation planning, and expert witness services involving historical airborne contaminant exposures (ASTM International, 2021; National Academies of Sciences, Engineering, and Medicine, 2022).
Chemicals of Concern
The principal chemical evaluated during this environmental forensic investigation was ethylene oxide (EtO), a highly reactive, colorless gas used extensively as a low-temperature sterilizing agent for medical devices and pharmaceutical products that cannot withstand conventional steam sterilization. Because of its effectiveness in eliminating bacteria, viruses, fungi, and bacterial spores while penetrating complex packaging materials, EtO has become an indispensable component of the global healthcare supply chain. However, EtO is also recognized as a hazardous air pollutant and a human carcinogen, making the evaluation of historical emissions and potential community exposure an important component of environmental engineering, exposure science, and environmental forensic investigations (U.S. EPA, 2016; IARC, 2012).
Unlike contaminants that persist in soil or groundwater, EtO exists primarily in the atmosphere following release and is transported by prevailing meteorological conditions. Wind speed, wind direction, atmospheric stability, mixing height, terrain, and building-induced turbulence all influence the dispersion and dilution of airborne EtO. Consequently, historical community exposure cannot typically be reconstructed using environmental sampling alone. Instead, scientifically accepted atmospheric dispersion models are used to estimate historical concentrations by integrating emissions inventories, engineering source characteristics, meteorological observations, and atmospheric transport physics. This multidisciplinary approach allows investigators to evaluate historical airborne concentrations over extended periods while accounting for changes in facility operations and environmental conditions (U.S. EPA, 2017; American Meteorological Society & U.S. EPA, 2019).
A major component of this investigation involved evaluating the influence of alternative source representations on predicted ambient concentrations. Industrial facilities may release contaminants through elevated exhaust stacks, building ventilation systems, process vents, or diffuse fugitive pathways distributed throughout the facility. Because uncertainty often exists regarding the relative contribution of these release mechanisms, multiple engineering scenarios were evaluated using different source configurations. Sensitivity analyses examined elevated point sources, distributed area sources, and other representative release geometries to determine how modeling assumptions influenced predicted community exposure. This approach provided a more comprehensive understanding of uncertainty than would have been possible using a single source configuration and demonstrated the robustness of the modeling results across a range of technically reasonable engineering assumptions (U.S. EPA, 2017; ASTM International, 2021).
The investigation also evaluated the influence of building downwash and local aerodynamic effects on contaminant transport. Buildings located near emission sources can significantly alter plume behavior by generating turbulent airflow that increases ground-level concentrations in the immediate vicinity of a facility. Accepted regulatory guidance recommends evaluating these effects whenever nearby structures have the potential to influence plume dispersion. Accordingly, sensitivity analyses incorporating building downwash were performed to evaluate whether aerodynamic interactions substantially altered predicted concentrations. These analyses provided additional confidence that the reconstructed exposure estimates appropriately represented the influence of local engineering and atmospheric conditions (American Meteorological Society & U.S. EPA, 2019; U.S. EPA, 2017).
Finally, the investigation considered the role of naturally occurring and regional background concentrations when interpreting modeled and measured ambient EtO concentrations. Numerous scientific studies have demonstrated that measurable EtO concentrations occur in ambient air even in the absence of nearby industrial sources because of endogenous production, natural biological processes, combustion sources, and regional atmospheric contributions. Consequently, distinguishing facility-related emissions from background concentrations required integrating engineering analyses, emissions reconstruction, atmospheric dispersion modeling, environmental monitoring information, and current toxicological literature. By combining these complementary scientific disciplines, the investigation produced a technically rigorous environmental forensic evaluation suitable for environmental consulting, regulatory investigations, environmental due diligence, remediation planning, and expert witness services involving historical airborne contaminants and community exposure assessment (Kirman & Hays, 2017; National Academies of Sciences, Engineering, and Medicine, 2022).
Methods
A comprehensive environmental forensic investigation was conducted to evaluate historical airborne ethylene oxide (EtO) emissions using accepted engineering principles, regulatory air dispersion modeling, atmospheric science, environmental chemistry, exposure assessment, and quantitative human health risk assessment methodologies. The investigation was designed to reconstruct long-term ambient air concentrations, evaluate uncertainty associated with key modeling assumptions, and determine the robustness of predicted community exposures under multiple technically reasonable engineering scenarios. Rather than relying upon a single deterministic air model, a series of independent sensitivity analyses were performed to evaluate the influence of source characterization, building effects, meteorological variability, and alternative emission representations on predicted ground-level concentrations (U.S. EPA, 2017; ASTM International, 2021).
The investigation began with a detailed engineering review of historical operating information, emissions inventories, publicly available regulatory records, process descriptions, and facility design characteristics. Historical engineering information was evaluated to characterize emission sources, release mechanisms, pollution control systems, operating schedules, and changes in facility operations over time. Particular attention was devoted to identifying potential point-source emissions, distributed process emissions, and fugitive release pathways that could contribute to long-term community exposure. Developing an accurate engineering understanding of the facility provided the foundation for constructing representative source terms suitable for atmospheric dispersion modeling and subsequent exposure assessment (Association for the Advancement of Medical Instrumentation, 2021; U.S. EPA, 2022).
Atmospheric dispersion modeling was performed using regulatory modeling methodologies consistent with current U.S. Environmental Protection Agency guidance. Source parameters, stack characteristics, release heights, terrain, building dimensions, and representative meteorological observations were incorporated into the modeling analyses to estimate long-term ambient EtO concentrations. Multiple meteorological datasets were independently evaluated to ensure that predicted concentrations reflected representative atmospheric conditions rather than anomalies associated with any individual year. Geographic information systems (GIS) were subsequently used to evaluate the spatial distribution of modeled concentrations and characterize long-term community exposure patterns surrounding the facility (American Meteorological Society & U.S. EPA, 2019; U.S. EPA, 2017).
A distinguishing feature of this investigation was the extensive use of sensitivity analyses to evaluate the influence of alternative engineering assumptions on modeled concentrations. Multiple source configurations were developed representing elevated point-source releases, distributed area sources, and other technically reasonable emission scenarios capable of representing potential fugitive releases across the facility footprint. Additional analyses evaluated the influence of building downwash, which can alter plume behavior by creating turbulent airflow that enhances near-field ground-level concentrations. Comparing these independent modeling scenarios allowed investigators to quantify model sensitivity, identify the assumptions exerting the greatest influence on predicted concentrations, and determine whether overall exposure conclusions remained consistent despite variations in engineering inputs. This systematic evaluation substantially strengthened the technical defensibility of the modeling results by demonstrating that conclusions were supported by multiple independent analytical approaches rather than a single modeling assumption (U.S. EPA, 2017; American Meteorological Society & U.S. EPA, 2019).
Finally, modeled concentrations were integrated with environmental monitoring information, toxicological reference values, and accepted exposure assessment methodologies to characterize long-term community exposure. Environmental monitoring data were interpreted in the context of analytical detection limits, regional background concentrations, atmospheric variability, and the inherent strengths and limitations of ambient sampling. Rather than relying upon any single line of evidence, engineering analyses, atmospheric dispersion modeling, environmental monitoring, exposure science, and toxicological evaluation were considered collectively using a weight-of-evidence framework. This multidisciplinary methodology produced a scientifically rigorous environmental forensic investigation suitable for environmental consulting, regulatory investigations, environmental due diligence, remediation planning, and expert witness services involving historical airborne contaminant releases and long-term community exposure (National Academies of Sciences, Engineering, and Medicine, 2022; U.S. EPA, 1989).
Results
The environmental forensic investigation demonstrated that historical airborne concentrations were influenced by multiple engineering and atmospheric factors rather than any single modeling parameter. Sensitivity analyses showed that the predicted concentration patterns remained generally consistent despite reasonable variations in source characterization, meteorological datasets, and engineering assumptions. This finding increased confidence that the exposure assessment reflected the overall behavior of the emission source rather than being an artifact of a particular modeling configuration. Evaluating multiple independent scenarios also reduced uncertainty by demonstrating that the principal conclusions remained robust across a range of technically defensible modeling approaches (U.S. EPA, 2017; ASTM International, 2021).
Comparison of alternative source representations demonstrated that engineering assumptions regarding emission geometry can influence predicted ground-level concentrations, particularly in the immediate vicinity of an emission source. Modeling scenarios representing elevated point releases, distributed area sources, and generalized fugitive emissions produced differences in localized concentration patterns while maintaining similar overall trends in long-term community exposure. These results emphasized the importance of understanding industrial operations when developing representative source terms and illustrated why sensitivity analyses are an essential component of environmental forensic air modeling. Rather than relying on a single emission representation, evaluating multiple technically reasonable source configurations produced a more comprehensive assessment of potential historical exposure (American Meteorological Society & U.S. EPA, 2019; U.S. EPA, 2017).
The investigation also evaluated the influence of building downwash on modeled concentrations. Building-induced turbulence can alter plume transport by increasing vertical mixing and drawing emissions toward ground level under certain atmospheric conditions. Incorporating building downwash into the modeling analyses demonstrated whether nearby structures materially influenced predicted concentrations and provided an additional measure of model robustness. The sensitivity analyses indicated that accounting for aerodynamic effects improved the completeness of the engineering evaluation while providing greater confidence that local structural influences had been appropriately considered during the exposure reconstruction (American Meteorological Society & U.S. EPA, 2019; U.S. EPA, 2017).
Meteorological sensitivity analyses further demonstrated the importance of representative weather data when reconstructing long-term airborne concentrations. Annual variations in wind direction, atmospheric stability, temperature, and mixing height influenced predicted plume movement and dispersion; however, the overall spatial distribution of long-term concentrations remained consistent across representative meteorological datasets. This finding indicated that the reconstructed exposure patterns were governed primarily by the interaction between facility emissions and prevailing regional climatology rather than isolated short-term weather events. Evaluating multiple years of meteorological data therefore strengthened the scientific defensibility of the investigation by reducing the influence of atypical atmospheric conditions (World Meteorological Organization, 2018; U.S. EPA, 2017).
Overall, the investigation demonstrated that integrating engineering evaluations, historical emissions reconstruction, atmospheric dispersion modeling, sensitivity analyses, meteorological science, geographic information systems (GIS), environmental chemistry, exposure assessment, and toxicology produced a technically rigorous environmental forensic evaluation of historical airborne contaminant exposure. The use of multiple independent modeling scenarios substantially reduced uncertainty, strengthened confidence in the reconstructed exposure estimates, and provided a scientifically defensible foundation for environmental consulting, regulatory investigations, remediation planning, and expert witness services involving historical industrial emissions and long-term community exposure. The investigation illustrates how sensitivity analyses can enhance environmental forensic investigations by demonstrating that conclusions are supported by multiple technically reasonable analytical approaches rather than any single modeling assumption (National Academies of Sciences, Engineering, and Medicine, 2022; ASTM International, 2021).
Conclusions
This environmental forensic investigation demonstrated that robust air dispersion modeling extends beyond the development of a single regulatory model and instead requires systematic evaluation of engineering assumptions, meteorological variability, source characterization, and atmospheric processes that influence predicted community exposure. By integrating environmental engineering, atmospheric science, industrial process evaluation, environmental chemistry, meteorology, exposure science, geographic information systems (GIS), and quantitative risk assessment, the investigation developed a comprehensive understanding of historical airborne contaminant transport while reducing uncertainty through multiple independent lines of scientific evidence. This multidisciplinary approach is consistent with accepted environmental forensic practice and provides substantially greater confidence than reliance upon a single deterministic modeling scenario (ASTM International, 2021; U.S. EPA, 2017).
A principal finding of the investigation was the importance of sensitivity analyses in evaluating the reliability of environmental exposure reconstructions. Engineering evaluations demonstrated that alternative assumptions regarding source geometry, building influences, meteorological conditions, and release configurations can affect predicted ground-level concentrations to varying degrees. Systematically evaluating these alternative scenarios allowed the investigation to identify the parameters exerting the greatest influence on model predictions while confirming that the overall conclusions remained scientifically consistent across multiple technically reasonable assumptions. Sensitivity analysis therefore served not only as a measure of uncertainty but also as an important quality assurance tool that strengthened confidence in the final exposure assessment (American Meteorological Society & U.S. EPA, 2019; ASTM International, 2021).
The investigation further demonstrated the value of integrating atmospheric dispersion modeling with engineering analyses and environmental monitoring information. Air dispersion models provide estimates of historical concentrations under representative operating and meteorological conditions, while engineering evaluations ensure that emission source characteristics accurately reflect industrial operations. Environmental monitoring, when available, provides an additional independent line of evidence for evaluating model performance and understanding regional background conditions. Considering these complementary datasets collectively provides a more scientifically rigorous assessment than interpreting any individual dataset in isolation and improves the technical defensibility of environmental forensic investigations involving historical airborne contaminant releases (U.S. EPA, 2017; National Academies of Sciences, Engineering, and Medicine, 2022).
This case study highlights the critical role of environmental forensic science in evaluating historical industrial emissions and reconstructing long-term community exposure. By integrating engineering analyses, historical emissions reconstruction, atmospheric dispersion modeling, meteorological science, environmental chemistry, GIS, exposure assessment, sensitivity analyses, and quantitative human health risk assessment, RoseyFields provides scientifically rigorous evaluations capable of supporting environmental consulting, regulatory investigations, environmental due diligence, remediation planning, and expert witness services. These multidisciplinary investigations provide objective, evidence-based scientific analyses that improve understanding of airborne contaminant transport, historical environmental exposure, and potential human health impacts while remaining consistent with accepted engineering practice, current environmental science, and evolving regulatory guidance (National Academies of Sciences, Engineering, and Medicine, 2022; U.S. EPA, 2017).
This investigation was conducted under the direction of Dr. Paul Rosenfeld, an environmental scientist and environmental forensic expert with extensive experience in ethylene oxide investigations, air dispersion modeling, sensitivity analysis, exposure assessment, and human health risk evaluation. Dr. Rosenfeld’s work focuses on complex environmental contamination matters involving historical industrial air emissions, community exposure reconstruction, AERMOD modeling, source characterization, fugitive and point-source emissions, building downwash, meteorological variability, and the evaluation of long-term airborne contaminant concentrations affecting nearby residential communities. His expertise includes developing and testing alternative source scenarios through the integration of industrial process engineering, emissions inventories, atmospheric science, environmental chemistry, toxicology, geographic information systems (GIS), environmental monitoring interpretation, and quantitative risk assessment to determine whether historical air modeling conclusions remain scientifically robust under multiple technically reasonable assumptions. Through RoseyFields LLC, Dr. Rosenfeld provides environmental forensic analysis, environmental due diligence, regulatory and compliance support, remediation evaluation, toxic tort and personal injury case assessment, and expert witness testimony involving ethylene oxide contamination, hazardous air pollutant emissions, air dispersion sensitivity analyses, source attribution, and long-term environmental and human health risks associated with historical industrial operations.
References
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