Environmental Forensic Investigation of Historical Airborne Metal Emissions, Coal Combustion Residual Management, Air Dispersion Modeling, and Human Exposure Assessment
Project Overview
Legacy industrial combustion facilities have historically generated large quantities of airborne particulate matter and coal combustion residuals (CCRs), creating complex environmental forensic questions regarding historical emissions, contaminant transport, soil deposition, and potential long-term human exposure. Evaluating these sites requires reconstruction of historical operations, characterization of emission sources, environmental sampling, air dispersion modeling, contaminant fate and transport analysis, and human health risk assessment. Because many industrial facilities operated for decades while undergoing changes in waste management practices, historical reconstruction frequently becomes one of the most important components of an environmental forensic investigation.
The investigation summarized herein evaluated historical airborne releases from a legacy industrial combustion and waste management facility that operated for many decades before transitioning into post-closure management and material handling activities. The primary objective was to determine whether historical facility operations, coal combustion residual management practices, and subsequent material handling activities contributed to off-site transport of particulate matter and metal-containing dust. Investigators integrated historical aerial photography, engineering documentation, environmental sampling data, air dispersion modeling, atmospheric deposition analyses, geographic information systems (GIS), and exposure assessment techniques to reconstruct historical contaminant migration and evaluate potential environmental and human exposure pathways.
Unlike investigations involving a single accidental release, this project evaluated multiple historical emission mechanisms occurring over extended periods of industrial operation. These included emissions associated with combustion processes, management of coal combustion residuals, excavation and relocation of historical waste materials, truck transportation, waste handling, and fugitive dust generated during material processing. Historical operational records indicated that source characteristics changed over time as facility operations evolved, requiring investigators to evaluate multiple emission scenarios rather than relying upon a single representative operating condition. Air emission inventories were therefore developed for several operational periods to characterize changing source strengths and contaminant release mechanisms throughout the facility’s operational history.
A major focus of the investigation involved determining whether airborne particulate matter containing trace metals migrated beyond facility boundaries and contributed to measurable contaminant deposition on surrounding properties. This evaluation required integration of environmental chemistry, atmospheric dispersion modeling, historical meteorological analysis, soil sampling data, and statistical evaluation of measured environmental concentrations. Investigators compared modeled deposition patterns with measured soil concentrations to evaluate the consistency between predicted contaminant transport and observed environmental conditions. This multiple-lines-of-evidence approach strengthened source attribution by combining environmental measurements with independent engineering analyses and contaminant transport modeling.
The investigation also included a comprehensive human exposure assessment evaluating inhalation of airborne particulate matter together with incidental exposure to contaminants deposited onto residential soils. Exposure estimates incorporated modeled airborne concentrations, atmospheric deposition rates, environmental sampling data, and established U.S. Environmental Protection Agency (EPA) exposure assessment methodologies. Cancer risk estimates and non-cancer hazard evaluations were performed using health-protective exposure assumptions and comparison with current regulatory screening criteria. By integrating environmental monitoring, engineering analyses, air quality modeling, contaminant fate and transport, and toxicological evaluation, the investigation developed a comprehensive scientific framework for evaluating historical environmental releases associated with long-term industrial operations.
Chemicals of Concern
The environmental forensic investigation focused on contaminants commonly associated with historical industrial combustion operations and the management of coal combustion residuals (CCRs). Combustion of coal produces airborne particulate matter containing trace metals and inorganic constituents that may be transported through the atmosphere before depositing onto surrounding soils, vegetation, and surface waters. Because the chemical composition of CCRs reflects both the source fuel and combustion conditions, environmental evaluations require consideration of multiple contaminants rather than a single chemical of concern. Investigators therefore evaluated particulate matter together with trace metals known to occur within coal combustion residuals, emphasizing contaminants with established toxicological significance and recognized environmental persistence.
The principal contaminant evaluated during the investigation was hexavalent chromium [Cr(VI)], a highly oxidized form of chromium recognized for its carcinogenic potential following long-term inhalation exposure. Hexavalent chromium may be present in coal combustion residuals and airborne particulate matter generated during combustion, ash handling, excavation, transport, and waste management activities. Unlike trivalent chromium, which serves as an essential trace nutrient, Cr(VI) exhibits substantially greater mobility, bioavailability, and toxicity under many environmental conditions. Because inhalation represents the primary exposure pathway associated with airborne Cr(VI), investigators evaluated both atmospheric transport and subsequent deposition onto residential soils as part of the overall exposure assessment.
Particulate matter (PM) represented another major contaminant group evaluated during the investigation because it serves as the primary transport mechanism for many trace metals contained within combustion residuals. Airborne particles generated during industrial operations can remain suspended for extended periods before settling onto surrounding properties. Particle size strongly influences environmental transport and potential human exposure. Larger particles generally deposit near the source, while smaller respirable particles may remain airborne longer and travel substantially greater distances depending upon meteorological conditions. Consequently, atmospheric dispersion modeling evaluated both airborne particulate concentrations and long-term deposition patterns to characterize historical contaminant transport beyond the facility boundary.
In addition to chromium, the investigation evaluated trace metals commonly associated with coal combustion residuals, including arsenic, lead, cadmium, mercury, selenium, nickel, and other inorganic constituents identified during environmental characterization. These metals exhibit differing environmental behavior depending upon oxidation state, particle size, soil chemistry, and atmospheric conditions. Some metals remain tightly associated with particulate matter following deposition, while others may become more mobile under changing geochemical conditions. Evaluating contaminant-specific environmental fate and transport therefore represented an important component of the investigation, allowing investigators to assess both atmospheric exposure and longer-term accumulation within surface soils. (Environmental Chemistry Evaluation; Historical Site Assessment; Exposure Assessment).
The investigation also evaluated coal combustion residuals (CCRs) as an environmental source rather than a single chemical contaminant. CCRs consist primarily of fly ash, bottom ash, boiler slag, and related combustion byproducts generated during coal-fired industrial operations. These materials contain complex mixtures of mineral particles and trace elements whose composition varies according to fuel characteristics and combustion conditions. Historical handling, excavation, transportation, and storage of CCR materials can generate fugitive dust emissions capable of transporting metal-containing particles into surrounding communities. Consequently, investigators evaluated both combustion emissions and subsequent waste management activities when reconstructing historical contaminant releases and developing source attribution analyses.
Because no single contaminant completely characterized potential environmental exposure, investigators integrated airborne particulate matter, trace metal concentrations, atmospheric deposition, soil contamination, and human exposure pathways into a comprehensive environmental chemistry evaluation. This multiple-contaminant approach provided a scientifically robust framework for assessing contaminant fate and transport while supporting air dispersion modeling, source attribution, exposure assessment, and human health risk evaluation. By considering both inhalation and soil-related exposure pathways, the investigation developed a comprehensive understanding of how historical industrial emissions may influence long-term environmental conditions and potential community exposure.
Methods
The environmental forensic investigation employed a multidisciplinary methodology integrating historical document review, engineering evaluation, environmental chemistry, emissions estimation, atmospheric dispersion modeling, geographic information systems (GIS), contaminant fate and transport analysis, environmental sampling review, statistical analysis, exposure assessment, and human health risk assessment. Because the facility operated over several decades with changing industrial processes and waste management practices, investigators reconstructed historical operating conditions using multiple independent sources of information rather than relying on any single environmental dataset. Engineering records, historical aerial imagery, regulatory documentation, emissions inventories, environmental sampling results, and air quality modeling were synthesized into a comprehensive environmental forensic evaluation capable of reconstructing historical contaminant releases and estimating long-term community exposure.
The investigation began with a comprehensive review of historical operational records describing industrial combustion activities, material handling practices, waste management operations, engineering modifications, and historical facility development. Historical aerial photography, engineering documentation, and available regulatory records were reviewed to identify changes in emission sources, waste handling practices, excavation activities, and post-operational site management. This historical reconstruction allowed investigators to divide facility operations into distinct operational periods reflecting changes in combustion activities, material handling, and contaminant release mechanisms. Reconstructing historical operations provided the foundation for subsequent emissions estimation and environmental exposure assessment.
A major component of the investigation involved developing site-specific emissions estimates for multiple operational scenarios. Rather than evaluating only stack emissions, investigators characterized numerous potential particulate emission sources, including industrial combustion processes, coal combustion residual handling, excavation activities, haul truck operations, heavy equipment movement, waste processing, and fugitive dust generation. Published emission factors, engineering calculations, operational throughput information, equipment activity data, and accepted environmental engineering methodologies were used to estimate historical particulate emissions associated with each source category. This comprehensive source-term development provided the basis for subsequent atmospheric dispersion modeling and source attribution analyses.
Atmospheric transport was evaluated using the U.S. Environmental Protection Agency’s AERMOD air dispersion modeling system. Modeling incorporated source-specific emission rates, meteorological data, terrain characteristics, receptor grids, particle properties, and atmospheric deposition algorithms to estimate historical airborne particulate concentrations and long-term deposition patterns throughout the surrounding area. Multiple operational periods were modeled independently to evaluate how changes in industrial activities influenced contaminant transport over time. Annual concentration isopleths, deposition contours, and receptor-specific exposure estimates were developed to characterize the spatial distribution of airborne contaminants and compare predicted environmental impacts among various operating scenarios.
Environmental sampling data were evaluated to determine whether measured soil concentrations were consistent with modeled atmospheric deposition patterns. Investigators reviewed available soil analytical results, compared measured contaminant concentrations with predicted deposition estimates, and statistically evaluated exposure point concentrations using accepted U.S. Environmental Protection Agency methodologies, including ProUCL. Exposure point concentrations were subsequently compared with EPA Regional Screening Levels (RSLs) and other health-based criteria to evaluate potential cancer and non-cancer risks associated with long-term residential exposure. Integrating modeled concentrations with measured environmental data strengthened source attribution while reducing uncertainty associated with either dataset independently.
Finally, engineering analyses, historical reconstruction, emissions estimation, atmospheric dispersion modeling, environmental chemistry, statistical evaluation, exposure assessment, and toxicological analysis were integrated into a unified environmental forensic investigation. Rather than relying solely upon environmental sampling or emissions inventories, investigators applied a multiple-lines-of-evidence methodology in which historical operating records, engineering calculations, air quality modeling, contaminant fate and transport, soil analytical data, and human health risk assessment were collectively evaluated to determine whether the available scientific evidence supported historical off-site contaminant transport and potential community exposure. This multidisciplinary approach provided a technically rigorous framework for environmental consulting, regulatory investigations, environmental litigation, source attribution, and expert witness testimony involving historical industrial air emissions.
Results
The environmental forensic investigation demonstrated that historical industrial combustion activities and subsequent management of coal combustion residuals (CCRs) represented multiple long-term sources of airborne particulate emissions. Review of engineering records, historical operating information, emissions inventories, environmental sampling data, and atmospheric dispersion modeling indicated that contaminant releases originated from both active industrial operations and post-operational material handling activities. Rather than a single emission source, the investigation identified combustion processes, ash handling, excavation, waste processing, haul truck traffic, heavy equipment operation, and fugitive dust generation as contributing sources of airborne particulate matter throughout different operational periods. Evaluating these activities collectively provided a more representative characterization of historical contaminant releases than consideration of stack emissions alone.
Atmospheric dispersion modeling demonstrated that airborne particulate matter generated by historical facility operations had the potential to migrate beyond the facility boundary under representative meteorological conditions. Modeling incorporated multiple operational scenarios reflecting changes in industrial activity, waste management practices, and source characteristics over time. Predicted concentration isopleths and atmospheric deposition patterns varied according to prevailing wind direction, source strength, particle size, terrain, and seasonal meteorological conditions. Integrating multiple emission sources into a single modeling framework produced a comprehensive reconstruction of historical airborne contaminant transport while identifying areas of relatively greater long-term particulate deposition.
Evaluation of environmental sampling data demonstrated that measured concentrations of metals within surface soils were generally consistent with the spatial distribution predicted by atmospheric deposition modeling. Comparison of modeled deposition patterns with measured soil analytical results strengthened the source attribution analysis by demonstrating agreement between independent engineering calculations and observed environmental conditions. Statistical evaluation of environmental sampling data further reduced uncertainty by incorporating accepted exposure point concentration methodologies rather than relying upon isolated sample results. This multiple-lines-of-evidence approach increased confidence in the interpretation of historical contaminant transport and long-term deposition patterns.
The investigation also demonstrated that emissions associated with coal combustion residual management continued to represent important particulate sources after routine combustion operations had ceased. Engineering documentation indicated that excavation, transportation, waste processing, heavy equipment activity, and material handling generated additional fugitive dust emissions capable of transporting particulate-bound metals into surrounding areas. Consequently, historical community exposure could not be evaluated solely on the basis of active industrial operations. Instead, investigators determined that post-operational site activities required independent characterization because they represented distinct emission sources with different temporal patterns and contaminant release mechanisms.
Human exposure assessment integrated modeled airborne concentrations, predicted particulate deposition, measured soil concentrations, and established U.S. Environmental Protection Agency exposure methodologies to estimate both cancer and non-cancer risks associated with long-term residential exposure. Exposure scenarios evaluated inhalation of airborne particulate matter together with incidental contact with contaminated surface soils. Comparison of calculated exposure point concentrations with EPA Regional Screening Levels (RSLs) and accepted toxicological benchmarks provided an objective framework for evaluating potential health risks while maintaining consistency with nationally recognized environmental risk assessment methodologies. Integrating air quality modeling with environmental sampling and toxicological evaluation produced a more comprehensive assessment than reliance upon either engineering modeling or environmental measurements independently.
Collectively, historical reconstruction, emissions estimation, atmospheric dispersion modeling, environmental chemistry, statistical analysis, environmental sampling, contaminant fate and transport evaluation, and human health risk assessment demonstrated the value of integrating multiple independent scientific disciplines into a unified environmental forensic investigation. Rather than relying exclusively on historical emissions inventories, investigators synthesized engineering analyses, environmental monitoring data, air dispersion modeling, exposure assessment, and toxicological evaluation to objectively reconstruct historical contaminant migration and evaluate potential community exposure associated with long-term industrial operations. This multidisciplinary methodology provided a scientifically rigorous framework for environmental consulting, regulatory investigations, environmental litigation, and expert witness evaluations involving historical industrial air emissions and contaminant deposition.
Conclusions
This environmental forensic investigation demonstrates that evaluating historical contaminant releases from legacy industrial combustion facilities requires substantially more than reviewing historical emissions inventories or individual environmental sampling events. A scientifically defensible assessment requires integration of environmental chemistry, engineering evaluation, historical reconstruction, atmospheric dispersion modeling, contaminant fate and transport, environmental sampling, statistical analysis, exposure assessment, and toxicological risk evaluation. By synthesizing multiple independent sources of technical information, investigators reconstructed historical emission scenarios, evaluated contaminant migration, and objectively characterized long-term environmental conditions while substantially reducing uncertainty associated with any individual analytical method.
The investigation further demonstrates the importance of evaluating multiple historical emission sources when reconstructing environmental impacts at former industrial facilities. In addition to routine combustion emissions, material excavation, waste handling, transportation, heavy equipment operation, and fugitive dust generation each represented distinct mechanisms capable of releasing particulate-bound contaminants into the surrounding environment. Evaluating these source categories independently, and then integrating them within a unified air dispersion modeling framework, produced a more representative reconstruction of historical emissions than evaluating stationary industrial sources alone. This comprehensive source characterization significantly strengthened both atmospheric transport analyses and environmental source attribution.
Another significant finding was the value of combining air dispersion modeling with environmental sampling as complementary lines of scientific evidence. Atmospheric deposition modeling predicted the long-term distribution of particulate matter and metal-containing dust under representative historical operating conditions, while soil analytical results provided independent environmental measurements capable of evaluating those predictions. Agreement between modeled deposition patterns and measured contaminant concentrations strengthened confidence in the source attribution analysis and reduced uncertainty associated with either engineering calculations or environmental sampling independently. This multiple-lines-of-evidence methodology represents a fundamental principle of environmental forensic investigations involving historical industrial emissions.
The investigation also highlights the importance of integrating human health risk assessment into environmental forensic evaluations. Air dispersion modeling, environmental chemistry, exposure assessment, and toxicological evaluation were combined to estimate potential long-term inhalation and soil exposure using accepted U.S. Environmental Protection Agency methodologies. Evaluating both cancer and non-cancer endpoints provided a comprehensive framework for interpreting environmental measurements within the context of established health-based screening criteria. This integrated approach ensures that environmental data are interpreted using scientifically accepted exposure assumptions and toxicological benchmarks rather than contaminant concentrations alone.
More broadly, this investigation illustrates how modern environmental forensic investigations combine environmental consulting, environmental chemistry, atmospheric science, engineering analysis, contaminant fate and transport, GIS analysis, air dispersion modeling, environmental sampling, statistical evaluation, and human health risk assessment to objectively evaluate complex historical contamination scenarios. Integrating historical operational records with environmental monitoring, engineering calculations, and multiple independent scientific disciplines provides a technically rigorous framework for supporting environmental litigation, regulatory investigations, environmental due diligence, remediation planning, and expert witness testimony. As legacy industrial facilities continue to undergo redevelopment and environmental investigation, multidisciplinary environmental forensic assessments remain essential for accurately reconstructing historical emissions, evaluating contaminant migration, and objectively characterizing long-term environmental and human health exposures.
This investigation was conducted under the direction of Dr. Paul Rosenfeld, an environmental scientist and environmental forensic expert with extensive experience in environmental exposure assessment, toxicology, air quality, environmental fate and transport, risk assessment, and environmental forensics. Through RoseyFields LLC, Dr. Rosenfeld provides scientific consulting, environmental forensic analysis, regulatory support, and expert witness services involving environmental contamination, human exposure, and public health. His technical oversight helped ensure that the methodologies, scientific interpretations, and conclusions presented in this case study are consistent with accepted scientific principles and current best practices.