Environmental Forensic Investigation of Industrial Odor Releases, Hydrogeologic Source Attribution, and Environmental Fate and Transport within an Urban Drainage System
Project Overview
Environmental odor incidents present some of the most technically challenging environmental forensic investigations because odors often originate from complex mixtures of volatile chemicals, reduced sulfur compounds, petroleum hydrocarbons, industrial wastewater, biological activity, or multiple simultaneous environmental processes. Unlike investigations involving a single contaminant release, odor investigations require integration of environmental chemistry, hydrogeology, contaminant fate and transport, atmospheric science, industrial process evaluation, environmental sampling, and historical site reconstruction to identify the most scientifically plausible source or combination of sources. The investigation documented in the project materials involved an extensive environmental forensic evaluation of a prolonged community odor event associated with a heavily industrialized drainage corridor containing petroleum infrastructure, historical industrial facilities, pipelines, stormwater conveyance systems, wastewater infrastructure, groundwater contamination, and numerous potential chemical sources. The primary objective was to determine which environmental mechanisms were capable of producing the observed odor event while systematically evaluating competing source hypotheses using multiple independent lines of scientific evidence.
The investigation began with a detailed reconstruction of the chronology of environmental conditions preceding the odor event. Historical information compiled from regulatory agencies, meteorological records, seismic activity, emergency response reports, and community complaint databases documented a sequence of events that included regional earthquakes, unusually warm weather, localized rainfall, a warehouse fire, observations of petroleum sheen within the drainage channel, and rapidly increasing public complaints describing strong sulfur-like odors. Community complaints ultimately prompted extensive environmental monitoring, emergency declarations by local governmental agencies, deployment of continuous hydrogen sulfide monitoring equipment, and comprehensive technical investigations into potential environmental sources. Establishing this chronology provided an important framework for evaluating whether observed environmental conditions were temporally consistent with any proposed source mechanism.
Rather than focusing on a single suspected release, the environmental forensic investigation evaluated numerous scientifically plausible source hypotheses. These included petroleum releases from historical industrial facilities and subsurface pipelines, groundwater transport of hydrocarbons, sewer infrastructure failures, unauthorized industrial discharges, stormwater inputs, landfill leachate migration, leaking oil and gas wells, sulfur-generating biological processes within channel sediments, and releases associated with nearby industrial activities. Each hypothesis was evaluated using historical site investigations, hydrogeologic information, groundwater monitoring data, pipeline records, subsurface utility mapping, stormwater infrastructure, environmental chemistry, and available analytical sampling results. By considering all reasonable alternatives before reaching scientific conclusions, the investigation followed a multiple-lines-of-evidence approach consistent with accepted environmental forensic methodology.
The investigation also incorporated extensive environmental sampling and chemical characterization. Ambient air samples were collected using SUMMA canisters at strategically selected locations along the drainage channel to characterize volatile sulfur compounds and other odorous constituents. Sampling locations were selected based upon complaint patterns, prevailing environmental conditions, channel configuration, and accessibility, while additional monitoring evaluated hydrogen sulfide concentrations and other sulfur-containing compounds potentially responsible for community odor complaints. The resulting analytical data were interpreted together with historical groundwater investigations, hydrogeologic conditions, industrial facility records, and published scientific literature addressing sulfur chemistry and odor generation mechanisms (Odor Sampling Plan for the Dominguez Channel; Dominguez Channel Sampling Results).
Because numerous historical industrial operations had occurred within the surrounding area, understanding regional hydrogeology represented another critical component of the investigation. Historical remedial investigation reports, groundwater elevation data, tidal influence studies, cross-sectional geologic profiles, contaminant distribution maps, and groundwater flow evaluations were reviewed to determine whether petroleum hydrocarbons or other contaminants could migrate from historical industrial facilities toward the drainage channel. Existing groundwater investigations documenting light non-aqueous phase liquid (LNAPL), benzene, total petroleum hydrocarbons, tert-butyl alcohol, diisopropyl ether, and other petroleum-related constituents were integrated with groundwater flow interpretations to evaluate potential subsurface migration pathways and determine whether previously documented contamination could reasonably contribute to the observed odor event.
By integrating historical reconstruction, hydrogeology, environmental chemistry, industrial infrastructure evaluation, contaminant fate and transport, environmental sampling, odor science, and multiple competing source hypotheses, the investigation developed a comprehensive scientific framework for evaluating one of the most complex environmental odor incidents involving industrial infrastructure and urban waterways. Rather than relying upon isolated analytical measurements, the investigation synthesized numerous independent datasets to objectively evaluate source attribution, environmental processes, and the scientific plausibility of competing explanations for the observed community odor event (Further Details – Dominguez Channel Odor Incident; Preliminary Assessment of Dominguez Channel Odor Incident).
Chemicals of Concern
The primary chemicals of concern evaluated during this environmental forensic investigation were hydrogen sulfide (H₂S) and a variety of reduced sulfur compounds capable of generating strong nuisance odors and adverse health symptoms at very low atmospheric concentrations. Because odor events often involve complex chemical mixtures rather than a single contaminant, the investigation also evaluated petroleum hydrocarbons, volatile organic compounds (VOCs), landfill gases, sulfur-containing wastewater constituents, and other naturally or anthropogenically generated odorants that could contribute to community-wide odor complaints. Rather than focusing exclusively on one contaminant, investigators evaluated the environmental chemistry, generation mechanisms, transport pathways, and persistence of numerous odor-producing compounds while comparing each with the observed monitoring data and documented chronology of the incident.
Hydrogen sulfide represented the principal odorant evaluated throughout the investigation because continuous air monitoring documented elevated H₂S concentrations concurrent with widespread community odor complaints. Monitoring data collected by regulatory agencies demonstrated temporal variations in hydrogen sulfide concentrations that closely corresponded with reported nuisance conditions and provided an objective dataset for evaluating potential source mechanisms. Because hydrogen sulfide possesses an extremely low odor threshold, even relatively small atmospheric concentrations can produce strong odor perceptions and nuisance complaints. The investigation therefore examined H₂S not only as an indicator of environmental contamination but also as a potential marker for underlying biological, industrial, or petroleum-related processes occurring within the drainage system.
The investigation also evaluated petroleum hydrocarbons as potential precursor compounds contributing indirectly to hydrogen sulfide generation. Historical investigations documented petroleum hydrocarbons, light non-aqueous phase liquids (LNAPL), gasoline, jet fuel, heavier petroleum products, benzene, tert-butyl alcohol, diisopropyl ether, and other hydrocarbon constituents within portions of the surrounding industrial area. These hydrocarbons were significant because petroleum contamination can provide a long-term carbon source capable of supporting sulfate-reducing bacteria under anaerobic conditions. Accordingly, historical petroleum releases, groundwater contamination, and previously documented hydrocarbon recovery operations were reviewed to determine whether they could contribute to biological hydrogen sulfide production within channel sediments or adjacent groundwater systems.
A substantial portion of the investigation focused on the microbiological processes responsible for hydrogen sulfide generation. Published literature reviewed during the investigation describes sulfate-reducing bacteria (SRB) as anaerobic microorganisms that obtain energy by oxidizing organic carbon while reducing sulfate to sulfide. The presentation explains that SRB preferentially inhabit oxygen-depleted environments rich in sulfate and organic carbon, including estuarine sediments, wastewater systems, petroleum-contaminated environments, and organically enriched aquatic sediments. Because both sulfate and organic carbon were potentially available within the drainage channel, investigators evaluated whether naturally occurring microbial activity could generate sufficient hydrogen sulfide to explain the observed odor event either independently or in combination with anthropogenic hydrocarbon sources.
The investigation additionally reviewed numerous alternative chemical source mechanisms, including sewer releases, unauthorized industrial discharges, stormwater inputs, landfill leachate, decomposing vegetation, ethanol releases associated with a nearby fire, leaking oil wells, and historical pipeline releases. Each hypothesis involved distinct chemical processes capable of producing odor-causing compounds under appropriate environmental conditions. Rather than assuming a single explanation, investigators compared the expected chemical signatures, environmental behavior, and transport mechanisms associated with each hypothesis against available monitoring data, hydrogeologic information, pipeline records, groundwater investigations, and historical site information. This systematic evaluation ensured that the final source attribution relied upon multiple independent scientific observations rather than any individual analytical result or isolated environmental condition (Further Details – Dominguez Channel Odor Incident, Hypotheses; Preliminary Assessment of Dominguez Channel Odor Incident, Potential Sources of H₂S Odor).
Methods
The environmental forensic investigation employed a multidisciplinary methodology integrating historical document review, environmental chemistry, hydrogeologic evaluation, pipeline assessment, environmental sampling, odor science, GIS analysis, contaminant fate and transport evaluation, and source attribution. Because numerous potential sources were capable of producing sulfur-containing odors within the industrial drainage corridor, the investigation relied on a multiple-lines-of-evidence approach that systematically evaluated each hypothesis against available scientific, engineering, and environmental data. Rather than assuming a single cause, investigators independently assessed historical records, environmental monitoring data, subsurface investigations, infrastructure mapping, and published scientific literature to determine which hypotheses remained consistent with the observed chronology and environmental conditions.
The investigation began with a comprehensive historical reconstruction of the odor event. Regulatory agency reports, emergency response records, meteorological observations, seismic activity, public complaint databases, and historical environmental investigations were reviewed to establish the sequence of events preceding and during the odor incident. Particular emphasis was placed on identifying environmental changes that occurred immediately before the onset of community complaints, including elevated temperatures, rainfall events, documented petroleum sheens within the drainage channel, nearby fires, earthquake activity, and regulatory monitoring activities. Developing an accurate chronology allowed investigators to compare the timing of each proposed source mechanism with the progression of observed odor complaints and measured hydrogen sulfide concentrations (Preliminary Assessment of Dominguez Channel Odor Incident, Chronology of Events; Further Details – Dominguez Channel Odor Incident, Chronology of Events).
Hydrogeologic and contaminant fate and transport evaluations represented another major component of the investigation. Historical remedial investigation reports, groundwater elevation measurements, cross-sectional geologic profiles, tidal influence studies, monitoring well data, groundwater flow interpretations, and regional hydrogeologic mapping were reviewed to determine whether petroleum hydrocarbons or other contaminants could migrate from surrounding industrial properties into the drainage channel. Existing investigations documenting light non-aqueous phase liquid (LNAPL), petroleum hydrocarbons, benzene, tert-butyl alcohol, and other contaminants were compared with regional groundwater flow directions, channel geometry, and tidal influences to evaluate potential subsurface transport pathways capable of contributing to odor generation.
A detailed infrastructure assessment was also performed to evaluate potential engineered sources of contamination. Investigators reviewed historical pipeline investigations, the National Pipeline Mapping System, utility records, substructure maps, stormwater conveyance drawings, sewer infrastructure maps, landfill investigations, and historical industrial facility information to identify active and abandoned pipelines, wastewater conveyances, storm drains, oil recovery systems, and other engineered pathways capable of transporting petroleum products or sulfur-containing materials to the drainage channel. Historical documentation describing previous petroleum releases, pipeline failures, remedial investigations, and groundwater recovery systems was incorporated into the evaluation to determine whether historical contamination remained capable of influencing present-day environmental conditions.
Environmental sampling provided an additional independent line of evidence supporting the investigation. Ambient air sampling locations were strategically selected using prevailing complaint patterns, channel accessibility, prevailing wind considerations, and suspected source areas. SUMMA canisters were deployed at multiple primary and secondary sampling locations to characterize volatile sulfur compounds and other odor-producing constituents throughout the drainage corridor. Hydrogen sulfide monitoring data collected by regulatory agencies were evaluated together with field observations, historical odor complaints, and laboratory analytical results to assess the spatial distribution and temporal persistence of odor-causing compounds. These environmental measurements were interpreted collectively rather than individually, allowing investigators to compare observed analytical results with each competing source hypothesis.
Finally, the investigation synthesized all available information through an environmental forensic source attribution framework. Each proposed hypothesis—including petroleum releases, sulfate-reducing bacterial activity, sewer failures, unauthorized industrial discharges, stormwater releases, landfill leachate, leaking oil wells, decomposing vegetation, and other potential odor sources—was evaluated against the historical chronology, environmental chemistry, hydrogeologic conditions, infrastructure assessments, sampling data, and published scientific literature. By integrating independent scientific disciplines rather than relying upon a single analytical technique, the investigation developed a technically rigorous and scientifically defensible assessment of the most plausible environmental processes contributing to the odor incident while identifying additional data needs that could further refine future investigations (Further Details – Dominguez Channel Odor Incident, Hypotheses; Preliminary Assessment of Dominguez Channel Odor Incident, Conclusions).
Results and Conclusions
The environmental forensic investigation demonstrated that the community odor incident was considerably more complex than a typical single-source release. Historical records, regulatory monitoring data, hydrogeologic evaluations, infrastructure assessments, and environmental chemistry collectively indicated that numerous potential sources were capable of contributing sulfur-containing compounds or petroleum hydrocarbons to the industrial drainage corridor. Rather than supporting a single definitive source based upon limited observations, the investigation established a scientifically defensible framework for evaluating multiple competing hypotheses using independent lines of environmental evidence. This comprehensive approach significantly reduced the potential for source misidentification while providing a technically rigorous basis for continued environmental investigation.
One of the most significant findings involved the strong temporal relationship between documented community odor complaints and measured hydrogen sulfide concentrations. Regulatory monitoring documented elevated hydrogen sulfide concentrations concurrent with widespread public reports of foul odors, while emergency declarations and public health responses reflected the magnitude of the community impacts. Review of complaint records, monitoring data, and field observations demonstrated that odor occurrences were neither isolated nor random, but instead represented a prolonged environmental event affecting numerous residential neighborhoods surrounding the drainage corridor. This consistency between public observations and environmental monitoring provided an important independent line of evidence supporting the occurrence of a significant odor episode.
Historical environmental investigations also demonstrated that petroleum contamination had previously been documented within portions of the drainage system and surrounding industrial properties. Earlier investigations identified petroleum hydrocarbons, light non-aqueous phase liquids (LNAPL), and recurring petroleum sheens at multiple locations near the drainage channel, while remedial investigations documented historical groundwater contamination and long-term hydrocarbon recovery efforts. Pipeline investigations, groundwater monitoring, and tidal studies further demonstrated that historical petroleum releases and complex groundwater conditions required careful evaluation as potential contributors to the odor event. These findings supported continued consideration of petroleum-related hypotheses rather than limiting the investigation to biological odor generation alone.
The investigation likewise determined that naturally occurring environmental processes warranted careful consideration. Review of the microbiological literature demonstrated that sulfate-reducing bacteria readily colonize anaerobic environments containing sulfate and available organic carbon, conditions that may occur within organically enriched channel sediments or petroleum-impacted environments. The investigation concluded that biological hydrogen sulfide generation represented a scientifically plausible mechanism capable of contributing to observed odor conditions, particularly if sufficient carbon sources and reducing conditions were present. However, the available information also indicated that biological activity should not be evaluated independently of historical petroleum contamination, hydrogeologic conditions, industrial infrastructure, or other potential environmental inputs capable of supplying organic substrates to sulfate-reducing microbial communities (Preliminary Assessment of Dominguez Channel Odor Incident, Sulfate-Reducing Bacteria Overview; Further Details – Dominguez Channel Odor Incident, Potential Sources and Hypotheses).
Overall, the investigation demonstrated the importance of integrating environmental chemistry, hydrogeology, contaminant fate and transport, historical site reconstruction, environmental sampling, infrastructure assessment, and source attribution into a single multidisciplinary evaluation. Rather than relying upon isolated analytical measurements or assumptions regarding a single contaminant source, the investigation synthesized historical investigations, regulatory monitoring, groundwater studies, pipeline evaluations, odor science, and environmental microbiology to objectively evaluate competing explanations for the odor event. This multiple-lines-of-evidence methodology represents a cornerstone of modern environmental forensic investigations and provides a scientifically defensible framework for addressing complex environmental litigation, regulatory investigations, and community exposure assessments involving industrial odor releases and mixed contaminant sources (Preliminary Assessment of Dominguez Channel Odor Incident, Conclusions; Further Details – Dominguez Channel Odor Incident, Conclusions).
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.