Historical Reconstruction of Chemical Releases

Reconstructing past chemical releases—when they occurred and who was responsible—is a well-established, multifaceted focus of the field of environmental forensics. Such analyses are important to understanding the source(s) and timing of a release and whether one or multiple releases occurred; key aspects in resolving insurance coverage disputes. Historical chemical release reconstruction enables identification of liable parties, apportionment of responsibility, and allocation of costs to remediate and/or compensate for environmental harm. When past chemical releases are better understood, cleanup and related assessments such as natural resource damage assessment (NRDA) can be optimized. This understanding serves as a basis for exposure reconstruction in toxic tort cases, and for establishing baseline and background levels of alleged contaminants (i.e., to recreate conditions that existed “but for” the release).

Historical chemical release reconstruction weaves together multiple strands of information and data that may include:


  • Present day patterns of contamination observed at the site
  • Site-specific historical operational information
  • General knowledge of the processes used, chemicals handled, and wastes generated
  • Physical setting of the site, including a detailed understanding of the soils, geology, hydrogeology, surface water drainage patterns, and climatology
  • Understanding of the chemical fate processes influencing the concentrations and chemical patterns observed at the site

Reconstruction of chemical releases typically include a thorough review of written records, operational histories, and chemical processes, as well as the application of advanced chemical forensics to determine chemical sources, the quantities and compositions of chemicals in the environment (i.e., chemical fingerprints), and the degradation or weathering patterns.

Exponent uses some of these key tools to reconstruct historical chemical releases:


  • Examination of aerial photographs and historical maps, including topographic maps and fire insurance maps
  • Review of historical patents and contemporaneous trade or peer-reviewed literature
  • Evaluation of utility maps and construction records, including historical and current sewer maps
  • Analysis of ownership and operational records
  • Evaluation of permits and violations
  • Chemical fingerprinting, including multivariate statistical analyses or chemical source modeling
  • Age-dating using chemical techniques
  • Fate and transport modeling 

Exponent’s multidisciplinary highly specialized team of environmental forensic scientists and engineers are well-qualified and litigation-tested, with expertise in chemistry and geochemistry, process engineering, and fate and transport modeling in groundwater, surface water, sediment and air. Our consultants address questions related to historical chemical release reconstruction at a variety of industrial sites, ranging from a single site such as a dry cleaning facility to complex, multi-party Superfund sites with numerous potentially responsible parties. We routinely leverage the knowledge and experience of more than 90 technical disciplines across our firm to support these efforts, including experts in industrial operations and engineering failure analysis.

Exponent has been engaged with historical chemical release reconstruction projects that include former manufactured gas plant (MGP) sites, wood-treatment sites, oil refineries, iron and steel works, non-ferrous smelters, brass foundries, battery manufacturers, aluminum smelters, petroleum refineries, pesticide manufacturers, dry cleaning facilities, glass manufacturers, retail gas stations, and multi-party and multi-industry sediment sites.

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