Forensic chemistry techniques are routinely implemented to develop defensible scientific conclusions regarding the source or age of chemical contamination. Such techniques require a combination of data interpretation skills, in-depth knowledge of analytical methodologies, and innovative statistical analyses. Gradient’s scientists employ these techniques to differentiate sources, define release timing, and predict weathering for constituents, such as petroleum hydrocarbons, fuels, tars, PAHs, PCBs, dioxins, solvents, and metals. In addition, our fate and transport modeling skills are often a useful adjunct to fingerprinting for source differentiation and release timing. We have even used “garbology” (also known as contemporary archeology), which is the study of trash often co-disposed with hazardous materials, to understand the timing and content of chemical contamination.
Saxe, JK; Bowers, TS; Reid, KR. 2006. “Arsenic.” In Environmental Forensics: Contaminant Specific Guide. (Eds.: Morrison, RD; Murphy, BL), Academic Press, Burlington, MA. p279-292.
Forensic Chemistry for Polychlorinated Biphenyls (PCBs) at a Rail Yard
Gradient evaluated the nature and extent of PCB contamination at a former rail yard Superfund site as part of a cost allocation case. We reviewed more than 15 years of chemical data from soil, sediment, and groundwater samples, and collected soil samples for advanced congener fingerprinting analysis using GC/MS-SIM to aid in determining the sources of contamination.
Evaluation of Sources of Residential Indoor Air Contamination
Gradient evaluated possible sources of residential indoor air contaminants by reviewing historical data on non-aqueous phase liquid (NAPL) releases in the area and collecting NAPL samples to determine the site’s current state. We reviewed groundwater data, fingerprinting analyses, and reports of petroleum odor-related complaints to assess the relationship between indoor air quality and the presence of NAPL on the water table.
Volatile Organic Compound (VOC) Source Identification
Gradient provided expert testimony on the sources of chlorinated solvents in a plume of contaminated groundwater adjacent to a former industrial site. We evaluated groundwater concentrations and contaminant travel times, directed the sampling and analysis of groundwater and NAPL for benzene via specialized carbon isotope analysis, and applied chemical fingerprinting techniques to distinguish industrial and non-industrial contaminant plumes.
Forensic Analysis of Waste Materials
Gradient reviewed soil sample results to determine the origin of a waste material generated during a manufacturing process. We reviewed elemental analyses, physical characteristics such as grain size, as well as scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) analyses to identify the chemical or physical signatures that differentiated the waste material from other samples.
Chlorinated Solvent Source Identification
In context of a property transaction, Gradient used compound-specific isotope ratio analyses on the perchloroethylene (PCE) and trichloroethylene (TCE) in soil and groundwater to differentiate between the sources of these contaminants. Our work was used in negotiations with the seller.