APPLIED FORENSIC GEOCHEMISTRY: CURRENT STATE-OF-THE-PRACTICE WITHIN THE ENVIRONMENTAL ENGINEERING/CONSULTING COMMUNITY

Environmental engineering/consulting companies now routinely conduct forensic geochemical investigations previously provided almost exclusively by academia. These investigations include the use of trace element analysis in soil and groundwater, fingerprinting of fuel spills using various geochemical methods, and age dating contaminant releases using stable and radioactive isotope analyses.

Trace elements can be used to track surface and groundwater contaminant plumes. Boron has been used to track leachate emanating from municipal solid waste landfills because it is extensively used in disinfectants, preservatives, and as a fluxing agent in glass and enamels; is readily soluble in water; and will travel greater distances than some hydrocarbons and most heavy metals. Rare earth elements have been used to track refinery effluent and sediment and waste soil dumped into rivers.

Fuel fingerprinting has been successfully used for more than a decade. Techniques include gas chromatography/mass spectrometry chromatogram pattern recognition, polycyclic aromatic hydrocarbon (PAH) analysis, and biomarker signature analysis, which also has been used to determine diesel release age dates to soil. Chlorinated volatile organic compound (CVOC) releases to groundwater, such as trichloroethane, have been age dated using mass balance techniques of degradation or daughter product concentrations collected over time. Other techniques use statistical data from multiple sites to identify and quantify trends and relationships between CVOC plume length and site hydrogeologic, biogeochemical, and physiochemical variables.

Isotope analyses include using stable lead isotopes to identify petroleum and gasoline source signatures and spill age dates. Stable isotope analyses (e.g., boron, lead, nitrogen, and strontium) are useful in identifying chemical processes, contaminant sources, and in differentiating ambient water from impacted water such as sewage effluent. Radioactive isotopes such as tritium (T), originally used in groundwater age dating, previously provided only "ball-park" ages. Now, coupled with helium-3 (He-3), T/He-3 ratios, groundwater can be dated to within several years for relatively young groundwater (percolated within about the last 40 years).