HAI’s Professional Forensic Expertise
Estimating Ages of Petroleum Hydrocarbon Releases:
Stable Lead Isotopes and Gas Chromatography
Estimating the year petroleum hydrocarbons were released into the environment and serving as an expert witness are important services offered by HAI. Development of the ALAS Model, which uses systematic increases in lead isotope ratios of alkyllead to estimate the age of gasoline releases, began circa 1990, with refinements and testing of the technique continuing through the present (e.g. Hurst, 2002). The ALAS Model and lead isotopic ratios have been effectively integrated with gas chromatographic data, providing clients with information required in matters involving liability, cost recovery, source apportionment, and decisions regarding cleanup strategy. Advantages of employing lead isotopes (ALAS Model) in forensic investigations of hydrocarbon releases include the:
- Improved age resolution, particularly for releases which occurred between 1965 and 1990 (+ 1-2 years);
- Ability to quantify contributions from multiple releases at a site;
- Minimal sample volumes required; and
- Recalcitrance of lead isotopes (no degradation or fractionation).
Reference: Hurst, R.W. (2002) Lead Isotopes as Age-Sensitive Genetic Markers in Hydrocarbons: 3. Leaded Gasoline. 1923-1990 (ALAS Model), Jour. Environ. Geosci., V. 9, No. 2, 43-50. [Abstract] [Download]
Sample Turnaround/Surcharges: Isotope analyses are more labor intensive than most environmental protocols. Clients should submit samples a minimum of 40-60 working days in advance of anticipated deadlines. HAI should be apprised of samples requiring expedited turnaround as soon as possible. Surcharges are applied for rapid turnaround (<30 working days) or large sample groups which require expedited analyses to meet imposed deadlines.
Isotopic (C; H; O; N; Cl; T; Sr; Pb; U) and Geochemical Fingerprinting
Examples of Applications Include—-
- Hydrocarbons: Statistical evaluation of gas chromatographic, geochemical, and isotope analyses of petroleum hydrocarbons/soils/groundwater are used to identify sources of hydrocarbon releases in the environment and evaluate oil-oil/oil-source rock correlations in petroleum exploration.
- Groundwater: Isotopic analyses of appropriate, naturally-occurring isotopes (e.g. strontium, uranium, tritium, nitrogen, chlorine, oxygen/hydrogen) in groundwater provide information needed to assess (1) aquifer recharge/continuity; (2) residence times; (3) sources of low-level radioactivity in landfill leachate; and (4) degradation of groundwater quality due to a variety of anthropogenic contaminants.
- Perchlorate and Chlorinated Solvents: Use of strontium, chlorine, and oxygen isotopes to are valuable in assessing sources and transport pathways of chlorinated solvent/perchlorate in groundwater.
- Heavy Metals (Pb, As, Cr): Lead isotopic analyses have been used to fingerprint sources of lead, arsenic, and chromium at sites impacted by heavy metals resulting from mining, smelting, military, agricultural (pesticides), and electronic component production operations. In addition, Pb/Pb dating of minerals, rocks, and crude oils is used extensively in the development and production of economic resources.
Mineralogy by X-Ray Diffraction (XRD) Analyses
- XRD analyses are employed in forensic studies to evaluate sediment transport/sources and apportion observed soil/rock geochemistry among the mineral phases present.
HAI has been retained by State/County agencies and geotechnical firms to translate results of scientific reports into documents written in nontechnical language for dissemination to the lay public as well as other non-science based professionals. Examples of projects include: (1) evaluating sources of low-level alpha and beta emissions in landfill leachate; (2) assessing the reliability of hydrocarbon release ages from gas chromatographic data; (3) discriminating among sources of heavy metals at a U.S. Naval Base on the eastern seaboard; and (4) determining sources of beach sediment in a wetland environment.
Project Design and Quotations
Each project is unique, with projects involving isotopic and/or geochemical analyses potentially requiring the integration of various techniques and tiered approaches. Quotations are provided following initial consultation with the client. Work proceeds upon receipt of an initial retainer and formal letter of retention.