Gil Oudijk

Applied Dendroecology and Environmental Forensics. Characterizing and Age Dating Environmental Releases: Fundamentals and Case Studies

Dendroecology, or the use of ring patterns to assess the age of trees and environmental factors controlling their growth, is a well-developed method in climatologic studies. This method holds great potential as a forensic tool for age dating, contamination assessment, and characterization of releases. Moreover, the method is independent of the physical presence of contamination at the time of sampling because it is focused on the effect rather than the cause. This review is one of the very few articles published to date exploring the forensic applicability of dendroecology. This article is organized in two parts: Part I describes the method principles and proposes a practical procedure for forensic applications; Part II exemplifies and validates the method through six case studies of successful forensic application (related to petroleum products and chlorinated solvent spills).

The Rise and Fall of Organometallic Additives in Automotive Gasoline

Refiners have used numerous gasoline additives since the 1920s to increase automotive performance and correct deficiencies. The history of organometallic additives, in particular lead-, manganese- and iron-containing compounds is discussed. Some of these additives can be helpful to environmental investigators for fingerprinting and age-dating leaded-gasoline releases. Knowing their history, investigators can decipher these releases more efficiently.

Fingerprinting and Age-Dating of Gasoline Releases—A Case Study

Abstract Several techniques are available to forensic researchers to age-date and fingerprint gasoline releases to the environment. These techniques include the use of isotopes, chemical ratios, and groundwater flow rates, among many others. A case study is presented which describes the use of these methods congruently to assess the time frame of a gasoline release and assess whether or not more than one release had occurred. The principles discussed herein can be used to estimate the age(s) of subsurface gasoline releases in the 50 United States and the U.S. Territories in the Caribbean.

Use of Dendrochronology and Dendrochemistry in Environmental Forensics: Does It Meet the Daubert Criteria?

Dendrochronological methods have been in use for more than 100 years, providing us a record of climate, human activities (archaeology), floods, fire, mudslides and other geological and biological events. More recently, dendrochemisty has been used to assess the time frames of the onset and existence of environmental contamination. This article assesses the scientific status of dendrochronology and dendrochemistry with respect to the admissibility of expert testimony and Daubert legal criteria. The purpose of this article is to identify the crucial scientific aspects of dendrochronology and dendrochemistry that address the Daubert criteria and Rule 702 as amended in 2000. To clarify terminology, dendrochronology is the precise and reliable assignment of the year of formation of tree rings. Dendroecology is the use of dendrochronology to understand ecological and environmental processes (Schweingruber, 1996). Dendrochemistry is a subdiscipline of dendrochronology that analyzes and interprets the wood chemistry of precisely dated tree rings. Forensic dendrochemistry applies dendrochemistry to resolve environmental disputes and generally deal with questions regarding the timing and/or the source of environmental incidents. One significant application of forensic dendrochemistry to expert testimony is to address issues of anthropogenic contamination. Forensic dendroecology is a similar term to forensic dendrochemistry, but forensic dendrochemistry will be used in this discussion as the latter term emphasizes the use of chemical detection methods. Because dendrochemistry is based on the foundation of dendrochronology, both the former specialty and the latter broader discipline will be discussed.

Age Dating Heating-Oil Releases, Part 2: Assessing Weathering and Release Time Frames Through Chemistry, Geology and Site History

The age of heating-oil releases from underground storage tanks (USTs) can be estimated by investigating the petroleum chemistry, the on-site environmental conditions, the extent of contaminant migration, the condition of the UST, site history and several additional factors. The heating-oil chemistry, and in particular the degree of weathering, can be assessed through an examination of: compound depletion, the carbon range, the n-alkane depletion and the size of the unresolved complex mixture (UCM). Each release site can be assigned a weathering regime, such as very aggressive, aggressive, moderate, weak and very weak. These designations are based on the on-site geological, hydrological and biological conditions. A matrix was constructed which compares the weathering regimes to the stages of petroleum weathering and provides potential age ranges. The matrix is a method to lead the investigator towards the correct age, but is not the final say on that age. The age ranges then need to be compared to site-specific characteristics, such as the UST age, the UST condition, the extent of contaminant migration and other extenuating factors. The error range for this method is estimated at ± 2 years; however, there are numerous limitations to the methods and instances will arise where the age can only be constrained.

On Age-Dating Distillate Fuels: A Commentary on the Methods of Hurst & Schmidt (2005) and Galperin & Kaplan (2008)

To say that the subject of age-dating distillate fuels released to the environment is under discussion in the scientific literature would border on trite. Today, it seems that this subject is very much in play, to borrow a recent quote from a colleague. Let us join the fray. Since publication of an empirical technique for age-dating middle-distillate fuel (diesel fuel) by Christensen and Larsen in 1993 (C&L), forensic experts and commercial laboratories have mademuch of the approach. Much confusion regarding the applicability of the C&L approach has resulted in a polarization within the environmental forensics community. However, as discussed in many articles published in this and other journals, there are numerous positives and negatives related to the C&L method. It is our opinion that the C&L method should be considered, but never exclusively relied upon. At present, from our viewpoint there are two regimens or ways of thinking with regard to age-dating distillate fuel releases, which are described here. The first regimenmight be termed the let it fly experts—those who apply the C&L approach widely and without discrimination. In the extreme are the interests who will age-date anything that comes into a laboratory. Single samples are their specialty. Such an approach effectively disregards the possibility of multiple different releases and is ignorant of site-environmental conditions. This group does not provide error ranges or any opinion on uncertainty. Age-dating of single samples, without consideration of any facet of petroleum degradation or site-specific conditions, does us all a great disservice. Unfortunately, many in the fields of engineering and science have been employing this approach, thereby abusing fundamentally accepted scientific principles. The second regimen might be termed the how are we going to work with this? thinkers. One must remember that there

Age Dating Heating-Oil Releases, Part 1. Heating-Oil Composition and Subsurface Weathering

Releases of no. 2 heating oil are a serious threat to groundwater resources throughout much of the world. Because of the significant remediation costs for heating-oil spills, insurance carriers and associated law firms often request information on release time frames. A semi-quantitative age-dating procedure is proposed that incorporates factors such as site history, petroleum composition and weathering, environmental conditions, extent of contamination and the condition of the underground tank. The procedure uses the principles of petroleum chemistry and compares them to the known site-specific environmental conditions. Each contamination case is specific unto itself and a universal approach, such as a mathematical equation, is not proper because it cannot incorporate all the needed parameters. Furthermore, the use of only petroleum chemistry as an age-dating criterion is inadequate. Accordingly, the investigator will need to evaluate all factors, such as environmental conditions, petroleum chemistry, underground tank condition, site history and the extent of contamination, and assess the importance of each, prior to providing an age-date opinion.

The Use of Atmospheric Contaminants to Estimate the Minimum Age of Environmental Releases Impacting Groundwater

Numerous age-dating techniques are available to estimate the time frame of contaminant releases impacting groundwater. One method, historically used in the hydrology field to assess recharge ages and rates of groundwater flow, can be applied to estimating the age of contaminant releases. Chlorofluorocarbons (CFCs) and tritium are anthropogenic substances present in the atmosphere over the past half century. These atmospheric contaminants recharge the groundwater through precipitation and can be used as age markers. In cases where the recharge water is in contact with contaminants, the CFCs and tritium may be used to estimate the minimum age of the contaminant release. Three case studies from New Jersey are provided which describe the methods used to age date releases of chlorinated solvents and petroleum products.

Estimating the Minimum Age of a Chlorinated Solvent Plume in Groundwater with Chlorofluorocarbon (CFC) and Tritium Methodologies: A Case Study

Numerous age-dating techniques are available to estimate the time frame of contaminant releases to the environment. One method, historically used in the hydrology field to determine recharge ages of groundwater, can be applied to estimating the minimum age of contaminant discharges. Chlorofluorocarbons (CFCs) and tritium are anthropogenic substances present in the atmosphere over the past half century. These constituents recharge the groundwater through precipitation and can be used as an age marker. In cases where the recharge water is in contact with contaminants, the CFCs and tritium may be used to estimate the minimum age of the contaminant release.

Compound-Specific Stable Carbon Isotope Analysis of MTBE in Groundwater Contamination Fingerprinting Studies: The Use of Hydrogeologic Principles to Assess Its Validity

Methyl-tert-butyl ether (MTBE) is an oxygenate added to gasoline in the United States and elsewhere to boost the octane ratio and reduce tailpipe emissions. Because of its known usage time frame, the presence of MTBE can help estimate the age of gasoline releases to the environment. However, because of its ubiquity, its presence can no longer be used to fingerprint, or differentiate, gasoline plumes in groundwater. Compound-specific stable carbon isotope analysis has recently become a method for differentiating MTBE sources and plumes affecting groundwater. In the present study, groundwater samples were collected from 20 monitoring wells located at two gasoline service stations in central New Jersey in an attempt to differentiate the dissolved gasoline plumes and possibly identify their sources. The carbon isotope ratio (13C/12C expressed as δ13C) values for each sample were determined through gas chromatography–isotope ratio–mass spectrometry (GCIRMS), and the impacted area for each plume was delineated. As biological degradation of MTBE proceeds, δ13C becomes heavier; petroleum-degrading bacteria preferentially assimilate the lighter 12C isotope, thereby enriching the residual MTBE in the heavier 13C isotope. The isotopic composition of MTBE at different locations demonstrated the varying degree to which MTBE had been altered by biodegradation. The δ13C values can also provide insight into the type of release and the magnitude of biodegradation. Two types of leaks occurred at the sites: a shallow piping leak and deeper leak from a tank system. δ13C values in the vicinity of the shallow leak were heavier, revealing increased biodegradation in the soil, while δ13C values in the vicinity of the tank leak were lighter, revealing the lack of biological degradation in non-aqueous phase liquid (NAPL) trapped beneath the water table. An assessment is provided where the physical site characteristics responsible for petroleum weathering are considered in comparison with the measured δ13C values.