Environmental forensics

The term "environmental forensics" describes the application of scientific approaches to the resolution of claims and litigation involving the sources of environmental contaminants and critical time periods concerning when the contaminants were released. Environmental forensics is especially useful in cost allocation and cost recovery litigation and toxic tort cases, which are personal injury lawsuits based on claims that the parties bringing the suits have been harmed by exposures to hazardous substances released into the environment. As evidence of the growing popularity of this subject, the American Academy of Forensic Sciences now includes an environmental subsection within its engineering sciences division (see Meet your testifying colleagues). The International Journal of Environmental Forensics also began publication online early this year (www.aehs.com/ijefhomepage.html).

Lesile Faust of Houston, who runs Forensic Science Degree, a website dedicated to forensic science education and resources, has created a list of 100 essential forensic science organizations, psychology and pathology publications, technology in forensic science, and other topics related to the field. You can see the list at http://www.forensicsciencedegree.org/top-websites-to-bookmark/.

The subject of environmental forensics is, of course, multi-disciplinary and approaches that are typically taken, while straightforward in concept, are nevertheless often controversial. Complete information is rarely available, so there is always a need for good scientific and engineering judgment.

Components of environmental forensics analysis
Determination of the potential source of one or more environmental contaminants is typically done through a combination of chemical analysis and interpretation, together with a determination of the possible migration pathways that could permit the transport of the material from the alleged source to its current location in the environment. The analysis becomes challenging when more than one source is capable of providing some or all of the contaminants that are found. Signature chemicals, which can be linked to a specific process or waste, can be helpful when present. Also, a variety of "chemical fingerprinting" techniques have emerged, many of which were originally developed for the identification of complex mixtures, such as petroleum hydrocarbons, polyaromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs).

The use of chemical fingerprinting is often controversial, since the composition of the mixture invariably changes due to a number of environmental "weathering" processes, such as biochemical degradation. Still, it is often possible to distinguish different petroleum hydrocarbon products or different AroclorsTM (PCBs) based on their chromatagraphic analysis ("pattern recognition techniques," or statistical comparisons for principal components). Fingerprints also can be created for other chemicals, such as families of chlorinated solvents and their environmental degradation products. Figure 1 exhibits the relationships among tricholoroethylene (TCE) and its daughter chemicals at various sites where TCE was released to groundwater. The relative proportions at different sites reflect the extent to which anaerobic dechlorination has occurred.

Once a suspected source is identified, it is necessary to confirm that a pathway exists along which the chemicals could be transported from that source to their current location in the environment. Here, a good understanding of the nature of the environment in question, e.g., a complex subsurface environment, a dynamic surface water system or an atmospheric transport situation, is essential. Mathematical modeling is also used as an aid to this analysis, and can be a useful tool, provided sufficient data exist to use the models properly.

Environmental contamination can often be dated, depending upon the type of contamination and the precision needed in determining the actual time of release. Often it is only necessary to demonstrate that the contamination occurred before or after a particular date. In this case, knowledge of the years in which chemicals became commercially available and the years in which some chemical products were banned, may be all that is needed (see Table 1).

Table 1

Dates of commercial availability or appearance of chemicals of frequent environmental interest


Date of commercial availability

Carbon tetrachloride


Trichloroethylene (TCE)


1,2-Dichloroethane (DCA)


Tetrachloroethene (PCE)














Gasoline additives:

Tetraethyl lead


Methyl cyclopentadienyl manganese tricarbonyl (MMT)


Tetramethyl lead


Methyl tert-butyl ether (MTBE)

1980s (region specific)

When more precision is required, or if specific release times are an issue, relatively sophisticated isotopic dating techniques may be applicable. The use of tritium and cesium 137 to date groundwaters and sediments, respectively, has seen wide application with well-demonstrated success (see Table 2).

Table 2

Isotope dating of groundwater and sediment

Environmental medium (age)

Isotope (half life, years (yrs))

Modern groundwater (0-40 yrs)

3Tritium (12.3)
6Helium (0.807 seconds)
8Helium (0.119 seconds)
85Krypton (10.8)

Sub-modern groundwater (40-1,000 yrs)

39Argon (269)
32Silicon (330)

Old groundwater (1000+ yrs)

14Carbon (5,730)


135Cesium (2.3 million)
137Cesium (30.2)

Techniques using ratios of other isotopes such as lead and carbon are also available. Other techniques use estimates of the degradation rates of particular alkane components of petroleum hydrocarbons. These techniques are somewhat controversial, however, in that biodegradation rates are necessarily site-specific. This will impact ages estimated using ratios calibrated to a different site.

Rounding out the analysis is "industrial paleontology." This term encompasses a range of activities applied to sort out the history of manufacturing and waste management practices at complex sites. Drawing upon such resources as Sanborn maps, historical aerial photographs, process flow diagrams and material balances, company records, public documents and news accounts, the history of the site can be reconstructed. This historical research, together with chemical fingerprinting, contaminant dating and migration pathway analysis, can provide the basis for a scientifically defensible determination of liability and cost allocation.

Entering the legal arena
Often, given the high stakes involved, parties simply do not agree, and the case goes to trial. When this occurs, people trained and skilled in science and engineering can find themselves scheduled for deposition and possible trial testimony, either as an expert or as a fact witness. Today, however, it is not enough to have a good scientific and engineering understanding of what probably happened. Instead, the witness must communicate this understanding to a judge and/or a jury composed of 12 citizens with varied educational backgrounds, under conditions that can be described as stressful, at best.

Clearly, good communication skills are essential, especially an ability to simplify scientific arguments while not making them too simplistic. Typically, an ability to facilitate understanding is valued, as opposed to a condescending or patronizing approach, which is often seen for what it is. Also, in today's high tech world, good use of computer graphics and demonstrations is an important asset.

Admissibility of expert testimony
While the use of experts in environmental litigation has been a standard practice since the first environmental statutes and regulations were enacted, the admissibility of an expert's testimony has been a controversial subject for many years, especially in product liability and toxic tort suits. In fact, many use the term "junk science" to express their feelings about the nature of some expert testimony. Even though standard rules of evidence had been developed, the role of an expert used to be broadly interpreted as anyone who, through his or her knowledge and experience, could provide assistance to the so-called trier of fact - i.e., the judge or jury. The same wide latitude was given to the admissibility of his or her testimony.

In 1993, however, a now-famous U.S. Supreme Court decision (Daubert vs. Merrell Dow Pharmaceuticals Inc., 509 U.S. 579 (1993)) reaffirmed an earlier decision that assigned to federal judges the role of gatekeeper of scientific testimony, and stressed the need for scientific testimony to be reliable. Although the Supreme Court did not provide specific criteria on how scientific testimony could be determined to be reliable, it did supply information concerning several of the factors judges believed were important to this decision. These factors included:

  • Whether the theory or technique in question can be (and has been) tested;
  • Whether the theory has been subjected to peer review and publication;
  • What the known or potential error rate of the theory is;
  • Whether standards controlling its operation exist, and how these standards are maintained; and
  • Whether the theory has attracted undisputed acceptance within a relevant scientific community.

This Supreme Court decision, which has been used to uphold rulings in subsequent cases - for example, the Joiner decision (General Electric Co. vs. Joiner, 522 U.S. 136 (1993)), a case involving the alleged development of lung cancer as a result of exposure to PCBs - has been understandably well-received by many in the regulated community. The Daubert decision reinforces the need to be sure that expert testimony rests on a firm, defensible scientific foundation.

Since many of the alleged abuses of scientific testimony could be found in product liability and toxic tort litigation, there was a concern that the Daubert decision applied to experts other than "scientific" experts. On March 23, 1999, in a case that involved charges of faulty automobile tire design (Kumho Tire Co. vs. Carmichael (97-1709) (131 F.3D 1433, reversed)(1999)), the U.S. Supreme Court ruled unanimously that federal judges do, in fact, have broad discretion to exclude the testimony of questionable expert witnesses, such as handwriting experts and engineers who don't meet standards of reliability.

Meet your testifying colleagues

The American Academy of Forensic Sciences (AAFS) provides an opportunity for testifying experts in the engineering sciences and those interested in testifying to network and to attend an annual forum. In February 1999, testifying experts in the fields of environmental chemistry, geology, engineering, toxicology and law presented topics that included:

  • Expert witnesses
  • Debunking junk science
  • Aerial photography
  • Microscopy
  • Government archives as sources of evidence
  • Computer uses for forensic investigations
  • Tree rings as a forensic tool
  • Natural vs. synthetic estrogen in surface waters
  • Subsurface investigations
  • Petroleum product identifications and sources

The engineering sciences section includes the following subsections:

  • Electrical safety and failures
  • Environmental
  • Fires and explosions
  • General forensic engineering topics
  • Imaging, illumination and visibility
  • Metallurgy and material science
  • Product liability
  • Vehicle accident reconstruction
  • Second and third collision issues (vehicle occupant dynamics)
  • Biomechanics and human factors
  • Walkway safety

For information about meeting abstracts and membership in AAFS, contact Jim Smith at (610) 383-7233 or at jsmith@trilliuminc.com. AAFS's Web site can be found at www.aafs.org.

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This article originally appeared in the 09/01/1999 issue of Environmental Protection.

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