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.

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:

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.