The liability for cleaning up historically contaminated properties is far reaching. Responsible parties have often searched for tools to help them prove that previous owners/operators caused the contamination. They would then pursue those parties privately for reimbursement of the cleanup costs, often using environmental forensics as a key tool in procuring evidence.

Prior to the absolute pollution exclusion introduced into CGL policies in 1986, exclusions in insurance claims for environmental cleanup were very limited. Therefore, claims that indicated that an environmental loss was incurred in 1986 or prior may be covered. Environmental forensics can be employed to pinpoint the date — and thus the age — of a contaminant release. This date can then be compared to the date of insurance coverage at that time.

Site Specifics

Historical research is the primary forensic tool in determining the age and origin of a release. There are many different ways to learn about a site's history. Some measures include studying aerial photographs, using Sanborn fire insurance maps, and conducting title searches.

Aerial photography interpretation is routinely used to identify the historical use of a property. It can also be used to help estimate the timing of a contaminant release. There are multiple sources used in gathering these photographs, including the U.S. Geologic Survey (USGS), the Aerial Photographic Library, the U.S. Department of Agriculture, the U.S. Army Corp of Engineers, and many private collections.

After reviewing the aerial photographs, the forensic expert can establish the historical information and practices for a specific site. Key environmental components — such as above-ground storage tanks, drum storage areas, spill areas, lagoons, and waste piles — often can be viewed in aerial photographs. This assists the expert in ascertaining crucial information about potential contaminant sources, the age of release, and the type of contaminant.

Sanborn maps are another viable source on which to rely, as they provide extensive information about building use, including factory owners' names and what was manufactured in them for the time period specified. Other features evident in such maps include pipelines, underground storage tanks, wells, dumps, and heavy machinery.

Title searches provide yet another investigative tool to identify the previous property owner(s) and historical operations. There are also less traditional — but equally effective — methods for historical research, including conducting research at local libraries and historical societies as well as interviewing neighbors, former employees, and town residents.Fingerprint Analysis

Forensic laboratory analysis is another method that is commonly used to determine the date of an environmental loss. Forensic laboratory analysis is often beyond the scope of the laboratory analysis that is generally required by regulatory authorities and therefore must be specifically requested. The most effective type of forensic analysis depends on the actual contaminant. In most cases, the contaminant release will originate from petroleum sources, such as gasoline, heating oil, waste oil, or solvents such as dry-cleaning fluids or degreasing agents.

For example, gasoline retailers use different proprietary additives such as anti-knock compounds, blending agents, anti-rust agents, and anti-icing agents. These additives are often replaced by new and improved additives over time. By determining the presence of these additives in the subsurface, experts can determine the date (or age) of the loss and identify the refiner that manufactured the gas.

Heating oil is not as refined as gasoline, so an analysis of additives does not play as significant a role in determining the timing of the contamination. Accordingly, laboratories that conduct forensic analysis on heating oil losses typically analyze the degradation products that are present in the subsurface from a heating oil loss. From that data, and the knowledge of how long it takes those degradation products to form, forensic experts can estimate the age of the contamination.

If dry-cleaning fluids are found, then it is necessary to employ a combination of methods, including groundwater transport modeling and analysis for daughter products.

Groundwater Modeling

A third technique for determining the age of a contaminant release is groundwater modeling. Groundwater modeling can be used to predict the age of a contaminant release when that release has impacted groundwater. This type of investigation consists of fully delineating the horizontal and vertical extent of a groundwater contaminant plume. Based upon the distance the plume has traveled, the forensic expert uses models that incorporate many factors, such as aquifer hydraulic properties, soil type, and chemical type to predict the rate at which the contaminant would have traveled. Once the distance of the plume and the rate of travel is known, the expert can predict how long the contamination has been present in the ground.

Nature's Detective

Dendroecology is the study of the ecological and environmental changes depicted in the annual rings of trees. The width and composition of rings are dependent upon environmental stresses such as floods, droughts, fire, and contamination.

Because trees have the ability to record the contaminant history in their rings, dendroecology has become an emerging field in environmental forensics (“Applied Dendroecology and Environmental Forensics. Characterizing and Age Dating Environmental Releases: Fundamentals and Case Studies,” Jean-Chritophe Balouet, Gil Oudijk, Kevin T. Smith, Ioana Petrisor, Hakan Grudd, and Bengt Stocklassa, Environmental Forensics, 8:1-17, 2007). According to dendroecologists, this tool can be used to estimate the age of a contaminant release; characterize the type of contamination; assess how the release occurred, such as a single event versus long-term exposure; and map the extent of the contaminant plume.

One of the noticeable advantages of dendroecology as opposed to other forensic methods is that the evidence remains in the tree even after the contamination itself degrades, thereby preserving the evidence. Experts within the field of dendroecology have demonstrated that the resolution of dendroecological methods as an age-dating tool compares favorably to other forensic methods. In fact, dendroecological methods offer a precision of one year, a figure that can sometimes be narrowed to a specific season.

Like any scientific method, there are limitations of using dendroecology as a forensic tool. For instance, not all contaminated sites have trees that are within the plume area. Furthermore, trees that have been replanted or significantly pruned may not be appropriate for dendroecology. Last, the rings of trees in warm climates (where seasonal change is subtle) are less distinguishable, thereby limiting the use of this technique in certain geographical locations.

The forensic techniques discussed require expertise in many disciplines, including environmental science, chemistry, hydrogeology, geology, and dendroecology. While these techniques can be used singularly, it may be necessary to employ a combination of forensic techniques for a more defensible conclusion.

John Brennan is the president of Brennan Environmental, Inc., an environmental consulting firm located in Summit, New Jersey. He may be reached at www.bei-env.com.