Questions regarding environmental forensics will come up at some level in almost every environmental project.
This can range from drawing conclusions about a release from a UST system to sophisticated analysis of large environmental datasets collected specifically to identify contributions from multiple sources. The purpose of forensic interpretation is to tell a story. The story becomes most interesting when some or all responsibility shifts from one party to another. In many ways, this is a natural extension of developing a site conceptual model (SCM), and much of the data required for telling the story is collected as part of most primary environmental investigations. Do you need forensic data interpretation or interpretation of forensic data?
To get the most value for your dollars spent, it might be helpful to think of forensic techniques as a specialized way in which environmental data is evaluated rather than as a series of analytical techniques. Commonly collected data can have significant forensic implications, boring logs, slug tests, GC chromatograms and tentatively identified compounds (TICs) all have a story to tell. Prior to investing in the collection of dedicated forensic data, a good consultant will fully understand what answers you need and evaluate how close you are to those answers using data you already have. It may be, for example, that the data required to delineate and characterize the basic fate and transport of a chlorinated compound in groundwater, for regulatory purposes, is also sufficient to constrain the potential release date with the required precision. Or, the presence or absence of various gasoline oxygenates in a BTEX plume may be enough to identify the decade in which the release occurred.
A number of specialized analytical techniques can provide specific data useful for environmental forensics.
Only after reviewing existing data in light of the SCM can you start looking at the analytical techniques people usually associate with environmental forensics. The most basic may be petroleum fingerprinting, looking at the composition of LNAPL or petroleum in soil or water to identify the type of product present and degree of weathering. Like everything else in life, this can be done quick and inexpensive with moderate precision or slower and at greater cost for greater precision and defensibility. There are no foolproof analytical methods to date petroleum releases. However, the Christensen and Larsen (1993) method is often used to estimate the date of diesel/#2 fuel oil releases. This method is based on observed changes in the ratio of compounds over time due to biodegradation. While used with success in many cases, the further your site conditions are from those on which the method is based, the greater the caution should be exercised in interpreting results.
Moving beyond petroleum, a wide range of forensic techniques are available for different circumstances with an equally wider range in cost. With the right circumstances, specific tools like PCB congener analysis, stable isotope measurements, extended PAH analysis or sediment and groundwater age dating can provide key information to distinguish multiple sources or refine the understanding of contaminant fate and transport. As always, there is a tradeoff between the cost of sample collection and analysis and the need to document results with sufficient certainty to stand up to hostile scrutiny.
Leveraging existing data can ensure your environmental forensic efforts get you the answers you need.
You hope that you know (and like) what results you get from a forensic investigation. But even starting with a well-developed SCM, expect some surprises when the analysis and data evaluation are performed. The real life messiness of even the best environmental data is, on its own, a good reason to develop specific and realistic goals for a forensic evaluation before data collection. Developing those goals is easier when you are making the best use of the data you already have.