FEATURE
Environmental Forensics Unraveling Site Liability An interdisciplinary analytical approach can unravel environmental liability at contaminated sites. SCOTT A. STOUT, ALLEN D. UHLER, THOMAS G. NAYMIK, AND KEVIN J. McCARTHY
our chances of reading about an environmental lawsuit in tomorrow's newspaper are high. Damages and large cleanup costs that can result from even small pollutant releases make dramatic headlines. Petroleum, frequently the subject of concern, is ubiquitous as an environmental contaminant. Its complex chemical composition makes determination of its true nature and origin difficult and makes responsibility for and ownership of contamination difficult to ascribe. Often, when faced with a lawsuit, a potentially responsible party's first reaction is to ask, "Am I wholly responsible for this contamination?" Resolution of this issue can be complicated. Environmental tort litigation frequently finds qualified professionals offering credible but conflicting technical opinions. Such conflicts have created a need for methods of formulating technically sound, defensible opinions regarding the age and sources of contamination. This has led within the last few years to the development of environmental forensics, the systematic investigation of a contaminated site or an event that has impacted the environment. Environmental forensics teams, which comprise both technical and legal professionals, seek to identify the nature and sources of contamination, understand its movement and fate, and identify and allocate responsibility among potentially responsible parties. Successful collaborative investigations employ an integrated approach in which historical data (chemical, geological, modeling, and site-specific) are used to formulate a technically defensible opinion that can be easily understood by the nonexpert. "The bot-
Y
2 6 0 A • JUNE 1, 1998/ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS
tom line is that any technical conclusions must be believable to a jury," said Todd Wells, head of environmental litigation at Cross Wrack's law offices in Detroit, Mich. Complex technical information must be presented in an easily explainable fashion, he added. Although a major element of an environmental forensics investigation involves chemical fingerprinting to identify contaminants, fingerprinting alone is not always sufficient to provide answers to questions of source and responsibility Environmental forensics has recently evolved beyond the chemical domain and now routinely incorporates an evaluation of sitespecific geologic components such as hydrogeology, stratigraphy, and soil properties. Chemometrics, the numerical analysis of chemical data, synthesizes all this complex information to make it more easily visualized by the layperson. Forensics investigations are further strengthened through access to equally important contaminated-site historical records. These often contain information useful for identifying candidate contamination source areas chemical parent product types from which contaminants have originated as well as release and spill histories The impact of environmental forensics on environmental torts is clear from the success of litigators who use environmental forensics teams. "Justice for potentially responsible parties can often be achieved by teaming legal talent with specialized environmental forensics scientists," said Keith Onsdorff, an environmental litigator with Holland and Knight, New York. "This new discipline brings highly qualified investtgators, using proven, state-of-the-art technology, to address the interrelated issues of origin, 0013-936X/98/0932-260AS15.00/0 © 1998 American Chemical Society
Levels of chemical fingerprinting (a) High-resolution gas chromatography fingerprints can distinguish among different types of petroleum or chemical products, including degrees of mixing and weathering. Gas chromatography/mass spectrometry has been used to fingerprint (b) extended polycyclic aromatic hydrocarbon distributions and (c) biomarkers like pentacyclic triterpanes.
environmental transport, and fate of contaminants," he commented. According to Wells, the environmental forensics team approach is essential in potentially responsible party liability cases, providing a comprehensive and compelling case which can illustrate the origin and migration of contamination. Chemical fingerprinting provides clues Environmental forensics investigations differ from traditional site assessments. The latter focus on the nature and extent of contamination, as determined by standard EPA assessment techniques and analytical methodologies developed to provide data for regulatory decisions (i), and do not meet the needs of environmental forensics investigations. In contrast, workers in the field of environmental forensics have drawn upon more sophisticated analytical techniques associated with petroleum exploration and production studies. These techniques, collectively referred to as chemical fingerprinting, provide greater precision regarding petroleum composition (2-5). Chemical fingerprints, like human fingerprints, provide unique signatures of different contaminants. The most common type of fingerprint is obtained using high-resolution gas chromatography (see figure above). This detection and measurement technique has been used to distinguish among fuel types— often from distinct sources—that commingle at a single location. A mixture of contamination sources can be quantitatively separated by identifying individual fingerprints, thus providing to allocate liability among potentially responsible parties. The technique is often the first tier of an environmental forensics investigation. It enables identification and mapping of contamination in the subsurface and may answer many forensics questions Additional chemical fingerprinting techniques may include measurement of stable isotopic ratios, primarily of 13C/12C, for nonaqueous-phase liquids (NAPLs) or soil/water extracts. Isotopic analysis can help investigators to distinguish between similar products. Use of stable isotopes to differentiate products often relies on information concerning the original types of crude oils or precursor chemicals used in refining or manufacturing the products. For example, in a case
where two sources of diesel fuel #2 had highresolution gas chromatography fingerprints that were virtually identical to each other and to the NAPL contamination downgradient, the degree of downgradient mixing could be determined by a mass balance of the different isotopic character of the two sources. The most powerful form of chemical fingerprinting relies upon gas chromatography/mass spectrometry (GC/MS), which can determine an individual compound's concentration in a complex mixture of compounds. The GC/MS technique is commonly used to recognize chemical patterns among groups of compounds, such as polycyclic aromatic hydrocarbons (PAHs) or biological markers (see figure above). Both can be highly source-specific, and their presence can make differentiation among similar contaminants possible. These indicator compounds can sometimes be used to identify unique sources. For example, PAHs and biological markers played a vital role in distinguishing naturally occurring oil seeps in Prince Willlam Sound from North Slope crude released from the Exxon Valdez oil spill (6) The utility of PAHs and biomarker fingerprints lies in their relatively low susceptibility to weathering which permits one to compare even highly weathered environmental samples Adding a geologic component During the past decade, chemical fingerprinting of contaminants was synonymous with environmental forensics. But although fingerprinting alone is sometimes sufficient to answer questions of source and responsibility, the emerging power of the discipline lies in the combined skills of environmental chemists and earth scientists. Geologic information can be used to construct sophisticated models that simulate and predict the fate and transport history of contaminants released at a specific site. The results can be compared to the site's known operational history or used to construct a likely site history that is consistent with chemical fingerprinting results. Stratigraphy, characterization of the three-dimensional distribution of soil or rock types at a contaminated site, provides useful information for environmental forensics investigations. An invaluable threedimensional picture of the subsurface can be obtained JUNE 1, 1998/ENVIRONMENTAL SCIENCE S TECHNOLOGY/NEWS " 2 6 1 A
derstand their utility. "Numerical simulators and hydrologic modeling are invaluable tools in (a) A groundwater surface contour map of a petroleum storage terminal shows groundwater flow environmental forensics investipaths (arrows perpendicular to groundwater elevation contour lines), (b) Useful transport property gations," said Mark White, audata (hydraulic conductivity (K); fraction organic carbon (f oc ); organic carbon partition coefficient thor of the Subsurface Transport (Koc); effective porosity |n,e)) can be determined on representative soils obtained from soil borings. Over Multiple Phases simulator at the U.S. Department of Energy's Pacific Northwest National Laboratory. They allow scientists to form quantifiable answers to questions, such as how far the contaminant has traveled and where it will migrate White noted but he cautioned that relying on a single investigative approach can be disastrous "However when used in conjunction with other forensics data numerical modeling can yield credible answers " he added Transport modeling can be used to test hypotheses generated from chemical fingerprinting data. When multiphase modfrom subsurface boring logs obtained from geologists els are properly constrained by site-specific parameters and county soil surveys. Knowledge of the layering, (stratigraphy, soil porosity, permeability, moisture capthickness, tilting or dip, and continuity of the differ- illary pressure parameters, organic carbon content, and ent strata allows for the creation of a subsurface pic- aquifer properties) and boundary conditions, they can ture of a site, which can be important in recognizing be used to constrain die time of a contaminant's rebarriers to, or preferred patiiways for, the transport of lease into the environment and potentially identify the most likely source (origin of contaminant release) arcontaminants. Knowledge of a second geologic component, the eas (see sidebar on p. 264A). Models can also be used direction and rate of groundwater flow within an to predict the degree of partitioning among phases and aquifer, is also valuable. Flow is characterized in terms rates of biodegradation. Characterizing subsurface con~ of the hydraulic gradient and hydraulic conductiv- taminants viafingerprintingtechniques requires consideration of how the composition have weathity, as determined from well-gauging data and pump/ slug testing of monitoring wells and observational ered since its release because of physical chemical and piezometers (see figure above). Predominant mecha- biological processes Changes are inevitable but ocnisms affecting contaminant flow within the subsur- cur to different degrees and at different rates in nearly face include gravity, capillary action, volatilization, ad- every situation vection, and diffusion. Daley's Law is generally thought to govern flow within soils saturated with ground- Historical records yield ground truth water, a single phase. However, vadose zone soils con- Historical records for a contaminated site completain at least two phases, water and air. In many cases, ment chemical and geologic data. Such records may NAPL contamination is also present; therefore a three- be available dirough Sanborn maps (7) or corporate phase system exists. Near or below the water table records and are publicly available from various fedat contaminated sites NAPL air and aqueous phases eral, state, and local government agencies. Research ofoften coexist which confounds the use of Darcy's Law ten reveals the presence of historic activities that may to predict contaminant flow have contributed to recently located contamination. The Because of its complexity, predicting contami- discovery of past contamination is common, for exnant behavior in multiphase systems requires nu- ample, in industrial waterfront areas that may have unmerical models that can consider the relative perme- dergone transition for a century or longer. Past site conability effects of one phase on the flow of another. A tamination may have come from historic sources such substantial understanding of multiphase flow in the as a dock fabricated from creosote-soaked planks in near-surface environments of contaminated sites is ob- the late 1800s, replaced by a manufactured-gas plant tained from the petroleum industry, where reservoir en- built on fill material in the early 1900s, and finally gineers routinely consider production from individ- replaced by an operating petroleum storage facility that ual reservoirs that contain formation water, oil, and gas. was built on the site in the 1920s. Unraveling sources On the basis of reservoir engineering principles, so- and ages of contamination at such sites would be difphisticated multiphase models have been applied in ficult without any historical perspective. the design of environmental remedial systems. The corporate archaeology aspect of environmenThese models have only rarely been used in envi- tal forensics provides corroboration. It can support ronmental forensics investigations, but researchers un- or refute possibilities determined to be viable by
Geologic components of an investigation
2 6 2 A • JUNE 1, 1998 / ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS
chemical fingerprinting or multiphase modeling. In the course of litigation, corporate records and interviews with current and former employees may become available. Day-to-day operations and practices at a facility provide insight that can help explain fingerprinting or modeling data. For example, high PAH concentrations in surface soils at one site were explained by a now-retired employee. "Well, sure, we used to spray fuel oil over there to keep die dust down," he said. Corporate archaeology should be conducted by individuals who are able to recognize key data that might otherwise be overlooked. In the past, investigations of records were typically performed by a legal team, whose limited experience in environmental science often led to a failure to incorporate valuable information within the environmental forensics investigations. In one case, discovered documents referred to disinfectants produced at an upgradient facility years before. This helped explain the prominence of cresylic acids (chemicals used in the production of phenolic disinfectants) in groundwater at die site and argued for shared liability in remediation. Regulatory impacts can also help unravel contaminant history. For example, changes in gasoline composition have occurred over time (see sidebar on p. 264A), which can be used to constrain the age of gasoline in the subsurface. Knowledge of how federal, state, and local regulations may have affected the composition of products used, produced, or distributed at a site can be useful.
clusions about sources and ages of contamination must convey a story mat can be constructed over the time line in question. Numerical analyses of chemical data, performed using mathematics to eliminate biases and inconsistencies that may creep into an interpretation based solely on qualitative comparisons, permit comparison among samples with any number of variables
Visualizing data with chemometric analysis The concentrations of 54 different polycyclic aromatic hydrocarbons (PAHs) groups in 12 different nonaqueous-phase liquid (NAPL) samples from a longoperating crude-oil storage terminal were compared using principal component analysis. The resulting factor score map (a cross-plot of the first and second principal components) reveals that three populations of NAPL exist at the site. The PAH distributions in two crude-oil plumes 1 and 2 are clearly distinct, and the degree of mixing is evident in commingled crude samples from plume 3. Records and further analysis of fresh crude oils showed that the two endmember populations correspond to the two main types and sources of crude oil that had been stored at the terminal, while the intermediate population is consistent with a mixture of these end-members. PC = principal component.
Making a clear case Effective presentation of collected information is an essential component of an environmental forensics investigation. Clients, lawyers, judges, and juries can be overwhelmed by the presentation of complex, collected results of chemical fingerprinting, multiphase modeling, and historical considerations. Moreover, con-
Visualization of underground contamination Computer-generated imagery reveals threedimensional images from a petroleum storage terminal where two crude-oil plumes 1 and 2 have joined to form the commingled third plume 3 that continues to move downgradient. The images of the nonaqueous-phase liquid (NAPL) plume distributions at the terminal were determined from chemical fingerprinting of the oils, multiphase modeling of the NAPL, and chemometric analysis of the oils' polycyclic aromatic hydrocarbon distributions.
JUNE 1, 1998 /ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS • 2 6 3 A
The formulation of gasoline and additives can provide clues to the age of contamination.
Gasoline formulation time line
Age-dating, an important aspect of environmental forensics investigations, is often at the center of potentially responsible party liability issues. An investigation can determine, or more typically, constrain the age of contamination by three principal methods: chemical fingerprinting, reverse fate-and-transport modeling (working backward in time), and historic (8) (site-inventory and maintenance) records evaluation. Chemical fingerprinting methods [9, 10) rely upon marker compounds that were used in products for limited periods of time (see gasoline time line). This approach is most appropriate for automotive gasolines, where knowledge of additives, refining practices, regulatory history, and historic gasoline surveys can constrain the age of subsurface gasoline contamination. Fate-and-transport models that consider multiphase migration can also age-date contamination. Unfortunately, site-specific information (partitioning, weathering rates, soil and groundwater properties, and volumes of NAPL originally released) required for such models is rarely available. Modelers must consequently make multiple assumptions, given the existing distribution and character of contamination, and work backward in time. Modeling is most useful in constraining or testing the age determinations made by other age-dating methods. The final method for evaluating contamination relies upon research into the operating history of a site, for example, lost inventory or maintenance records. Multiple methods that limit a contaminant's age to a similar time or age range increase the technical credibility and defensibility of an opinion.
and add credibility to an opinion. Chemometrics, like principal component analysis, can synthesize complex chemicalfingerprintingdata sets into simple pictures (see figure on p. 263A) in which distances between sample points affirm that there are chemical differences among analyzed samples. The results of principal component analysis (and other numerical analyses) are more easily visualized by the layperson. Chemometric techniques can quantify the degree of mixing of contaminant plumes, thereby allowing one to numerically separate the mixtures. This technique is extremely useful for allocating liability potentially responsible parties. The most successful visualization techniques use sophisticated software that can portray chemical, geologic, and modeled data in three dimensions, using landmarks (such as tanks and buildings). This method of data presentation effectively allows the layperson to look underground and visualize the contamination scenario being described (see figure on p. 263A). According to Steve Howe, an engineer and visualization expert with Unocal's Environmental Group in Brea, Calif., a worm's-eye view can help the viewer understand the relationship between a contaminant and its setting. Using a combination of results from chemical fingerprinting of different samples, site-specific geologic, hydrogeologic, and modeling results as well as chemometrics, a coherent picture of contamination present in the subsurface at any given site is produced. Whereas the final image may appear simplis2 6 4 A • JUNE 1, 1998/ENVIRONMENTAL SCIENCE & TECHNOLOGY/NEWS
tic—the very quality that makes it understandable to a judge or jury—the data and level of sophistication that support production of this image and the interpretation it conveys are substantial. References (1) (2) (3) (4) (5) (6) (7)
(8)
(9) (10)
Uhler, A. D.; Stout, S. A.; McCarthy, K. J. Soil Groundwat. Cleanup Jan. 1998, 13-19. Bruce, L. G.; Schmidt, G. W. Am. Assoc. Petrol. Geol. Bull. 1994, 78(11), 1692-1710. Sauer, T. C; Uhler, A. D. Remediaiion Winter 1994/ 1995, 23-30. Zemo, D. A.; Bruya, J. E.; Graf, T. E. Ground Water Monit. Remed. Spring 1995, 147-156. Kaplan, I. R.; Galperin, Y.; Alimi, H.; Lee, R.-E; Lu, S.-T. Ground Water Monit. Remed. Fall 1996, 113-124. Boehm, R D.; Douglas, G. S.; Burns, W. A; Mankiewicz, R J.; Page, D. S.; Bence, A. Mar. Pollut. Bull. 1997, 599-613. Sanborn Fire Insurance Maps; Reference and Bibliography Section, Geography and Map Division, Library of Congress, U.S. Government Printing Office: Washington, DC, 1867-1890. Semi-Annual Gasoline Surveys; National Institute for Petroleum and Energy Research, U.S. Bureau of Mines, U.S. Government Printing Office: Washington, DC, 1919present. Hurst, R. W.; Davis, T. E.; Chinn, B. D. Environ. Sci. Technol. 1996, 30(7), 304A-307A. Christensen, L. B.; Larsen, T. H. Ground Water Monit. Remed. Fall 1993, 142-149.
Scoff Stout, Allen Uhler, and Kevin McCarthy are geochemical researchers at Battelle, Duxbury, Mass. Thomas Naymik is a hydrogeologic rerearcher at Battelle, Columbuss Ohio.
