Independent Consultants in Environmental and Forensic Chemistry
Volume 2, Issue 1, Winter 1998
Can Diesel Fuel, #2 Fuel Oil or Home Heating Oil Be Age-dated?
A recent peer reviewed paper* claims accurate age-dating of biodegraded diesel fuel spills can be accomplished from fresh releases to 20-year-old releases within "2 years with 95% confidence. The authors use the ratio of concentrations of two specific compounds found in the fuels. Both compounds contain seventeen carbon atoms but have different structures. This premise is reasonable because scientists agree that the rate of aerobic biodegradation of compound A (heptadecane) is faster than that of compound B (pristane). Therefore, a high ratio of A to B would indicate that the petroleum product is less degraded than a sample having a lower ratio. The authors showed a linear relationship between the decreasing ratio and the age of the release. Since publication of this paper, many so-called experts have used these data to age-date diesel fuel spills. But, is the use of these data for age-dating petroleum product releases valid?
Closer review of the paper reveals several conditions that must be met to use this approach:
$ The average of all soil samples (not free product) must be used to determine a ratio for the site although the number of samples necessary for this ratio to be used successfully is not noted.
$ Ratios are not constant for freshly produced diesel fuel. With 95% confidence, freshly refined diesel fuel can be from 0 to 15 years old using the ratio of the selected compounds.
$ To be used in this age-dating process, the samples must be taken greater than 1 meter deep and from the unsaturated zone beneath a paved area. Also, the diesel fuel concentration must be greater than 100 ppm.
Although the results presented in this paper indicate that the ratios of compounds A and B decrease linearly with time, the age of the spill depends not on the amount of degradation but on the rate of degradation. The rate at which the decrease occurs is dependent on the conditions at the sampled location. In his book Biodegradation and Bioremediation, Dr. Martin Alexander discusses many conditions affecting the rate of biodegradation (see Book Review). Conditions change from location to location even within a given site. Therefore, the rates of degradation also change. Applying the rate of biodegradation obtained by the authors to other sites assumes that all other conditions are identical. This is highly unlikely. Unless conditions can be shown to be identical, application of the rate reported by the authors to other sites is invalid, and the practice of age-dating a biodegraded spill using this method is technically unfounded.
* Christensen, L.B. and T.H. Larsen, "Method for Determining the Age of Diesel Oil Spills in the Soil," GWMR, Fall 1993, pp 142-149.
Book Review: Biodegradation and Bioremediation, Martin Alexander, Cornell University
Bioremediation, the process of utilizing microbes to degrade or destroy contaminants in the environment, is the hottest remediation technology going for man-made and natural organic chemicals. "Biodegradation and Bioremediation" by Martin Alexander discusses the many variables that exist that have a bearing on the relative rates of biodegradation of organic chemicals. These variables include temperature, soil moisture, changes in bacterial consortium, acclimation time, changes in predators, presence or absence of micronutrients, presence or absence of air, amount of release, toxicity of the chemicals to microbes, solubility of the chemicals in water, adsorption of the chemicals to soil, the bioreaction rate order, and whether co-metabolism is operating. If the right combination of these variables is not present, biodegradation will occur at an imperceptible pace or not at all.
Under perhaps only slightly different conditions, biodegradation may occur at a maximum rate. The almost infinite number of combinations between the two extremes will yield numerous rates of contaminant degradation, and, thereby, makes it close to impossible to predict the rate of biodegradation in a given system without extensive research on the effect of the various parameters in the given system.
This is a no-bull-spit book on biodegradation and on the dependency of biodegradation rates on many different environmental variables. Dr. Martin Alexander of the Department of Crop, Soil and Atmospheric Sciences of Cornell University has consolidated the basic principles of biodegradation of organic chemicals into 16 compact chapters and 285 pages. The subjects are very well documented with recent research literature references. This book is recommended for environmental engineers, scientists and attorneys concerned with age-dating releases of petroleum products and chlorinated solvents using biodegradation rates (see the President's Corner). From one of the world's experts on the topic, this book is the book to read to learn about biodegradation and bioremediation. Being revised for a late 1998 release, "Biodegradation and Bioremediation," published by Academic Press in 1994, is well worth the current price of $53.
How Valuable Is a Team of Experts?
In Dedham Water Company v. Cumberland Farms Dairy, Inc., the Dedham Water Company sued Cumberland Farms for contamination of drinking water supply wells with solvents such as trichloroethylene (TCE) and 1,1,1-trichloroethane (TCA). Admittedly, chlorinated solvents were used at Cumberland Farms which was upgradient of the water supply wells, and housekeeping at the facility was not considered impeccable. Chlorinated solvents were most likely released at the site. Based on hydrogeology alone, the plaintiff had an apparent open-and-shut case.
However, many environmental investigations or litigations can benefit from the interaction of several experts in different overlapping technical fields. In this case, the defense assembled a team of experts to prepare its technical case. The team consisted of a hydrogeologist, civil engineer, environmental engineer, chemist, and sewer engineer. The facts were viewed from different technical perspectives with each discipline offering its opinion as to the source of the contamination. After years of meetings, arguments, and playing devil=s advocate, these experts were able to interpret all of the data into a consistent scenario to identify the true source of groundwater contamination and its pathway to the supply wells.
Although some cases may appear to be obvious, the obvious may not necessarily be true. A team of experts from various disciplines can often use available data to unravel past events. In addition to members contributing expertise in their own areas, they often have considerable knowledge in adjacent areas. The combined effect of such a team of experts can pose a formidable tool for elucidating past events and forming a strong technical case.
An expert environmental chemist can be a major contributor to that team. In addition to expert knowledge in chemical properties and consequent behavior of chemicals in the environment, the environmental chemist must also have a working knowledge of geology, hydrogeology, climatology, biology, physics, agriculture, history and industrial practices. In the Dedham v. Cumberland case:
AThe only chemist to testify at trial was Cumberland=s witness, Dr. James Smith, who impressed the court as having considerable experience in groundwater contamination investigations. The court, therefore, accepts his testimony and relies on it in making these findings.@1
Can Field Laboratories Produce Quality Data?
The investigation and remediation of a site normally proceeds in three phases, all of which require chemical analyses:
1. Investigation and Characterization. What types of contamination are present and where are they?
2. Excavation or Installation. Have we found all the contamination?
3. Compliance and Closure. Have we done the job we were contracted to do?
Using a field laboratory during the first two phases and a fixed or "certified" lab for the last phase is common practice. Any number of reasons are cited for using a field laboratory - convenience, cost-savings, rapid turnaround time, etc. But a larger number of horror stories have been told about using a field lab. Some simple guidelines can allow a field laboratory to produce quality data efficiently and effectively.
1. QA/QC is not optional. Many sampling and analysis plans will state "There will be confirmation of X% of the samples by an off-site lab, so a full QA/QC program is not required by the field lab." This is a danger signal. At a minimum, you should require a thorough calibration of each instrument every day the lab operates, a method blank with every set of samples analyzed, and a triplicate analysis of one random sample in every batch of samples analyzed. Beyond these requirements, you should check with a consulting chemist on what is a reasonable amount of quality control for the particular study conducted.
2. Do not wed yourself to a particular analytical method. The analytical methods developed by local, state and federal programs are only applicable as guidelines. Most analytical methods are not specific enough or are not tailored to your specific application. In addition, most of the methods were not designed to extract weathered contaminants. Take the time to discuss your site with an environmental chemist so that you might understand all the factors that can affect the data.
3. Limitations exist on what any lab - field or fixed - can do. If you task any lab with more samples than they have capacity for, they cannot complete the work in a timely manner. The desire to collect samples while conditions are favorable is understandable, but, if the lab is designed to handle 50 samples per day, that is all you are entitled to expect. Anything more is unrealistic.
The average variation in results between fixed labs analyzing ideal samples under ideal conditions is "100%. The average variation within a single lab is oftentimes "30%. However, a properly controlled field lab can generate data with less than 25% variability in the random replicate QC samples (see point 2, above). With this precision, a field lab can produce comparable, if not better, data than can be supplied by most fixed labs in the country - in which case, you can use your field lab for compliance and closure analyses as well!
Data Validation: Is a Checklist Enough?
Data validation is often limited to a "checklist approach" in which the specifications from one of almost fifty EPA or state-agency published guidance documents are applied, sample results are qualified, and data tables are provided to the client. Professional technical judgment is minimized and, generally, not desired. Consistency with respect to how the data are evaluated is the primary goal.
Some problems are inherent in this approach. The use of less-than-qualified personnel to perform data validation is encouraged, and the data are subjected to a largely clerical, rather than technical, review. Most of the guidance documents concede that, in some instances, professional judgment must be applied; no simple way exists to define the "correct" approach for all possible circumstances. Also, a checklist does not provide sufficient room for discussion or explanation and, as the only documentation of the validation, leaves the data user with a limited understanding of what was actually found in the data package.
The use of performance-based methods (PBMs), in which the laboratory is free to select any appropriate analytical method, will only exacerbate the problem. Without specific reference methods or QA/QC specifications, the multitude of guidance documents will become largely irrelevant. A validation checklist will become less appropriate and more inadequate as the trend toward PBMs continues. Professional judgment by qualified analytical chemists will become essential in evaluating laboratory data.
To ensure that data quality is sufficient to meet the needs of the project, the role of the data validator should be expanded to include participation in the preparation of the Quality Assurance Project Plan (QAPP), in the coordination of the field samplers and laboratory personnel, and, ultimately, in the interpretation of the site data. Third party data validation must allow for professional judgment and must be performed by qualified personnel. It must go beyond the checklist approach.