Petroleum is a complex mixture of thousands of different organic compounds formed from a variety of organic materials that are chemically converted under differing geological conditions over long periods of time. The infinitely variable nature of these factors results in distinct chemical differences between oils formed under dissimilar conditions and/or environments. While oil from one crude oil field is readily distinguishable from another, differences in the makeup of oils from the same crude oil field can sometimes be observed as well. Refined oils are fractions usually derived by distillation of crude oil. Two refined oils of the same type differ because of dissimilarities in the characteristics of their crude oil feed stocks as well as variations in refinery processes and any subsequent contact with other oils mixed in during transfer operation from residues in tanks, ships, pipes, hoses, etc. Thus, all petroleum oils, to some extent have chemical compositions that differ from each other.
The characteristic properties of an oil can be explored by a variety of analytical methods. The results of analysis by any of these methods can be presented in graph form. In general, when the graphical data for two oils produced by a particular method are compared, the differences between the graphs reflect differences between the oils.
The Oil Identification System (OIS), developed during the mid-1970s at the Coast Guard Research and Development Center, is based on a multi-method approach to "fingerprinting" oils. In 1978, the Central Oil Identification Laboratory (COIL) was established as the operating facility to implement the OIS. In 1988, COIL was renamed the Marine Safety Laboratories (MSL), and in 1996 Marine Safety Laboratories became Marine Safety Laboratory. OIS is designed to determine the unique, intrinsic chemical properties of oils via analytical techniques and establish whether or not a common source relationship exists between samples of spilled oil and samples of oil from a suspected source.
Oil sample preparation, testing and storage are conducted in accordance with American Society for Testing and Materials (ASTM) consensus standards. MSL currently utilizes three primary analytical techniques: Gas Chromatography (GC) (ASTM D-3328), Infrared Spectroscopy (IR) (ASTM D-3414). Gas Chromatography-Mass Spectrometry (GC-MS) (ASTM D-5739). A rigorous laboratory quality assurance program monitors both instrument performance and sample preparation to ensure that data are accurate and reproducible.
All samples in a given case are initially analyzed by one method to determine the class of petroleum product. Samples can be excluded from further analysis based on results from the initial analysis. Further analyses are performed on samples which are potential matches to the source of the oil.
The Supervisor of Analysis interprets the data from all test methods performed and draws conclusions concerning whether or not certain spilled oil and suspected source samples were derived from the same chemical source. Data interpretation in oil spill source identification is non-trivial and fundamentally different from typical chemical analyses because the chemical properties of spilled oil are altered when oil is introduced into the environment. From the moment oil enters the environment, evaporation, dissolution, photochemical oxidation, biodegradation and other forces begin to alter the oil's characteristics or "fingerprint". These combined processes are termed "weathering" and can significantly complicate data interpretation. Contamination of the spilled oil with other oils or substances is another complicating factor. The experienced oil spill analyst is familiar with the complexities of the weathering processes and is able to distinguish real differences between two oils from those apparent differences resulting from weathering alterations. Interferences from contaminants can usually be recognized as such and discounted when weighing the test results. However, at times, severe weathering and/or contamination can mask many of the inherent differences between oils of a similar type.
The typical MSL OIS Report consists of four parts: case identifying information, a listing of analysis techniques performed, the results section and the conclusions section. The results section describes the types of petroleum observed in the samples provided, and comments on chemical similarities or dissimilarities between spill samples and/or between spill and suspected source samples. In all cases the Supervisor of Analysis bases the written results on interpretations from the aggregate of all data generated.
The conclusions section establishes whether or not a common source relationship exists between samples of spilled oil and samples of oil from a suspected source. There are two outcomes most frequently found in the conclusions section of the typical MSL OIS Report: "derived from a common source" and "not derived from a common source". However, to maintain the high degree of reliability for both "common source" and "not a common source" determinations, it is necessary to exclude some comparisons from these categories. Oil spill cases vary widely in possible explanations for why a determination could not be made. Instead of using only a statement of "inconclusive", the comments will concisely explain the reason for the outcome for each individual case. For example, some sources are highly inhomogeneous, and a sample of such a spill may not reflect the composition of the product remaining in such a source. The spill may contain very little oil, or it may be excessively weathered or contaminated. Of important note, MSL conclusions address chemical comparisons and not physical aspects of evidence. Additionally, chemical evidence provided in a MSL conclusion that is other than "common source" might still be used by the investigating officer, when combined with physical evidence to establish a preponderance of the evidence argument against an alleged responsible party.
MSL OIS Reports are submitted to Sector units for inclusion, as chemical evidence, in MISLE enforcement cases. The outcomes in the conclusions section of the OIS Report define the nature of the chemical evidence provided. Investigating personnel are advised to combine the chemical evidence provided in the MSL OIS Reports with physical and circumstantial evidence developed during the investigation when writing enforcement cases. Inquiries challenging the technical content of MSL OIS Reports by representatives of the alleged responsible party should be handled at the Hearing Officer level. Explicit guidance describing the communications process between the Hearing Officer and the MSL Supervisor of Analysis on technical issues involving chemical evidence is given in Commandant (G-LMI) memorandum 16460 dated 26 January 1981.
MSL laboratory technicians performing sample preparation and testing are graduates of the Coast Guard Marine Science Technician School. Each MSL technician has successfully completed a comprehensive training program at the MSL facility. Additionally, many have received supplemental training at leading civilian institutions in their specialty area.
The Supervisor of Analysis monitors all aspects of the analysis, certifies and interprets the test results, and prepares the final MSL report. This individual is a professionally trained chemist experienced in oil spill source identification.
A more technical description of the OIS is contained in Report CG-D-52-77 "Oil Spill Identification System", Final Report, June 1977, USCG R&D Center. This document is available through the National Technical Information Service, Springfield, VA 22161.
For information concerning the ASTM standards used in Oil Spill Identification, consult "Oil in the Environment", Martha S. Hendrick, Ph.D., ASTM Standardization News, April 1991.
For additional information regarding the applicability of the Coast Guard's OIS, see "Chemical Identification of Oil Spill Sources", Alan P. Bentz, Ph.D., The Forum, Volume XIII, Number 2, Winter 1978. Dr. Bentz was a research scientist at the Coast Guard Research and Development Center and a recognized expert in the field of oil spill source identification. He was closely involved with most of the development work leading to the present state-of-the-art.