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Abstract
The age of heating-oil releases from underground storage tanks (USTs) can be estimated by investigating the petroleum chemistry, the on-site environmental conditions, the extent of contaminant migration, the condition of the UST, site history and several additional factors. The heating-oil chemistry, and in particular the degree of weathering, can be assessed through an examination of: compound depletion, the carbon range, the n-alkane depletion and the size of the unresolved complex mixture (UCM). Each release site can be assigned a weathering regime, such as very aggressive, aggressive, moderate, weak and very weak. These designations are based on the on-site geological, hydrological and biological conditions. A matrix was constructed which compares the weathering regimes to the stages of petroleum weathering and provides potential age ranges. The matrix is a method to lead the investigator towards the correct age, but is not the final say on that age. The age ranges then need to be compared to site-specific characteristics, such as the UST age, the UST condition, the extent of contaminant migration and other extenuating factors. The error range for this method is estimated at ± 2 years; however, there are numerous limitations to the methods and instances will arise where the age can only be constrained.
Acknowledgments
These two articles were reviewed by Dr. Yakov Galperin of Geochemistry Consultants, Inc. in Moorpark, CA and Dr. Paul Philp of the University of Oklahoma in Norman, OK. They were also reviewed by several colleagues at Triassic Technology including Michael Obolensky and Karen Polidoro. I am also indebted to three anonymous reviewers supplied by the journal. All these people helped to improve the articles, but responsibility for any errors, if any, remain my own.