Age-dating Diesel Fuel Spills: Using the European Empirical Time-based Model in the U.S.A.

In 1993, a paper was published by Christensen and Larsen that offered a method for determining the age of diesel oil spills in soil (Christensen and Larsen, 1993 Ground Water Mount. R . Fall , 142-149). It presented an empirical time-based model of the degradation of diesel fuel in soils using chemical data gathered at petroleum release sites in Denmark and the Netherlands. Now, evaluation of the validity of the application of this work to subsurface petroleum releases in other countries remains. In the U.S.A., investigations assessing date(s) of release of diesel fuel in soils, e.g. age dating of subsurface petroleum contamination, have considerable interest. Litigation-driven scientific investigations with accompanying expert testimony in a court of law are underway. The number of instances where application of the Christensen and Larsen empirical time-based model to petroleum-contaminated properties is growing in the U.S.A. This paper presents two case studies which evaluate the applicability of the Christensen and Larsen empirical time-based model to petroleum-contaminated properties in general. It illustrates the approach using gas chromatographic data from two recently-completed projects evaluating the applicability of the Christensen and Larsen model to a No. 2 fuel oil/diesel fuel surface spill in the U.S.A. Results showed that the application of the model to petroleum-contaminated soils was scientifically valid, provided its applicability was evaluated using hypothesis testing for specific changes in the characteristics of the petroleum hydrocarbon distribution in a number of soil samples collected over time at one site. The paper offers observations on the application of the Christensen and Larsen model to petroleum found in the light non-aqueous phase liquid (LNAPL) phase and groundwater.     

Application of Aerial Photography and Photogrammetry in Environmental Forensic Investigations

Historical aerial photography can be a powerful tool in environmental forensic investigations. Historical aerial photography is available for many sites from the 1930s on. It is researched and obtained from both public and private sources. Most of the photography consists of vertical stereoscopic film annotated with the date of the photomission. A current photomission can be flown using airborne GPS for precise registration of the photomosaics. The photography is scanned at a very high resolution and registered in a coordinate system using a digital stereoplotter that removes terrain distortion and allows the precise measurement of objects. The digital stereoplotter is used to produce photomosaics and to interpret environmentally significant features in the photography. The accuracy of the environmental interpretations is dependent on the skill and experience of the interpreter as well as the resolution of the photography and quality of the equipment used. The photomosaics are then registered in a geographic information system along with the interpretations of environmentally significant features. In a similar manner, historic maps are scanned and registered into the same coordinate system. The interpreted images and maps form a significant part of the expert report. A computer projection system is used to show the interpreted images at trial.