Fluorescence has been used for several decades as an oil exploration tool to identify trace amounts of crude oil in soil or marine sediment samples. Recently, the technique has been used for characterizing petroleum contaminants in environmental site investigations. The bench top analytical method is very sensitive to low concentrations of petroleum, rapid and very cost effective as a site screening tool. The EPA has recently tested a portable spectrometer at a refinery site and results were compared to laboratory results using a conventional spectrometer.

Aromatic hydrocarbons in crude oils fluoresce at different wavelengths according to the number of aromatic rings present in the compound. Usually, larger aromatic molecules fluoresce at longer wavelengths. A relationship results between the aromatic composition of a petroleum product and the maximum peak fluorescence position. For example, gasoline fluoresces with a strong single peak at 290nm which represents single ring mono-aromatics. Diesel fluoresces with its strongest peak at 320nm representing the two ring di-aromatics. Peaks at 350nm, 410nm and 480nm represent even larger aromatic ring compound. As a result of this relationship, ratios of fluorescence band peak intensity can distinguish different products.

Products that can be detected using fluorescence include most refined petroleum products with some aromatic content The sensitivity of the method allows low part per million quantities of most contaminants to be detected in soil sample extracts without concentrating the extract. Less sensitive mixtures, such as PCBs could be concentrated if needed for lower detection limits. Spectra of these extracts can be fingerprinted to known contaminants or LNAPL extracts using simple statistical methods. This data can provide a correlation ranking that can be plotted on a map along with fluorescence intensity or a calculated contaminant concentration to track plumes of different contaminant sources.

Solvent extracts of soil or ground water samples, LNAPLs or DNAPLS are analyzed by a synchronous scan UV-fluorescence technique. The scanning method reveals several fluorescence emission bands that are related to the aromatic hydrocarbons distribution in petroleum based products and crude oils. The relative amount of different aromatic groups can be measured using peak height methods. Ratios of these groups can be compared to known products or contaminants. Fluorescence scanning methods have improved in recent years to provide more detailed information than previous techniques. Examples of refinery soil extracts and LNAPL samples from monitoring wells are shown with fingerprinting comparisons.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas