Method for Determining the Age of Diesel Oil Spills in the Soil

Abstract

AbstractThis study evaluates the changes in the composition of diesel oil as a function of the time during which the oil has been present in the vadose zone. The study also develops a reliable method for determining the age of diesel oil in the subsurface soil environment at service stations, oil terminals, and similar locations where the diesel is protected from direct exposure to factors increasing the rate of microbial activity.Analyses demonstrate that n‐alkanes are the dominant components of fresh diesel oil and isoprenoids the dominant components of degraded diesel oil. The analyses also show that the composition of fresh diesel oil produced in 1992 and that produced in 1974 is basically the same.The difference in composition between fresh and degraded oil is the basis for defining a degradation ratio or rate of alteration in the composition of the diesel oil expressed in terms of a ratio between n‐alkanes and isoprenoids. At 12 test locations where the date of property damage was known, the C17/pristane ratio had by far the highest correlation factor (.89) with the residence time of the diesel based on the average degradation ratio for each location. Based on this high correlation factor, the C17/pristane ratio can be used to estimate the age of a diesel oil spill. The standard error of such an estimate is approximately two years.