Age significance of n-C17/Pr ratios in forensic investigations of refined product and crude oil releases: Discussion

Abstract

Hurst and Schmidt (2005) report that they have refined a method first advanced by Christensen and Larsen (1993) and can pinpoint the age of diesel-fuel or crude-oil releases to ±1.5 yr. The work that they have completed is commendable and hopefully will be useful to investigators in the field. Despite their findings showing a successful use of the Christensen and Larsen (C&L) method, I point out some drawbacks that were not discussed in their article and could be useful information to Environmental Geosciences readers. Hurst and Schmidt do admit that there are limitations to this method, and site-specific considerations must be taken into account, but I feel that these limitations were not sufficiently elucidated in their article. The C&L method essentially assumes that the ratio of the n-C17 alkane (heptadecane) to pristane (n-C17/Pr) found in soil (and possibly separate-phase) samples has a linear relationship to the petroleum age. The n-C17/Pr ratio has been used for several decades …