Utilization of the Carbon and Hydrogen Isotopic Composition of Individual Compounds in Refined Hydrocarbon Products to Monitor Their Fate in the Environment

EPA Grant Number: R83-0633-010

Title: Utilization of the Carbon and Hydrogen Isotopic Composition of Individual Compounds in Refined Hydrocarbon Products to Monitor Their Fate in the Environment

Investigators: R. Paul Philp (pphilp@ou.edu) and Tomasz Kuder (tkuder@ou.edu)

Institution: University of Oklahoma

EPA Project Officer: Bala Krishnan

Project Period: 9-1-04 to 8-31-05 (Year one of 2 year project)

Project Amount: $155,481

Research Category: Petroleum Environmental Technology - Natural attenuation

Description:

A major benefit for management of contaminated sites is the ability to demonstrate natural attenuation of the contaminants. A tool that clearly demonstrates biodegradation in ground water is essential to evaluate the feasibility of natural attenuation at such sites. Site-characterization data at most gasoline release sites are adequate to evaluate attenuation in contaminant concentrations over time or distance. Demonstrating natural biodegradation currently requires expensive and time-consuming laboratory microcosm studies. If attenuation can be successfully demonstrated however, relief from clean-up procedures may be available from the regulatory agency to permit the contaminant(s) to degrade under natural, supervised conditions. However attempts to evaluate onset, rates, or extent, of intrinsic remediation of contaminants such as MTBE and related oxygenates, refined products, or additives, are often limited by absence of appropriate reference points against which such changes may be measured.

The work described in this proposal will focus primarily on gasoline oxygenates such as MTBE and TBA, and to a lesser extent, lighter hydrocarbons such as the BTEX compounds and evaluating the use of stable carbon and hydrogen isotopes of these individual compounds to monitor their natural attenuation at contaminated field sites. In addition to simply studying the potential of this tool for monitoring natural attenuation, the work will also involve the application of the same approach to evaluating aerobic, anaerobic, and abiotic degradation of such contaminants. Preliminary results suggest that variations in the isotopic compositions can be used to differentiate between various mechanisms for the degradation of MTBE, TBA and related products. Isotopic enrichments have been observed during the attenuation of MTBE, TBA, BTEX and chlorinated ethenes, in laboratory experiments and under field conditions. Quantification of such changes provides a means to determine the extent of intrinsic remediation. The majority of work to date has been undertaken with groundwater samples. A preliminary investigation of soil samples will also be undertaken in this proposal to evaluate whether similar changes are observed with adsorbed contaminants.

Preliminary results from a retail gasoline release site have shown that under anaerobic conditions, ¹³C of MTBE in monitoring wells increased by up to 30‰ (–25‰ to +5‰) along with a forty-fold decrease in MTBE concentrations. Anaerobic incubations in laboratory microcosms indicated up to hundred-fold reduction in MTBE concentrations with a corresponding increase in ¹³C of MTBE of up to 31.2 ‰ (–26.5‰ to +4.7‰) in live microcosms. Little enrichment was observed in autoclaved controls. These preliminary observations provide a strong indication that changes in the ¹³C values of MTBE, and other contaminants, have the potential to be used as “indicators” of in-situ MTBE biodegradation but a great deal of additional work needs to be done to support this hypothesis and these studies will form the basis of this proposal.

Samples for the work proposed within this study will be supplied from a number of industrial participants, particularly BP and ChevronTexaco, both within the state and on a national level. Sites contaminated by refined products will be characterized to extend the database for isotopic evidence of biodegradation, and in turn the use of this approach as an indicator for the onset of natural attenuation. Field observations will be supplemented where necessary with laboratory microcosm studies of MTBE, TBA and/or BTEX, to further develop a method based on changes in isotopic compositions as a means to determine natural attenuation and quantify intrinsic remediation.