Environ. Sci. Technol. 1997, 31, 1416-1418
Lack of Correlation between Organic Acid Concentrations and Predominant Electron-Accepting Processes in a Contaminated Aquifer DON A. VROBLESKY,* PAUL M. BRADLEY, AND FRANCIS H. CHAPELLE U.S. Geological Survey, Stephenson Center, Suite 129, 720 Gracern Road, Columbia, South Carolina 29210-7651
Long-term (1992-1995) monitoring data from a petroleum hydrocarbon-contaminated aquifer were used to examine the hypothesis that concentrations of low molecular weight (LMW) aliphatic organic acids reflect terminal electronaccepting processes. During the period of study, concentrations of dissolved hydrogen (H2) indicated that methanogenic, sulfate-reducing, and iron(III)-reducing conditions predominated at the site. However, there was no correlation between LMW organic acid concentrations and concentrations of dissolved H2. These results indicate that organic acid concentrations are not a reliable indicator of local redox conditions at this site.
Introduction Organic acids in groundwater influence dissolution of minerals (1-3), influence the chemical evolution of deep groundwater (4), and are intermediate products in the anaerobic biodegradation of petroleum hydrocarbons (5). Recent investigations have shown that concentrations of aliphatic organic acids increase as electron acceptors become depleted (4, 6-8). Such observations raise the possibility that the presence of organic acids in groundwater can be used as an indicator of redox processes. The purpose of this study is to test the hypothesis that the presence of organic acids in petroleum hydrocarbon-contaminated groundwater can be an accurate predictor of local predominant microbial terminal electron-accepting processes (TEAPs). The study area was a petroleum-tank farm, referred to hereafter as the facility, in Hanahan, SC (9). The primary contaminants were benzene, toluene, ethylbenzene, and total xylenes (collectively termed BTEX) (9). To determine whether the presence of organic acids could be an accurate predictor of predominant TEAPs, concentrations of low molecular weight (LMW) organic acids were compared to concentrations of H2 in contaminated groundwater. The contaminated groundwater contained two distinct ranges of LMW aliphatic organic acid concentrations. The first range of concentrations (
