Temporal variations in parameters reflecting terminal-electron-accepting processes in an aquifer contaminated with waste fuel and chlorinated solvents

A fundamental issue in aquifer biogeochemistry is the means by which solute transport, geochemical processes, and microbiological activity combine to produce spatial and temporal variations in redox zonation. In this paper, w e describe the temporal variability of TEAP conditions in shallow groundwat er contaminated with both waste fuel and chlorinated solvents. TEAP paramet ers (including methane, dissolved iron, and dissolved hydrogen) were measur ed to characterize the contaminant plume over a 3-year period. We observed that concentrations of TEAP parameters changed on different time scales and appear to be related, in part, to recharge events. Changes in all TEAP par ameters were observed on short time scales (months), and over a longer 3-ye ar period. The results indicate that (1) interpretations of TEAP conditions in aquifer s contaminated with a variety of organic chemicals, such as those with petr oleum hydrocarbons and chlorinated solvents, must consider additional hydro gen-consuming reactions (e.g., dehalogenation); (2) interpretations must co nsider the roles of both in situ (at the sampling point) biogeochemical and solute transport processes; and (3) determinations of microbial communitie s are often necessary to confirm the interpretations made from geochemical and hydrogeological measurements on these processes. (C) 2000 Elsevier Scie nce B.V. All rights reserved.