Evaluating Behavior of Oxygen, Nitrate, and Sulfate during Recharge and Quantifying Reduction Rates in a Contaminated Aquifer

• Published in: Environmental science & technology 2002-06, Vol.36 (12), p.2693-2700
• Main Authors: McGuire, Jennifer T, Long, David T, Klug, Michael J, Haack, Sheridan K, Hyndman, David W
• Format: Article
• Language: English
• Subjects: Applied sciences; Aquifers; Bacteria, Aerobic - physiology; Bioremediation; Contamination; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Exact sciences and technology; Groundwater; Groundwaters; Hydrology. Hydrogeology; Natural water pollution; Nitrates; Nitrates - analysis; Nitrates - chemistry; Nitrates - metabolism; Oxidation-Reduction; Oxygen; Oxygen - analysis; Oxygen - chemistry; Oxygen - metabolism; Pollution; Pollution, environment geology; Soil; Soil Microbiology; Sulfates - analysis; Sulfates - chemistry; Sulfates - metabolism; Water resources; Water Supply; Water treatment and pollution
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es015615q

This study evaluates the biogeochemical changes that occur when recharge water comes in contact with a reduced aquifer. It specifically addresses (1) which reactions occur in situ, (2) the order in which these reactions will occur if terminal electron acceptors (TEAs) are introduced simultaneously, (3) the rates of these reactions, and (4) the roles of the aqueous and solid-phase portions of the aquifer. Recharge events of waters containing various combinations of O2, NO3, and SO4 were simulated at a shallow sandy aquifer contaminated with waste fuels and chlorinated solvents using modified push−pull tests to quantify rates. In situ rate constants for aerobic respiration (14.4 day -1), denitrification (5.04−7.44 day-1), and sulfate reduction (4.32−6.48 day-1) were estimated. Results show that when introduced together, NO3 and SO4 can be consumed simultaneously at similar rates. To distinguish the role of aqueous phase from that of the solid phase of the aquifer, groundwater was extracted, amended with NO3 and SO4, and monitored over time. Results indicate that neither NO3 nor SO4 was reduced during the course of the aqueous-phase study, suggesting that NO3 and SO4 can behave conservatively in highly reduced water. It is clear that sediments and their associated microbial communities are important in driving redox reactions.