In Situ Assessment of the Transport and Microbial Consumption of Oxygen in GroundwaterEPA Grant Number: R824787
Title: In Situ Assessment of the Transport and Microbial Consumption of Oxygen in Groundwater
Investigators: Yoshinari, Tadashi , Bohlke, J. K. , Revesz, K. , Smith, Richard L.
Institution: The State University of New York at Albany , United States Geological Survey [USGS]
Current Institution: Wadsworth Center: New York State Department of Health , United States Geological Survey [USGS]
EPA Project Officer: Packard, Benjamin H
Project Period: October 1, 1995 through October 1, 1998 (Extended to September 30, 1999)
Project Amount: $350,000
RFA: Water and Watersheds (1995) Recipients Lists
Research Category: Water and Watersheds , Water
Description:The purpose of this project is to assess the transport and microbial consumption of oxygen in a sand and gravel aquifer contaminated with dilute treated sewage on Cape Cod, MA. We are currently taking two different approaches to achieve this goal.
The first approach is to directly measure in situ aerobic respiration in a large (> 5 km) contaminant plume at the experimental site. Respiration was examined for different oxygen supply vs. oxygen demand situations using small-scale, natural gradient tracer tests with sodium bromide as a conservative tracer. In one study, the ambient oxygen concentration in the aquifer was increased with air and, in a second study, 18O2 was injected at the ambient level. Oxygen levels were measured in ground water moving downward from the injection site and respiration rates were determined. In conjunction with the field experiments, oxygen uptake kinetics were determined in laboratory incubations with aquifer core material at in situ temperature. We are also assessing bacterial respiration in the contaminant plume by measuring electron transport system (ETS) activity of bacteria in sediment cores and groundwater using various tetrazolium salts (INT, CTC, XTT) as artificial electron acceptors. Total bacterial numbers, percentage of respiring bacteria, and levels of respiration have been quantified through a vertical profile in the aquifer. Preliminary results from experiments conducted at in situ temperature suggest that respiratory activity throughout the aquifer is low and that only a small percentage of the microbial community is measurably active. Respiratory activity in core and water samples measured by direct oxygen consumption and ETS activity is intended to be compared with results derived from in situ measurements gained through 18O tracer studies.
These studies will yield information on the utility of using laboratory methods (oxygen uptake and ETS activity) to measure in situ bacterial oxygen consumption in the subsurface. This study will provide a better understanding as to the relative importance of aerobic respiration in controlling ground water geochemistry and how to enhance the process in situ as a mechanism for bioremediation.