HR: 17:30h
AN: B42E-07    [PDF]
TI: Field Experiment to Stimulate Microbial Urease Activity in Groundwater for {\it in situ} Calcite Precipitation
AU: * Fujita, Y
EM: fujiy@inel.gov
AF: Idaho National Engineering and Environmental Laboratory, P. O. Box 1625, Idaho Falls, ID 83415 United States
AU: Taylor, J L
EM: tayljl@if.uidaho.edu
AF: University of Idaho-Idaho Falls, 1776 Science Center Dr., Idaho Falls, ID 83402 United States
AU: Tyler, T L
EM: richtl@inel.gov
AF: Idaho National Engineering and Environmental Laboratory, P. O. Box 1625, Idaho Falls, ID 83415 United States
AU: Tyler, T L
EM: richtl@inel.gov
AF: Idaho State University, P.O. Box 8007, Pocatello, ID 83209 United States
AU: Banta, A B
EM: bwab@pdx.edu
AF: Portland State University, P. O. Box 751, Portland, OR 97207 United States
AU: Reysenbach, A L
EM: reysenbacha@pdx.edu
AF: Portland State University, P. O. Box 751, Portland, OR 97207 United States
AU: Delwiche, M E
EM: mde1@inel.gov
AF: Idaho National Engineering and Environmental Laboratory, P. O. Box 1625, Idaho Falls, ID 83415 United States
AU: McLing, T L
EM: tm1@inel.gov
AF: Idaho National Engineering and Environmental Laboratory, P. O. Box 1625, Idaho Falls, ID 83415 United States
AU: Colwell, F S
EM: fxc@inel.gov
AF: Idaho National Engineering and Environmental Laboratory, P. O. Box 1625, Idaho Falls, ID 83415 United States
AU: Smith, R W
EM: smithbob@uidaho.edu
AF: University of Idaho-Idaho Falls, 1776 Science Center Dr., Idaho Falls, ID 83402 United States
AB: Groundwater contamination by radionuclides and metals from past weapons processing activities is a significant problem for the United States Department of Energy. Removal of these pollutants from the subsurface can be prohibitively expensive and result in worker exposure, and therefore {\it in situ} containment and stabilization is an attractive remediation alternative. One potential approach for the immobilization of certain radionuclides and metals (e.g., $^{90}$Sr, $^{60}$Co, Pb, Cd) is to induce geochemical conditions that promote co-precipitation in calcite. Many aquifers in the arid western US are calcite-saturated, and calcite precipitated under an engineered remediation scheme in such aquifers should remain stable even after return to ambient conditions. We have proposed that an effective way to promote calcite precipitation is to utilize native microorganisms that hydrolyze urea. Urea hydrolysis results in carbonate and ammonium production, and an increase in pH. The increased carbonate alkalinity favors calcite precipitation, and the ammonium serves the additional role of promoting desorption of sorbed metal ions from the aquifer matrix by ion exchange. The desorbed metals are then accessible to co-precipitation in calcite, which can be a longer-term immobilization mechanism than sorption. The ability to hydrolyze urea is common among environmental microorganisms, and we have shown in the laboratory that microbial urea hydrolysis can be linked to calcite precipitation and co-precipitation of the trace metal strontium. As a next step in the development of our remediation approach, we aimed to demonstrate that we can stimulate the native microbial community to express urease in the field. In 2002 we conducted a preliminary field trial of our approach, using a well in the Eastern Snake River Plain Aquifer in Idaho Falls, Idaho, USA. A dilute molasses solution (0.00075%) was injected to promote overall biological growth, and then urea (50 mM) was added to the aquifer. Results from the field experiment indicated that following the molasses addition, total cell counts and ureolytic cell numbers increased by one to two orders of magnitude. Ureolysis rates increased from $<$100 pmol L$^{-1}$hr$^{-1}$ to $>$25,000 pmol L$^{-1}$hr$^{-1}$. DNA extracted from groundwater was analyzed for 16S rRNA and urease gene diversity, and indicated that distinct changes in the microbial community resulted from our substrate additions. Following urea injection, calcite precipitation in the formation occurred. These results are promising with respect to the potential of this approach for remediation of radionuclides and metals in groundwater.
DE: 1045 Low-temperature geochemistry
DE: 1831 Groundwater quality
SC: Biogeosciences [B]
MN: 2003 Fall Meeting