HR: 1340h
AN: B43C-0295    [Abstracts]
TI: Evaluation of Nitrate Sources and Nitrate Management Strategies in California Suburban Growth Areas
AU: * Singleton, M J
EM: singleton20@llnl.gov
AF: Lawrence Livermore National Laboratory, 7000 East AVE, Livermore, CA 94550 United States
AU: Moran, J E
EM: moran10@llnl.gov
AF: Lawrence Livermore National Laboratory, 7000 East AVE, Livermore, CA 94550 United States
AU: Esser, B K
EM: esser1@llnl.gov
AF: Lawrence Livermore National Laboratory, 7000 East AVE, Livermore, CA 94550 United States
AU: Leif, R N
EM: leif1@llnl.gov
AF: Lawrence Livermore National Laboratory, 7000 East AVE, Livermore, CA 94550 United States
AU: McNab, W W
EM: mcnab1@llnl.gov
AF: Lawrence Livermore National Laboratory, 7000 East AVE, Livermore, CA 94550 United States
AU: Carle, S F
EM: carle1@llnl.gov
AF: Lawrence Livermore National Laboratory, 7000 East AVE, Livermore, CA 94550 United States
AU: Moore, K B
EM: kearam@hotmail.com
AF: Lawrence Livermore National Laboratory, 7000 East AVE, Livermore, CA 94550 United States
AB: Population growth in California has pushed the boundaries of suburban communities into formerly agricultural areas. As a result there is considerable uncertainty as to whether nitrate contamination in groundwater wells results from current sources or is a legacy of agriculture. Fertilizer application for historical agriculture is frequently assumed to be a major source, but septic system leachate, other animal waste, and residential fertilizer application may also contribute. Potential remediation strategies may include improved fertilizer management and/or conversion from septic tanks to sewer systems, but the sources of nitrate and pathways to groundwater must first be identified in order to develop a plan of action. We combine the detection of trace organic compounds that are specific to domestic waste with isotopic compositions of nitrogen and oxygen in nitrate in order to determine nitrate sources. Under anaerobic conditions and in the presence of an electron donor such as organic carbon, microbially mediated denitrification may transform nitrate to harmless nitrogen gas, and fractionate the isotopologues of any residual nitrate. The occurrence of saturated zone denitrification is detected by measuring excess dissolved nitrogen gas with a field-portable membrane inlet mass spectrometer system. Groundwater age dating using the ³H/³He method provides a means of tracking the history of nitrate inputs to groundwater, including changes in nitrate flux after implementation of a remediation program. Groundwater that pre-dates agricultural or suburban activity is used to define natural background levels of nitrate. Study areas in California include Chico, Livermore, and Gilroy. This work was performed under the auspices of the U.S. Department of Energy by University of California, Lawrence Livermore National Laboratory under Contract W-7405-Eng-48.
DE: 0469 Nitrogen cycling
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 1803 Anthropogenic effects (4802, 4902)
DE: 1831 Groundwater quality
DE: 1884 Water supply
SC: Biogeosciences [B]
MN: Fall Meeting 2005