HR: 16:55h
AN: H34A-03    [Abstracts]
TI: Major Ion Chemistry and Mixing Proportions of Nitrate Sources in Urban Groundwater
AU: * Munster, J
EM: jmunster@notes2.cc.sunysb.edu
AF: Geosciences Dept., Stony Brook University, Stony Brook, NY 11794, United States
AU: Hanson, G N
EM: Gilbert.Hanson@stonybrook.edu
AF: Geosciences Dept., Stony Brook University, Stony Brook, NY 11794, United States
AU: Bokuniewicz, H
EM: Henry.Bokuniewicz@stonybrook.edu
AF: Marine Science Research Center, Stony Brook University, Stony Brook, NY 11794, United States
AB: Working with Dr. Gilbert Hanson has allowed me to apply general mixing equations to identification of nonpoint sources of groundwater contamination. These methods have not commonly been used in hydrologic studies, as they involve a more classical petrologic approach, one which Dr. Hanson has pioneered. Our drinking water supplies are becoming more susceptible to contamination and knowing the chemistry of contaminate sources will yield precise determination of potential sources to groundwater and allow government agencies to adopt policies to reduce or prevent contamination. The geochemistry of soil water from below fertilized turfgrass sites and of sewage from septic tank/cesspools was used to place constraints on the sources of nitrate in groundwater of an unconsolidated aquifer in Suffolk County, Long Island, New York, USA. Twenty four sewage samples were acquired from Suffolk County Public Works. Soil water samples, from suction lysimeters, were acquired monthly during 2003, totaling 70 samples. We found that soil water concentrations were elevated in Ca, Mg and SO₄ relative to sewage and sewage had higher concentrations of Cl, N-NO₃, PO₄, Na and K. This difference in the major ion chemistry allows identification of the source signatures in groundwater. We then compared the source signatures to 28 groundwater wells on binary ion diagrams of SO₄, Cl and N- NO₃ and created a cation sorption model for Na, Ca, Mg and K, in order to model cation concentrations on binary ion diagrams. These diagrams allow estimates of the relative contributions of each source to each well. Groundwater wells plotted according to their major land use and show that wells of similar land use have similar geochemistry and similar source contributions. The estimates of source contributions show that the proportions of soil water and sewage increase as residential land use increases. Although volumetric source proportions to groundwater wells are similar for soil water and sewage within a given land use, sewage contributes a greater proportion to the nitrate concentration in groundwater wells. For example, sewage contributes between 86-100% of the nitrate in wells sourced in medium density residential land use, even when accounting for a 50% reduction in nitrate concentrations from the septic tank/cesspool system. Our results indicate that to decrease the nitrate concentrations in groundwater one must reduce the load from septic tank/cesspool systems.
DE: 1803 Anthropogenic effects (4802, 4902)
DE: 1831 Groundwater quality
SC: Hydrology [H]
MN: 2007 Joint Assembly