HR: 0800h
AN: H11C-0684    [Abstracts]
TI: Sources of Nitrate to Tucson, Arizona Groundwaters.
AU: * Dejwakh, N
EM: dejwakh@hwr.arizona.edu
AF: University of Arizona, Department of Hydrology and Water Resources, Tucson, az 85721, United States
AU: Meixner, T
EM: tmeixner@hwr.arizona.edu
AF: University of Arizona, Department of Hydrology and Water Resources, Tucson, az 85721, United States
AU: McIntosh, J
EM: jenmc@hwr.arizona.edu
AF: University of Arizona, Department of Hydrology and Water Resources, Tucson, az 85721, United States
AB: The quality of groundwater is of major concern in the Southwest where water resources are scarce and we highly depend on groundwater for domestic use. Due to adverse health effects, waters with high nitrate concentrations (>45 mg/L) have been banned for domestic use by the Environmental Protection Agency. Furthermore, nitrate contamination is the leading cause for removing wells from drinking water consumption in Arizona and the United States. Therefore, it is important to consider the different sources and possible processes affecting nitrate concentration. Many studies have shown that anthropogenic sources such as agricultural fertilizers and waste water have been the dominant sources of nitrate contamination. Others have attempted to quantify the natural contributions. In this study, we focus on groundwater beneath the Tucson, Arizona basin where agricultural practices are not significant and waste water is allowed to infiltrate and recharge ground waters. We assume our groundwater to be a mixture of infiltrated rainwater, waste water and Central Arizona Project (CAP) water. We analyzed ground water samples collected along a several transects: 1) along an established flow path and 2) along two cross-sections downstream from a waste water treatment plant. In addition, surface water samples were collected from ephemeral washes during rain events, from a waste water dominated stream and from the CAP. Preliminary nitrate data show some fluxes along the first transects with an overall increase downstream (from 10 to 18 mg/L with a peak of 43.8 mg/L. In the two cross-sections downstream from the waste water, the nitrate concentrations doubled down gradient (from an average of 38 to 79 mg/L). In both transects, concentrations were highest in the middle (61 and 237 mg/L) and decreased sideways. These perplexing trends either decreasing or increasing along the flow paths cannot be explained based on geochemical concentrations alone. We are awaiting key isotopic data (d15N and d18O of nitrate). Thanks to the distinct isotopic signatures of our source waters, this data will allow us to tease apart the nitrate sources between anthropogenic and natural processes.
DE: 1800 HYDROLOGY
DE: 1806 Chemistry of fresh water
DE: 1831 Groundwater quality
SC: Hydrology [H]
MN: 2007 Fall Meeting