State Water Resources Research Institute Program

Project ID: 2007AZ213B
Title: Sources of Nitrate in Groundwaters of the Tucson Basin
Project Type: Research
Start Date: 3/01/2007
End Date: 2/29/2008
Congressional District: 7
Focus Categories: Geochemical Processes, Nitrate Contamination, Hydrogeochemistry
Keywords: Nitrate, Sewage Effluent, mixing models
Principal Investigator: Meixner, Thomas
Federal Funds: $ 9,121
Non-Federal Matching Funds: $ 18,173
Abstract: While it is generally assumed that high nitrate levels in groundwater are associated with human activities (irrigation, fertilizer use, feed lots, septic tanks and municipal sewage), in arid states like Arizona this is not always the case. Often times elevated nitrate in groundwater can be due purely to natural processes, a combination of natural and human processes, or neglected human impacts on the environment (e.g. atmospheric nitrogen deposition). Since understanding the mechanism of contamination is the first step to understanding how to solve any contamination problem, significant efforts have been expended in the past to understand the sources and mechanisms of nitrate contamination in groundwater. This project will utilize two differing flow path transects within the Tucson basin to investigate the sources of nitrate to groundwater in the Tucson basin. The research has three objectives

  1. Use geochemical and isotopic techniques to quantify groundwater sources.
  2. Quantify nitrate isotopes to connect groundwater nitrate to various nitrate sources and sinks.
  3. Develop conceptual model of nitrate sources and processes along the two flowpaths using results of first two objectives and existing nitrate and groundwater geochemical data.

To achieve these objectives we will collect water along two flowpath using Tucson Water wells. The first transect will traverse the Tanque Verde and Rillito creek drainages and look at an increase in nitrate along this transect. The second Set of wells will be across the Santa Cruz river in the neighborhood of the Sweetwater recharge facility where there are high nitrate concentrations near the river and lower nitrate concentrations farther from the river. The first transect allows us to focus on the sources of water and nitrate in the groundwater system while the second transect allows us to investigate the relative importance of denitrification or mixing around the sewage recharge facility. Samples from each transect will be analyzed for major geochemical composition and sulfur, water and nitrate isotopes. These suites of geochemical and isotopic analyses should allow us to partition the reasons for nitrate variability in Tucson groundwater between water sources, biogeochemical sinks and mixing.

Progress/Completion Report, PDF

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