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Investigation into Contributions of Nitrate-Nitrogen to Plum Creek, Geronimo Creek and the Underlying Leona Aquifer

Project Goals/Objectives: This project will analyze groundwater from the Leona Aquifer and surface water from Plum Creek and Geronimo Creek for nitrate-nitrogen and its isotopes of nitrgoen and oxygen to determine possible sources of nitrate-nitrogen, i.e.human, animal or fertillzer. Through this project there will be an increase in understanding of the interaction between surface water and underlying groundwater and evaluate strategies and practices for reducing nitrate levels in the surface water and groundwater.

Project Background: Since monitoring of Plum Creek and Geronimo Creek began in the late 1990’s, these creeks have shown elevated concentrations of nitrate-nitrogen.Currently, because the state stream water quality standards are not numeric for nutrients, exceedences of a screening concentration of 1.95 mg/L nitrate-nitrogen have been used to designate a stream as having a concern for nitrate-nitrogen. The possible sources of the nutrient concern are numerous.Plum Creek is effluent-dominated and is also fed by springs that come from the Leona Aquifer, known to have elevated concentrations of nitrate-nitrogen.Geronimo Creek is also fed by springs from that same aquifer.Stakeholders in both watersheds have long suspected fertilizer use as the source of the nitrates in the Leona, but oddly enough, elevated concentrations of nitrates had been seen in well testing long before commercial inorganic fertilizers came into use.Septic systems, organic fertilizers, nitrifying plants and atmospheric deposition round out the list of possible sources The Plum Creek and Geronimo Creek Watershed Partnerships have not waited for “impaired waterbody” status to start working on best management practices that could reduce sources of nitrates. In order to help direct efforts and funding toward the most likely or most influential source(s) of nitrate, this project will look to isotopic signatures of nitrogen and oxygen in the nitrates.The ratios of the isotopes of nitrogen and oxygen in nitrate often are useful for determining sources of nitrates in groundwater and surface water.

Project Location: Plum Creek in Travis, Hays and Caldwell Counties, Geronimo Creek in Guadalupe and Comal Counties, and Leona Aquifer in Guadalupe and Caldwell Counties.

Project Cost: Federal ($162,000), Non-Federal ($54,113), Total ($216,113)

Project Participants: TSSWCB, Guadalup-Blanco River Authority

Project Workplan13-07

Project QAPP: 13-07

"Protecting and Enhancing Natural Resources since 1939."

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