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Lower Sabinal River: A TMDL Project for Nitrate-Nitrogen

A completed project to improve water quality in the Lower Sabinal River. The total maximum daily load (TMDL) is adopted and the implementation plan (I-Plan) is approved; together, they provide the road map for improved water quality.

photo of the Lower Sabinal River

The Lower Sabinal River

Counties: Medina, Uvalde
Parameter: Nitrate-nitrogen
River Basin: Nueces River
Segment: 2110

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Segment 2110 of the Lower Sabinal River begins near the city of Sabinal in Uvalde County and ends at its confluence with the Frio River in Frio County. In 2000, assessment by the TCEQ indicated that concentrations of nitrate-nitrogen were sometimes higher than recommended for use of the Lower Sabinal River as a source for drinking water.

The goal of this project was to reduce nitrate-nitrogen to levels that make the river more useful as a source for drinking water treatment facilities.

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The study to determine the TMDL concluded that the source of the nitrate was from the Sabinal wastewater treatment facility (WWTF) and its lagoons, which were located in the 100-year floodplain. The implementation plan for the TMDL recommended construction of a new WWTF located outside of the floodplain.

The new facility was granted a permit and construction began early March 2010. The facility came online July 27, 2011. As expected, nitrate levels declined with the new facility. The status of the water body was changed from “not supporting” to “of concern” for nitrate, according to the 2020 Texas Integrated Report of Surface Water Quality. Nitrate sampling will continue.

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Adopted TMDL

The TMDL was adopted by the commission on August 10, 2005. The EPA approved it on October 13, 2005, at which time it became part of the state's Water Quality Management Plan.

  • One Total Maximum Daily Load Adobe Acrobat PDF Document for Nitrate-Nitrogen in the Lower Sabinal River
    Segment 2110
    The TCEQ did not receive any comments from the public regarding this TMDL.

Updates to TMDLs

From time to time, it is necessary to revise TMDLs to account for changing conditions in the watershed, such as new or amended permits, or urban growth, or to correct oversights in the original TMDL report. Revisions to the load allocations in TMDLs are made via the state’s WQMP, which is updated quarterly.

The WQMP provides projected effluent limits for use in planning and permitting activities under the Texas Pollutant Discharge Elimination System (TPDES). The TCEQ reviews all applications for new and amended permits for conformance with applicable portions of the WQMP, including adopted TMDLs.

Revisions to the TMDL are documented in the approved WQMP updates listed below.

Learn more about  WQMP updates and about opportunities to comment on revisions to them.

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The commission approved this I-Plan on August 23, 2006.

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For More Information

Please e-mail and mention the Lower Sabinal River nitrate project in the subject line. Or call us at 512-239-6682.

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