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Lower Sabinal River

This is a completed project to improve water quality in the Lower Sabinal River. The total maximum daily load (TMDL) was adopted and the implementation plan (I-Plan) has been approved. Together, the TMDL and I-Plan are the road map to improved water quality.

photo of the lower sabinal river
Lower Sabinal River

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

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In 2000, assessment by 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. TCEQ completed a total maximum daily load project to determine the measures necessary to restore water quality. The goal of a TMDL is to determine the amount (or load) of a pollutant that a body of water can receive and still support its designated uses. The allowable load is then allocated among the categories of sources within the watershed, and stakeholders work with the state to develop measures that reduce pollutant loads.

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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Watershed Description

The Lower Sabinal River watershed is located in southwest Texas in Uvalde and Medina counties and covers 222 square miles. The Lower Sabinal River begins from a point upstream of State Highway 127, one mile north of the city of Sabinal, and flows to the confluence with the Frio River. The area is dominated by a mixture of live oak, Ashe juniper, and mesquite, with grasslands and limited row crop production.

The City of Sabinal wastewater treatment facility (WWTF) is the only permitted discharger in the watershed. However, during most conditions, there is no surface discharge from the facility. There is one registered concentrated animal feeding operation in the watershed, the Driskill Feedlot, but it does not discharge to the river.


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 2022 Texas Integrated Report of Surface Water Quality. Nitrate sampling will continue.

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Adopted TMDL

The Commission adopted this TMDL 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 for Nitrate-Nitrogen in the Lower Sabinal River
    Segment 2110
    The TCEQ did not receive any comments from the public regarding this TMDL.

Revisions to TMDLs

From time to time, it is necessary to revise TMDLs to account for changing conditions in the watershed. Revisions to the load allocations in TMDLs are made via the state’s Water Quality Management Plan (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.


Updates are made to account for changing conditions in the watershed, such as new or revised wasteload allocations, permits that have been canceled or have expired, or changed facility names. Updates use the same units of measure as the original TMDL.

  • January 2009, pgs. 10-12

WQMP updates may be viewed in person at the TCEQ Library, Building A, 12100 Park 35 Circle, Austin, Texas. 

For WQMP updates prior to 2014, use the TRAIL Search the TCEQ engine as outlined below. The main search box on the page will only conduct a simple search with no exclusionary parameters and should not be used.

  1. First, limit your search to TCEQ only. Do this via the advanced search feature on the left of the page. To limit a search to TCEQ content, enter “” or “” into the “From the Host” search box.
  2. Refine your search to narrow down results. The other search boxes on the left of the page allow for search terms to be included, excluded, or used in an exact phrase search. Date ranges can be used as well.

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Approved I-Plan

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

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Contact the TMDL Program

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

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