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Gilleland Creek Stormwater Retrofits

The University of Texas monitored the effectiveness of a stormwater detention basin retrofit in reducing bacteria pollution in Gilleland Creek.

Background

Since 1999 Gilleland Creek (Segment 1428C), in northeast Travis County, has not met water quality standards because bacteria concentrations exceeded the criteria used to evaluate attainment of the contact recreation use. These bacteria are naturally found in the intestines of humans, livestock, wildlife, and pets. Although they are not generally disease-causing, their presence in water indicate the potential presence of disease-causing microorganisms from fecal contamination. Therefore, higher levels of fecal bacteria in water mean a higher risk to humans of contracting diseases by ingesting water during swimming, wading, or kayaking—activities, called “contact recreation,” in the state’s standards for water quality.

In 2005, the Lower Colorado River Authority used historical water quality data and conducted stormwater monitoring to determine the source of fecal bacterial contamination in the watershed. Malfunctioning septic systems, storm sewers, agriculture, pet and wildlife waste, and other natural sources were identified as probable sources of nonpoint source pollution.

To address this impairment, TCEQ adopted a total maximum daily load (TMDL) in 2007. Stakeholders then developed a TMDL implementation plan for Gilleland Creek, which the commission approved in 2011. This stormwater project supported implementation of the TMDL implementation plan.

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Project Description

University of Texas (UT) personnel installed and operated an automated valve in a stormwater detention basin outlet in the Gilleland Creek watershed which allows all the stormwater runoff to remain in the detention basin. This causes larger amounts of bacteria to be removed from the water through sedimentation and exposure to sunlight. The valve then opens after a specified amount of time, discharging the runoff into Gilleland Creek.

UT determined the valve's effectiveness in reducing the amount of bacteria, sediment, and phosphorus released by the detention basin into the creek by comparing runoff water quality to that of a standard flood control basin without a valve. The goal was a 50% reduction in each of the sampled pollutants (E. coli and fecal coliform). Although this goal was not met, results did show a decrease in fecal bacteria at the retrofitted basin. The project was completed in August 2014.

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For More Information

To find out more about the NPS Program, call 512-239-6682 or e-mail us at nps@tceq.texas.gov.

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