Gilleland Creek Intensive Bacteria Survey Addendum




Texas Stream Team

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Gilleland Creek finds its natural origin at Ward Spring northwest of Pflugerville, but runoff has caused the beginning of Gilleland Creek to be upstream near the intersection of I-35 and TX 45 Toll. It flows southeast for approximately 32 miles, draining about 76 mi2 (197 km2). The majority of the 6.5 million gallons per day that flow into the Colorado River come from six wastewater treatments plants that pipe treated wastewater into the creek. The land use in the watershed is primarily undeveloped and agricultural with increasing residential development. In 2004, Gilleland Creek was placed on the Texas Commission on Environmental Quality (TCEQ) 303(d) List of Impaired Water Bodies because of repeated high bacteria levels. As a result, the TCEQ contracted the Lower Colorado River Authority (LCRA) to develop a Total Maximum Daily Load (TMDL) program, which determines the extent to which a pollutant load can be reduced, and an Implementation Plan, which describes how that can be carried out. On December 3rd and 15th, 2008, the Texas Stream Team along with LCRA, TCEQ, the City of Austin, the City of Pflugerville, and the Texas Department of Transportation conducted an intensive bacteria survey. This document is an addendum to that survey, which is available at It is intended to assist with the carrying out of the Implementation Plan. The following data was collected by volunteer monitors for the Texas Stream Team and the LCRA. The standard established by the EPA for a single sample of E. coli bacteria in surface water is 394 cfu / 100 mL. The standard for a geometric mean is 126 cfu / 100mL. A cfu is a colony forming unit. This is a measure of how many bacteria there are in every 100 mL could multiply into a colony. At this level, 1 in 125 people might get sick if the water is ingested. At least ten samples from the last seven years with approximately the same interval between sample times are required for a water body to be listed on the 303(d) list. The assessment period for Gilleland Creek bacteria spans from 10/29/05 to 2/15/2010, and the data covered in this report shows the geometric mean for this period is 143.97 cfu / 100mL. In alignment with Texas Stream Team’s core mission, monitors attempt to collect quality-assured data that can be used by government agencies and other decision-making entities to promote a healthier and safer environment for people and aquatic inhabitants. Information collected by Texas Stream Team volunteers utilizes a TCEQ and EPA approved quality assurance project plan (QAPP) to ensure data are correct and accurately reflects the environmental conditions being monitored. All data are screened for completeness, precision and accuracy where applicable, and scrutinized with data quality objective and data validation techniques. Sample results are intended to be used for education and research, baseline, local decision making, problem identification, and others uses deemed appropriate by the data user. The data for this assessment came from the Colorado River Watch Network and the Texas Stream Team database. The graphs are displayed in order from upstream to downstream, with the exception of Swenson Farms which is located on a tributary. TCEQ standards are marked in red. The conductivity standard is a maximum mean. The temperature standard is a maximum. The dissolved oxygen standard is a minimum. The pH standard is a range.



water quality, bacteria, Gilleland Creek


Texas Stream Team. (2010). Gilleland Creek intensive bacteria survey addendum (Report No. 2010-06). Texas State University-San Marcos, San Marcos, Texas.


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