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Process Framework for Identifying and Prioritizing Water Quality Improvement for Meeting TMDLs in Texasby Samantha Lye-Ming Hon, M.S.E., Michael E. Barrett, Ph.D., Joseph F. Malina, Jr., Ph.D. ABSTRACT The Clean Water Act of 1972 was amended in 1987 to include storm water discharges. Under this act, states were required to assess the condition of surface waters to determine whether they are fishable and swimmable. When the water quality of a particular water body is not sufficient to support these beneficial uses, the water body is considered to be impaired and is required to be reported to the Environmental Protection Agency (EPA) as part of Section 303(d) of the Clean Water Act. The document that contains the list of impaired water bodies in the state is referred to as the Section 303(d) list. EPA requires that a total maximum daily load (TMDL) be developed for each of the listed water bodies for the constituents that are contributing to the impairment. After a TMDL is developed, dischargers may be required to implement Best Management Practices (BMPs) to reduce their contribution of the pollutant. The Texas Department of Transportation (TxDOT) could be a potential discharger of pollutants in stormwater runoff from roads and highways. The objectives of this research are to help TxDOT anticipate the requirements of the TMDL process and to have the data at hand to respond if TxDOT is identified as contributing to the impairment. An interactive GIS map of the impaired streams was created in ArcGIS to aid TxDOT in identifying where the impaired segments are in relation to major highways and roads. Runoff quality data from TxDOT facilities in the state were compiled and compared to water quality standards to determine constituents of concern. Existing BMPs were assessed for their effectiveness in treating highway runoff. A toolbox of appropriate BMPs for specific pollutants was developed from this assessment. These tasks were performed to prioritize and identify needed improvements for existing TxDOT highway facilities. The results from this study indicate that the major causes of impairment of water bodies in Texas are bacteria and low dissolved oxygen concentrations. Highways could be a possible contributor of these impairments because the concentrations of indicator organisms and nutrients in highway runoff exceed the existing and proposed standards. However, highway runoff is a small fraction of total runoff in terms of volume and therefore, mass loadings of indicator organisms and nutrients may not be significant. Studies also have shown that highways do not appear to be a significant source of pathogens. In addition, there are currently no BMPs that effectively address pathogens and nutrients. Therefore, it is not cost effective for TxDOT to address these problems by implementing new BMPs or retrofitting BMPs to existing facilities. It is recommended that TxDOT pursue a pollutant trading program as an alternative to implementing BMPs if required to reduce loadings of pollutants to impaired segments. Under this strategy, TxDOT can contribute financially to reduce pollutant loadings from other sources and use that to offset TxDOT’s pollutant loadings. The highlighted links that follow are connected to Adobe pdf files of the corresponding material. To view them you must have the Adobe Acrobat Reader 3.0. View the Report...(2454 KB)
These materials may be used for study, research, and education, but please credit the authors and the Center for Research in Water Resources, The University of Texas at Austin. All commercial rights reserved. Copyright 2002 Center for Research in Water Resources. |
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