Quality of Highway Runoff Water in Austin, Texas Area

Course Summary:

Nonpoint pollution resulting from storm water runoff has recently been recognized as one of the leading causes of the degradation of the quality of receiving waters in the United States. The area southwest of Austin is part of the recharge zone of the Barton Springs portion of the Edwards aquifer. This is a karst aquifer, which is characterized by numerous caves, sinkholes, and other solution features. Recharge enters the aquifer directly through fractures and other openings a the surface, so very little filtration of the runoff occurs before entering the aquifer. The aquifer provides the sole source of drinking water for approximately 35,000 residents of Hays and Travis counties. Construction of new highways in the recharge area of the aquifer led to the concern that nonpoint source pollution from highway runoff could pose a serious threat to the quality of the groundwater and the health of area residents.

Learning Objective:

This portion of the research study focused on the characterization of the quantity and quality of runoff from existing sections of the MoPac expressway and estimation of the pollutant loads resulting from runoff from existing and newly completed sections of highway under different vehicle use patterns. The effects of drainage system type, traffic volume, and surrounding land use on highway storm water runoff characteristics were investigated. In addition to the average quality of runoff, the temporal variation in quality was also studied. A “first flush” effect (i.e., higher concentrations of pollutants at the beginning of runoff events) has been reported in several studies and is often used as the justification for the design standards which require capture and treatment of the first 1/2 inch (or other arbitrary volume) of storm water runoff. The information developed in this study should result in improvement in the design of drainage and treatment systems for highway storm water runoff. Better designs will act to reduce the impact of highway derived nonpoint source pollution on the environment.

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Course Content

Course Author: University of Texas