Water Quality and Quantity Impacts of Highway Construction and Operation: Summary and Conclusions

By Michael E. Barrett, Joseph F. Malina, Jr., Randall J. Charbeneau, and George H. Ward

ABSTRACT

This report contains a summary of a four-year study of the impacts of highway construction and operation on water quality and quantity of stormwater runoff. Monitoring of water quality in one of the creeks below a highway construction site indicates that even an extensive system of temporary controls is not sufficient to prevent large amounts of suspended sediment from entering receiving waters. Parameters commonly used to characterize geotextile fabrics were found to have little relevance for estimating their sediment removal abilities or hydraulic characteristics under field conditions.

The quality of highway runoff was determined by monitoring the quality of storm water runoff from three sites along the MoPac Expressway. The quality of the runoff was similar to that reported in other highway studies across the United States. The concentrations of pollutants appeared to be affected by changes in traffic volume, rainfall intensity, and other factors.

A computer model was developed that will predict the quality of runoff from operating highways in the Austin, Texas area. The majority of the variation observed in highway stormwater loading could be explained by causal variables measured during the storm event, the antecedent dry period, and the previous storm event.

Structural controls built on the new highway segments to protect the Edwards Aquifer from stormwater runoff have not performed effectively. The hydraulic performance of the vertical sand filters has been uneven, resulting in little apparent improvement in runoff quality. A grassy swale was found to be effective for reducing runoff volumes and pollutant concentrations.

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TABLE OF CONTENTS

FRONT MATTER
Title Page
Acknowledgements
Abstract
Table Of Contents
List Of Tables
List Of Figures

1. INTRODUCTION

2. TEMPORARY EROSION CONTROLS: USE AND EFFECTIVENESS

3. EFFECTS OF HIGHWAY CONSTRUCTION AND OPERATION
3.1 Construction Effects
3.2 Highway Operation Effects

4. QUALITY OF HIGHWAY RUNOFF IN AUSTIN, TEXAS

5. FACTORS AFFECTING THE QUALITY OF HIGHWAY RUNOFF
5.1 Model of Highway Runoff Quality
5.2 Distribution of Highway EMCs

6. PERFORMANCE OF PERMANENT RUNOFF CONTROLS
6.1 Pollutant Removal Effectiveness of a Grassy Swale
6.2 Field Performance of Vertical Sand Filter Systems
6.3 Laboratory Filtration Experiments

7. CONCLUSIONS

BIBLIOGRAPHY