Washington State's Stormwater Management Program

Abstract

To comply with state and federal laws, the Washington State Department of Transportation developed a Stormwater Management Program. The program included an outfall inventory and retrofit program, a Highway Runoff Manual (HRM), and stormwater research. Field crew inventoried sites where highway stormwater runoff is collected and discharged to surface water, ground water, and municipal storm sewers. Pipes, ditches, and stormwater structures that provide quantity and quality control were inventoried. The screening assessment for potential water pollution problems was made via observation and sampling kit. The sampling kit was found to be ineffective at identifying illicit connections. Inventoried sites were mapped using global positioning and geographic information system technology. Research was conducted on sites to determine watershed characteristics, potential environmental effects, and Best Management Practice (BMP) retrofit options. A computer data base of information is maintained to facilitate stormwater management activities. A prioritization scheme was developed to identify priority sites for retrofit, based on the following factors: receiving water body, beneficial uses, pollution loading, percent highway drainage, cost-pollution benefit, and values trade-off. The HRM was developed to direct stormwater management for existing and new state highways, rest areas, park-and-ride lots, and ferry terminals. Water quality and quantity issues for construction and maintenance are addressed by meeting the minimum requirements of the manual. Thirteen research projects have been funded to evaluate experimental BMPs, to determine BMP pollutant removal efficiencies, and to assess the costs and benefits of retrofitting outfalls. Research included bench-scale work, field projects, and a department survey.