Environmental Planning for the Metropolitan Area Cedar-Green River Basins, Washington. Part II. Urban Drainage Study. Appendix C. Storm Water Monitoring Program,

The quantity and quality of stormwater runoff in the Metropolitan Seattle, Washington area was measured over a seven-month period. Survey sites were selected on the basis of land use and included single and multiple family residential, commercial and industrial areas. Quantity measurements involved continuous recording of stormwater runoff and rainfall volume and intensity while quality measurements were made for 29 parameters with samples taken at specified intervals during the course of six storms. Rainfall intensity was light for the monitoring period, resulting in a relatively low percentage of stormwater runoff factors, which varied from 5 percent for low density residential areas to 64 percent for commercial areas. Pollutant washoff loading varied with land use pattern. The pollutants of major concern were solids, BOD, COD and oil. Nutrient and heavy metal loading values with some exceptions, were relatively low. Coliform values were high but not of apparent sanitary significance.