How to Read this Report

Between September 2004 and August 2005, researchers evaluated 12 stormwater treatments for water quality performance and storm volume reduction during 11 rainfall-runoff events with a range of characteristics. This analysis assessed water quality parameters such as pH, temperature, dissolved oxygen, specific conductivity, and turbidity, as well as pollutant removal, peak flow reduction, maintenance, cost of installation, and materials.

The evaluation revealed distinctive trends. Several LID designs exhibited pollutant removal efficiencies of 80 to 99 percent. In contrast, traditional approaches did poorly to moderately. Manufactured system performance varied—systems with storage volumes were the most effective, those without, the least. The treatment of total suspended solids (TSS) depends largely on the size of particles and their concentration in influent. A TSS annual event mean concentration of 37 milligrams per liter was observed with particle sizes (D50) suspected to be less than 100 microns. This will be the subject of further research. Certain design elements, regardless of the treatment, promoted pollutant removal. These included increased hydraulic residence time, infiltration and filtration mechanisms, low turbulence, and using dense root mats and herbaceous plants.

We have summarized the analysis for each stormwater treatment in the following pages. However, this data should not be interpreted to mean that there is one treatment that is appropriate for all situations. Treatment size, site constraints, cost, operations, maintenance, and performance all must be taken into account.