The Washington State Department of Transportation (WSDOT) designs, operates, and maintains stormwater detention basins. These basins are used to control storm water runoff from highways, thereby controlling flows in down gradient areas. Historically, storm water basin design has been based solely on hydraulic considerations. Recent initiatives by the Washington State Department of Ecology have indicated that storm water quality has become a high priority. Consequently, future design must consider water quality as well as flood control. To have control of the variables associated with removal efficiencies (flow rate, contaminant type, contaminant concentrations, particle size distribution, and basin configuration) a scale model of a typical detention basin was constructed. Experiments to determine removal efficiencies for suspended solids with diameters <75 micrometers were conducted and the results were compared with the Type 1 sedimentation theory for an ideal basin. Preliminary investigations into the removal efficiencies for Pb, Zn, Cd, and Cu were performed at one flow rate and optimized piping configuration. The removal of suspended solids range from 65-80%. Type 1 sedimentation theory for an ideal basin yielded good predictions of sediment removal. This implies that Type 1 sedimentation theory could be used to estimate sediment removal in full scale systems under similar conditions. Care should be taken when predictions are required at high-surface overflow rates or highway runoff that contains a significant fraction of small particles. The removal of metals ranges from 28-40% indicating that removal of smaller particles is necessary to achieve better removal efficiencies for metals.