Pollutant concentrations of stormwater and captured sediment in flood control sumps draining an urban watershed

Levee sump systems are used by many riverine communities for temporary storage of urban wet weather flows. The performance and transport of stormwater pollutants in sump systems, however, have not been systematically studied. Although flow of stormwater through a sump system is regulated solely by flood-control requirements, these sumps may function as sedimentation basins that provide purification of stormwater. The objective of this paper is to present a case study of stormwater and sediment analysis for conventional pollutants in flood control sumps in an urban watershed. Two sumps of highly variable physical and hydraulic characteristics were selected for analysis. The results suggest that: (1) first-flush samples may not give an accurate picture of outfall concentrations of stormwater to the sump; (2) time-variable concentrations of pollutants in a sump are related to the hydraulic characteristics of the basin; and, (3) post-event sediment analysis provides verification of pollutant capture in the sumps. This study is an initial step toward development of a more comprehensive management model for flood control sumps that incorporates their hydraulic performance for quantitative assessment of pollutant loads, pollutant discharges, and pollutant removals with respect to the sumps.