Systematic Evaluation of Pollutant Removal by Urban Wet Detention Ponds

Abstract

Three urban wet detention ponds in the Piedmont of North Carolina were monitored to investigate long-term pollutant removal as a function of surface to area ratios. Eleven storm events were monitored over a sampling period of 13 months. Urban runoff originating from the study area was characterized by event-mean concentrations for total suspended solids (135 mg/L), total Kjeldahl nitrogen (0.88 mg/L), total iron (6.11 mg/L), and total zinc (66 ug/L). Concentrations of copper and lead were consistently below the detection limits of 30 ug/L and 100 ug/L, respectively. The observed event-mean concentrations were generally lower than the national values reported by the Nationwide Urban Runoff Program. Particle sizes of sediment discharged in runoff were much finer than the national averages due to the predominant clayey soils in the region. This study demonstrates that surface to area ratio can be a useful predictor of wet pond performance. Utilizing 1–2% of the watershed area for the development of wet detention ponds at strategic locations could reduce pollutant loadings to meet targeted requirements of water quality improvement.