ATTENUATION OF SOLUBLE POLYCYCLIC AROMATIC HYDROCARBONS IN A DETENTION POND SYSTEM: DOES IT WORK?

Between May and August 2001 and followed up by a campaign lasting from March 2003 into January 2004, the concentrations of the soluble polycyclic aromatic hydrocarbon fraction (PAH) fraction were determined in a detention pond system in Providence, Rhode Island. The detention pond system received stormwater runoff from surrounding urban areas and roadways. PAH associated with runoff is a typical nonpoint source pollution problem. Our data set shows that influent and effluent PAH concentrations were similar, indicating that soluable PAH moved mostly unhindered through the detention pond system. Under no-flow conditions, comparably unpolluted water that flowed into the ponds at end of a storm, apparently equilibrated with PAH contaminated sediment trapped in the detention pond system. Together with evapoconcentration, this equilibration process evidently caused the PAH concentration in the ponds to rise. Because no solid samples were analyzed in this study, it is not know if the equilibration process was completed and how the aqueous PAH concentrations compare to those of the solid phase. Low molecular weight PAH (e.g. acenaphthylene) were present at the highest concentrations. Also, seasonable differences existed, i.e. higher PAH flow rates were measured in Summer compared to Spring and Fall. In addition, year-to-year differences in PAH concentration were noticed and were probably related to the precipitation history and singularities such as accidents or spills involving petroleum hydrocarbons. Overall, this study provided evidence that contaminated sediments trapped in the detention pond system can re-contaminate stagnant water in the ponds. Therefore, periodic cleaning and maintenance of the ponds may be needed to reduce the PAH flux into receiving waters.