CHEMICAL RETENTION CAPACITY OF A NEWLY CONSTRUCTED ROADWAY RUNOFF DETENTION POND SYSTEM

Storm generated runoff pollution from roadways presents a significant problem for water quality planners. Roadway runoff generally contains elevated concentrations of petroleum hydrocarbons, which negatively impact the quality of both surface and subsurface waters. The adverse effects of the runoff on water quality can be minimized through the use of best management practices (BMP’s), which prevent or reduce the pollution of water. The newly constructed Gano Street retention pond system in downtown Providence, RI, is an example for a structural BMP. The system’s three pools were designed to retain runoff until the contaminants associated with suspended solids settle out. In addition, one of the three pools is a created wetland that removes contaminants by interaction with plant material.

While BMPs generally work well in retaining contaminants associated with solids, there is concern about their effectiveness in retaining dissolved contaminants. We selected dissolved polycyclic aromatic hydrocarbons (PAHs) as target contaminants and investigated their removal from runoff flowing through the Gano Street system. During three storms (between May and August 2001), stormwater samples and water quality data (pH, temperature, conductivity) were collected at 7 locations within the system. The water samples were analyzed for selected PAHs based on EPA Method 610 using a GC-FID. Our results indicate that the retention pond system does not significantly retain dissolved PAHs. For example, during a storm in mid-August, the PAH concentration was similar or even higher in the system’s effluent than in the stormwater entering it. We explain the increase in PAH concentration as remobilization of contaminants during storms in combination with redissolution of PAH from contaminated sediments within the pools.