SEDIMENTATION OF POLYCYCLIC AROMATIC HYDROCARBONS WITHIN AN URBAN STORM WATER BASIN DRAINING COAL-TAR SEALED PARKING LOTS

Polycyclic aromatic hydrocarbons (PAHs) are known carcinogens which can be harmful to aquatic and terrestrial life. In some urban areas, coal-tar sealants are a major source of PAHs to the watershed. Coal-tar sealants are used as protective coatings on roads, parking lots, and driveways and break-down by erosion and tire abrasion into particles which contaminate stream sediments. This study assesses the concentrations, spatial distribution, and sources of PAHs within sediment deposits in an urban storm-water detention system. The detention system has three sub-basins which collect runoff separately from coal-tar sealed parking lots and other non-coal tar urban surfaces. Thirty sediment samples were collected from channel and adjacent bottom areas within the basin and analyzed for PAHs. USEPA urban PAH₁₆ concentrations ranged from 3,280 to 537,250 ppb with 63% of the samples above the probable effects concentration of 22,800 µg/kg which may indicate toxicity to aquatic life. The highest concentrations of PAHs were located in the sub-basin that receives direct runoff from a coal-tar sealed parking lot. The outlet sub-basin also had increased levels of PAHs resulting from the mixture of particles in runoff from coal-tar sealed parking lots with runoff from other urban sources. Basin soil and sediment samples collected from higher elevations had lower PAH concentration compared to samples taken within or near trickle channels. These results show that coal-tar sealants contribute a significant amount of PAHs into this basin system. However, PAH concentrations vary spatially due to surface elevation, source influence, and sedimentation patterns within the basin.