How did USGS study parking lot runoff?
USGS researchers sampled runoff at 13 parking lots in Austin. They also took scraping samples of parking lot surfaces to compare source materials to particles in the runoff. Scraping samples and the water and particles in the runoff samples were analyzed for a suite of PAHs, major elements, and trace elements. The researchers sprayed water on four different types of parking lot surfaces: lots sealed with coal-tar based sealcoat (left photo), lots sealed with asphalt-based sealcoat, unsealed asphalt lots, and unsealed concrete lots. The runoff was collected behind spill berms, pumped into containers (middle photo) and filtered through Teflon filters to collect the particulates for analysis (right photo). The particulates, the filtered water, and samples of sealcoat scraped from the parking lot surfaces were analyzed for PAHs at the USGS National Water Quality Laboratory in Denver, Colorado. Concentrations and yields (the amount of PAHs coming off a parking lot per unit area) were used t
