URBAN HIGHWAY SEWERSHEDS AS GEOCHEMICAL CONTRIBUTORS TO NATURAL WATERS: MAJOR IONS AND SELECTED TRACE METALS

Understanding the geochemical contribution of storm water runoff from urban highways is an important part of discerning the overall impact of nonpoint source pollution on receiving waters. Populations continue to shift to new suburban regions where contaminants accumulate on an ever-increasing amount of impermeable surfaces, which can then supply potentially toxic waters to the aquatic environment from a growing area. Heavy metals resulting from traffic related activity are of particular interest because they are not degraded in the environment. Trace metal clean techniques were used to collect water samples from a storm sewer outfall emptying into the Olentangy River. The sampled urban sewershed drains a major highway (SR 315) in Columbus, Ohio, with a traffic volume of 114,000 vehicles per day. Environmental factors such as antecedent water conditions, traffic volume, roadway surface, and rainfall rates were considered. Four precipitation events were sampled during autumn, winter, spring, and summer and analyzed for major ions, dissolved organic carbon (DOC), total suspended solids (TSS), and selected trace metals (Cu, Mo, Ni, Pb, U, Zn). Large concentration ranges were observed in all analytes. Cl- concentrations ranged from 66 mg/L–1397 mg/L during summer and autumn to 2685 mg/L after the application of road de-icing salts during early spring. DOC concentrations ranged from 174 mg/L at the onset of a runoff event to 25 mg/L towards the end of the same hydrograph. TSS, DOC, and all major ions showed this strong “first-flush” effect, although the magnitude of the phenomenon varied among different ions. Discussion will include the relative dilution of different major ions throughout the hydrograph, as well as comparisons among different sampling and hydrologic conditions. Preliminary trace metal data show that concentrations of all the selected elements also had a strong first-flush dependence. The trace metal data provide important insight into urban highways as an environmental source of heavy metals.