Trace Metal Variation in Atlanta Region Streamflow and Street Runoff
Ghazi, A. Mohamad
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Trace metal (Zn, V, Cr, Co, Ni, and Pb) and major ion concentrations were measured at 15 stream and three urban/suburban street locations within the Atlanta metropolitan region (AMR) and surrounding region. The primary focus of the study was Peachtree Creek, draining a populated area of Atlanta, and samples were acquired under a wide range of hydrological conditions (e.g. baseflow, stormflow and recession). Zinc was the most concentrated of all the metals within most of the 172 samples collected during the study. This is likely the result of automotive (tire) pollution and extensive use of zinc alloys. The other metals approached "background" concentrations (i.e. < 10 ppb) in most of the stream samples. Zinc concentrations within street runoff (median = 905 ppb) were significantly greater than within storm runoff (median = 60 ppb) which were in turn greater than non-storm runoff (median = 14 ppb). Metal and major ion concentration variability indicates "hysteresis" is occurring, where concentrations at a given discharge are not equivalent with respect to the rising and falling limb of the storm hydrograph. A simple endmember mixing calculation suggests that a large portion of the zinc washed into Peachtree Creek from street runoff is likely sorbed by the highly turbid runoff at near neutral storm water pH values.