Comparative zinc dynamics in Atlanta metropolitan region stream and streetrunoff

Zinc, major ion, and other trace metal (V,Cr, Co, Ni, Cu, Cd, and Pb) conce ntrations were measured within 172 street and stream runoff samples in the Atlanta metropolitan region and in relatively undeveloped watersheds within the Georgia Piedmont and Blue Ridge Provinces. Peachtree Creek draining a densely populated area of Atlanta, was the primary sampling location and sa mples were acquired under a wide range of hydrological conditions. Zinc con centrations within street runoff [median (Zn)(urban street runoff)=905 mug/ l] were significantly greater than zinc concentrations within storm runoff [median (Zn)(Peachtree Creek)=60 mug/l], which were, in turn, greater than zinc concentrations contaminants within non-storm runoff [median (Zn)(Peach tree Creek)= 14 mug/l]. Zinc concentrations were not significantly greater within urban base flow than within non-urban base flow, indicating that the primary source of pollution is "event water" or street runoff. Zinc :he on ly heavy metal present in greater than example of large-scale "background" concentrations (i.e., > 10 mug/l), which is likely the result of automotive pollution that is :present within the study area. Analysis of commonly fou nd in all storm alkalinity dilution trends indicate that simple mixing betw een polluted street runoff and ground-water cannot account for the zinc con centrations observed within storm and recession flows. A two end member mas s balance model suggests that a large proportion of the zinc present in the street runoff is adsorbed and transported on surfaces of the suspended sed iment. Adsorption is readily possible at the near neutral pH (similar to6.5 ) of turbid storm discharge.