THE ROLE OF ANTHROPOGENIC HYDROLOGY ON THE TRANSPORT, PARTITIONING AND SOLID-PHASE DISTRIBUTION OF HEAVY METALS IN URBAN STORM WATER – IMPLICATIONS FOR TREATMENT

Storm water runoff, impacted by both urban transportation activities and associated urban transportation infrastructure, transports significant loads of dissolved, colloidal and suspended solids in a complex heterogeneous mixture that includes heavy metals, inorganic and organic compounds. Compared to drinking water and domestic wastewater, storm water treatment continues to pose uniquely difficult challenges due to the unsteady and stochastic nature of processes including traffic rainfall-runoff, heavy metal partitioning and transport of entrained solids. Urban storm water levels of Zn, Cu, Cd, Pb, Cr, and Ni are significantly above ambient background levels, and for many urban and transportation land uses often exceed surface water discharge criteria on an event basis for both dissolved and particulate-bound fractions. Storm water transports a wide gradation of particulate matter ranging in size from smaller than 1-μm to greater than 10,000-μm. From both a water quality and treatment perspective, entrained solids having reactive sites and large surface-to-volume ratios mediate transport of heavy metals while serving as reservoirs for reactive constituents.Since storm water is complex phenomena with interactions between urban and traffic contaminant loadings, urban hydrology and storm water solid and aqueous chemistry; more than a single unit operation or process will be required for control, treatment or re-use. Viable treatment will likely require a combination of physical operations for particle separation and chemical processes focused on solute removal or conversion and finally, disinfection. These treatments will be applied for storm water source control and in-situ treatment (de-centralized) and for centralized treatment. Analogies for storm water treatment can be made with respect to the roles of de-centralized domestic wastewater treatment and centralized wastewater treatment in the USA. The environmental and ecological stakes are just as great in this upcoming storm water treatment debate. The reality is both de-centralized and centralized storm water treatment will be developed and will require application of unit operations and processes. With respect to unit operation and process treatment design, storm water can be separated into particulate-based separation and solute-based removal or conversion.