Master of Science in Civil Engineering (MSCE)
Civil and Environmental Engineering
In urban environments, anthropogenic activity deposits potentially hazardous residuals onto impervious surfaces. To investigate the process of wet-weather constituent transport, twelve rainfall/runoff events collected at an experimental catchment site in Baton Rouge, Louisiana were analyzed for temporal delivery of aggregate constituents (SSC, COD, TDS) as well as dissolved and particulate-bound metal concentrations (Cd, Cu, Pb and Zn). Event mean concentrations for the parameters analyzed often exceeded USEPA discharge limits. Rainfall-runoff events were characterized as either mass-limited or flow-limited. Events designated as mass-limited exhibited a high runoff volume, low vehicle to volume ratio (VPV), high stream power and a low correlation between aggregate constituent pollutographs and event hydrographs. Mass-limited events transported aggregate constituents and metal loads with disproportionate delivery as compared to the hydrograph, frequently exhibiting a classic concentration based first flush (CBFF). The remaining events were designated as flow-limited, typically producing a proportionate delivery of aggregate and metal constituent mass throughout the event. When investigating the average delivery of all aggregate and metal constituents analyzed in this study, approximately 80% of the total load was transported in the initial 74% of the total flow, irrespective of flow designation, constituent type and phase association (particulate-bound versus aqueous). Such results suggest that control strategies designed to treat the initial portion or first flush of an event are inadequate with respect to control of constituent loads (such as the common designation of the first 20% of a rainfall-runoff event). Utilizing water quality analyses, measured ion balances and a speciation model, results for Cd and Zn indicated that divalent ionic forms of these metals dominated the dissolved species for all events. Pb was predominately associated with dissolved organic matter (DOM) while Cu was predominately associated with carbonate species or DOM. Examination of aqueous speciation and partitioning of these metal elements transported in urban rainfall-runoff events is critical when evaluating the potential fate, control and bioavailablity of such constituents. Results from this study indicate that effective control of storm water metal elements require physico-chemical mechanisms that account for the ionic, complexed and particulate-bound species as well as the hydrology at the upper end of the urban watershed.
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Dean, Christopher Michael, "The interaction between hydrology and water quality for urban rainfall-runoff: implications for management strategies" (2002). LSU Master's Theses. 560.
John J. Sansalone