| Urban highway surfaces are sources of contaminants, such as metals, phosphorus, trash and debris, and oxygen demanding substances, in part, related to atmospheric deposition (Harned, 1988). Rainfall-runoff from urban highway surfaces often transports significant loads of pollutants in a complex heterogeneous mixture that includes particulate and dissolved solids, metals, phosphorus and organic compounds. Control of runoff particulate matter is challenging due to the variability in flow, variable particulate matter transport and, varying mass and concentration during a wet weather event as compared to conventional wastewater treatment loadings.;This study investigated physical indices of particulate matter delivered in source area rainfall-runoff as a function of hydrologic transport and quiescent settling on an event basis. Four mass and flow-limited events, whose volume and particulate load were fully-captured and recovered from settling tanks receiving runoff from a 1088 m2 paved urban watershed in Baton Rouge, LA, were analyzed. Results indicate that mass and flow-limited behavior results in separate particulate matter delivery and relationships which are transformed to a single particulate matter relationship after unit operations such as settling. While flashed from urban surface into storm water runoff and transferred to natural water body during a storm event, equilibrium partition of phosphorus, COD and metals in dissolved and particulate phase in urban rainfall-runoff was examined before and after 60 minutes of quiescent settling for both two classes of events. Phosphorus has a high partition in particulate phase and can be removed with solids by quiescent settling, metals can be partially removed by settling process but needs a further treatment in order to reach national recommended water quality criteria, and COD cannot be effectively removed by quiescent settling.;Granulometry, transport and solubility of dry deposition particles was investigated with a purpose of discovering the source and pathway of contaminants in rainfall-runoff from an urban highway land use. In addition, metal species bonded with dry deposition particles were examined and arithmetic mean concentration of metals across the entire size gradation was ranked as Cd < As < Cu < Pb < Zn < Mg < Fe < Ca constantly. Cumulative mass distributions (CMDs) of particulate matter, all modeled with a cumulative gamma distribution function, were translated a finer particle size gradation during the transport from dry deposition into rainfall-runoff, with D50m decreasing from 330.7 µm to 13.7 µm along the runoff stream.;The settling velocity is a key variable while studying the transport mechanism of particles throughout their entire pathways from dry deposition, carried into urban rainfall-runoff, and finally discharged to different water bodies. In this study, settling velocity of particles were measured as a function of salinity, particle size and suspended sediment concentration (SSC) to illustrate various scenarios of in situ particle delivery. Salinity was found to have no significant effect on settling velocity, while particle size and SSC were dominant effects in the particle transport. |
