TREATMENT OF ELEVATED HIGHWAY RUNOFF USING CLARIFICATION TECHNOLOGY

A significant portion of the world's population lives within 100-kilometers of a coastline, resulting in increased traffic and associated traffic-generated pollution, in particular heavy metals. Storm water runoff from roadways transports significant loads of these heavy metals and a wide gradation of particulate matter to receiving waters. Heavy metals, either in dissolved or particulate-bound phases, are not degraded in the coastal environment and as a result, constitute an important source of potentially acute and chronic toxic contaminants. Although NPDES Phase II legislation requires the implementation of a comprehensive storm water control program, full compliance is not required until March 2003. Consequently, highway runoff is currently discharged directly and without treatment to the surrounding environment. This is particularly true for the challenging conditions prevalent in the coastal regions of Louisiana, where inter-urban transportation infrastructures are frequently elevated over water. These difficult physical constraints are compounded further by the stochastic nature of storm events and associated runoff. These constraints have historically been prohibitive to the development of a viable treatment methodology for this waste stream. A passive treatment system, sorptive buoyant media clarifier (SBMC), adopted from in-situ adsorptive-filtration partial exfiltration trench systems was installed to treat storm water from an elevated section of eastbound Interstate 10 (eastbound average daily traffic count of 87,000) in Baton Rouge, Louisiana. Results indicate pollutant removal efficiencies approaching 95% on a mass basis could be realized for total suspended solids (TSS), turbidity and particulate-bound chemical oxygen demand (COD). Removal efficiencies were not affected by a highly variable influent composition or extended periods of non-operation between storms. Treatment capacity of the prototype system, at breakthrough, was measured at 1000 pore-volumes treated for storm water runoff. This study documents how the logistics of elevated highways over water, influence the treatment performance viability and operational design of a SBMC for storm water runoff from an elevated infrastructure.