Hydrodynamic Separators Improve Runoff Quality for Ohio Highway Project
Running through a central business district of Columbus, Ohio’s largest city, the Interstate-70/Interstate-71 interchange is a 2-mile stretch of highway that is undergoing a $1.5-billion, multi-year modernization to reduce congestion, reduce crashes, increase aesthetics and reduce its environmental impact. Phase 2B of the project was designed to improve the quality of storm water runoff coming from the interchange and separate the runoff from the city’s combined sewer.
Phase 2B required treatment of 75 cu ft per second of runoff. A manufacturer approved on the Ohio Department of Transportation’s (ODOT) Qualified Products List for Manufactured Water Quality Structures was to provide treatment. Contech Engineered Solutions is one of four approved manufacturers. This phase was treated similarly to a design-build project, so neither the design engineer nor ODOT gave design pre-approvals; it was up to the contractor and manufacturer to supply a solution that met project specifications.
Challenges associated with the project included designing a system to fit within a predetermined footprint, as well as determining the most cost-effective way to provide treatment in accordance with scaling for ODOT’s treatment performance criteria.
To meet all of these requirements, Contech proposed a system consisting of four 10-ft-diameter CDS hydrodynamic separators. The separators use continuous deflective separation—a combination of swirl concentration and indirect screening—to screen, separate, and trap debris, sediment, and hydrocarbons from storm water runoff. Each unit is approximately 25 ft deep. A precast diversion box splits the flow to each unit. Treated flow from each unit discharges to a precast vault before being discharged to the storm conveyance system.
Installation occurred in two phases: the CDS manhole sections and the internals. First, the manholes were installed; each consisted of a base slab, three barrel/riser sections and a top slab. A Contech representative then installed the fiberglass internals and screen. The manufacturer provided installation oversight and guidance to the contractor throughout the entire installation process of the units. With the installation of these units, storm water from the freeway is no longer connected to the city’s combined sewer. Instead, freeway storm water is treated with the CDS units before flowing into the nearby Scioto River.
