The construction of a new Maintenance-Repair-Operations (MRO) facility at the Nashville International Airport called for a new stormwater treatment system to meet local regulations that call for the removal of 80% Total Suspended Solids from stormwater runoff.
The main challenges of the site were the large drainage areas that generated flow rates of 33 cfs and 13 cfs from the new building's rooftop and the vast concrete apron surrounding the structure. Underground utilities and the karst topography were also elements of concern.
To treat the large volume of runoff, engineers from Garver U.S.A. designed a treatment train consisting of two Vortechs hydrodynamic separators and a dry detention pond. The two Vortex systems are 22’x33’ and 14’x21’. Vortechs is a hydrodynamic separator that combines swirl concentration and flow controls into a shallow treatment unit that traps and retains trash, debris, sediment, and hydrocarbons from stormwater runoff.
Vortechs systems are usually precast and delivered to a site in two pieces – a vault and a top slab. However, engineers determined it would be more cost effective to focus the pollutant capture into two centralized locations rather than dividing up the drainage areas and utilizing many structures. Because of the size of the two structures, the Vortechs systems were cast-in-place.
Contech personal worked with the contractor to ensure smooth construction of the two units. First, the concrete vault floor and walls were formed and poured. Next, all the materials to build the internals were placed inside. Then, the concrete ceiling was formed and poured. Once this was complete, the internals were bolted in place.
Because of curing times, the concrete vaults took several weeks to construct, but once the ceilings were poured and cured, the internals took just one day to install for each unit.