T.F. Green Airport completed an $11 million overhaul of its 11-acre site, including the terminal, parking areas, apron and taxi lanes. Following the renovation, the airport experienced a welcome, albeit unanticipated, volume of business. Subsequently, land was annexed at the end of a runway to provide 1,000 additional parking spaces. The project was undertaken by HNTB Corporation, a national multiservice architectural and engineering firm.
Runoff from this impervious site discharges into a freshwater wetland area, and is subject to stormwater quality standards administered by the Rhode Island Department of Environmental Management. The regulations call for 80% removal of total suspended solids a challenging goal on a heavily trafficked parking lot that includes long-term automobile parking.
The seven acres of impervious surface in the parking area alone would produce a two year design storm flow rate of 17.7 cfs. Originally, drainage plans called for five small-capacity stormwater treatment tanks placed throughout the large area to meet the strict water quality requirement. Because of the number of units and resulting complex pipe layout, these systems carried a hefty price tag.
Gilbane Building Company, in conjunction with site contractor Cardi Corporation, sought out a more cost- effective stormwater treatment option. Acting upon a suggestion from the Rhode Island Airport Corporation, the contractors contacted Contech to investigate replacing the five tanks with a single Vortechs System model 11000, which treats a much wider range of storm events.
The proposal was submitted to HNTB project engineer Marc Caufield, who agreed the arrangement would meet or exceed regulations, and quickly approved the modified plan.
The revised plan greatly reduced the amount and size of pipe required to provide proper drainage, ultimately saving the contractors substantial labor costs. In addition, the client saved approximately $100,000 in product and installation costs. At the same time, superior treatment capacity and high pollutant removal efficiency was provided at the environmentally sensitive site.