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Underground system allows more space for buildings and amenities
After the Wilmington Housing Authority completed construction of the affordable housing complex Taylor Estates in Wilmington, N.C., it successfully applied for $6.7 million in Low Income Housing Tax Credits from the North Carolina Housing Finance Agency in 2009. That helped kick off the development of New Brooklyn Homes in spring 2010.
New Brooklyn Homes at Taylor Estates consists of 12 multi-family buildings and a community building, creating a total of 32 town homes and 16 apartment units for rent. The 4.5-acre development site offers many onsite amenities, including parking, a picnic area with tables and a grill, sitting areas and a playground. Additionally, the design of the housing complex retains a number of existing oak trees, preserving a touch of greenery for the benefit of the community.
These buildings and amenities did not leave much room for the engineers at ESP Associates in Cary, N.C., to install a detention pond to manage storm water runoff onsite. State regulations require developments to store and treat 100% of storm water runoff onsite. To comply, the engineers used a best management practice that had already proved to be an effective and successful method during the Taylor Estates’ first construction phase – a CULTEC underground infiltration chamber system.
The engineers designed the CULTEC system to retain and treat storm water at New Brooklyn Homes. The sandy soil was conducive for installation of an infiltration system, allowing storm water to infiltrate back into the ground, thus removing pollutants from runoff and recharging groundwater. The infiltration system might also detain storm water due to Wilmington’s low-elevated Coastal Plain location, which might cause chambers to hold water after a heavy rainfall.
ESP Senior Engineer Neal Kochis worked closely with CULTEC’s technicians to select the chamber that would be the best fit for Taylor West. The groundwater was deep enough to allow the use of one of CULTEC’s largest chambers, Recharger 330XL. The model is 30.5 in. high, 52 in. wide and 8.5 ft long and has a capacity of 7.5 cu ft per linear ft. Each chamber holds nearly 475 gal and provides a minimum of 80 cu ft of storage per unit when surrounded in stone.
The CULTEC system provided 24,100 cu ft of storage and was installed in five beds throughout the site, occupying the total area of 11,500 sq ft. The beds had to be located at least 10 ft away from the foundations of the adjacent buildings and were concealed underneath grassy areas, a playground, parking lots and driveways.
While hidden from sight, the underground system allowed engineers to use the space above the chambers for other uses while satisfying federal and state storm water requirements. CULTEC’s solution now works to capture high-volume runoff and infiltrate it into the ground, eliminating pollutants and preventing groundwater contamination.