Case Study: Making Stormwater Controls Fit the Project Site

Green space and parking areas at a Wilmington, N.C., housing development left little room for a stormwater detention pond, so engineers used a proven underground infiltration system.

New Brooklyn Homes at Taylor Estates consists of 12 multi-family buildings and a community building, creating 32 townhomes and 16 apartment units for rent. The 4.5-acre development site offers many onsite amenities, including ample parking, a picnic area with tables and a grill, sitting areas, and a playground. The design also retains several existing oak trees.

Taylor Estates is an affordable housing complex in Wilmington, N.C., built by the Wilmington Housing Authority. The agency in 2009 applied for Low Income Housing Tax Credits from the state's housing finance agency and received $6.7 million that it used to develop New Brooklyn Homes.

The design of newer development did not leave much room for engineers at ESP Associates in Cary, N.C., to install a detention pond to manage stormwater runoff. State regulations require developments to store and treat all stormwater runoff onsite. To comply, the engineers used a best management practice that was successful for Taylor Estates’ first construction phase – an underground infiltration chamber system from CULTEC.

According to Walter Kusek, a sales representative for the chamber company and president of Kusek and Associates, the installation of the initial systems went quickly and smoothly, contributing to the engineers’ decision to select the company’s product for the second project phase.

“We came up against two main challenges: the first was horizontal site constraints and the second was fitting the system onsite to accommodate the proposed buildings and a number of existing old oak trees,” said Terry Boylan, landscape architect with ESP Associates.

The engineers designed the system to retain and treat stormwater. The sandy soil was conducive for installation of an infiltration system, allowing stormwater to filter back into the ground, thereby removing pollutants from runoff and recharging groundwater. According to Kusek, this infiltration system might also detain stormwater 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 company technicians to select the best chamber for the project. The groundwater was deep enough to allow the use of one of the largest chambers, Recharger® 330XL, which is 30.5 inches high, 52 inches wide, and 8.5 feet long. It has a capacity of 7.5 cubic feet per linear foot. Each chamber holds nearly 475 gallons and provides a minimum of 80 cubic feet of storage per unit when surrounded in stone.

“It makes sense to select the tallest chamber possible because the larger the unit is, the less cost per cubic foot you get,” Kusek said.

The system, installed in five beds throughout the site, provided 24,100 cubic feet of storage. The beds had to be located at least 10 feet away from the foundations of the adjacent buildings and were concealed under 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 stormwater requirements.

This year, CULTEC marked 25 years since the company introduced its first plastic stormwater chamber. The second-generation, family-owned company was involved in excavation, building, and the precast concrete business in 1986, supplying, among other products, concrete leaching galleries. Company founder Robert DiTullio, Sr., developed the idea of a structurally sound plastic chamber after observing how heavy and labor-intensive galleries are. After a septic chamber was introduced to the market, the company saw the potential of the product in the stormwater industry.

Source: CULTEC