LEED-certified outlet stores center benefits from underground chamber system
When Tanger Factory Outlet Centers Inc., known for its outlet shopping locations, embarked on the redevelopment of its center in Bluffton, S.C., the company employed Ward Edwards Inc. to oversee the engineering aspects of the project. Redesigning the existing storm water management system was at the top of a to-do list for the Ward Edwards engineers, who had to find a modern solution to replace a network of detention ponds constructed 20 to 30 years ago.
“There were no records to show the design of the existing storm water system, so we designed the replacement detention and water quality system to make the post-redevelopment discharge rate less than a pre-development rate,” said Willy Powell, P.E. with Ward Edwards.
The 177,000-sq-ft center, consisting of four buildings, is located on a 20-acre site. The redesigned center also features about 1,000 parking spaces, so taking up land with an aboveground storm water solution was an issue. According to Powell, had the engineers used an aboveground stormwater system, they would have lost about 10 to 15%, or two to three acres, of the development area. To maximize the development area, the engineers chose an underground chamber system provided by Cultec Inc. As the groundwater level was high—four to five feet deep—the company’s lower-profile Recharger 150 HD was considered the best fit for the site. The chamber is 33 in. wide, 18.5 in. tall and works well for installations with depth restrictions.
“The new storm water system had to accommodate a large volume of runoff because we are located in a hurricane-prone county. We also needed to avoid increasing discharge into the adjacent wetland,” said Carl Close, project manager with Tanger Outlet Centers. “Cultec’s system gave us the needed storage capacity and, at the same time, fit in the tight space allowed by the high water table.”
Designed to handle a 25-year storm event as required by the local regulations, Cultec’s system offers 168,958 cu ft of storage and operates in conjunction with two bio-retention swales that drain the runoff into the chambers. The chamber system then discharges runoff to a wetland located to the west of the site. The high groundwater did not allow for infiltration, so the open-bottom chamber system functions as a detention solution.
The system included 4,402 units of the Recharger 150 HD installed in eight beds under the parking area, which featured both impervious and pervious surfaces in a ratio of 2:1. The inlets were equipped with Trash Guard screens to ensure that debris-free runoff enters the detention system.
According to the engineer, the system became the solution for the project due to ease of installation. Cultec employed its own in-line side portal manifold, eliminating the need for a costly external pipe header. Such a system was easier to install than a conventional manifold system and was also more cost-effective. Additionally, the system used less stone than other comparable systems on the market and required no heavy installation equipment.
“The system went together so easily and without the need of any specialty tools,” confirmed Close.
The redesigned center is the first LEED-certified retail location in the state, and the storm water system contributed points to earn this recognition based on the following credits: SS Credit 6.1: Stormwater Design: Quantity Control and SS Credit 6.2: Stormwater Design: Quality Control.