John Rotondo, P.E.

When Tim Green, a managing partner with Commercial Real Estate Associates, began coordinating the construction of Aquia Park, a 12.65-acre commercial development, he faced two major issues: How could his company maximize space while providing storm water detention, and how could that system meet both quantity and quality considerations?

Through the project's engineer, Victor Amole of Vitech Engineering, Green found the answer with Rotondo Environmental Solutions LLC . Over an eight-day period, project manager Joe Bailey of W.C. Spratt directed the installation of the company's precast concrete open-bottomed storm water detention/infiltration system.

Underground efficiency

The system provides storage for approximately 193,000 cu ft of water and treatment for the water quality volume, and it meets groundwater recharge requirements. Throughout the U.S., shrinking land availability for building structures calls for the most efficient storm water treatment. Thus, developers wrestle with the decision of proprietary versus nonproprietary approaches.

"In this part of the country, we typically build ponds as storm water retention systems," Bailey said. Some property owners have to dedicate up to 20 percent of their land to pond systems. While detention ponds may cost less to install, there are other monetary factors to consider.

"You're trying to get every square foot of building and parking space out of the land you can," Bailey said. "The financial yield is much greater with underground systems. Storm water management ponds clog up… They are a maintenance nightmare."

Quality and Quantity

Aquia Park, flanked by Rte. 1 and I-95, includes wetlands and is located in the Chesapeake Bay Watershed. As such, Commercial Real Estate Associates had to address water quality and quantity controls. Several options were considered. One of these options was weak on infiltration concerns, while another was more expensive and did not allow for separation of water quality and quantity in the same area.

Because of the commercial and parking needs for the space, the design needed to be "creative" to allow for storm water management, water quantity, buildings and parking lots, and to meet landscape requirements. The Rotondo system was an "engineering fit," Amole said. "This county really doesn't like having the water treatment quality and quantity control the same area. However, we had to provide for two times the water quality volume for the site and contain that within 48 hours and release it to the ground."

The internal outlet control structure provides volumetric controls for the first inch of runoff storage volume at 48-hour hydraulic residence time and storm water detention for the 10-year flood with a one-year, 24-hour storage, Amole said.

Water quality control was achieved by constructing a 3-ft bed of surge stone underneath the precast units. Actual infiltration rates were used to size the trench bed area required for groundwater recharge volume while the one-year, 24-hour volume was stored in the void of the 3-ft gravel bed at the base of the precast units, Amole said. The flow rate exiting the structure was controlled by an internal precast outlet-control structure.

With the decision made and the designs complete, it was up to W.C. Spratt to do the installation. Bailey said putting everything together was "a breeze."