Location: Old Tappan, NJ
Application: Detention
Number of Basins: 3
Product Used: 5′-3”, 6’-0’’ and 7’-0’’ DoubleTrap
Number of Pieces: 160, 123, 150
Total Water Stored: 139,487 cf
Foundation: Stone
Consulting Engineer: PS&S
General Contractor: HRP Construction
Installing Contractor: Esposito Construction
The 200 Old Tappan is a 19-acre mixed-use development in Bergen County, New Jersey. The proposed project consists of the construction of a multi-family apartment and a mixed-use building, 99 townhomes, and 21,000 sf retail area, as well as associated parking, residential access roadways, and associated infrastructure. With the site alterations, stormwater management systems were needed to comply with the local water quality and quantity regulations.
As a redevelopment project, surface stormwater facilities were not feasible to meet the project requirements. PS&S partnered with StormTrap to design three underground detention systems to reduce the stormwater runoff peak flows to pre-development conditions, as required by the NJDEP Stormwater Management Rules.
The challenges for this project included very limited areas for placing the stormwater management facilities due to layout requirements, site grading limitations, and the need to convey the runoff from the three basins to an existing downstream storm manhole within the municipal storm system via gravity.
“The invert out of the existing manhole was relatively high, so we had to set up the basins elevations carefully,” explained Gary Yin, P.E., Sr. Engineer at PS&S. The basins were built with 5′-3”, 6’-0’’ and 7’-0’’ DoubleTrap modular units with low cover. “Systems #2 and #3 also required to be watertight since we couldn’t lower the systems elevations.”
Two detention systems (#2 and #3) were installed under a lawn area between townhouse buildings. The other one (#1) was placed in the front of a multi-family building and is partially under the parking area. All the systems have an outlet control structure to properly manage runoff release and partially provide water quality treatment with the required extended detention time.
The installation was successfully completed in December 2021. The three basins together can store approximately 139,487 cf of water, and they “significantly increased the available area for redevelopment while accommodating the site constraints,” stated Yin.
