Location: Northbrook, IL
Application: Detention & Rainwater Harvesting
Product used: 10′ – 0” & 11’ – 4’’ DoubleTrap
Number of pieces: 861 Units/ 1722 Pieces
Total water storage: 1,033,503cf / 23.77+acre-ft/ 7,731,139 gal
Project Owner: The Village of Northbrook and Northbrook Park District
Green Infrastructure Partner: Metropolitan Water Reclamation District of Great Chicago (MWRD)
Project Engineer: Baxter & Woodman Consulting Engineers
General Contractor: V3 Companies of Illinois
Suburban Stormwater Facility Utilizes StormTrap DoubleTrap Solution For Detention Needs and Water Harvesting
The Village of Northbrook and its park district selected DoubleTrap for its efficiency in storage and timely installation
The village of Northbrook has been addressing flood damage within its boundaries since the early 1990s. The village, located 25 miles northwest of Chicago, currently serves a population of 33,170 and covers 13 square miles. Two major flooding events, first in 1982 and then in 1987, were the impetus for the village’s storm water management plan, first developed in 1993. During those flooding events, the village experienced 6.5“ and 7.75” rain events, respectively. Following the 1987 storm, 818 properties, or one in 12 properties in Northbrook, had experienced flood damage that required special debris pickup.
After additional flooding events—6.5” of rain in 2008 and 5.25” of rain in 2011—the village made moves to update its plan, reviewing proposed past projects and adding more. One major project on the village’s list was building a detention facility at Wescott Park, which is located within a subdivision. Originally that subdivision was built in the 1950s without any detention facilities and with storm sewers that were undersized compared to today’s standards, according to Kelly Hamill, director of public works for the village of Northbrook. Wescott Park was chosen as the site for the project as it was the only open space within the neighborhood.
Before the StormTrap system was installed, two to three blocks in the area would become impassable for emergency vehicles during flood events. In addition, 10 homes would have been affected by a 25-year storm event.
Design and Time Restraints
The village of Northbrook and its project engineer, Baxter & Woodman Consulting Engineers, chose to build an underground detention facility with StormTrap’s DoubleTrap solution because it provided the efficient storage needed within the short construction timeframe. This option also offered the ability to add green infrastructure to the project through a rainwater harvesting system. The project provides 25-year flood protection for all homes, eliminates the impact of a 10-year flooding event on the 10 homes previously affected and provides benefits to 83 other homes in the area.
Wescott Park, which includes two ballfields, is owned and heavily used by the Northbrook Park District. The park is also adjacent to Wescott Elementary School. “The (nearby) school uses the park as well, so having an option to preserve the current land use of the park was ideal. With an opportunity to improve the park amenities, that’s where the underground storage option with StormTrap came into play,” said Paul Siegfried, assistant water resources department manager at Baxter & Woodman Consulting Engineers. “It was the perfect solution for what the village wanted for the park.”
It was determined that the land available for a detention facility would be located solely on Park District property, and that construction would not impact the park’s south ballfield programming. The village of Northbrook and the Park District also agreed on an eight-month construction window so that the north ballfield would be unavailable for just one season. The study phase of the project began in the fall of 2014, and work began in March 2016.
Choosing a Storm Water Solution
The project team considered several options before selecting StormTrap. It needed a storage system that could provide a 23-acre-foot underground detention facility with minimum HS-20 loading, in case an emergency vehicle or truck drove over the storage system without knowing what was underneath. And because the team wanted the detention facility to drain via gravity, the height of the storage wall was limited to 10 feet.
It was determined plastic or resin systems wouldn’t work with the project’s height limitations. Cast-in-place concrete required structural engineering, and the curing times did not work within the eight-month construction window. A chamber with reinforced stone piers and walls would only offer 64 percent efficient storage, which would not work within the parameters of the project. Corrugated metal pipe raised concerns over durability, and there were limitations with the warranties that came with the products.
The project team decided to specify StormTrap’s DoubleTrap solution, which provided 93 percent efficient storage and a modular precast concrete system to meet the particular dimensions of the project. The StormTrap DoubleTrap does not rely on void space storage, and the product’s warranty stood out to the village from other options.
“[With] a lot of the other products we looked at, like the void space in the backfill and circular pipes, the storage efficiency was a little lower, and we had these very defined project limits,” Siegfried said. “Having a product like StormTrap available was the perfect fit for our project just because of the openness of the structure and the efficient nature of the storage.”
It was decided to build the system in two sub-sections, with a 11’4” system in the sump area to accommodate rainwater harvesting and 10” in the rest of the detention facility. Delivery of the more than 1,700 pieces for the system was limited during the day to avoid affecting pick-up and drop-off at the nearby school. “Their coordination and their scheduling with us went really well,” said Michael Famiglietti, director of construction for V3 Companies, the contractor on the project. “The StormTrap project managers were always very helpful, and the field support was helpful as well.”
In the system, 23.7 acre-feet of total water can be stored. The village of Northbrook will use the rainwater harvesting system to irrigate the ballfield or pump the sump area in order to use the full capacity of the detention facility. The harvested rainwater is filtered and treated with UV before it is used for irrigation or for other non-potable purposes, such as street cleaning.
Construction on the Wescott Park project was completed in November 2016. Famiglietti said he would recommend the StormTrap system in the future. “It maximizes the available area and provides a good, efficient storm water detention system,” he said. “From that standpoint, when we have an opportunity to recommend a new type of system in a new development, we’d certainly recommend it.”