Location: Arlington Heights, IL
Application: Detention and Treatment
Product used: 5’-8’’ SingleTrap
Number of basins: 1
Number of pieces: 91
Total water storage: 58,836 cf
Owner: Arlington Heights School District 25
Consulting Engineer: Eriksson Engineering Associates, LTD.
Installing Contractor: Stark & Son Trenching Inc.
General Contractor: Nicholas & Associates
Project Details: Windsor Elementary School, located in Arlington Heights, IL, is expanding due to the increase in student enrollment over recent years. The renovation started soon after school ended and is scheduled to be finalized by the start of the 2017/2018 school year. Approximately 11,000 sf of new classrooms and a 7,000 sf gymnasium are being constructed, as well as new site amenities, including a reconfigured parking lot and poured-in-place rubber playground surface. Due to the addition of these new facilities, it was necessary to make site infrastructure improvements and provide additional stormwater management for the site. An underground stormwater management system was designed to meet project goals and satisfy the stormwater requirements of both the Village of Arlington Heights and The Metropolitan Water Reclamation District of Greater Chicago (MWRDGC).
Challenges: The project is located within the delineated combined sewer limits within the MWRDGC’s jurisdiction. Josh Cap, Design Engineer at Eriksson Engineering Associates, LTD., explains “due to the project being located within the limits of the MWRDGC’s combined sewer area we were responsible for designing infiltration based BMPs that are required to maintain a minimum separation of 3.5’ from the seasonal high groundwater table (SHGWT) to the bottom of the proposed infiltration practice.” A geotechnical report indicated a seasonal high groundwater elevation that ranged to as close as 8’(Elevation+/-669 MSL) from existing grade. Because of the limited available depth and the corresponding MWRDGC requirements, the stormwater detention system had to be water tight.
Solution: StormTrap worked with Eriksson Engineering Associates, LTD. to design the 1.35 acre-feet system, which was installed under the school soccer play field, so that it complied with MWRDGC stormwater regulations. The 5’-8’’ SingleTrap basin, composed of 91 precast pieces, was installed on a reinforced concrete foundation and is capable storing 58,836 cf of stormwater.
As an additional BMP measure to treat the runoff from the site and to meet water quality requirements, a SiteSaver, a hydrodynamic separator, was installed upstream of the outlet control structure as to alleviate long term maintenance concerns in regards to the restrictor orifice becoming clogged with larger debris. SiteSaver is composed of a disposable net, inclined pates, oil baffle, and collects trash, sediments, hydrocarbons and other impurities before the water is discharged to the municipal storm sewer. “We proposed the use of the SiteSaver as a substitute to make up and accommodate for the volume control (infiltration practices) that was unable to be provided on site due the high seasonal groundwater noted in the geotechnical report” clarifies Cap.
The StormTrap detention system, together with the SiteSaver treatment device, provided a flexible option to the owner to meet total water storage requirements and treat stormwater runoff on site, while providing a usable area above the system which will be utilized by the students for leisure.