The city of Springfield, Ill., faced a number of problems with the storm water runoff that occurred at its public works garage facility. Primarily, runoff from the facility—particularly the city’s salt dome—introduced harmful pollutants into the sewer system, and the volume of water that was entering the sewer during rain events was causing frequent backups. To address these problems, the city teamed up with design firm Hanson Professional Services to create a bioswale and reuse solution that not only will address the health of the sewer system, but also provide a new water resource.
The bioswale captures storm water from the western half of the 5-acre site and filters it using engineered soil composed of topsoil, compost and wood mulch, planted with salt-resistant grass. The storm water from the east half of the site is pretreated in a hydrodynamic separator before being stored in underground tanks. The stored water then is fed through a prefilter, sand filter and chlorinator and stored in a 10,000-gal tank. Sewer-jetting trucks and street sweepers use the treated water in lieu of potable water; the system is expected to save the city 1.4 million gal of potable water per year.
Adding the storage tanks to the site created some issues.
“The largest challenge during construction was the excavation for the underground storage, which is 18 ft deep,” said Lee Bloome, P.E., water and sewer infrastructure engineer for Hanson. “In addition, the city’s public works garage facility is an active facility with equipment constantly being moved and raw materials stored on site. Equipment normally stored at the facility had to be moved to alternate sites, and the normal flow of traffic was altered during construction to keep the site safe.”
An Illinois Green Infrastructure Grant covered much of the project cost. Work on the project began in October 2014 and was completed in May 2015.