Urban stormwater retrofits require innovative solutions
Site redevelopments often require runoff treatment to comply with stormwater regulations. Urban sites are often the most challenging. Existing drainage systems may be undersized, shallow or non-existent. Soils may contain contamination or other limiting features.
What kind of solutions work with urban redevelopment properties? One case study examines such a site and the workable solutions within a downtown industrial region in Madison, Wisconsin.
When tasked with designing a stormwater solution on the Madison Water Utility’s urban site, we identified the various constraints. The site had high groundwater and a shallow storm sewer system. This limited the space for stormwater treatment or volume control. Furthermore, the presence of contaminated soils prohibited infiltration for the protection of groundwater.
An innovative solution solved the site’s unique problems. We designed an underground stormwater treatment vault to provide stormwater treatment through the removal of pollutants. The tank was assembled using pre-cast concrete modular units to handle buoyancy concerns. It was installed with a two-layer impermeable liner to prevent the surrounding contaminated groundwater from entering the tank.
The underground stormwater treatment removes sediment and other pollutants from stormwater runoff. The underground tank system can handle heavy vehicle loads and captures oil and grease from parked vehicles and on-site fueling through a baffle system. The shallow storm sewer system limited the site’s ability to provide needed active stormwater storage volume, so a rooftop garden was incorporated to reduce runoff volumes. As an added benefit, the rooftop garden satisfied the city’s greenspace requirement.
By identifying the constraints, we developed a workable solution that met multiple project requirements. The city now has a new water utility facility that is a showcase of innovative stormwater solutions.
READ MORE about this award winning project
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