CONSTRUCTED WETLANDS FOR TREATING COMBINED SEWER OVERFLOWS: An Alternative Solution for Implementing the CSO Strategy

Finding practical and economical solutions to Indiana's CSO Strategy for addressing water quality standards in the waters of our State is a daunting task. Through a grant from IDEM in late 1998, the City of Elkhart has constructed an artificial wetland at a CSO outfall to capture and treat overflows prior to discharge into the Elkhart River. The project was constructed as a demonstration of an alternative to CSO separation while addressing improved in-stream water quality achieved through overflow minimization. Covering approximately ½ acre in a residential neighborhood in southeastern Elkhart, the CSO wetland's design and construction consists of three components: an ecology-based treatment system, a technology-based monitoring and analysis system, and an interactive public educational element. The treatment process consists of a) bar screen/sedimentation basin to remove grit and floatables, b) nearly 30 different species of native aquatic and transitional vegetation (all strategically planted for ecological competitive advantage), and c) a downflow drainage and collection system to enhance biological removal of dissolved organics and inorganics, dissolved metals, and suspended particulates. The CSO chamber is monitored continuously for flow rate using an automated flowmeter. An automatic sampler, linked to a rain gage and the flow meter, is used to capture first flush events as well as extended duration storm flows. Samples of the wetland's influent and effluent are analyzed to assess wetland performance. The wetland's water surface levels and the surcharge levels in the upstream sewer collection system are monitored with a remote telemetric signal received by the Wastewater Treatment Plant's SCADA system. The wetland is located adjacent to, and linked with, Elkhart's “River Greenway,” the existing river urban trail system. This encourages public interaction with the wetland. This interaction promotes education on water quality, benefits of natural systems and CSO impacts within the community. The wetland will be operated by the City of Elkhart, continually collecting and analyzing data over the next few years to assess the wetland's performance in relation to the State's CSO strategy goals.