Dissolved Oxygen Water Quality Standards for the Chicago Area Waterway System: Costs and Environmental Impacts of Compliance

The Metropolitan Water Reclamation District of Greater Chicago (District) manages the ChicagoArea Waterway System (CAWS), an engineered waterway system that is the receiving stream forthe District's largest water reclamation plants. The District operates in-stream aeration stations ona portion of the CAWS that has a dissolved oxygen (DO) water quality standard (WQS) of 4.0mg/L and sidestream aeration stations on a portion the waterway that has a 3.0 mg/L DO WQS On October 26, 2007, the Illinois Environmental Protection Agency (IEPA) presented proposedWQS for the CAWS to the Illinois Pollution Control Board after conducting a Use AttainabilityAnalysis (UAA) on the CAWS. The DO standard specified in the proposal is significantly morestringent than the current DO standard for the waterway.In establishing these uses and the associated criteria, IEPA did not address the effects ofintermittent low DO as a result of wet weather discharges, even though these effects wererecognized as being present in the UAA. This presentation will include continuous monitoring dataand receiving water quality modeling information that shows that wet weather discharges cause theDO to drop below the proposed criteria. District studies have identified that precipitation andduration of storm effects on low DO levels in the CAWS are well correlated. The magnitude,frequency and duration of these low DO conditions varies from location to location and storm to storm.This presentation will detail the capital, operating costs, energy footprint and resulting carbonfootprint associated with meeting the proposed DO standards on the CAWS and compare thecapital, operating costs, energy footprint and resulting carbon footprint of meeting an alternativeproposal which includes less stringent standards and allows for wet weather relief from the standards.