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With limited budgets for capital improvements, communities are being asked to treat wet weather wastewater flows well beyond the design capacities of their existing facilities. Plant operators must balance competing requirements to maximize treatment of wet weather flows while complying with dry weather-based effluent limits usually based on extreme low-flow conditions in the receiving stream. Alternative wet weather permitting that recognizes real-time conditions in the system could potentially save Indiana's CSO communities hundreds of millions of dollars of capital expense.

Wet weather permitting strategies are particularly because the State's 105 combined sewer communities have NPDES permits requiring them to maximize wet weather flow to and through their wastewater treatment facilities, and because Indiana does not currently have a practical method for permitting the wet weather portion of a WWTP's effluent. Moreover, they are important because they could help provide cost-effective treatment for wet weather flows.

This paper discusses alternative wet weather permitting strategies for regulating effluent quality from wastewater treatment plants (WWTPs) in Combined Sewer Overflow (CSO) communities. The alternative strategies were considered during the development of the Indianapolis CSO Long Term Control Plan (LTCP). The City considered several strategies (e.g., mass, seasonal and tiered limit strategies) used in other states, as well as a new approach referred to in the City's CSO LTCP as the “flow-proportional limit” strategy.

The paper also describes the wet weather treatment process and associated flow-proportional limit strategy recommended for the control of wet weather overflows at the 125 MGD Indianapolis Belmont Advanced Wastewater Treatment (AWT) plant.

The technology based treatment and flow proportional permitting strategies described in this paper and in the City's Combined Sewer Overflow Long Term Control Plan and Water Quality Report (April, 2001) are currently under negotiation between the City and U.S. EPA, and may be applicable to other CSO communities faced with a need to control wet weather discharges.

Document Type: Research Article


Publication date: 2002-01-01

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  • Proceedings of the Water Environment Federation is an archive of papers published in the proceedings of the annual Water Environment Federation® Technical Exhibition and Conference (WEFTEC® ) and specialty conferences held since the year 2000. These proceedings are not peer reviewed.

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