Improving Our Community Waterways Together

Integrated Overflow Abatement Plan (IOAP)

The vision of Louisville’s Overflow Abatement Plan Approach is to provide a long-term plan to control CSOs and unauthorized discharges in both the CSS and SSS.  Implementing the integrated program, known as the Integrated Overflow Abatement Plan (IOAP) is expected to improve water quality in both Louisville Metro streams and the Ohio River.  The expected water quality benefits of the IOAP include reductions in the peak levels of bacteria in the Ohio River and Beargrass Creek and a reduction in the number of days that bacteria levels exceed water quality standards during periods of wet weather.  Due to the smaller size of the Beargrass Creek watershed, and the greater percentage of pollutant loads contributed by overflows, the water quality improvements will be more noticeable in Beargrass Creek than in the Ohio River.  

Sewer overflow control is essential to improving water quality, specifically for bacteria, pathogens and in some cases dissolved oxygen and metals, and is an important component of an overall approach to meeting water quality standards.  Water quality monitoring and modeling clearly demonstrates that overflow control alone is not enough to consistently meet water quality standards.  In light of this challenge, MSD plans to use the IOAP as one of its key contributions to broader water quality improvement efforts in the community.  In particular, the IOAP will complement other wet weather and water quality programs managed by MSD and/or by other community partners.  The current complementary programs and efforts include; the Mayor’s Green City Initiative, the Partnership for a Green City, Louisville Metro’s Municipal Separate Storm Sewer System (MS4) stormwater permit, and initiatives of Jefferson County Public Schools (JCPS), private developers, and other entities.  

Driven by a values-based benefit-cost analysis, the IOAP reflects a balanced mix of green infrastructure and gray solutions to prevent and control sewer overflows.  “Green infrastructure” solutions include options such as vegetated roofs, rain gardens, rain barrels, porous pavement, and bioretention, while “gray” solutions include options such as storage, treatment, conveyance/transport, and sewer separation.  As a guiding principle, MSD’s IOAP has been developed based on front-end consideration of source control and green infrastructure.  This means that more traditional “gray” infrastructure in the IOAP has been sized after considering both (1) the anticipated flow-reduction benefits of programmatic and site-specific green infrastructure solutions and (2) the anticipated effectiveness of other source control approaches, including reduction of private sources of I/I.  

Green solutions in the IOAP will be implemented during the early phases of projects, to allow data to be gathered on the flow reduction benefits that occur.  Approximately 17 percent of the Final CSO LTCP budget is allocated to green infrastructure, and most of that is planned to support projects in the first six years of IOAP implementation.  Prior to the final design of supporting gray solutions, the actual flow reduction performance will be documented and compared against the estimated targets.  The final sizing of the gray solutions will then be based on actual documented performance of green infrastructure solutions, as well as any further green and source control investments justified by performance information.  Green infrastructure investments are estimated to reduce the initial costs of CSO gray infrastructure projects by $40 million; potential future savings could double or triple this amount.  

The IOAP is a response to a Consent Decree negotiated with EPA and KDEP.  As such, the IOAP will be a federally enforceable action plan for sewer overflow abatement.


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