Stormwater Solutions Under the Surface

The Metropolitan Sewer District’s efforts will prevent harmful overflow and protect the Ohio River

By Julia Edinger

In a climate where severe weather events, like rainstorms, are repeatedly testing the existing infrastructure systems, it is vital to think about how cities can better protect the natural waterways of the region.

The Midwest has been struck by increasingly severe storms in recent years, making stormwater overflows more common. The water systems in Louisville, Kentucky have been undergoing improvements as a part of a long-term plan to improve their reliability and protect the Ohio River.

As a part of the larger effort to protect waterways, MSD has built a collection of underground storage basins and a tunnel.
Combined Sewer Overflows (CSO)

Louisville and Jefferson County’s Metropolitan Sewer District (MSD) have been moving toward a more controlled infrastructure system since 2005. The long-term plan has an estimated cost of $1.15 billion, and will be carried out through the year 2024.

The concern with combined sewer systems is that they can release stormwater and untreated wastewater into local waterways. Although MSD modified the sewers, heavy rain events can still overload the combined sewer systems and cause overflow into local streams and the Ohio River.

As a part of the larger effort of MSD to prevent sewage overflows into waterways, MSD has built a collection of underground storage basins and a tunnel. The project has been designed and implemented in order to benefit the community, both by revitalizing parts of land and by helping to protect ecosystems like the Ohio River. The thoughtful design process resulted in a community grateful for the change.

Underground infrastructure helps mitigate risks to the existing green infrastructure and the wildlife that inhabits the area.

“The community has been highly supportive of the engineering marvel being built below our city,” stated Jacob L. Mathis, P.E., Engineer III of MSD.

With three basins and an impressive underground tunnel, the community in Jefferson County has reason to be excited about this development.

Building From the Underground Up

The project was unique in that so much of the building process took place underground. Additionally, a high level of community involvement improved the community impact.

For example, the construction of the Southwestern Parkway CSO Basin, known to the public as Shawnee Park Basin, took place in the Great Lawn of Shawnee Park. This could potentially disrupt activities, but as a result of the public outreach program and involvement with community stakeholders, no planned events in the park were interrupted. Furthermore, the operations building for the basin was buried under the park road to avoid deducting from the park’s recreational areas, making it predominantly invisible to the public. The project also allowed for new amenities at the park, including restrooms and a pavilion, improving the existing area for the community.

This basin is the largest underground CSO basin within MSD’s program, and due to a new strategy, MSD managed an impressive feat.

“This was MSD’s first time using Progressive Design-Build, which resulted in the project being delivered ahead of schedule and under budget,” explained Mathis.

The basins are part of MSD’s 20-year Integrated Overflow Abatement Plan to mitigate combined sewer overflows.

The Portland CSO Basin had a similar effect on the community, restoring the construction site and improving the area. This basin restored a previously unusable area of a park, transforming a gravel storage lot with a field into an extension of the park’s recreational space – in addition to adding a large rain garden for pretreatment and infiltration of run-off.

The most unique design feature of the Portland CSO Basin is that it is the only circular basin within the program. As such, the basin uses a central flushing system as opposed to measures used at the other sites. With the construction site being a former landfill, adjacent to both a park and an embankment levee, the process required meticulous planning.

The support of excavation used for the project was a concrete slurry diaphragm – a contrast from the traditional support of excavation – the design and measurements of which had to be planned with extreme care to prevent any movement of the embankment.

The Clifton Heights basin, alternatively, was located in a floodplain on a rocky site. The excavated rock helped to build a parking lot for Veterans Medical Center in Louisville. Building in a floodplain added the risk of floatation but, by anchoring concrete floors and walls with prestressed rebar anchors, the foundation was solid. The rocky site provided additional support in constructing the foundation, as it allowed a reduced wall thickness and provided savings on construction costs.

This basin, which opened in December of 2018, will store seven million gallons of wastewater and stormwater in times of heavy rain, gradually releasing it for treatment at MSD’s Water Quality Treatment Center. This basin will help to protect Beargrass Creek along with other waterways from noxious overflows.

A Tunnel’s Vision

The Waterway Protection Tunnel is an innovative resolution that replaced four of the planned CSO basins, acting as a comprehensive solution. This more cost-efficient method had public support behind it, as the tunnel had a lower construction disturbance to members of the community and a larger storage capacity.

At 200 feet below ground, the four-mile-long, 20-foot-wide tunnel is an engineering feat to behold.

Underground infrastructure helps mitigate risks to the existing green infrastructure and the wildlife that inhabits the area. Reducing environmental risk is central to a project aimed at protecting the important ecosystems of the Ohio River.

“Since the tunnel is 18 stories below ground, the project was able to avoid impacts to wetlands and endangered species’ habitat,” Mathis explained. “The Waterway Protection Tunnel will be the final project under MSD’s Consent Decree Long-Term Control Plan to mitigate combined sewer overflows.”

At about 200 feet below ground, the four-mile- long, 20-foot-wide tunnel is an engineering feat to behold. The excavation of two 33-foot-wide shafts at a depth of 200-feet permitted the boring machine’s insertion and assembly underground.

The basins’ construction allowed for improved parks and restored areas of land for the community.
Progress Underneath the Surface

While much of the recent construction has remained invisible and out of the public eye, the progress is evident to the community nonetheless.

The basins in this project resulted in improvement of recreational areas within parks, as well as the hidden benefit of improved water infrastructure systems underground. MSD predicts a greatly reduced CSO volume in a typical year; and the larger endeavor to keep the waterways clean will endure.

Creeks and waterways are a vital part of the environment; these waterways host a diverse collection of species of wildlife, from plants to animals. Protecting these habitats should be a guiding factor in the prioritization and design of new stormwater and wastewater infrastructure developments.

Julia Edinger is an Assistant Editor for American Infrastructure Magazine. She can be reached at

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