Underground storage is part of MSD’s endeavor to prevent wastewater from overflowing into Louisville’s waterways. The Portland Combined Sewer Overflow (CSO) Basin is the last of 10 basins contained in MSD’s Consent Decree. The 10 basins provide a total storage capacity of nearly 195 million gallons, protecting our local waterways and public health and safety. MSD’s Waterway Protection Tunnel, which is under construction, will add another 55 million gallons of storage capacity.
The MSD Portland CSO Basin sits under a restored grassy lawn in Lannan Memorial Park. When it rains, the basin is hard at work protecting the Ohio River and the neighborhood from combined sewer overflows.
Rainwater enters the combined sewer system through stormwater pipes and catch basins. This added water can overwhelm the sewer system sending a combination of wastewater and rainwater into the Ohio River. The Portland CSO Basin will capture and store 6.7 million gallons of wastewater and stormwater during rain events. The contents will gradually release back into the sewer system when treatment capacity is available. The mixture of rainwater and wastewater then flows through the sewer system to MSD’s Morris Forman Water Quality Treatment Center for proper treatment and release into the Ohio River. When the basin is empty, water is flushed through the structure to clean any remaining debris.
The basin, which is now complete, has a unique shape, as it is our only circular basin. It is also underground and invisible to the public. Above ground are a control building and parking area for MSD vehicles. The project replaced a gravel lot used by Louisville Metro Parks for storage. Surrounding and over the basin site, the gravel lot has been replaced by a grassy lawn and rain garden, which contains native plant species providing pollinator habitat. Other amenities from the basin project are a newly paved roadway—which has curves added to slow traffic—and a sidewalk connecting Northwestern Parkway with the park.