To support Louisville/Jefferson County Metropolitan Sewer District’s (MSD) Consent Decree program, STV provided geotechnical field exploration and construction observation services for the new 20-million-gallon Combined Sewer Overflow (CSO) basin beneath Shawnee Park. The 449-foot by 207-foot by 49-foot underground facility captures and stores untreated wastewater and stormwater during heavy rain events, reducing overflow into the Ohio River. Once sewer capacity becomes available, stored water is pumped back into the system for treatment –significantly improving long‑term water quality and system resilience.
What challenges did STV address?
The CSO basin required excavation, stability and uplift resistance solutions in complex geotechnical conditions beneath a historic public park. MSD needed to ensure the basin could safely withstand buoyancy forces, lateral earth pressures, and potential seepage risks while maintaining structural integrity during construction. Additional challenges included preventing groundwater migration, mitigating sand washouts and managing construction adjacent to active recreation areas.
What solutions did STV deliver?
STV performed seven soil test borings, rock coring, piezometer installation, and laboratory testing to evaluate soil strength and permeability. The team conducted geotechnical analyses for seepage, earth pressure, bearing capacity and buoyancy. During construction, STV reviewed submittals for sheet‑pile excavation support, backfill methods, pipe support capacity and auger‑cast pile installation. When voids developed from sand washout, STV performed additional borings and coordinated grouting to stabilize the structure. The resulting design features auger‑cast piles, tie-back‑anchored steel sheet pile walls and cast-in-place concrete walls on a robust mat foundation.
How does this project benefit the region?
The new basin is largely invisible to the public, preserving the character of Shawnee Park while significantly reducing untreated overflows to the Ohio River. It enhances local water quality, supports regulatory compliance, and strengthens MSD’s wastewater system’s resilience for decades to come.
Key stats and accolades
- 20 million‑gallon underground CSO basin
- 374 auger‑cast piles
- 21,000 cubic yards of concrete
- Built beneath historic Shawnee Park
