The Clean Water Plan also calls for ALCOSAN's North Side plant to expand. As a result, the current capacity of 250 million gallons per day will be increased to 480 million gallons per day by the end of 2025 and to 600 million gallons per day by the end of 2027. This additional capacity will assist with reducing the number of overflows caused by excess stormwater and groundwater entering the system.

Expanding the wet weather treatment capacity by optimizing and augmenting the existing plant facilities has long been a cornerstone in ALCOSAN’s strategy for reducing sewer overflows during wet weather. ALCOSAN’s strategy dates back to its 1996 Act 537 Plan which envisioned phased plant expansions and upgrades to support economic development and sewer overflow reduction.

Watch and Learn about how ALCOSAN is expanding the treatment processes for wet weather flows.

About the Expansion

The expansion of ALCOSAN’s treatment plant will be completed in two major phases.  Phase 1 was complete in 2005 and Phase 2 has an anticipated completion of 2027.

Phase 1

Phase 1 included the following:

  • Expansion of primary (physical) and secondary (biological) treatment capacities, 
  • Conversion of the gaseous chlorine disinfection system to safer liquid sodium hypochlorite,
  • Upgrading of the biosolids processing and handling facilities, 
  • Extensive odor control system upgrades, 
  • Various upgrades to the plant’s electrical system, and
  • Expansion of the treatment plant capacity from 200 mgd to 250 mgd. 

Phase 2

2 phases of plant expansion.


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ALCOSAN also completed major capital improvements at the plant to prepare for the implementation of the second phase of plant expansion. These improvements included the construction of new Operation and Maintenance facilities and the upgrading and expansion of the main pump station that lifts the wastewater from ALCOSAN’s deep tunnel conveyance system to the surface for treatment. 

Phase 2 of the Treatment Plant expansion focuses on wet weather treatment capacity to allow more sewage to be captured and treated, thereby reducing overflows during rain and snowmelt. 

Major projects include: 

  • Wet weather pump station – to provide 120 mgd of additional wet weather pumping capacity,
  • Wet weather preliminary treatment to provide for a preliminary treatment capacity of 600 mgd, 
  • Two additional primary sedimentation tanks to provide 600 mgd of capacity,
  • Two additional final settling tanks to boost secondary treatment capacity to 295 mgd,
  • New secondary treatment and wet weather treatment disinfection facilities using sodium hypochlorite and dechlorination to protect aquatic life in the Ohio River, and 
  • Construction of a new primary discharge outfall and utilizing the existing outfall for wet weather.

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Stormwater protection with native plants and gravel
ALCOSAN’s GROW Program Announcement

Grants available up to $10 million per project.

See Press Release for Details