Why Expand the Plant?

Expanding the wet weather treatment capacity by enlarging existing plant facilities has been a cornerstone in ALCOSAN’s strategy for reducing sewer overflows. This strategy dates to the 1996 Act 537 Plan which envisioned phased plant expansion and upgrades to reduce overflows.

As a result of expanding, the current capacity of 250 million gallons per day (mgd) will be increased to 480 mgd by the end of 2025 and to 600 mgd by the end of 2029. This additional capacity will help reduce the number of overflows caused by excess stormwater entering the system.

About the Plant Expansion Program

Construction for the current phase of ALCOSAN’s Plant Expansion Program has been under way since 2019.

The Plant Expansion Program has been broken down into several design and construction packages, so that the construction can be phased in a manageable and timely manner over the next decade. The packages include:

  • A new East Headworks facility, which will increase the plant’s preliminary treatment capacity to 600 mgd
  • Two new primary sedimentation tanks, which will increase the plant’s primary treatment capacity to 600 mgd
  • Two new final clarifiers, a new final disinfection tank, and a new outfall at the north end of the plant, which will increase secondary treatment capacity to 295 mgd
  • Reconfiguration of the existing disinfection tank and outfall, which will increase the plant’s wet weather capacity to 600 mgd
  • Various upgrades to the plant’s electrical system
  • A new Wet Weather Pump Station to convey 120 mgd from the Regional Tunnel System to the plant for treatment
2 phases of plant expansion.


Click image to download a larger map (PDF)

Plant Expansion Projects

Quick Links

Clean Water

Assistance Fund

Are You Eligible?
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