The Clean Water Plan is our blueprint for improving the water quality of our local waterways. See how we got to this point and what lies ahead in our journey to cleaner rivers.

Explore Timeline


The Allegheny County Sanitary Authority is created under the Pennsylvania Municipal Authorities Act to provide regional wastewater conveyance and treatment. Negotiations begin with local municipalities to join the ALCOSAN system.


ALCOSAN's system goes live. Until that time, all but 2% of sewage was delivered to our region's rivers and streams, with little or no treatment. Overflows from combined pipes (carrying both sewage and stormwater) during heavy rain and snow melt were built into the system.


The federal Water Pollution Control Act of 1948 is expanded and reorganized as the Clean Water Act, establishing a new regulatory structure for controlling water. ALCOSAN’s proactive planning beginning in the late 1960s results in compliance with new regulations by 1973.


ALCOSAN begins planning for requirements under the Clean Water Act and the U.S. Environmental Protection Agency's Combined Sewer Overflow (CSO) Policy.


After decades of discussion and planning, ALCOSAN signs its first consent decree to comply with the Clean Water Act, which gives ALCOSAN 18 years to repair broken sewer lines, reduce inflow and infiltration from streams and groundwater, reduce the frequency and volume of CSOs and eliminate overflows in the portions of the system with separate pipes for stormwater and wastewater.


ALCOSAN releases a $3.6 billion plan to the public. Municipalities express great concern that the cost to families and businesses is too great. Members of the public ask for the inclusion of green stormwater technology in meeting the Clean Water Act requirements. ALCOSAN also provides two other, more affordable options that partially meet regulatory requirements.


Faced with a legal deadline, ALCOSAN presents the required plan but asks the agencies for more time to make changes so the plan will be affordable and include green technologies. Based on the options provided, the regulatory agencies begin negotiations with the authority to create a plan that emphasizes water quality, adaptive management and affordability.

ALCOSAN begins its study of source controls.


ALCOSAN creates its Green Revitalization of Our Waterways (GROW) program to assist municipalities with funding and technical assistance for green infrastructure projects.


The regulatory agencies conclude negotiations, giving ALCOSAN until December 31, 2036 to complete the first phase of the Clean Water Plan, costing $2 billion, which will eliminate almost seven billion gallons of overflow every year. The process of inter-agency approval continues through 2019.

ALCOSAN also begins work on Controlling the Source, a science-based evaluation of all methods of source control. This evaluation will provide data to municipalities on where they can build projects that are cost-effective and are most beneficial to control overflows.


Planning concludes on plant expansion, conveyance system optimization, flow reduction studies and development of a preliminary design report.

ALCOSAN makes best faith effort to take ownership of 200 more miles of large, municipal-owned sewers and associated facilities in its service area.

Construction begins on plant expansion.


Construction begins on the second phase of plant expansion to 600 million gallons per day. Construction begins on the Ohio River tunnel segment.*

ALCOSAN will submit a revision to the Clean Water Plan that identifies projects necessary to control overflows from regionalized sewers.

*Projects subject to change


Plant expansion to 480 million gallons per day and 295 million gallons per day of secondary treatment is completed.

Plant expansion to 600 million gallons per day is completed and Ohio River tunnel work is completed.*

Construction begins on the Allegheny River tunnel segment.*

*Projects subject to change


Construction begins on the Monongahela River tunnel.*

Construction completed on the Allegheny River tunnel.*

Construction completed on the Monongahela River tunnel.* Regulators evaluate the effectiveness of the Clean Water Plan.

*Projects subject to change


ALCOSAN has embarked on a comprehensive, long-term Clean Water Plan that will improve water quality by significantly reducing overflows into the region's waterways.

View Clean Water Plan