Wet Weather Issues

When it rains or when snow melts, excess water can overload the sewer system resulting in sewage overflows into area creeks, streams and rivers. This flow also carries pollutants from untreated sewage as well as grit and debris found littered along roadways.

Combined Sewer Overflows (CSOs)
A combined sewer overflow (CSO) occurs when storm water and sewage, carried in a single pipe, overload the sewer system and flow untreated into rivers and streams. CSOs usually carry a variety of pollutants, including debris, chemicals, bacteria, and animal waste.

Correcting the sewage overflow problem is a priority for ALCOSAN and the 83 municipalities it serves. Under the United States Environmental Protection Agency’s Combined Sewer Overflow (CSO) Policy, combined sewer overflows as well as the pollutants discharged, must be controlled.  On January 23, 2008, a binding Consent Decree was approved in federal court in which ALCOSAN, under the mandate of the EPA, the Pennsylvania Department of Environmental Protection and the Allegheny County Health Department, agreed to a comprehensive plan to greatly reduce the annual discharge of untreated sewage into area waterways by 2026. 

ALCOSAN Draft Wet Weather Plan
In accordance to the federal Consent Decree, ALCOSAN released a draft Wet Weather Plan (WWP) on July 31, 2012  for public review and comment.  It provides a blueprint on how the region will adress federal regulations for sewer overflows and represents what will be the largest capital infrastructure project in the region's history. The public comment period runs from July 31 to October 19, 2012, and a final version of the Plan ill be submitted to regulators by January 30, 2013.  For complete WWP information including an electronic version of the Plan in its entirety, please visit our Wet Weather Plan page.

A Shared Responsibility
ALCOSAN, customer municipalities and homeowners can all play a significant role in addressing the problem of sewer overflows.  To learn what measures you can take as a homeowner to make an immediate and long-term impact on public health and the environment, please download our What Can You Do? brochure.

Sewer Overflow Advisories
The Allegheny County Health Department's CSO Alert Program and ALCOSAN's Sewer Overflow Advisory Key (SOAK) are complimentary advisory programs to warn the general public of possible river contamination from CSOs. While these programs do not prohibit or discourage river recreational activities, they do caution recreational users to limit contact with river water when boating, fishing, water skiing or engaging in other river recreational activities.

EPA Nine Minimum Controls
In the future, Combined Sewer Overflow (CSO) communities will be required to apply for and maintain NPDES permits. As a result, communities will also be required to implement what the EPA has identified as the nine minimum controls under a long term CSO control plan.

1. Proper operation and regular maintenance programs for the sewer system and CSO outfalls
2. Maximum use of the collection system for storage
3. Review and modification of pretreatment requirements to ensure that CSO impacts are minimized
4. Maximization of flow to the POTW (ALCOSAN plant) for treatment
5. Elimination of CSOs during dry weather
6. Control of solid and floatable materials in CSOs
7. Pollution prevention programs to reduce contaminants in CSOs
8. Adequate public notification of CSO occurrences and CSO impacts
9. Monitoring to effectively characterize CSO impacts and the efficacy of CSO controls

Rainfall Data
Quality-assured data is gathered from 33 rain gauges throughout Allegheny County and is combined with NEXRAD Radar data to create this comprehensive, realtime map located on the 3 Rivers Wet Weather Program site.
View Rainfall Data

Click on the above link to view rainfall data.  Creating a "New User" account will allow you to download rainfall data and save searches for future use.  (Please complete all fields. Individuals may use "home" in place of an organization.)  If you wish to view data without the ability to save or download, please select "Guest Login" and follow the instructions on the screen.

ALCOSAN System Mapping
To view detailed maps of the ALCOSAN conveyance and treatment system, including sanitary and combined sewer outfalls, outfalls in the regional collection system as reported by customer municipalities,  major water recreation areas in Allegheny County and continuous flowing streams and rivers listed as impaired by the Clean Water Act, please visit our System Mapping Page.