Combined Sewer Overflows (CSO)

What is a CSO?

CSOs (Combined Sewer Overflow), also known as regulators are used in sewer systems that not only take in sewage but also take in the storm water from the basins in the street. These types of systems are known as combined systems. In a heavy rain event a combined system can become surcharged.   To reduce the excess flow and to prevent possible damage to homes and sewer systems, regulators are designed to open at a predetermined level of flow and discharge the excess flow to a river or stream. Once the flow has reduced the   regulator closes and all flow is directed back into the sanitary system. The Scranton wastewater collection system is over 2/3 a combined system and   uses two different types of regulators, Type I and Type II.

Type I Regulators

The first type of regulator is the Type I regulator. These regulators employ 3 or 4 separate chambers, each serving a different purpose. The picture below shows the Type I schematic. The first chamber called the baffle chamber, employs a concrete baffle for flow energy dissipation. This chamber is only employed at very large Type I regulator installations. The second chamber,   or diversion chamber, is where the first step in flow regulation occurs. During dry weather, all sanitary flow is diverted to a third chamber, the   regulator chamber. During wet weather, only the projected dry weather sanitary flowrate plus a margin of about 25 percent is diverted to the regulator chamber, by means of a diversion weir located within the diversion chamber, while the rest of the flow overflows the weir into a fourth chamber, the tide gate chamber, then into the receiving stream. The tide gate provides backflow prevention, in event of high river conditions.




Type II Regulator

The diversion weir regulators, designed as “Type II” regulators are much simpler in design relative to the Type I regulators and are employed at locations that yield lower combined flows. The picture below shows the Type II   schematic. There are 40 of the Type II regulators which employ one or two chambers in the Scranton sewer system. The first chamber, the diversion chamber, is very similar to the Type I regulator diversion chamber. The Type II diversion chamber utilizes a diversion weir as in the Type I regulator, and also employs a sluice gate in front of the regulated flow pipe for manual flow control setting. The other chamber, not included in all Type II regulators, is the tide gate chamber which houses the tide gate in the same fashion as in the Type I regulator. Many of the Type II regulators do not have tide gates because they are located at elevations above the typical high river or stream flow stages.




How do you identify a CSO?

All Combined Sewer Overflows in the Scranton/Dunmore area have a sign near the discharge pipe to the river or stream that has the CSO number on it. If you see a discharge to a stream or river near one of these signs please report it by calling 570-348-5337. Customers can also call our Customer Service Center at 1-800-565-7292, M-F, 7 a.m. - 7 p.m. For emergencies, we're available 24/7 at this number.

CSO Locations

Kane CSO Locations
McKeesport/Portvue CSO Locations
Duquesne CSO Locations
Dravosburg CSO Locations


Pennsylvania American Water's Scranton wastewater operations have adopted local ordinances to ensure that all commercial/industrial waste dischargers into the sewer system meet approved limits. In addition to adoption of local restrictions on the characteristics of wastewater, we are also required to abide by factors set forth by the Code of Federal Regulations specifically, 40 CFR Part 403 that outlines the National Pretreatment Program for non-domestic discharges. To accomplish this task, the Pennsylvania American Water follows the federal guidance in classifying Industrial Users. The EPA defines an Industrial User as an industry that:

1.  Is considered a categorical user, defined by EPA or:

2.  Any non categorical user that:

  • Discharges 25,000 gallons per day of process wastewater or,
  • Contributes a process stream which makes up five percent or more of the average dry weather hydraulic or organic capacity of the treatment plant or,
  • Has a reasonable potential, in the opinion of the Scranton Wastewater Operations, to adversely affect the treatment plant


If you have any questions regarding the Municipal Industrial Pretreatment Program (MIPP) or any Industrial User related questions, please contact our Customer Service Center, M-F, 7 a.m. - 7 p.m. at 1-800-565-7292.