Norristown Municipal Waste Authority



235 E. Airy Street, 2nd Flr
Norristown, PA 19401
Phone: 610-270-3190

Fax: 610-270-3192


Office hours (M/F):
8:00 A.M. to 4:00 P.M.

After Hours Emergency Number


Infiltration and Inflow

How a Sanitary Sewer System Works


A sanitary sewer system carries sewage (from sinks, toilets, showers/bath tubs, washing machines) from homes and businesses through privately-owned sewer laterals or pipes to publicly owned sewer mains, which are usually in the street, and then to the wastewater treatment plant located on East Washington Street (see diagram below).  The sewer mains and the wastewater treatment plant are owned and operated by the Authority.

A storm water sewer system carries rainwater from streets, parking lots, sidewalks, and roof leaders (or downspouts) to publicly owned sewer mains, which are owned and operated by the Municipality of Norristown and not the Authority.


Infiltration and Inflow


Norristown residents and businesses have an important role to play in improving our sanitary sewer system.


Without knowing it, many properties may be contributing to the flow of unwanted rainwater entering the sanitary sewer lines.  This extra flow may not seem like a major problem, but when Norristown experiences a heavy rainfall it can cause sewage to backup into homes or overflow manholes and run down our streets.


During heavy rainstorms large amounts of water, which is supposed to flow into the normally separate storm sewer system, instead often finds its way into the sanitary sewer system.  The technical term for this problem is Infiltration and Inflow or “I and I” and its source just may be your home.


Homes that have downspouts connected to the lateral are contributing Inflow by bringing rainwater directly into the sewer system.  Likewise, floor drains and sump pumps connected to the laterals are also sources of Inflow.  Even the curb vents or cleanouts in your yard or sidewalk may play a role.  If the vent is loose or lies below grade, rainwater can enter and flow into the sanitary sewer system (see the discussion under Sewer Vent and Cleanout Repairs).


Infiltration is a less obvious problem because its source is underground.  Tree roots can cause breaks or cracks in your lateral, allowing water in the ground to seep into the broken pipe.  Sections of sewer pipe under your yard or sidewalk may have separated over time, providing another way for water to enter into the sewer system.


Most people don’t realize how minor sources of I and I can add up to a major problem.  One or two downspouts connected to laterals may not seem like a big deal, but when downspouts from hundreds of homes are tied into the sewer system, they can create a major surge during a rainstorm.  And even if I and I is not having a direct impact on your property, it could be contributing to a sewer backup into your neighbor’s basement down the street.


I and I is not limited to private homes.  Public sewer mains also become broken and cracked, and rainwater can seep through the pipe as well as the joints in manholes.  So, the solution to I and I can only come through the efforts of both the Authority and the residents and businesses of Norristown.


This issue is more important now than ever.  The costs of operating the treatment plant are rising and are to a large extent dependent on the amount of sewage flowing through the facility.  As a result of I and I, it is not unusual for the flow during a heavy rainfall to be six or sever times the normal flow.  Higher flows from I and I mean higher operating costs, which in turn mean higher sewer rates……


So we need to start reducing Infiltration and Inflow NOW.  The Authority is currently involved in a multi-year program to televise all the public sewer mains in Norristown and to repair or replace those sewer mains and manholes in the worst condition.  When sanitary sewer improvement work is occurring in the Municipality, the Authority will normally provide a schedule and location of the work on its website so that residents and businesses can plan accordingly.


Sewer Vent and Cleanout Repairs


The Authority has begun a public safety program of repairing the sewer cleanout or vent on selected properties in the Municipality of Norristown.  Generally, the sewer cleanout or vent can be described as a capped pipe, which provides access to the sewer lateral connecting a home’s plumbing to the sewer main in the street.  If this cleanout or vent is not properly installed or maintained, it could permit rainwater to enter the sewer.


In an effort to address this problem, Authority personnel are installing, at no cost to the property owner, a yellow mechanical plug in the vent or cleanout (pictures of the top and side of the mechanical plug are shown below).  This plug is vented with a small hole to allow sewer gases to escape.  Please note that your home likely has sewer gas venting by way of roof and/or foundation vents as well.  The Authority personnel will place a door hanger on the property when the work is completed.  If you or your plumber need access to the vent or cleanout, the plug can be easily removed and reinserted.