Peters Township Sanitary Authority
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3 Rivers Wet Weather Demonstration Project -- www.3Riverswetweather.org

 

 

 

 

 

Inflow and Infiltration

Inflow and infiltration (I/I) creates a major problem within the sanitary sewer collection, conveyance, and treatment system. I/I is the introduction of water, other than normal sanitary wastes, that is normally not present in the system such as rain and/or surface water from various sources.

Illegal Connections

Inflow is water that is directly connected to this system from roof drain leaders, driveway drains, foundation drains, and the like. This type of connection was more than likely intentionally performed. However, these types of connections to the sanitary sewer system are illegal.

Infiltration

Infiltration is the surface and ground water which leaks into the aging sewer lines. This occurs when the rainfall increases the ground water table to above the buried sewer lines. The sewers are at atmospheric pressure but the height of the increased water table creates a pressure which will force the water into the sewer through minor cracks and joints.

During a rainfall event, the quantity of the I/I will be many times the normal sewage flow. Frequently, during substantial rainfall events, the I/I will increase the flow to the treatment plant by a factor of ten. The sanitary sewers must carry this increased flow and the treatment plant must be capable of treating all that is delivered to it without creating a plant upset or degrading the plant effluent. Failure to do so will pollute streams and is a violation of State and Federal regulations.

Controlling Inflow / Infiltration

In order to handle the I/I, PTSA is forced to oversize both sewers and treatment plants. It is necessary for PTSA to continually try to control this I/I to avoid the additional capital expenditures required for ever increasing larger pipe and treatment plants. If left uncontrolled, I/I would result in an expensive and expansive construction project, thereby increasing the rates charged for service.

In an effort to control I/I, PTSA has been engaged in an extensive and expensive program to repair and/or enlarge its own sewer lines. This has and is being undertaken with only minor rate adjustments over the years. However, this alone will not be enough. Some engineering professionals estimate that as much as 80% of the I/I enters the system from private service laterals. These are the lines maintained by the homeowner that connect the dwelling to the main public sewer. The I/I enters the service laterals much the same way it enters the main sewers.

Inspection Ports

Inspection ports are now being installed on all new service laterals and on older service laterals as they become properly exposed. An inspection port is a six-inch pipe that extends from the service lateral to the ground surface and is installed at a point on the lateral, which is at or near the point of connection to the public sewer line. This inspection port permits the visual observation of the service lateral to observe for excess flow.