Inflow/infiltration describes groundwater and stormwater that flows into a sanitary sewer system through leaky sewer lines and manholes, and from direct sources such as catch basins, roof drain connections and sump pump connections.

Inflow/infiltration increases the quantity of wastewater a municipality must treat, thus reducing the capacity of sewer lines, pumping stations and the wastewater treatment plant. This raises the cost of operating and maintaining wastewater infrastructure, and that cost is passed along to businesses and residences through rate hikes. By reducing capacity, inflow/infiltration also limits future sewer connections.

A successful program to address inflow/infiltration can save a municipality considerable money and resources. The goals of such a program typically include:

• Reducing the overall quantity of inflow/infiltration in the sanitary sewer system,
• Maintaining compliance with State Discharge Permits during wet weather flows,
• Reducing treatment costs and freeing up capacity at the wastewater treatment plant, and
• Improving reliability in the sewer system by eliminating surcharges and backups caused by excessive flows.

Inflow/Infiltration Gallery Click images to enlarge.

Powerful and even illumination of sewer line water infiltration

Severe water infiltration in 8" AC pipe

Crack in 8" terracotta mainline

8" terracotta mainline with inflow from leaking main

However, inflow/infiltration cannot be corrected until it is identified. Fortunately, environmental inspection specialists like Envirosight offer a wide range of tools designed to inspect pipelines and other wastewater infrastructure. Several common techniques are used to identify inflow/infiltration:

Sewer Camera Inspection involves sending a self-propelled, steerable camera crawler like Envirosight's ROVVER through sewer lines to observe and document conditions. Defects such as water infiltration, broken or cracked pipes, and root intrusion are easily detected with a professional-grade crawler like the Rovver.

House-to-house Inspection is the evaluation of a property's exterior and interior. An inspector checks for illegally connected roof, yard, driveway, basement and foundation drains, as well as sump pumps. These inspections typically take less than 10 minutes.

Manhole Inspections are performed using a pole-mounted zoom camera like Envirosight's patented QuickView to assess the condition of a manhole without the inspector ever entering it. QuickView reveals the presence or evidence of inflow/infiltration from the cover, cone, walls, joints, lift holes, pipe connections, steps, bench and trough.

Smoke Testing involves filling a sewer line with nontoxic, odorless smoke. Defects are identified where smoke is seen exiting the ground or other connection, such as a roof leader or yard drain. Improperly connected plumbing or drains inside a home can also be identified with smoke testing.

Once detected, inflow/infiltration can be corrected using any of several methods and technologies. Modern techniques allow for sewer lines to be inspected, cleaned and even replaced without traditional open-cut excavation. By utilizing trenchless technology, sewer rehabilitation and repair can often be performed without interruption of sewer service or disruption of traffic. Depending on the source, specific techniques exist to fix inflow/infiltration. For sewer lines, these techniques include:

• Manhole-to-manhole lining (cured-in-place, fold-and-form, slip or other),
• Pipe bursting,
• Dig-and-replace repair,
• Spot repairs using a sectional cured-in-place liner, and
• Spot repairs using dig-and-replace.

And for manholes, these techniques include:

• Exterior coating or grouting,
• Interior lining,
• Replacement,
• Inflow dish installation, and
• Raising or replacing the manhole cover and frame.

Inflow can also be corrected by disconnecting a directly connected source. Examples include:

• Disconnecting roof leaders, sump pumps, foundation drains and other illegal or improper connections from the sanitary sewer system,
• Encouraging the removal of private inflow sources through enforcement of state and local regulations and incentive programs,
• Raising manhole covers that are located in low areas where stormwater may pond, and
• Diverting stormwater that flows to manhole covers.

For more information on identifying and correcting inflow/infiltration, contact the video pipeline specialists at Envirosight today.

This technical paper excerpts text and images presented in a report entitled "Inflow and Infiltration: Overview and Summary, I/I Investigation and Removal" by the town of Mansfield, MA.