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Inflow/Infiltration - What is Inflow / Infiltration (I / I)?
Inflow / Infiltration (I / I) is water that enters the sanitary sewer system through cracked pipes, leaky manholes, or improperly connected storm drains, down spouts, and pumps. Most inflow comes from storm water and most infiltration comes from groundwater. I / I affects the size of conveyance and treatment systems and, ultimately, the rate businesses and residents pay to operate and maintain them. Limiting I/I is important in order to maximize current capacity at our wastewater treatment facilities, to limit public health and safety problems, for environmental benefit, and to minimize the cost of treatment. If the system becomes overwhelmed, such as in a storm event, sewage can back up and cause potential overflows to the environment.
Inflow
- Surface water that enters the wastewater system from yard, roof, and footing drains, from cross-connections with storm drains, downspouts, and through holes in manhole covers.
- Inflow occurs as a result of storm events such as rainfall, snowfall, springs, or snow melt that contribute to excessive sewer flows.
- Inflow can also occur in sewer pipes or facilities that are subject to excessive sewage flows due to direct or indirect connections to a water body or operational inflows such as water system connections for sewer cleaning.
- Peak inflow can occur during heavy storm events when storm sewer systems are surcharged, resulting in hydraulic backups and local ponding.
Infiltration:
- Water enters sewer pipes (interceptors, collectors, manholes, or side sewers) through holes, breaks, joint failures, connection failures, and other openings.
- Infiltration quantities often exhibit seasonal variation. .
- The highest infiltration flows are observed following significant storm events or following prolonged periods of precipitation.
How do you find I/I?
While there are two general approaches to finding and dealing with I/I, there are a variety of methods to determine if and where the problems are located.
- Proactive Detection - If you are proactively looking to find I/I, before there is a problem, there are several tests that can be used to examine the condition and susceptibility of the sanitary sewer system for I/I. A few of these tests include:
- Smoke Testing: This method includes blowing smoke from a smoke bomb into a specific section of sewer pipe and observing and documenting where smoke exits.
- Depending on the specific circumstances, the exiting smoke can indicate the location of a broken pipe, manhole, catch basin, or where roof or foundation drains might be connected to the sewer system. This could show where infiltration or inflow might enter the sanitary sewer system.
- Dye Testing: By using a fluorizine dye, inappropriate connections can be determined.
- For instance, if a dye is introduced to a catch basin and the dye is then observed in the sanitary sewer downstream from that point, the evidence would indicate that that catch basin is directly connected to the sanitary sewer system.
- TV Inspection: Recording conditions using a TV camera within the pipes.
- TV cameras have been developed that can be slid down sanitary sewer lines and record a "movie picture" of the conditions that are found in that section of sewer.
- This can identify breaks, root intrusion, leaking water (especially infiltration from groundwater), and general deteriorating conditions.
- Estimates can be made for how much infiltration might occur from such leaks.
- Smoke Testing: This method includes blowing smoke from a smoke bomb into a specific section of sewer pipe and observing and documenting where smoke exits.