How to Reduce I&I with Manhole Rehabilitation

December 1, 2021

technician performing manhole rehabilitation.

How to Identify & Stop Inflow and Infiltration (I&I): Prevention and Mitigation Solutions

With aging and deteriorating sewer structures and collection systems, municipalities have to deal with a lot of potential issues. Inflow and infiltration is a common concern for old infrastructure. Unless treated, inflow and infiltration (I&I) can strain sanitary sewer treatment plants and lead to unplanned expenses for the municipality. Learn what I&I is, how you can identify warning signs like manhole leaking and discover manhole rehabilitation solutions to mitigate I&I.

What is inflow and infiltration (I&I)?

Inflow and infiltration, also known as I&I, occurs when groundwater and stormwater enter the sewer system. This excess water can cause collection systems to exceed capacity and lead to discharge of untreated wastewater, residential sewer backups and flooding.

What is the difference between infiltration and inflow?

Infiltration occurs when groundwater enters the collection system through cracks in pipes, manhole leaking through gaskets and seals and failed pipe joints and lateral gaskets. It is usually triggered by large storms or prolonged precipitation.

Inflow occurs when stormwater runoff or surface water enters the collection system through sump pumps and other pathways of least resistance including manhole covers, downspouts and chimney sections. Inflow is the result of heavy rainfall, snowfall and snow melt.

Why is inflow and infiltration a problem?

An overwhelming amount of inflow and groundwater infiltration in sewers has the potential to damage sewage pipe structures, manholes and residential homes from sump pump backups. In addition to the potential damages caused by I&I, it also strains wastewater treatment facilities and inflates costs for municipalities and residents. Clear water, or water that enters the sanitary sewer system through I&I, is not sewage water so it should not require treatment. However, because it is entering the sanitary sewer system it gets transported to the wastewater treatment facility to be unnecessarily treated. This results in higher costs for the utility and its customers. If I&I is not addressed, sanitary sewer pipes become unable to handle peak flow and need to be sized up. This type of pipeline project is extremely expensive and does not solve the root of the I&I problem.

How to check for I&I

Aging structures and collections systems experiencing manhole leaking provide easy access for clear water to enter the manhole through inflow and infiltration. To help prevent I&I, it is vital to schedule regular manhole inspections to evaluate drainage and identify joint leaks that may be contributing to the problem.

As part of HK Solutions' full range of inspection services, we offer CCTV and 3D manhole inspections that provide detailed scans of the interior surfaces of manholes. The cutting edge technology identifies deficiencies as small as 1 mm in size. Each scan is analyzed by a MACP certified inspector and the results are compiled in a report listing the identified defect by type and severity.

Another option to find inflow and infiltration in the sewer system is through smoke testing. Smoke testing is an efficient and cost effective way to locate and identify cracks and leaks causing infiltration problems in sewer systems. The process involves blowing air and smoke into the sanitary sewer system. Regardless of the depth, the smoke will fill up and eventually rise to the ground, identifying the location of a pipeline leak.

inflow infiltration pipeline inspection

How is inflow and infiltration in sewer systems measured?

To gather an accurate depiction of the impacts of inflow and infiltration, flow data must be consistently collected. This data is collected by monitoring the amount of flow in the collections system and comparing it against estimates for standard flow before I&I. Overall impact of inflow and infiltration can be monitored through measurement of sewer flows received at the wastewater treatment facility. If this is higher than what is expected of the collections system, then there is an issue with I&I and reduction solutions should be explored.

Once inflow and infiltration has been identified it is important to take steps to reduce the effects it has on the sanitary sewer system and treatment facility through mitigation and reduction techniques.

Inflow and Infiltration Reduction

When it comes to storm and groundwater infiltration in sewer systems, the most effective strategies to reduce I&I include proactive maintenance of the sanitary sewer system and acting quickly when issues are discovered. Fortunately, there are a few key manhole rehabilitation methods which can help with I&I.

Manhole Rehabilitation to Stop I&I Caused by Manhole Leaking

Manholes and sewer structures are susceptible to deterioration and aging, which can lead to easy access for I&I. Manhole rehabilitation is a great option to restore existing sewer structures and decrease the potential of inflow and infiltration, without the hassle of excavation.

Trenchless manhole restoration or rehabilitation is an ideal option for addressing inflow and infiltration in sewer systems. Trenchless solutions allow the leaking manholes to be repaired or restored without excavation. In turn, this limits disruptions to communities like the need to reroute traffic or turn off utilities.

It is always best to begin with a detailed manhole inspection prior to deploying a manhole rehabilitation solution. A team of experienced manhole rehabilitation contractors will analyze output from the inspection and complete assessment of the existing sewer structure. Once they determine deficiencies with the system, they will recommend a manhole rehabilitation solution. For systems which need manhole repairs but not a complete structural restoration, manhole rehabilitation services to reduce I&I include:

  • Mainline pipe joint and lateral connection grouting
  • Manhole barrel joint and pipe connection grouting
  • Manhole lining
  • Manhole chimney seal installations
  • Replacement of worn castings and covers with new units that have gasketed lids

These solutions seal the existing manhole and sewer structures so that groundwater and stormwater cannot make their way into the collections system.

Monoform™ & Monoform PLUS™ for Structural Manhole Rehabilitation

For manholes and other sewer structures which require full structural restoration to reduce I&I, HK Solutions Group turns to the Monoform™ and Monoform PLUS™ solutions.

Monoform™ Manhole Rehabilitation Solution for Inflow and Infiltration Reduction

Monoform™ is a manhole rehabilitation system which restores an existing manhole from within, using an ABS plastic forming system and ready mixed concrete. This solution is fully structural and offers the same performance specs as replacing the manhole entirely, but at a cost savings. When manhole leaking is leading to increased flow in the sanitary sewer system, Monoform is a great solution to mitigate I&I long-term.

Monoform PLUS™ for Manhole Leaking & Other I&I Issues

Overtime, manholes can be affected by corrosion and other symptoms of aging that lead to manhole leaking and I&I. The Monoform PLUS™ manhole rehab solution addresses high levels of H2S and associated corrosion by combining the traditional Monoform™ solution with an HDPE 100% corrosion resistant liner. Like traditional Monoform™, this process is trenchless and fully structural, so it is equivalent to a full manhole replacement.

Before and after image of manhole rehabilitation.

Benefits of Monoform™ & Monoform PLUS™

HK Solutions technicians perform manhole rehabilitation using Monoform™ and Monoform PLUS™ with confidence knowing they are providing clients with a trusted solution. Benefits include:

  1. Limited traffic and community disruptions
  2. Projects are typically completed within a few working days
  3. Fraction of replacement cost
  4. Engineered design-life equal to replacement
  5. No backfill compaction issues like those that can occur when replacing a manhole via excavation
  6. External sewer bypass pumping is not required.

Contact HK Solutions Group for I&I Reduction

Our expertise and innovation help us tackle the toughest jobs. Contact HK Solutions Group to learn more about our manhole inspections and manhole rehabilitation services and see how we can help you fight against inflow and infiltration in your collections systems. Contact us online or give us a call today at 515-283-0500.

photo of Matt Huston
Matt Huston

Matt’s expansive career spans 30 years working with trenchless, structural manhole rehabilitation technology to provide no-dig sewer solutions for industrial and municipal customers throughout the Midwest.

Over the years, Matt has been heavily involved with the Wisconsin Rural Water Association and Wisconsin Wastewater Operators’ Association, working his way through numerous committee positions to provide leadership to peers in the industry. He has also hosted impactful presentations for the associations outlining sewer system maintenance and structural manhole rehabilitation techniques.

Learn More About Matt