Inflow and Infiltration: A Guide to Addressing Wastewater Treatment Plant Challenges

Wastewater systems play a vital role in public health and environmental protection. However, inflow and infiltration, often referred to as I&I, are persistent issues that can overwhelm these systems, leading to inefficiencies, environmental risks, and increased costs. Read on to better understand I&I, where it comes from, how to detect it, and the problems it causes. This guide will equip you with strategies to mitigate I&I’s impact on your city’s wastewater treatment plant.

What is inflow and infiltration (I&I) at a wastewater treatment plant?

Inflow and infiltration are terms used to describe unwanted water entering the sanitary sewer system from external sources. Wastewater treatment plants collect water from sewer systems connected to the city’s homes, businesses, and facilities. When excess water like stormwater and groundwater enters the system, it contributes to I&I, causing more challenges for the treatment facilities. I&I is a concern for municipalities because it causes the system capacity to exceed the influx of water from various sources, which, in return, requires more energy and raises costs or requires the cleaning of a higher quantity of water.

There is a difference between what is categorized as “inflow” and what is considered “infiltration.”

Inflow is the direct flow of stormwater or surface water into wastewater systems through improper connections. These can include roof downspouts, storm drains, and sump pumps. For example, rainwater from a misconnected roof downspout can surge into the sewer system during a storm, overwhelming its capacity.

Infiltration occurs when groundwater seeps into sewer systems through structural defects like cracks, deteriorated joints, or aging pipes. This type of intrusion is more subtle but can continuously strain infrastructure, especially in areas with high groundwater levels.

What are the sources of inflow and infiltration?

Sources of Inflow:

1. Improperly Connected Roof Downspouts: Stormwater from rooftops improperly connected to sanitary sewers.
2. Storm Drain Connections: When storm drains connect to sanitary sewers instead of stormwater systems.
3. Flooding and Manhole Entry: Floodwater can enter sanitary sewers through poorly sealed manhole covers.
4. Yard Drains or Sump Pumps: Homeowners may inadvertently or improperly connect sump pumps or yard drains to sewer systems.

Sources of Infiltration:

1. Aging Infrastructure: Cracked, broken, or offset pipes leak because of their physical damage.
2. Deteriorated Pipe Joints and Materials: Seals between pipe segments can fail over time.
3. Poorly Sealed Manhole Covers: Water can seep into sanitary sewers through inadequately sealed manholes.
4. High Groundwater Levels: In areas with high water tables, groundwater exerts pressure on buried sewer lines, increasing infiltration risk.

How can inflow and infiltration be detected?

Detecting I&I is a critical step in addressing the issue. Utilities use a combination of monitoring and inspection techniques to identify problem areas. There are three ways your city can start tracking I&I to understand better how it impacts the energy and efficiency of your wastewater treatment plant.

1. Monitoring Flow Rates

Monitoring flow rates is an important way to find problems with inflow and infiltration. By looking at flow data, sudden spikes during or after rain can show where extra water enters the system. Comparing dry and wet weather flow rates can also reveal differences that point to inflow and infiltration. This method helps identify trouble spots in the sewer system for further investigation.

2. Flow Monitoring Techniques

Flow monitoring techniques help detect problems in sewer systems caused by inflow and infiltration. Temporary or permanent flow meters are tools used to measure the amount and speed of water moving through sewer lines, which helps find unusual changes in flow. Hydraulic modeling is another method that simulates how water flows under different conditions. This allows utilities to see which parts of the system are most impacted by inflow and infiltration, making it easier to target repairs.

3. Inspection Methods

Inspection methods are important for finding problems in sewer systems caused by inflow and infiltration. CCTV inspections use cameras to inspect sewer lines and spot cracks, leaks, or bad connections. Smoke testing helps find unwanted openings by pumping non-toxic smoke into the system—the smoke shows where water might be getting in. Dye testing works by adding colored dye to storm drains or other areas to check if they are connected to the sewer system. Finally, groundwater level surveys measure how high the groundwater is, which can reveal spots where water might seep into the pipes.

What problems are caused by inflow and infiltration?

Unchecked I&I can lead to significant operational, environmental, and financial challenges for cities like yours.

I&I Operational Impacts

• Overloaded Treatment Plants: I&I can overwhelm wastewater treatment plants by the amount of excess water in the system. This extra water takes up space for actual wastewater, reducing the plant’s efficiency. In many cases, the overload becomes so severe that costly expansions to the treatment facility are needed to handle the increased flow.
• Increased Energy Costs: When I&I adds extra water to the system, it requires more energy to pump and process that water. This higher energy use drives up operating expenses, making the treatment process more expensive and less efficient over time.
• Higher Solids Disposal Costs: The additional water from I&I dilutes the wastewater, which makes treating it more difficult. This often requires extra steps to process the diluted solids, leading to higher costs for disposal and treatment.

System Damage

• Accelerated Wear and Tear: I&I puts extra strain on wastewater system equipment, such as pumps and treatment machinery. This constant overuse causes the equipment to wear out faster, shortening its lifespan and increasing the need for repairs or replacements. The added stress also raises maintenance costs and disrupts the system’s performance.
• Reduced Capacity for Wastewater: When excess water from I&I enters the sewer system, it takes up space for actual wastewater. This reduced capacity can lead to backups, overflows, and inefficiencies in the treatment process. As a result, the system becomes less effective at handling the wastewater it was designed for, causing further operational challenges.

Environmental and Compliance Issues

• Sanitary Sewer Overflows (SSOs): I&I can cause sanitary sewer overflows, where untreated wastewater escapes the system and enters the environment. These overflows contaminate rivers, lakes, and other water bodies, posing serious risks to public health and ecosystems. SSOs are a direct consequence of overloaded sewer systems that cannot handle the excess water from I&I.
• Regulatory Fines: When untreated wastewater from overflows is released into the environment, it often violates discharge permits and environmental regulations. This non-compliance can result in costly fines for municipalities and utilities. These penalties add financial strain and highlight the importance of addressing I&I to maintain regulatory standards.

Economic Costs

• Higher Maintenance Costs: I&I leads to frequent system failures and inefficiencies, significantly increasing maintenance costs. Constantly repairing damaged pipes, pumps, and other equipment strains budgets and resources, making managing the overall wastewater system more difficult.
• Costly Capacity Upgrades: Expanding infrastructure to compensate for the increase in capacity often becomes necessary. These upgrades, such as building larger pipes or treatment facilities, are expensive and time-consuming. However, many of these costs can be avoided by proactively managing and mitigating I&I issues.

If your city is facing these challenges, schedule a no-obligation facility assessment with our team to learn how to overcome these issues on time, on budget, and without change orders. Click here to learn more about all the water services Performance Services offers.

What are strategies to mitigate and prevent inflow and infiltration?

Addressing I&I involves a combination of infrastructure improvements, regulatory measures, and community engagement. Below is a six-point checklist to overcome these challenges.

1. Disconnect Improper Connections: Enforce regulations to disconnect downspouts, sump pumps, and other improper connections.
2. Implement Stormwater Management: Encourage practices like rain gardens, retention basins, and permeable surfaces to reduce runoff.
3. Replace Aging Infrastructure: Upgrade deteriorated pipes and manholes to seal potential entry points.
4. Trenchless Repair Techniques: To restore damaged pipes without extensive excavation, use methods like cured-in-place pipe (CIPP) lining.
5. Educate Property Owners: Inform the public about the impact of improper connections on wastewater systems.
6. Public Outreach Campaigns: Encourage residents to report suspected I&I issues and participate in mitigation efforts.

Conclusion

Inflow and infiltration are common challenges all wastewater treatment plants experience, but they can be effectively mitigated with proactive management. Municipalities can improve system efficiency, reduce costs, and ensure compliance with environmental regulations by identifying sources, employing modern detection methods, and implementing targeted mitigation strategies.

Contact us today if you think your municipality would benefit from a no-obligation facility assessment.