Envirosight’s newest poster details the causes of inflow and infiltration, or I&I. Inflow occurs when water from aboveground sources enters sewer systems through illegal or faulty connections or openings. Infiltration happens when stormwater seeps through cracks, joints or manholes into sewer pipes. Together, I&I consists of water that does not have to be treated but ends up in a treatment plant anyway. 

When sewer systems work, they’re largely invisible to the public. Wastewater flows, unseen, through pipes from homes, businesses and industries to treatment plants, where it is cleaned and returned to the environment. 

But standing pools of water and foul odor—signs a sewer is not functioning properly—are increasingly common.

Recognizing your collection system is suffering from inflow & infiltration (I&I) is the easy part, but identifying the problem areas and addressing them effectively is where the challenges come in.

It takes more than just general maintenance and repairs to make a real impact on the inflow and infiltration (I&I) entering your sewer collection system. Without a strategic, proactive approach to evaluating and addressing the costly issue, it can feel like an uphill battle.

Sewer laterals often don’t get much attention during regular CCTV inspections. Because homeowners are responsible for their care, they are frequently left off the usual schedule. This can leave a large portion of a collection system un-inspected, un-repaired and ready to cause problems. When laterals do end up on the docket, it’s usually for one of three reasons:

Inflow and infiltration (I&) is a risk in any waste system. Yet in regions with older infrastructure, groundwater and stormwater that enter a sewer system can account for as much as 50% of flow. The cost of this disruption should not be underestimated; in 2014 the EPA reported that wastewater collection and treatment expenses ranged from $2 to $5 per thousand gallons. An annual I&I volume of 150 million gallons would cost between $300,000 and $750,000 per year to transport and treat. Given that even small amounts translate into substantial costs, where should you draw the line on I&I? How much is too much?

Inflow and infiltration (I&I) can be a costly problem for many wastewater systems and pose major risks. How much do you know about inflow and infiltration? Take Envirosight’s Sewer IQ quiz to find out, then challenge your coworkers to beat your score.

When a sewer fails, the solution is seldom cheap or easy. Digging it up can be particularly costly, as well as disruptive to residential customers and road traffic. To avoid this, methods have emerged allowing sewers to be fixed without excavation. These methods are referred to collectively as “trenchless technologies.”

No two sewers pipes are alike. Many differ significantly in terms of size (both diameter and length), pipe material, effluent characteristics, service connections, soil composition and water table. Pipes also fail in different ways: they can crack, leak, settle, erode, corrode and collapse. These failures can be localized, or they can be pervasive. Moreover, the goal of rehabilitation can vary to include:

Like other civil infrastructure in the U.S., many of our sewer, storm and water lines are over 50 years old (BAFuture). One of the biggest issues facing underground infrastructure is corrosion. A study from NACE International estimates the annual direct cost of corrosion for the water and wastewater industry is $36 billion. This cost includes replacing extremely corroded lines; lost water from cracks and breaks; application of corrosion inhibitors, internal linings and external linings; external coatings and cathodic protection.

Manholes are a critical part of every sewer system as they provide necessary ventilation and an access point for cleaning and inspecting sewer lines. The EPA estimates that there are about twenty million manholes in the United States—one manhole for every 400 feet of pavement. Many of these manholes are seriously decayed or in need of immediate rehabilitation or replacement. Manholes generate a disproportionate amount of inflow and infiltration (I&I) and play a unique role in the structural integrity of roadways. From an operational standpoint, inflow and infiltration of groundwater reduces capacity of the collection system as a whole. From a structural standpoint, deterioration and corrosion within a manhole can cause cave-ins (Water World).