Wastewater Inflow & Infiltration

know your flows

Inflow & Infiltration (I&) in your wastewater / sanitary sewer collection system increases the influent flow to the treatment plant. Worse yet, I&I adds otherwise clean ground or stormwater to the collection system that otherwise wouldn’t need to be treated; but since it’s mixed with wastewater, it all gets treated just the same. And, if there’s enough I&I in a system during wet weather, some really bad stuff can happen. Raw sewage back-ups and overflows can occur, releasing potential pathogens into homes, streets, and waterways. This brings public and environmental health risks, liability, and fines from state and federal environmental agencies, along with shortening the capacity and permit life of your treatment plant [we warned you it was bad!].

so what is I&I exactly?

I&I is simply water that enters your collection system through non-sanitary fixtures (toilets, showers, sinks, etc.). I&I breaks down into its two primary cause categories: inflow – rain and stormwater entering the collection system; and infiltration – groundwater entering the collection system.

causes of I&I:

a formidable opponent, but worth the fight

Identify and eliminate, sounds easy right? It’s not usually that simple. I&I can manifest in many ways and every system will be different, but that doesn’t mean you should give up. Understanding the complex challenges is the first step to overcoming them.

First, know that all systems (even new) have some level of I&I and that’s ok. Low levels of I&I won’t hurt and the quest for zero I&I would be a foolish one. Evaluating flow and weather data, along with staff input, should tell you if you have excessive I&I in your collection system.

Second, no one can guarantee I&I reductions. Collection systems are complex, data on them can be far from complete, and water will always seek the path of least resistance. So if a problem on 1st street is corrected, there’s no way to predict if the same problem could occur at 2nd street, until after the correction. You could feel like you’re trapped in a budget blowing game of Whack-A-Mole.

So with all the challenges facing I&I, we can certainly understand why many do not budget towards fighting it. Instant needs and guaranteed solution projects take priority. However, if I&I is left untreated, it could lead to the instant need to fund a plant upgrade, because influent flows are exceeding permit and design capacity. We approach the I&I battle as a long-term maintenance program, rather than a project. Just like changing the oil in your car, you shouldn’t worry if you miss or delay the occasional one or two, but if you never do it, you’ll soon be looking for a new ride.

see our I&I approach