A New Approach to Quantifying I&I

Your utility could benefit from a different approach to quantifying I&I and measuring success

A New Approach to Quantifying I&I

George Kurz

George Kurz knows inflow and infiltration, and he’s willing to help your utility, free of charge.

Kurz, P.E., DEE, is a consulting engineer with a specialty in I&I quantification and reduction. He has 29 years’ experience in municipal engineering focused on reducing overflows and designing rehabilitation projects to reduce I&I. He has performed contract work for JACOBS, ResourceTek, BWSC (Nashville, Tennessee) and JMT (Sparks, Maryland).

At the recent No-Dig conference in Chicago, he presented a paper: “Simple Tool for Operators to Quantify I&I, Detect Leaks & Measure Rehab Progress.” This paper was the most recent installment representing seven years of his personal research on measuring I&I in municipal systems and included measurements for every municipal NPDES permitted system (523) in the states of Tennessee and North Carolina.

Kurz says his study represents the first time I&I has been quantified for every municipal system in a state. Additionally, at the end of his presentation he offered to analyze a year’s worth of data for any municipal system in the U.S. and Canada — for free. Later, I caught up with Kurz to discuss his research.

I&I: I&I studies have been conducted ever since the implementation of the Clean Water Act in 1972. How does your research differ from that earlier work, and how does it benefit our industry? 

Kurz: That is correct, I&I studies were part of the 201 planning process (Section 201 of the Clean Water Act). Those early studies were generally conducted by engineering companies for individual municipal agencies needing funding for new facilities or expansion of existing facilities. Sometimes the results were published as articles or presented as papers for those individual systems. However, extensive compilations of the I&I results are not generally available. Except for a study for Maryland, which projected I&I statewide from the results for 50 systems, I found nothing in the literature for other statewide studies. I hope the results from this study will eventually stimulate development of a comprehensive national strategy for I&I reduction based on facts rather than estimates.

I&I: So, how did the U.S. Environmental Protection Agency conduct its gap study (formally: Clean Watersheds Needs Survey) to estimate the cost of I&I correction reported to Congress in 2012?

Kurz: That information was mostly based on surveys by state agencies of municipalities to compile their estimates about the magnitude of their local I&I problem. It was not based on systematic and uniform I&I measurements of every public system in a given state. I suspect such estimates grossly underestimated the actual amount of annual I&I. This suspicion was corroborated when I compiled the individual estimates of I&I included as part of every municipal NPDES permit application in the state of Tennessee. The aggregate amount of annual I&I statewide estimated from the permit applications was about 20% — less than half of the measured annual I&I in those same systems.

I&I: What volume of I&I did you measure in public systems in Tennessee, and how was that measured?

Kurz: The Tennessee study evaluated daily influent flows, influent organic load (BOD or CBOD), and rainfall for one year for each of the 243 systems. This is the information typically recorded by operators for their Monthly Operating Reports (MORs) sent to the state. The raw data was transcribed into a simple Excel spreadsheet and analyzed using the formulas described in the No-Dig paper. The results showed that those systems treated 120.79 billion gallons of clearwater annually. That represented 45.38% of all influent to Tennessee wastewater treatment facilities. Additionally, I&I represented more than half the annual flow in two-thirds of those systems. Very conservatively, I&I is costing Tennessee ratepayers about $217 million annually based on operation and maintenance costs alone. Using rehabilitation project experience from large projects in Tennessee, it may likely cost over $1.14 billion to reduce I&I by 50%. If municipal agencies have the vision and determination to invest in the future, that means the savings in O&M costs over time would pay for rehabilitation projects in 11 to 12 years (not considering interest rates).

I&I: Have you shared this with the state of Tennessee?

Kurz: Yes, over the past two years the Tennessee Division of Water Resources is using the individual I&I results and the spreadsheet to evaluate requests from municipal agencies for moratorium relief. The Tennessee Division of Water Resources analyzes the annual I&I and the rainfall-dependent I&I for successive years to determine if rehabilitation work conducted by a municipality has been effective for I&I reduction.

I&I: Was your method just a variation of the method published by the U.S. EPA in its 2014 guidance?

Kurz: No, it differs in two ways. First, the method described in this No-Dig paper can be applied to current and historical treatment plant data recorded daily. No adjustments or estimates are needed. In contrast, the 2014 EPA guidance requires a measurement of the low nighttime flows (midnight to 6 a.m.) for calculating groundwater infiltration. The problem that I observed with the EPA method was that none of the 528 treatment plants recorded data for that specific six-hour interval. All of the data on the MORs were reported for 24-hour periods. It is certainly feasible for operators to record the six-hour flow results in the future, but that means the historical plant data cannot be analyzed with the EPA method. Second, I found that analyzing influent BOD concentrations gave an indication of dry-weather infiltration that may be missed by traditional methods that only rely on hydraulic analysis. I wanted to make this a simple method that operators could use to diagnose I&I in their own systems. This spreadsheet is not intended to replace a comprehensive engineering study (if that is ultimately needed), but it can be a starting point for communities with limited funds.

I&I: Is your offer of a free analysis limited to the No-Dig conference?

Kurz: My offer applies to any system in the U.S. or Canada. Anyone (engineer, private citizen or public agency) can contact me through my website — www.sewercapacitymanagement.weebly.com — for information on how to submit annual data to get a report. My intention is to broaden the base of my study, and this seemed like a good way to obtain public data.



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