How can we improve combined sewer overflow reporting? We need a smarter approach

Reporting accurate and meaningful combined sewer overflow (CSO) data has long been a challenge. That’s especially true in the Northeast United States, where unpredictable weather patterns and an increasing frequency of severe weather events create the need for extensive long-term analysis of metering data against predictive models. Variables like the amount of snow on the ground during a rainstorm, temperature fluctuations, or local groundwater levels all impact the ability for consistent measurement and confident reporting.

However, a growing need for a real-time approach to CSO reporting—in some cases requiring municipalities to report a CSO spill within hours—is driving our market to take a more holistic, consistent approach to monitoring and modelling. Increasingly, our clients are recognizing the fact that a full picture can’t be achieved without taking a systematic approach to the analysis of CSO flows that is supported by comprehensive historic data.

The U.S. Environmental Protection Agency’s CSO Control Policy has urged utilities to develop a thorough understanding of the wet weather hydraulic responses of their combined sewer systems. To support continuous system improvement, the EPA directed permittees to follow nine minimum controls, with the ninth control requiring that permittees: “Monitor to effectively characterize CSO impacts and the efficacy of CSO controls.”

To adapt to this challenge, we’re increasingly working with clients across New England to advise on strategies for greater accuracy in monitoring and reporting. We’re also preparing them for a more real-time reporting approach.

From CSO projects in South Boston to CSO abatement in Providence, and long-term control plans in between, we’ve learned that if there’s one consistency in this work, it’s that all clients require a tailored solution.

A multi-pronged approach

New advances in metering technology have allowed municipalities to gain a more accurate picture over levels and flows, but that metering information is only as good as the quality of data that’s being recorded. We’ve found that, to gain an accurate picture, there’s a great deal of follow-up research and data validation needed. There’s always the chance of a meter malfunction or an uncertain meter placement (such as along an outfall experiencing high river levels) that can skew results.

Metering on its own isn’t especially informative. The full picture truly comes into view when metering data is paired with modelled simulations that have been calibrated and validated over a long period of time during a range of storms.

As you can imagine, this validation and calibration takes time and resources. Our team works with many municipalities for annual reporting that not only takes into consideration metering and monitoring data but also the impacts of external factors. By taking a parallel review of influences like tidal elevations, river levels, and National Oceanic and Atmospheric Administration (NOAA) data, we’re able to paint a more in-depth picture that takes all variables into account.

With the need in many municipalities for a greater frequency in CSO spill report analysis (in some cases requiring CSO spill data to be validated in a monthly report as opposed to annually), how can this extensive analysis and validation be streamlined?