EPA to Begin New Rulemaking Process for Blending

June 2, 2018
In a move that took many in the water industry by surprise, the U.S. EPA announced it will begin a new rulemaking process to provide certainty and clarity surrounding the use of “blending” by wastewater treatment plants.

By Vanessa M. Leiby

In a move that took many in the water industry by surprise, the U.S. Environmental Protection Agency (EPA) announced on April 17, 2018, that it plans to begin a new rulemaking process to provide certainty and clarity surrounding the use of “blending” by wastewater treatment plants. The goal is to help facilities optimize wastewater treatment plants during wet weather events. As part of the process, the Agency will be reaching out to states, local communities, and stakeholders.

Blending is typically used by wastewater treatment plants to manage high flow events while still maintaining compliance. According to the EPA press release, “rain and snowmelt can take Publicly Owned Treatment Works (POTWs) offline when excess water enters the wastewater collection system and exceeds the POTW’s capacity to treat all incoming wastewater. POTWs often manage excess wet weather flow by routing some of the incoming water around the secondary (biological) treatment units and then ‘blending’ it back in with secondary treatment effluent for disinfection prior to discharge.” This prevents damage to existing biological or advanced treatment units or other wastewater treatment processes.

The issue of blending is not new to the Agency. In fact, back on December 22, 2005, the Agency published a notice of availability and request for comment in the Federal Register (FR) on National Pollutant Discharge Elimination System (NPDES) Permit Requirements for Peak Wet Weather Discharges from Publicly Owned Treatment Works Treatment Plants Serving Separate Sanitary Sewer Collection Systems.1 While EPA never finalized the rulemaking for blending, NPDES permit bypass procedures are codified in the 40 CFR §122.41(m).2

Fast-forward to 2014 when EPA published a FR notice on April 18 announcing an Experts Forum on Public Health Impacts of Blending at Publicly Owned Treat Plants3 that was held in June of that year. EPA assembled a group of public health experts to discuss the public health implications of blended effluent discharges from POTWs into waterways. These public health experts were enlisted to ensure that EPA had up-to-date information on the pollutant discharges that may be associated with the different engineering options available to address wet weather blending at POTWs in order to consider the potential public health implications of these different options.

The expert’s forum did not include discussion of the application of the Agency’s bypass regulation at 40 CFR §122.41(m) going forward (the bypass regulation prohibits the intentional diversion of waste streams from any portion of a treatment facility except where necessary for essential maintenance to assure efficient operation). Rather, the forum was solely concerned with the potential public health impacts of blended discharges from POTWs.

Additional background information regarding the Agency’s past actions on blending4 as well as its current efforts5 can be found on the EPA website. This may have significant impacts on POTWs — make sure you are part of the discussion!

About the Author: Vanessa M. Leiby is the executive director of the Water and Wastewater Equipment Manufacturers Association (WWEMA), a non-profit trade association founded in 1908. WWEMA’s vision is to be the “voice of water and wastewater technology providers” and its mission is to promote the advancement of technology solutions for clean water that ensure a future sustainable environment and to improve its members’ economic viability. More information about WWEMA can be found at www.wwema.org.


1. Draft policy outlining possible approaches to managing peak weather discharges as published in the FR notice can be found at https://tinyurl.com/npdes-draft.

2. Codification of NPDES permit bypass procedures can be found at https://tinyurl.com/40cfr122.

3. A copy of the April 18, 2014, FR Notice can be found at https://tinyurl.com/fr-notice.

4. Additional background information can be found at https://tinyurl.com/npdes-experts-forum.

5. For more information on current efforts, visit https://tinyurl.com/municipal-wastewater.

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