Antidegradation Process Allows Utilities to Increase Flexibility and Save Money

Running a municipal wastewater utility is a complex job, and the circumstances of a community are constantly changing. Economic and population shifts, new discharge permit limits, and other factors can mean a utility needs to expand its wastewater treatment capacity, develop a new discharge location to combine resources, or reconfigure assets to increase flexibility or reduce costs. But making these changes sometimes means applying for new or modified discharge permits. To do this, a utility discharging to surface waters needs to follow its state’s anti-degradation process and demonstrate that the changes it intends to make won’t degrade water quality, prove that some degradation of water quality is justified based on social and economic opportunity, or account for the costs associated with more advanced treatment alternatives to further limit degradation. The stories of two Midwestern utilities show how this process can be used to make needed changes, save money, and set the stage for the long-term health of the community and its water resources.

How the anti-degradation process works

In the state of Missouri, when a utility wants to modify its existing discharge by adding a new discharge or increasing its discharge, it must prepare an anti-degradation evaluation. The report requires a detailed investigation into the drivers for a modified discharge, the proposed water body’s ability to handle the new or expanded flow and pollutant load, and the expected social and economic benefits that will result from the modified discharge. In addition, the evaluation requires analysis of at least three less-degrading alternatives, which typically entail more advanced and costly levels of treatment.  The evaluation is intended to determine if the use of more advanced treatment that would limit degradation is warranted and economically justified. In the State of Missouri, any more-advanced treatment alternative that is within 120% of the cost of the base project is typically deemed economically viable over a less-advanced treatment alternative that would have increased pollutant loads (degradation) on the receiving water.      

The report is then submitted to the regulatory agency issuing the permit (the Missouri Department of Natural Resources), and if the proposed change does not significantly impact water quality in the receiving water — or important social and economic benefits are presented to justify some degradation — it can be approved. Social and economic factors, however, cannot justify reducing water quality below the state’s water quality standards.

How the report is prepared, how thoroughly it is supported with evidence, cost impacts, support from the community, and other factors can influence the outcome and the ultimate decision from the State to allow the proposed discharge modification. 

Winning approval to allow flexibility

The two examples below show how a carefully planned and executed anti-degradation report can unlock flexibility and savings for communities in a wide range of situations. In the first case, the City of Troy, Missouri, maintained two separate wastewater treatment facilities inside the city limits. Both treatment facilities needed major upgrades and had experienced violations in the past due to the age and condition of the facilities. 

Troy was also under enforcement action from the U.S. Environmental Protection Agency (EPA) because of these past permit violations. Working with Woodard & Curran, the city determined that by converting one of the facilities to a pump station and making upgrades to the other to handle the higher capacity and better treat the combined flow, it could save significant money in operations and maintenance costs over the short and long term. These upgrades would also allow the city to achieve compliance with more stringent ammonia-nitrogen limits in its discharge permit. This change would, however, require eliminating a discharge at one facility and securing state approval to increase the discharge permit at the city’s upgraded facility.

To make this possible, Woodard & Curran prepared an anti-degradation evaluation that looked at the change in flow, the quality of the effluent, and the characteristics of the receiving water, the Cuivre River. The report demonstrated that the combined discharges would not result in the receiving water body falling below Missouri’s water quality standards and showed an opportunity for the city to save significant money in operations and construction costs by consolidating to one centralized treatment facility. The increased capacity of the upgraded facility will also allow the city to welcome new business and population growth. 

Less than 30 miles away, the City of O’Fallon, Missouri, was facing a different situation with a similar solution. In this case, population and economic growth combined with wet weather flows were pushing the capacity of the city’s existing treatment facility. To accommodate demand and provide capacity for future growth, major plant upgrades were needed.

The existing WWTP discharge includes an effluent pump station with a 6-mile force main to its outfall at the Mississippi River. Due to peak flows, combined with increased discharge pressure on the effluent pumping system when the Mississippi River is under flood conditions, the existing effluent pump station was not able to convey all the flow to which it was subjected. This resulted in surcharges at the WWTP into upstream unit processes such as the UV disinfection system as well as within the collection system. 

Facing $8 million in effluent pump station upgrades, the city worked with Woodard & Curran to evaluate alternatives to meet the needs of the growing community. Through the anti-degradation evaluation process, several alternatives were evaluated, and it was determined that a new high-flow discharge to Peruque Creek, which runs adjacent to the WWTP, provided significant social and economic value to the city. The report evaluated several alternatives, including upgrading effluent pump station capacity, installing a second parallel force main to the Mississippi River and additional on-site equalization. All the alternatives would have been at a significant cost to the city.  As partners with the city and with outside-the-box thinking, a second high-flow treated effluent discharge was evaluated to alleviate the hydraulic capacity on the existing effluent pump station. 

In lieu of costly upgrades to the existing effluent pump station, a second high-flow discharge to Peruque Creek was proposed as a second treated effluent outfall to be used only during high flow periods when the existing effluent pump station could not keep up with the flow through the WWTP. During dry weather periods, Peruque Creek has very low flows and thus a continuous discharge to the creek was not a viable alternative for the city due to the stringent effluent limits that would be required for this discharge. The report demonstrated that during high flows at the WWTP, the receiving stream would also be at high flows and water quality would not be lowered beyond the state’s requirements with a portion of the city’s treated effluent being discharged to Peruque Creek. The mixing and dilution associated with a discharge into Peruque Creek at high-flow conditions also allowed for reasonable effluent limits on par with the City’s limits for its existing discharge to the Mississippi River. The Missouri Department of Natural Resources approved the report, allowing O’Fallon to proceed with upgrades at a fraction of the cost of other alternatives. These savings have allowed the city to provide additional improvements to its wastewater system that would have otherwise not been possible.  This was also the first time in the history that a dual discharge such as this has been implemented and permitted in Missouri.     

With support from Woodard & Curran, both of these communities were able to plan their infrastructure upgrades, unlock short- and long-term benefits, and save millions of dollars using the anti-degradation process. This shows how careful planning, detailed investigation into water quality, and execution of these projects lead to win-win outcomes.



Robert Polys

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