Combined Sewer Overflows a Two-Billion-Gallon Problem in Cincinnati

Combined Sewer Overflows Addressed with Green Infrastructure

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MaryLynn Lodor is environmental program manager for the Metropolitan Sewer District of Greater Cincinnati.

John Lyons is manager of the Cincinnati office of Strand Associates, Inc., the design firm that helped develop the Lick Run Alternative.

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Posted: Wednesday, September 21, 2011 6:00 pm

What does a city do with billions of gallons of stormwater runoff?

That's the challenge for the Metropolitan Sewer District of Greater Cincinnati as it nears its 2018 EPA Phase 1 mandated consent decree deadline to capture, treat or remove two billion gallons of annual overflows from its combined sewers. Plus, the city must eliminate the overflow of another 100 million gallons from sanitary-only sewers.

In addition to the U.S. EPA, the mandate comes from the state of Ohio EPA and the Ohio River Valley Water Sanitation Commission (ORSANCO).

MSDGC is not only looking at traditional ways to meet its challenge, but novel ways to control and detain excess water while improving water quality in an innovative plan it calls the Lick Run Alternative, named for the Lick Run watershed that contains the district's largest CSO.

But, first, some background on CSOs.

According to the EPA's website, CSOs are sewers designed to collect rainwater runoff, domestic sewage and industrial wastewater in the same pipe. Most of the time, combined sewer systems transport all of their wastewater to a sewage treatment plant, where it is treated and then discharged to a water body.

During periods of heavy rainfall or snowmelt, however, the water volume can exceed the capacity of the sewer system or treatment plant. For this reason, combined sewer systems are designed to overflow occasionally and discharge excess water directly into nearby streams, rivers, or other water bodies.

The problem is that the CSOs contain, in addition to stormwater, untreated human and industrial waste, toxic materials and debris.

Not only is this a problem for Greater Cincinnati and surrounding Hamilton County - which is among the top five locations in the U.S. for urban CSOs with more than 100 overflows annually - it is a major water pollution concern for some 770 other cities that have combined sewer systems.

The EPA established a CSO control policy through the National Pollutant Discharge Elimination System (NPDES) permitting program. According to the EPA, the policy resulted from negotiations among municipal organizations, environmental groups and state agencies. It provides guidance to municipalities and state and federal permitting authorities on how to meet the Clean Water Act's pollution control goals as flexibly and cost-effectively as possible.

The CSO Policy was published April 19, 1994. The first milestone was the Jan. 1, 1997 deadline for implementing nine minimum technology-based controls to reduce the prevalence and impacts of CSOs and were not expected to require significant engineering studies or major construction.

Cincinnati and other communities with CSOs were also expected to develop long-term CSO control plans that would ultimately provide for full compliance with the Clean Water Act, including attainment of water quality standards.

In June 2004, MSDGC entered into a global consent decree with the U.S. EPA and the Department of Justice, Ohio and ORSANCO to "address wet weather issues including significantly reducing the number of sanitary sewer overflows...CSOs and water-in basement issues. The consent decree mandates that MSDGC complete its wet weather program by February of 2022 unless the capital costs are expected to exceed $1.5 billion."

Since then, MSDGC has embarked on a multi-year, multi-billion dollar initiative - Project Groundwork - to resolve the public health and environmental issues by rebuilding and improving the sewer system through hundreds of sewer improvements and stormwater control projects. The estimated $3.5 billion cost will primarily be funded by MSDGC customers (ratepayers) through quarterly and monthly sewer bills.

Project Groundwork is a unique three-pronged approach using different strategies:

• Storage and conveyance: Constructing large sewers to move wastewater to treatment plants, or large underground storage tunnels to capture excess water.

• Product control: Upgrading existing treatment plants to handle more wastewater or building high-rate treatment plants to treat flows at the CSO outfall before discharge.

• Source control: Solutions that control the source of the overflow problem, i.e. natural or piped stormwater/natural systems to convey water and provide water quality enhancements, bio-infiltration basins, retention basins, pervious pavement, rainwater harvesting systems, etc.

Under source controls, Cincinnati is proposing to deal with its overflow issue emphasizing a sustainable green infrastructure, most notably exemplified by the Lick Run Alternative, according to MaryLynn Lodor, MSDGC environmental program manager, and John Lyons, office manager of Strand Associates, Inc., Cincinnati office, the design firm that helped develop the Lick Run Alternative.

Lodor said a major focus of Project Groundwork is the Lower Mill Creek Watershed, which overflows more than seven billion gallons into the Mill Creek, half of the 14 billion gallons MSDGC has to deal with. As part of the consent decree, MSDGC has to develop a specific plan to resolve two billion gallons of overflows by 2018 from the Lower Mill Creek Watershed, which includes several smaller watersheds, including the 2,700-acre Lick Run.

Like many older, urban core communities, Lick Run is in the economically depressed neighborhood of South Fairmont on the west side of Cincinnati and is the location of the city's largest CSO #5, which discharges about 1.7 billion gallons of sewage and stormwater each year into the Ohio River through its Mill Creek tributary. That is 12 percent of MSDGC's total CSO volume.

MSDGC's Lick Run Fact Sheet says that to eliminate two billion gallons of annual overflows within Lower Mill Creek, regulators are requiring a "storage and conveyance" solution - an underground tunnel about 30 feet in diameter and 1.2 miles long that would store excess flows during heavy rains and eventually discharge it to an enhanced high-rate treatment plant.

But regulators are also allowing MSDGC to explore alternatives or to supplement the tunnel to meet the 2018 deadline, said Lodor. MSDGC has developed a sustainable watershed evaluation planning process (SWEP) approach to develop long-term, large-scale solutions.

Strand Associates and a Cincinnati landscape design firm, Human Nature, Inc., have assisted MSDGC in developing this approach, which is now used in other watersheds within the district. This alternative, said Lyons, would not restore the historic Lick Run stream that once was there, but it could emulate it with a mix of sustainable engineering practices.

The Lick Run stream has been diverted underground via sewer since the 1900s. But, with a sustainable bioengineering approach, a new open channel stormwater system could be developed as the foundation of a targeted sewer separation program. Planners think that could be the best option for improving water quality and could act as a catalyst for community revitalization.

"It (the Lick Run Alternative) is a significant change. The decisions we made in the past, like deciding to divert stormwater into sewer pipes, are a significant liability today," said Lodor, emphasizing MSDGC's strong desire not to repeat history. One of those decisions was converting storm sewers to CSOs in the late 1800s.

Benefits of the sustainable solution extend beyond CSO abatement, said Lyons. "Models indicate that watershed-based solutions in the Lick Run will keep about 1.26 billion gallons of clean stormwater from being conveyed and treated as wastewater each year, resulting in annual energy savings of 450,000 MW and 320,000 metric tons of CO2 emissions just from pumping the flow into a treatment facility, not including the energy used throughout the treatment facility

"Additional benefits include reduction of the annual overflow volume of the CSO by more than 1.1 billion gallons," he added.

Digging a tunnel is a tried-and-true option, but a tired one, observed Lodor. "It would be underground and no one would see any change at Lick Run. We have an obligation to reduce CSOs and an opportunity to do so in a way that restores natural systems within an urban area.

"This project could result in measurable benefits that improve water quality. Plans could include improved or enhanced forested natural park areas and a potential aboveground urban waterway, while retaining the current underground CSO for conveyance of sanitary flow and flows not separated completely. The plan also could include bio-infiltration basins, bioswales and other green features, bioengineering Lick Run to mimic the original system."

She said three-quarters of the wet weather overflow from CSO 5 is stormwater and natural drainage. The other 25 percent is raw sewage. "It's diluted, but still not good for water quality. We must change that," said Lodor.

Lyons said the EPA is not only telling communities that they have to mitigate and clean up stormwater overflows, but the agency is also encouraging green infrastructure.

"Cincinnati is looking at it from a different perspective. MSDGC is mandated to spend several millions of dollars to reduce overflows in Lick Run to solve our CSO problem in Lower Mill Creek. We can do the tunnel, or we can spend the money and achieve something beyond our reduction goal, potentially at lower cost.

"The Lick Run alternative could be transformational for the urban core neighborhoods. We are not just talking about a few rain gardens, but an investment that could achieve favorable outcomes in addition to meeting regulatory obligations, an investment that could serve as a catalyst for public and private development," continued Lyons.

He added there is much to be said for opting for the more sustainable option that would add so much visible physical beauty to South Fairmont. MSDGC has initiated several other pilot stormwater control projects in the neighborhood, including large-scale rain gardens, bioswales, pervious paving and tree plantings.

Lodor stressed that she and her MSDGC colleagues are trying to find what makes most sense and is most cost-efficient in an economy in which all communities are struggling. "We can't take a one-size-fits-all approach. We have to tailor solutions to the specific geographics in a watershed. No matter how big a tunnel you build, it will always have limited capacity.

"With our Lick Run Alternative and the SWEP approach, it appears that MSDGC can develop a more cost-effective solution using green management and source controls," she said.

MSDGC is on the cutting edge with this, said Lyons. "Strand Associates is working with a number of cities on CSO issues and with aggressive green programs. We have not seen a project of this magnitude. MSDGC is to be commended because it is obviously concerned for its community and sticking its neck out with a visionary solution.

"And," Lyons concluded, "What is it that the present government is leaving behind? What will the MSDGC ratepayers get for their money?"

Residents have been given three opportunities to provide input before a final decision is made. The first of three public design workshops was held on Aug. 11; others will be held in October and in February 2012. MSDGC is also working with Lick Run Watershed residents, businesses and property owners. A Master Plan will be developed and submitted to local policy makers for review and approval and ultimately a proposal will go to federal and state regulators.

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