City of Columbus, Ohio, Designs ‘Blueprint’ to Control Overflows
November 13, 2014Columbus, Ohio, is an up-and-coming city in the Midwest. Unlike many cities in the so-called ‘Rust Belt,’ Columbus has a growing population and a thriving business community. Home to The Ohio State University, as well as the state capitol, the City has an international and vibrant flair that makes it an attractive location for young professionals and business startups.
Yet, like many of its neighbors, Columbus suffers from an aging sewer system that is prone to overflows during wet weather events. Columbus is one of many cities in the Midwest and across the country that has been ordered by the EPA to control overflows to both its sanitary and combined sewers. Work to comply with the consent decrees, involving planning and constructing solutions, has been ongoing for more than a decade. To date, the City has completed treatment plant improvements and the first of several planned large storage and conveyance tunnels. That tunnel — the OARS Tunnel — will begin paying dividends in terms of improved water quality when it goes online in the near future. Most of the work completed to date has provided substantial benefits to the combined sewer system.
However, as the City began to enter subsequent phases of the tunnel program that focuses on controlling separate sanitary overflows, it decided to take a different tack. Rather than continue to build out the tunnel program, the City decided to address the cause of the overflows rather than the symptoms by refocusing its efforts on eliminating inflow-and-infiltration (I/I) through a comprehensive rehabilitation program and green infrastructure improvements. City officials believe that this approach — dubbed Blueprint Columbus — will achieve greater water quality benefits in a manner that will offer economic and social advantages that will benefit the City for generations to come.
“We have spent over a billion dollars on treatment plant and other CSO improvements, and those investments are already showing a big payback in terms of system performance,” said Dax Blake, administrator of the Division of Sewerage and Drainage. “But as we looked to the future components of the program, we saw that they were basically convey-and-treat solutions that only addressed sanitary sewer overflows but ignored stormwater and provided no benefit in the neighborhoods, so we began to think, ‘Is there a better way?’ ”
That better way became Blueprint Columbus (Blueprint), an integrated stormwater and I/I program. While Blueprint is still in its initial phases, officials are confident that it can provide better value — i.e. ‘bang for the buck’ — vs. the traditional convey-and-treat approach. Additionally, the inclusion of stormwater within the Blueprint approach positions the City for potential future environmental regulations regarding the handling of stormwater and stormwater runoff — something with the previous plan did not address.
The City of Columbus Department of Public Utilities serves more than 1.1 million customers through its water and sewer systems. The sewer system includes two wastewater treatment plants with a total capacity of 480 mgd and some 6,000 miles of sewer and drain pipes. The City developed a wet weather management plan in response to EPA consent orders to address SSOs (2002) and CSOs (2004). While the SSO consent order did not include a firm completion date, the CSO consent order mandated a completion date of 2025 — including a July 1, 2010, date for establishing a “substantial reduction,” which led the City to begin constructing CSO solutions first.
As constructed, the OARS Tunnel is able to capture a large volume of CSO overflows, officials say, which will provide a significant improvement in water quality as soon as it goes online. Future phases, however, would provide only incremental improvements with equal construction costs.
“The remaining consent order projects consisted primarily of two large and expensive tunnels that probably would have had to be constructed in three phases each,” Blake said. “The tunnels alone we estimated to cost about $2 billion to construct, plus additional work to construct relief sewers to convey the excess flows to the tunnels. Additionally, we felt that the tunnels would be underutilized, on the order of four to five times per year. Those factors helped lead us to a new integrated approach.”
The idea of holistic rehab is not new. Sewer system operators have recognized for a long time that relining the mains alone is not necessarily going to eliminate I/I — and, in some cases, main line relining can have virtually no impact. Getting a full handle on I/I means addressing the entire system — mains, manholes and laterals. The holistic approach historically has had two major hurdles: funding and dealing with private property I/I.
“The integrated approach is going to help us improve stormwater quality and address sewer overflows,” Blake said. “The stormwater work also presents social and environmental benefits.”
For the City of Columbus, funding was less of an issue. The City had already committed to spend billions of dollars to build out the tunnel system, so the rehab and green infrastructure programs meant re-directing funds that had already been planned, rather than starting from scratch. Dealing with the private property I/I, however, has always been a tricky proposition.
“There are legal considerations when you are trying to do work on private property,” said John Newsome, SSES manager of the Division of Sewerage and Drainage. “We are going through the process now of gaining approval to do the work.”
As part of the approval process for completing private property work, the City is embarking on an extensive outreach program with the public. “We need to get community buy-in that the Blueprint approach is the best approach to take,” Newsome said. “We’ve had training with our survey crews and we’ve had training with our outreach consultants to make sure that they understand they are guests on people’s yards. Customer service is very important.”
Part of the investigation process is televising the laterals to get a better indication of their condition. Crews are also doing select downspout investigations. Combined, this information will help planners determine how much I/I they can expect to remove from the system, which in turn will help define the City’s hydraulic model.
When up and running, the private property I/I reduction program will include full lateral lining to the foundation of the home, downspout re-direction and voluntary sump pump installation, Newsome said. He added that cured-in-place pipe (CIPP) is likely to be used for the lateral lining. “CIPP has a long history of success in the main lines, so we feel comfortable using that technology,” he said.
When the Blueprint program gets up and running, officials plan to start with an extensive pilot project in the City’s Clintonville neighborhood, a mature neighborhood just north of the Ohio State campus. In that area, the City will be rehabbing all mains, manholes and laterals. In addition, the City will build green infrastructure solutions to handle stormwater that is being diverted away from the sewer system through the improvements.
For the manholes, officials are considering corrosion-resistant, cementitious-type products. They believe that reducing the amount of stormwater in the system will result in higher concentration levels of hydrogen-sulfide gas, which can accelerate corrosion.
The City is still in the process of enacting code changes that will allow for mandatory rehabilitation of laterals on private property. That, Blake said, is key to the Blueprint approach. “On the lateral lining, it was our conclusion that we cannot do this on a voluntary basis,’ he said “We can’t voluntarily ensure that we comply with the consent order obligation, so we need to have a mechanism to make the private property owners — particularly where there we have high levels of I/I — participate.”
Based on previous experience with lateral lining on a voluntary basis, the City got about 50 percent participation initially and an addition 30 percent once residents saw their neighbors getting work done. “There was a tremendous amount of effort to get 50 percent signed up initially and that still left us with 20 percent untouched in the end, so we knew it was not feasible to proceed on a voluntary basis,” Blake said
Sump pump installation, however, will be on a voluntary basis. “We are concerned about the fact that sump pump installation is much more invasive,” he said. “So, we are trying to educate people of the benefits of installing a sump pump. With the laterals lined and sump pumps installed, we can seal off any cross connection that may exist.”
The City plans to submit its plan for EPA approval by Sept. 15, 2015. Assuming acceptance, work in the Clintonville area is expected to begin in 2016. Following the Clintonville project area, the City will turn its attention to areas with the highest amounts of I/I.
“We find most of the I/I coming from areas in which the homes were built between about 1920 and 1950,” Newsome said. “And we are planning to continue in our comprehensive approach. Water is resilient so you can’t line just certain sections of the sewer — water will find its way into the system through the weakest link.”
In addition to the Blueprint Columbus program, the City will continue its structural rehab program that has continued to evolve over the years. “The program we have in place for doing CIPP on our main lines now is vastly different from what it was 10 years ago,” Blake said. “We don’t even hire design professionals any longer to help us with these things; we’re bidding the work and directing the contractor where to go next. It is working out well and has saved a tremendous amount of money. We’re probably doing double the footage of pipe through our annual lining budget.”
With all of the attention on rehab and I/I, Blake sees a tremendous benefit to the green infrastructure component, as well. “The way we are approaching stormwater is a paradigm shift,” he said. “It used to be that you would put in a catch basin and pipe it to the nearest river and forget about it. The green infrastructure will have a maintenance burden down the road, but we see that as an advantage; it is going to bring a lot of economic benefits to the community because we are going to have to maintain that, which is going to mean jobs. That is on top of the local contractors we hire to build the infrastructure and perform the rehab.”
Throughout the process of developing a new approach, Blake said that the EPA has been a good partner. Historically, the agency has taken a firm stance in its consent decree enforcement. There was little wiggle room in the deadlines, targeted capture level or types of improvements that were accepted. Over the past few years, however, the agency has been more likely to tailor the terms of the agreement in response to new ideas or unique needs of communities.
The broader approach to enforcement helped to open the door for a new approach like Blueprint, Blake said. “There has been a genuine change in the EPA’s philosophy in dealing with sewer overflows. I believe they are beginning to look at the Clean Water Act more holistically and on a watershed basis, rather than just the sewer overflow aspect. They are recognizing the complexity of all the regulations and their impact on water quality. They have been a good partner as we have moved through the process.”
So as Columbus enters its next phase of sewer management, many communities and regulators will keep an eye focused on its progress.
“I think there is a big faction off people at Ohio EPA who are really excited to see us get serious about I/I reduction and address the private property side,” Blake said. “Those are areas that many communities across the state need to deal with, and it is likely that we will be setting an example.”
Jim Rush is editor of Trenchless Technology.