Reducing inflow/infiltration in sanitary sewers
Regional partnership to address I/I wins national award
The innovation and success of this region’s program to reduce inflow and infiltration in the sanitary sewer system has garnered national recognition.
In March, the National Association of Clean Water Agencies announced that it will bestow a 2009 Operations Award for Environmental Achievement on Metropolitan Council Environmental Services (MCES) for the Inflow and Infiltration Reduction Program. The award recognizes outstanding initiatives in wastewater treatment operations that are cost-effective and environmentally sound.
Working with the Council, communities around the region are reducing excess clear water in the sanitary sewer system, which threatens regional sewer capacity, groundwater recharge and public health.
“This program is a true partnership with our local government stakeholders,” said MCES General Manager William Moore. “It could not be successful without them. It’s an honor to receive this recognition.”
“The I/I program is truly innovative,” Moore said. “It’s helping the region achieve big results, with a comparatively low level of investment.”
The alternative is much worse
“It is not entirely painless,” Maplewood Public Works Director Chuck Ahl said of the I/I program. “There is a short-term investment. But we recognize the significant long-term benefit and savings. I might compare it to investing in a crown for your tooth now to avoid a root canal in the future. You just have to do it.”
In fact, communities around the region are making such good progress on reducing I/I that the Council hasn’t had to actually impose surcharges on a single community, which it has the ability to do, Moore said.
“To their credit, local governments have really stepped up to this challenge,” he added. “Meanwhile, we at MCES are making investments of our own to address I/I that has been identified in the regional pipe system.”
The current I/I program was launched in 2006 to reduce the amount of clear water that makes its way into sanitary sewers in one of two primary ways. In the first scenario, groundwater infiltrates or seeps into sewer pipes via cracks or leaky joints. In the second scenario, known as inflow, clear water from illegal connections of sump pumps, rain leaders and foundation and area drains is channeled directly into sanitary sewer pipes.
Sanitary sewer pipes are designed to handle peak flows and also have reserve capacity to accommodate future growth in the region. A small amount of inflow and infiltration of clear water is allowable, but in excess, this water gobbles up the reserve capacity.
Either way, it uses up capacity that’s needed for wastewater and could result in sewer spills. It’s also costly for communities and residents because it needlessly puts clear water through the wastewater treatment process.
In addition, putting clear water through the treatment process means it’s discharged into the rivers. That prevents clear water from seeping back into the groundwater to replenish area aquifers.
Local solutions much less costly
Rather than invest nearly $1 billion in additional sewer infrastructure, primarily to provide capacity during big rain storms, a task force of local officials and MCES staff proposed solving the problem for a fraction of the cost. By requiring communities with excessive I/I to invest in local remedies to reduce I/I, the region could solve the problem for roughly $150 million.
Dozens of communities throughout the region are on board.
The City of Maplewood, for example, disconnected two stormwater pipes from the sanitary sewer system. That reduces the amount of clear water flowing into the sanitary sewer system, with the added benefit of saving the city some $135,000 in wastewater treatment costs.
In Golden Valley, as in many other mature communities, I/I is being addressed both publicly and privately. The city is doing its part -- lining and repairing local sanitary sewer mains, annually cleaning and televising portions of the system and replacing manhole covers to prevent clear water from getting into the system.
But city officials knew that private property owners also had to be part of the solution.
The city owns about 113 miles of sanitary sewer mains. Private property owners own about 147 miles of pipe that connect to the public system.
Issues on private property were identified primarily through an inspection program. The problems ranged from sump pumps that drain into laundry tubs or the sanitary sewer, to foundation drains that are connected to the sanitary sewer, and broken or cracked sewer pipes that run from the house to the local pipe in the street. In some cases, the sewer pipe was completely missing!
Regional grant program covers some costs to residents
It costs money to remedy these situations. In Golden Valley, however, home and business owners may be eligible for a grant of up to $2,000 to help pay the cost of the repair or disconnection fee. That’s because the city is participating in a Metropolitan Council grant program to help defray some of the costs associated with reducing I/I.
A Golden Valley resident welcomes an inspector into her home. The equipment will televise the condition of the home's private sanitary sewer pipe. (Photo courtesy City of Golden Valley.)
“Reducing I/I has been a tremendous challenge for our community and will continue to be a challenge for the region,” said Jeannine Clancy, Golden Valley’s Director of Public Works.
“After carefully studying the issue, our city council recognized the community needed to address the public side as well as the private side of the system. To respond, we launched a property inspection program in 2007. As part of the program we had to invest a fair amount of time in educating residents and business owners, but we did it because we wanted to be good regional citizens and good stewards of the environment.”
A total of 46 communities were identified in 2007 as having excessive I/I. As part of the Council’s I /I program, communities could choose to either submit a plan to reduce their I/I, or starting in 2007, pay a surcharge on their regional wastewater bill, and receive reimbursement as they expend money to eliminate I/I.
To date, no community has had to pay a surcharge, which means they’re all making progress in one form or another. In fact, seven communities have completed their local remedy and have been removed from the program altogether.
“We’re very pleased with the results,” said Moore. “We recognize communities face additional financial challenges because of the economic downturn impacting us all. But the I/I reduction program is a less expensive option for everyone. We’ve been very encouraged by the local accomplishments to date and the commitment shown toward resolving this challenge in a unique regional/local partnership.”