Utility Takes Care of Sewer Overflows

Duluth tackles serious inflow and overflow problems and completes consent decree requirements ahead of schedule.
Utility Takes Care of Sewer Overflows
Chris Anderson checks the controls of the Vactor 2100 while cleaning a sewer line with Erick Fronden and Brice Aikin.

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“Without them, nothing would have happened.”

That’s Todd Carlson, program coordinator in the engineering office of the Duluth, Minnesota, Department of Public Works and Utilities, talking about his city’s successful program to eliminate wet weather overflows and meet the terms of a consent decree a year ahead of the deadline.

By “them,” he’s not referring to consultants, contractors, regulators or city officials. He means the public.

“The public was a critical part of this project,” Carlson says. “Sixty percent of our sewer system is on private property. Without the cooperation of our property owners in our city, we’d still be fighting the problem.”

Wet weather issues

Age and topography have had a lot to do with wet weather overflows in Duluth. The infrastructure is old, with many sewers consisting of 8-inch clay lines dating to the late 1800s. Plus, homes and businesses are situated on a steep ridge that drops about 800 feet to the shore of Lake Superior.

In a previous Municipal Sewer & Water article on the utility, John Center, project coordinator for sanitary sewer overflows, described how flows come straight downhill at 40 mph to T-connections at the interceptors. “We’ve had data loggers in manholes simply washed away,” he reported.

Through the interceptors, Duluth contributes an average daily flow of about 10 mgd to the regional Western Lake Superior Sanitary District Plant.

Even more problematic are the foundation drains, common to homes and buildings constructed before 1970. These drains come to a center manhole in the basement, connected to a 6-inch iron pipe. “Eighty percent of our buildings had that,” Carlson explains. The design caused frequent hydraulic overflows and basement backups, contributing both to wet weather overflows and citizen complaints.

Leaky sewer laterals, averaging about 60 feet from home to street, contributed even more to storm flows in the system. Carlson estimates that between 1995 and 2004, Duluth averaged 30 overflows per year, amounting to 47 million gallons all told. Many were in the downtown business and hotel district.

Fixing the problems

Duluth’s program to eliminate the overflows is not new, although the consent decree, signed in 2009, gave the effort a big boost.

“Our I&I reduction project really started in the early 1990s,” Carlson says. “Our city staff recognized the need to separate the foundation drains and install sump pumps in the basements.”

In 1994, largely through the efforts of Steve Lipinski, manager of utility operations, Duluth was able to get the state Legislature to pass legislation that allowed public money to be used on private property. That move paved the way for the city to help property owners disconnect their foundation drains and install sump pumps, as well as improve landscaping and steer downspouts away from foundations.

“We needed to eliminate wet weather overflows at the source,” Carlson says. “Every gallon we removed was one less gallon to overflow or overwhelm the treatment plant. In that first year, we got some really good things done.”

Still, the city experienced occasional overflows, with every incident resulting in a violation. Then in 2003, excessive rain and snow produced an abnormally wet year, with numerous releases coupled with power outages. That, according to Carlson, brought a cease and desist order from state and federal agencies in 2004 and galvanized public awareness. “We knew we needed to get this fixed,” Carlson recalls.

As negotiations leading to the consent decree commenced in 2004, Duluth redoubled efforts to eliminate overflows, focusing on leaky laterals and the basement foundation drains. “We continued to push,” Carlson says. “That carrot at the end of the stick (consent decree) really helped.

“The key was to work upstream in the basins with the most inflow and infiltration,” Carlson says. “It was critical to know what was coming into the system.”

Divide and conquer

Based on seven designated consent decree overflow points around the system, Duluth had divided the city into 30 sub-basins, with one additional basin added later on. Extensive flow monitoring was conducted in each basin, using Teledyne Isco 4150 Series flow loggers and 2100 Series flow modules, which have a temperature reading feature that enables the team to measure runoff from the spring snowmelt because of the temperature change of the water.

The goal was to search out 250 homes and identify at least 175 candidates a year for lateral replacement. Crews used an Explorer mainline pan-and-tilt camera from UEMSI to inspect block-to-block during wet weather. In addition, manholes were opened during rain events to visually monitor flow. “We worked in those basins where we saw the most water,” Carlson says. “We used city crews for the work, rather than an outside contractor.”

Lateral connections were televised from the city mains. When the inspections revealed problems, the videos were shown to homeowners. “By mail, we invited homeowners to public meetings where we could show the videos,” Carlson explains. “We used the videos to teach and to convince property owners they had a problem. TV has been a great tool for us.”

Duluth also initiated a demonstration program showing how laterals could be lined with CIPP technology instead of open cuts.

The city sweetened the deal by providing grants to fund a large portion of the sump pump and lateral replacement programs. Up to $2,150 was available as a grant for disconnection of the footing drain, removal of the house trap, and the installation of a sump pump to reroute the water outside. Plus, the city paid 80 percent of the first $5,000 required to replace or rehabilitate (CIPP lining) a failing lateral.

Carlson says the lateral reimbursement funds come from a clean-water fee on the utility bill implemented in 2009. Funds to install sump pumps came from a rate increase of 10 to 15 percent enacted during the mid-1990s. “That was the biggest bang for the buck — installing the sumps and getting the storm flows outside the house and away from the foundation,” Carlson says.

The clean-water surcharge fee is used to fund the lateral grant program and capital improvement costs related to the wastewater storage tanks; this funding will sunset in 2018.

Once a property owner agreed to remediate the issue, the city continued to engage and support. “We gave the property owners the control,” Carlson says. “It was not us as city employees making the decisions. We allowed them to pick the contractor. We could send the grant money directly to the contractor, or to the homeowner who could then pay the contractor when the work was completed to their satisfaction. We held their hand through the whole process.”

The extra efforts to create a partnership with customers have paid off handsomely. Not only has the consent decree deadline been met with time to spare, Carlson estimates the overflow prevention program is removing an average of 29 million gallons per rain event. “Except for severe flooding in 2012, we haven’t had an overflow since 2010,” he says.

“With the help of the public, we’ve taken control of the system, rather than the system controlling us.”



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