The city has taken several steps to reduce flooding from backed-up sewer lines in north Lincoln during big rainstorms.
City staff are diverting wastewater from several thousand homes and businesses east of North 41st Street from the Theresa Street wastewater treatment plant to the Northeast treatment plant.
Last year, 60 homes in the Huntington area had sewers backup during the May 7 rainstorm.
The city also has 15 monitors, up from four, in the Huntington area, so staff can make earlier decisions that would limit the sewer backups into basements in that area.
But those are the only quick and easy fixes for the Theresa Street plant backup problems, according to city staff in a presentation to the City Council last week.
So staff are recommending businesses and homeowners in the area install back-flow preventers.
The city will continue to work on long-term solutions, but nothing will solve completely the problems created by a 100-year or 200-year rain event, said Donna Garden, assistant director of Public Works and Utilities.
Last spring around 200 homes and businesses in north Lincoln -- about 150 of those in the Huntington area -- were flooded by sewer water from the Theresa Street plant during a 200-year storm event.
Backup sewage also flooded almost that many homes in October 2014, during a 100-year rain event.
When wastewater -- combined with rainwater that had gotten into sewer pipes -- overwhelmed the Theresa Street plant, that water backed up through interior drains and toilets in neighboring homes and businesses.
The city eventually stopped the flooding by diverting raw wastewater into Salt Creek, relieving the pressure on the Theresa Street plant.
There had not been any widespread flooding problems related to sewer backup since a major rainstorm in the 1980s, according to Garden.
City staff and consultants did not find any large holes in the wastewater system during research this winter.
“We are not able to say we found a hole and we plugged it. That is not the case,” said Garden.
The biggest problem is infiltration of rainwater into the wastewater pipes through cracks and holes and through sump pumps discharging into the wastewater system rather than discharging outside. Curing that is on the city's long-term project list.
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City staff are taking several immediate steps and looking at several long-term activities to help reduce the sewer backup problems, based on research and recommendations included in a Wet Weather Report given the council.
The city will temporarily divert wastewater for a pocket of homes in the Huntington area, east of 41st Street, from Theresa Street to the Northeast wastewater treatment plant, she said.
That will take about 3 million gallons of water per day from the Theresa Street plant, Garden said.
Though the Theresa Street plant officially can handle 81 million gallons of water, it can handle more as a practical matter.
In last Monday's rainstorm the plant handled about 98 million gallons of water with no backup problems.
In May 2015, the plant was receiving about 107 million gallons of water when the backup flooding into homes and businesses occurred.
During the rainy season the city will temporarily divert wastewater from buildings east of North 41st Street to the Northeast plant, where it costs more to treat the wastewater.
Eventually the city will add equipment at that plant to reduce the treatment cost and permanently divert wastewater from this area and a small neighboring area to the northeast plant, Garden said.
That diversion directly helps about 60 homes flooded in May 2015, and it also relieves pressure on the system for the other 90 homes on the west side of North 41st Street in the Huntington area that had sewers backup last year because of the overwhelmed Theresa Street plant, according to Brian Kramer, with the city's sanitary sewer system.
Long-term solutions, identified in the Wet Weather Report include:
* Increase pumping capacity at Theresa Street plant.
* Create pilot programs in areas known to have high infiltration to determine specific problems with city wastewater pipes or private pipes going to homes and businesses.
* Continue rehabilitation of older wastewater pipes to prevent infiltration of groundwater.
* Strengthen the city’s requirement that home sump pumps pump to the outside, not into an inside drain, through a change in the plumbing code or a broader inspection program.