City awaits options for resolving sewer line clog
City officials could have options within three months about how to address the grout that is blocking the sewer line beneath the Washington Avenue storm tunnel.
Timothy Moot, a principal with the firm Clark Patterson Lee, told the Common Council’s Finance and Audit Committee this past week that his architectural and engineering firm is looking at the sewer line blockage “very comprehensively.” He said the firm should have a final report with evaluations within three months.
“We are looking at alternatives to possibly abandoning this tunnel structure altogether for sewer and having a pump station,” Moot said. “There’s costs associated with that. And there’s risks involved with some of this stuff.”
Moot said the firm also would look at drilling out the grout blocking the tunnel, among other options. He said the firm’s job is to do a cost-benefit analysis and risk management assessment so city officials can make the best decision possible.
In March, City Engineer Ralph Swenson asked the Finance and Audit Committee to authorize spending an additional $1.2 million to remove the grout blockage using a directional drilling method. In response, the committee asked Swenson to instead look into alternative solutions for removing the blockage or improving the system so the city potentially could abandon the sanitary sewer line in that part of the tunnel.
Swenson issued requests for proposals from firms that could evaluate the city’s alternatives, and Clark Patterson Lee was hired for $72,500.
The grout blockage occurred during the project to repair the sinkhole that opened on Washington Avenue in April 2011. The sinkhole was blamed on a leaky century-old underground stormwater tunnel, and to repair it an archway was built below the road’s surface and above the tunnel to prevent the soil from giving way again. The affected portion of Washington Avenue didn’t reopen to traffic until two months ago.
The archway measures 50 feet high and 175 feet long, and it weighs 10,000 tons. Grouting from the repair project somehow got inside a new sewer liner and blocked the pipe.
Moot said the grout blockage situation is complex and is complicated by the confined space. He said his firm has a subconsultant, familiar with deep tunnel work, who could enter and evaluate the tunnel.
Swenson also said there was some recent heavy rainfall in the area that led to some localized flooding. He said a temporary pump handling stormwater near the blocked tunnel was unable to handle the capacity due to the intensity of the rain.
Alderman Reynolds Scott-Childress, D-Ward 3, said a resident not affected by the sinkhole had the basement of her home flooded during that recent storm. He asked what the city could do to help that resident given that the temporary pump solution to the grout blockage seemed to have caused the problem.
Swenson said the resident would need to file a claim with the city.