The Washington Avenue sinkhole may have been filled in but it continues to drain city finances as work is continuing to clear a blocked sewer line that, officials say, was caused by the sinkhole remediation effort.
Last week, the Common Council approved a $1.4 million bond to continue the work. The appropriation brings the total amount of taxpayer funds spent on sinkhole-related issues to over $10 million.
The issue dates to the spring of 2011 when the yawning sinkhole opened one day on Washington Avenue, near its intersection with Linderman Avenue. Engineers blamed the chasm on the deterioration of a century-old stormwater and sewage tunnel buried 80 feet below Washington Avenue, and soil erosion around a vertical shaft to the tunnel that was installed in the 1990s to improve stormwater drainage in the neighborhood. The sinkhole resisted multiple efforts to fill it in until 2015 when the city undertook a major effort to stabilize the ground beneath Washington Avenue once and for all.
The work, carried out by contractor GEA Engineering, included diverting the course of a brook flowing beneath the roadway and packing the earth around the vertical shaft using vibrating steel piles. The remediation effort also included pumping grout underground to create a protective arch over the crumbling tunnel. Engineers hoped the arch would prevent soil from coming through holes in the brick-lined tunnel, contributing to further erosion and the re-opening of the sinkhole.
But city engineer Ralph Swenson believes the strategy backfired. Not long after work on the sinkhole was completed in the fall of 2015, a 185-foot section of sewer line running through the former sinkhole site became blocked. Engineers later determined that grout injected into the earth to form the arch had made its way into the sewer line.
Since then, a new contractor, Arold Construction, has taken on the fiendishly complex and laborious task of clearing grout from the sewer line. The job involves a robot equipped with a grinding wheel and others outfitted with cameras and other tools, as well as workers who descend into the tunnel each day and work chest-deep in raw sewage to manually remove the debris. Swenson said the job is complicated by the fact that it remains unclear how much of the sewage line is blocked, contractors were hampered by the tight confines and concerns that one of the robots could become trapped in the sewer line.
“Initially we only had an estimate of how long the work would take; we really didn’t know until we got down there and started using this equipment,” said Swenson. “You have to be very judicious in the tools you use and how you use them. That impacts the pace of the work.”
The initial cost estimate on the job, formulated before the full extent of the blockage was known, totaled between $1.1 million and $2.5 million. The council has already approved the $1.1 million. Last week’s vote will bring the total funding packing in line with the high end of the cost estimate. Swenson said he council’s approval of the funding reflected optimism that the excavation would eventually clear the sewer line.
“We feel that we’ve gotten sufficient production out of the work that it should continue,” said Swenson.
City officials are also hoping that a lawsuit filed against the contractors who carried out the remediation effort will offset, or maybe even pay entirely, for the ongoing work. The lawsuit filed earlier this year alleges that the design and implementation of the sinkhole project was flawed and caused the blocked sewer lines. Alderman Rennie Scott-Childress (D-Ward 3), who represents the neighborhood around the former sinkhole, said there had been discussion of holding off on further work on the sewage line until after the lawsuit was settled. But, he said, he and other aldermen expressed concern that a final settlement could be years off.
“I’m very optimistic that we will recoup a large chunk of what we’re paying now,” said Scott-Childress. “But if we don’t borrow the money now and we wait for the lawsuit to play out we could be waiting for 10 years.”
Since 2011, the city has spent or authorized the expenditure of just over $10 million to fix the sinkhole and deal with the aftereffects. Some $1.1 million of that total came in the form of a federal grant. The remainder came in the form of city-issued bonds. In addition to those costs, the city is also defending itself in a civil suit brought by eight homeowners who live adjacent to the former sinkhole and claim that their homes suffered major structural damage during the remediation effort.
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