As city officials scramble for a fix, the news emanating from a large sinkhole on Washington Avenue keeps getting worse.

The sinkhole, which returned in March, a year after it was first filled in, is growing larger, causing more damage to underground infrastructure and, for the first time, threatening the city’s sewage treatment plant.

At a City Hall press conference last Friday, Mayor Shayne Gallo reassured residents that the city was “on the right track” in addressing the situation, but warned of “very serious consequences” if the problem was not fixed quickly. Experts have traced the sinkhole to a tunnel buried 80 feet below Washington Avenue. The tunnel was built by the agency that would become the New York City Department of Environmental Protection between 1909 and 1912 as part of the construction of the Ashokan reservoir system. The tunnel was intended to divert sewage to Rondout Creek from the then-impounded Esopus Creek. In the early 1990s the city installed a vertical shaft to carry stormwater runoff and improve drainage in Uptown Kingston.

Sometime in the past few years, however, officials believe a hole developed in the roof of brick arch tunnel, allowing dirt to enter and creating the void which caused the sinkhole. Officials believe other voids above the tunnel are probably contributing to the problem. Since the sinkhole reappeared, Central Hudson has had to shut off gas lines to five homes and install propane tanks. The city, meanwhile, has had to re-route water lines and install new utility poles to skirt the gaping pit. Perhaps most vexing for neighborhood residents, the sinkhole has left a stretch of Washington Avenue, a major artery through the city, closed to traffic for months.

Late last month, however, the mess onWashington Avenue took a turn for the fiscally ominous when dirt believed to originate from the area of the sinkhole began showing up in sediment tanks at the city’s sewage treatment plant. The development suggests that a breach has developed in the barrier between the stormwater and sewage portions of the tunnel. So far, according to Department of Public Works Superintendent Mike Schupp, the dirt infiltration is being controlled through “operational changes” at the treatment plant, including cleaning out and hauling away dirt from the sediment tanks. But, Schupp warned, if the problem gets worse and begins to overwhelm the tank’s capacity, the department would be forced to divert sewage around the damaged portion of the tunnel using pumps and above-ground hoses.

“It wouldn’t be cheap and it would be disruptive to traffic,” said Schupp. “It’s really not a scenario any of us want, but it’s something that needs to be discussed.”

Pipe lining

A multi-stage repair plan is expected to launch soon using $1.8 million in bonds approved by the Common Council earlier this year. The first, and experts say most critical, phase involves getting workers down into the tunnel to install a lining in a 160-foot section where the roof has been breached. Saugerties-based contractor American Structure has been awarded the contract after entering a low bid of $327,000 for the work. Materials for the job are on order and city engineer Ralph Swenson said that safety experts will begin examining the site within the next week. Among the issues the safety team will have to determine is weather a new vertical shaft will need to be installed to allow workers access to the tunnel. Currently the only access is through a 30” diameter stormwater drain, Swenson said. If the safety team determines that another access shaft is needed, Swenson said, the work could add significant costs to the remediation project. Swenson said that materials alone for a new vertical shaft could run upwards of $50,000.

Sinkhole photo by Phyllis McCabe/photo illustration by Rick Holland.