Washington Ave. sinkhole could be filled by Thanksgiving

Engineer Steven Gamelsky answers a question at the public meeting. (Photo: Phyllis McCabe)

Engineer Steven Gamelsky answers a question at the public meeting. (Photo: Phyllis McCabe)

The Kingston Common Council’s Finance and Audit Committee has signed off on a $3.3 million effort to fix the Washington Avenue sinkhole once and for all. The 4-1 vote came after a public meeting Monday night in the Council Chambers where representatives from GEA Engineering and Mueser Rutledge Consulting Engineers outlined the proposal for an audience of about 75 residents and city officials.

The sinkhole, near the corner of Washington and Linderman avenues, first appeared in May 2011. Since then it has resisted numerous remediation efforts, been linked to a major sewage overflow into Twalfskill Creek and vexed two mayoral administrations with spiraling costs and deepening public dismay. The sinkhole’s origins can be traced back a century when, between 1909 and 1912 New York City’s Board of Water Supply (precursor to the Department of Environmental Protection) constructed a brick tunnel 80 feet below Washington Avenue. The tunnel was intended to redirect combined stormwater and sewage from the Esopus Creek (which local officials feared would dry up with the construction of the Ashokan reservoir system) to the Rondout Creek. The tunnel was later bisected to separate sewage and stormwater. In the early 1990s, Kingston officials installed a vertical shaft linked to the tunnel to hasten stormwater drainage in the neighborhood. But it had an unintended effect — engineers believe that, over the years, groundwater and vibration from stormwater going down the tunnel loosened the soil around the vertical shaft and below a section of the tunnel which runs through dirt between two solid masses of bedrock. The resulting voids around the tunnel and the shaft created a “chimney,” conveying dirt deep below ground and creating the sinkhole above.

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Since 2011 the city has bonded for $3.78 million in sinkhole funds to deal with the sinkhole. The money has been spent to reline the interior of the tunnel and vertical shaft and perform other work to stabilize the area and prevent further damage to underground infrastructure. The next phase in the project, however, is intended as a long-term solution which would allow the city to finally fill in the sinkhole and open the stretch of Washington Avenue to traffic for the first time in three years.

“It’s a long-term approach that’s going to solve the problem,” said Steven Gamelsky of GEA at the public meeting.

Changes above and below

The approach proposed by the engineers involves work above and below ground to dry out the area and condense soil to prevent erosion caused by groundwater. The Tannery Brook, according to the proposal, would be rerouted to reduce groundwater infiltration into the earth around the pipe and vertical shaft. Long, vibrating steel beams would be temporarily driven deep below Washington Avenue to condense a layer of sandy soil above the tunnel. Engineers would then pump a mix of Portland cement and water into the ground to create a solid, permanent “arch” bridging the two sections of bedrock and encasing the tunnel. To cut down on harmful vibrations, the vertical shaft would be fitted out with a toilet-like “vortex structure” to smooth the flow of water down into the tunnel. The project would also restore the streetscape to usable condition. The entire project is expected to cost $3.3 million and require another $2 million bond from the city (the U.S. Economic Development Administration has awarded the city a $1.12 million grant to offset costs of the project, but the city must bond for the money first and then get reimbursed).

Gamelsky explained that the project would begin with a two-month final design and bidding process that could start as early as next month. Preliminary work could begin this spring with a survey of houses around the work site to help residents file compensation claims in the event their homes suffer structural damage. Work would begin in earnest over the summer and could wrap up by Thanksgiving, Gamelsky said.

Questioned by members of the Finance Committee about potential cost overruns, Gamelsky said that the final tab would be impacted by the cost of concrete — which can swing by as much as 30 percent each year — at the time of purchase. Gamelsky also conceded that damage to houses caused by the below ground work could drive up the price of the project. Gamelsky added that a another cheaper option proposed after the city sought a second opinion on the GMA proposal would be too risky and would not accomplish the long term fix sought  by city officials.

“I would be deceiving you if I guaranteed anything,” said Gamelsky. “But this is approach presents the least risk of any of the alternatives.”

Will seeks further review

ktx K101 sinkhole swenson

City Engineer Ralph Swenson. (Photo: Phyllis McCabe)

Committee member Brad Will (D-Ward 3) who has been a vocal critic of the city’s handling of the sinkhole, was the sole “no” vote on the authorization to proceed with the GMA proposal. Will, citing an unnamed “DEP engineer” he had spoken to, said he believed the committee should at least take more time to weigh whether the cheaper, less disruptive alternative proposal would be viable. Several committee members also raised the possibility of simply abandoning and filling in the century-old tunnel and building a new stormwater and sewer line through the area. But City Engineer Ralph Swenson said that such a solution would take time that the city doesn’t have.

“Right now, we could have a catastrophic failure at any time, then where would we be?,” said Swenson. “We don’t have a five-year window, we need to fix this now.”

At the public information session preceding the committee meeting, residents raised concerns about damage to homes and disruption in the neighborhood caused by the proposed work. Longtime residents of the area said they worried the engineers were not paying enough attention to the presence of underground springs in an area known to early Dutch settlers as “The Vly,” or “the swamp.” Others blamed the neighborhood’s persistent flooding issues on the rerouting of water into the area from new development adjoining the area. Many expressed skepticism that the proposal put forth by the engineers would in fact lead to the end of the long municipal nightmare that is the Washington Avenue sinkhole.

“If you think you’re going to do this in two months, after the past three years,” said neighborhood resident Rich Van Kleeck, “I think that’s extremely conservative at best and foolish at worst.”

Multiple requests for comment from Mayor Shayne Gallo went unacknowledged.

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