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Oxford sinkhole may soon give up its secrets


Results could take four to six weeks after surveyors arrive in Oxford

OXFORD, N.S. – About 70 residents of Oxford gathered at a public meeting at the Capitol Theatre Thursday night hoping to learn more about the Oxford sinkhole.

They’ll have to wait.

“Until we can map those underground caverns we really can’t tell you whether the ground around the park area is safe at this point,” said Garth DeMont, liaison geologist with the Nova Scotia Department of Energy and Mines.

A Request for Proposals (RFP) to map the subsurface near the sinkhole closed on Wednesday, and it’s hoped geophysical surveyors will soon be in Oxford to get a better picture of what’s happening beneath the sinkhole.

“What we’re hoping is that we’ll be able to see a model of the cavern under the ground’s surface and see how much space there is between the cavern and the actual ground surface,” said DeMont.

After surveyors arrive, it could take four to six weeks for underground maps to be complete.

“They say four to six weeks but, quite often, that’s to get the final report configured, but some companies, when they look at the data, they can give you a sense of what’s going on sooner than that,” said DeMont.

The RFP issued by Oxford asked for several different types of geological surveys to be complete.

“That’s good thing, because we don’t know which one is going to work here,” said Demont. “Some surveys, you can process the data quickly, other times it takes quite a bit of work.”

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During the meeting, DeMont explained how the sinkholes form, and showed a video as well.

Groundwater flows into and dissolves bedrock, often gypsum, creating voids and tunnels, and the rock collapses on itself. The rock is carried away, creating caverns. Surficial materials, such as topsoil and sand, eventually fall into the caverns creating a sinkhole.

“It’s an underground cave system that the water moves through. The problem is that, the more water that moves through, the more it expands the caverns,” said DeMont. “Where the water is coming from and where it’s going is anybody’s guess right now.”

He does not believe the sinkhole is connected to the nearby swimming pond.

“The water level of the pond is actually quite a bit higher elevation than the water in the sinkhole and that’s why we think they’re not connected together.”

The sinkhole has remained relatively stable over the past week, meaning that the flow of water out of the sinkhole has been blocked off.

“Right now, the sinkhole doesn’t appear to have any water moving in it at all, so obviously there’s nothing flowing down and out of it, so the cavern itself is at this point is full of water,” said DeMont. “We don’t know why it’s full of water. It’s obviously backed up somewhere.”

The sinkhole devoured several trees, including a 50-footer. DeMont wonders if trees are plugging the hole temporarily.

“You could get a big storm event that flushes those trees out and opens the pipe again,” said DeMont.

Rachel Jones, chief administrative officer for the Town of Oxford, said the surveys will study three areas.

“One is, specifically, the peninsula, including the Irving gas station and Tim Hortons because that is the primary area,” said Jones. “The secondary area of interest expands to include the Parkview (restaurant) and a little bit more of Main Street and towards the back of the properties.”

The third area is the Trans-Canada Highway.

“That is not our jurisdiction, however, we have knowledge of some things there, so we’re hoping that the information can be passed on to the department of transportation and they would take the information between the federal and provincial government and look at that more closely,” said Jones.

Besides a sinkhole, Oxford also has a 10-year-old school not in use because it is being repaired while students go to school in Pugwash.

One person in attendance said he has a solution to both problems.

“I actually have a suggestion, or solution, that would fix two problems at the same time,” said the man. “Since we have a high school that’s collapsing, why don’t we use it to plug the hole?”

Many people laughed. A few did not.

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