Station street closed in Hillsburgh; dam issue creates concern for council

Station Street is now closed.

While the road was officially closed prior to the Dec. 6 council session, road superintendent Larry Van Wyck provided a report on the reasons behind the move.

Van Wyck stated that in November 2010, settlement – movement of the road – was observed.

Then during late September and October following a period of heavier than usual precipitation, significant settlement occurred on the road surface, particularly in the eastbound lane (south side of the road) where it has been monitored since Oct. 26.

Since then, more than 100mm of movement has been detected.

A site visit Oct. 26 also revealed significant bubbling on the outlet end of the culvert, leading staff to believe the flow was under pressure and lacking air.

Conversations with Credit Valley Conservation staff who visited the site offered no suggestions on remediation or repair, simply that they be kept aware of the situation.

“Supervisory staff of the CVC became involved and demanded a meeting on site with the town and the MNR,” Van Wyck said,

CVC and the MNR were advised the town is not the owner of the dam.

Those agencies then requested information about the owner.

They then arranged a meeting with owner Marci Quayle, while neighbour Vic Bako joined the discussion and walkabout.

There is a concrete box culvert under Station Road that outlets to a channel which runs to the mill. The south end of the culvert was filled over, and the embankment widened at the south end of the road.

Van Wyck wrote that it does not appear water is flowing through the culvert and no permanent measures were taken to fill the void of the culvert.

The next structure is a rectangular intake structure that appears to be connected to a pipe – which, on the south side, is a corrugated steel pipe.

Van Wyck said it is not known if that steel pipe is part of the original installation or was added later for widening of the road.

Regardless, he stated the joint between the two pipes is suspect. He said there are obvious issues with the intake structure. There are two slots in the concrete structure to accommodate screen and boards to somewhat regulate levels, but the structure is essentially an overflow outlet and is not functioning that way.

There is physical evidence of settlement on the south side of the road, over the pipe. There is concrete protruding above  the pavement,

Staff have been told that is a result of eight cubic yards of concrete slurry placed in a hole that previously developed.

There are no records to indicate if the pipe was blocked and if water is bypassing or has been bypassing the pipe.

Ground penetrating radar has been completed to determine if there are any voids below the surface and to determine what is exactly below the surface.

On Nov. 29, that report confirmed a void of about 6.5 by 9.8 feet, extending to a depth of up to 11.5 feet.

Van Wyck proposed the town go into the pond to examine the intake structure and remove any wood from it. In addition, the intent is to measure the inside of the structure and provide that information for boards to be installed.

Town staff would install the boards to stop the flow and force the water through the dam until levels rise above the boards.

Staff would remove debris in the vicinity of the dam and break the top four to six inches off the concrete patch and smooth the road surface following completion of the ground radar work.

“Due to the lack of information and the uncertainty of the stability of the road in the area of the dam, a decision was made to close the road until such time as the town had some assurance this area was structurally sound and not likely to collapse,” Van Wyck wrote.

In a Friday afternoon update, he said, “The road is closed and will remain closed until such time as the town can confirm there is no threat to public safety.”

Town staff have installed boards in the inlet structure in an attempt to limit flow

Van Wyck said significant water flow continues to come through the boards as several appear to be compromised.

He added an attempt was made to put a sewer camera thru a culvert, but the significant volume of water flowing through prohibited the camera from going all the way through the pipe.

A cedar log was found inside the pipe.

The pipe is a large diameter corrugated steel and greater than 24 inches. The culvert is installed approximately 4.5 metres below the surface of the road.

Van Wyck added that no further repairs can be attempted on culvert until such time as flow is greatly reduced or eliminated.

Not only is the dam privately owned, but so is the pond where the culvert has its outlet.

Van Wyck stated the town has been in touch with the dam owner, the MNR and the Credit Valley Conservation Authority and are working cooperatively  to devise a plan for dealing with repairs of the culvert.