April 21, 2008

IAN COCKBURN

Water from tunneling activity in North Vancouver passes through a series of holding ponds where most of the sediment is removed before the wataer flows into the Seymour River.

Stormtec Filtration treats Grouse Mountain ‘tunnel muck’ with organic flocculent

Richard Gilbert

staff writer

A Vancouver company provided an international tunnelling contractor with a solution for sediment control during construction of a major water utility project in North Vancouver.

Bilfinger Berger is using two tunnel-boring machines (TBMs) on the construction of two tunnels under Grouse Mountain in North Vancouver.

The German contractor was hired by Metro Vancouver in 2004 to construct twin tunnels with a combined length of 14.2 km, in order to pump water from the Capilano reservoir to the new Seymour Filtration Plant.

A significant milestone in construction of the project was the deployment of the first of two tunnel boring machines in May-June, 2006.

For the last year and a half, the pair of TBMs cut through granite seven days a week for 18-20 hours a day, however work was recently halted because of safety concerns.

The material cut away from the tunnel face by the cutting wheel is made up of rock dust and sediment that needs to be pumped out to the surface.

This tunnel muck is a big concern for the contractor, because it can run into streams, river and lakes.

If allowed to drain into the Seymour watershed, this material would reduce the amount of sunlight reaching aquatic plants, clog fish gills, smother aquatic habitat and spawning areas, and impede fish navigation.

Bilfinger Berger hired Stormtec Filtration Inc. as a subcontractor to treat the tunnel muck.

The Vancouver-based company is responsible for removing sediment from the water before it is discharged from the site to stay in compliance with government minimum turbidity requirements.

“Organic flocculent is a chemical used in the treatment of water because it won’t harm fish. The use of StormKlear, which is manufactured by HaloSource, has grown quickly in the last 15 years,” said Art Cote, president of Stormtec.

“In Washington state, StormKlear is the only chemical used in an aquatic habitat, anything else is a criminal offence. These are the guys who helped us import this technology into B.C.”

The organic flocculent used by Stormtec is called Chitosan.

It is a naturally biopolymer that is derived from the shells of crustaceans, such as shrimp, crabs and insects.

“The organic flocculent is a polymer made from the membrane between the shell and the flesh of shrimp and crab. This stuff is organic and green. It is just like fish food,” explained Cote.

“The system takes the muck from the tunnel construction, reads the PH level and injects CO2. The muck goes into a static mixer, where the gas is mixed into the water, just like soda water.”

The water is then passed through a series of holding ponds where the flocculent is added. In these holding ponds, the flocculent causes the particles of dust and sediment to clump together, settle and sink to the bottom.

“The water comes out like chocolate milk when the TBM is running. The water gets progressively clearer as it goes through a series of gravel barriers to reach the last pond” said Cote.

“The clear water is discharged directly into the Seymour River. What makes this process unique is that the chemical is recycled and non-toxic.”

Turbidity is the measure of the degree to which water loses its transparency due to the presence of suspended particles such as rock dust and sediment.

The more suspended soils are in the water, the murkier it seems and the higher the turbidity.

Turbidity is measured in nephelometric turbidity units (NTUs).

The water from the construction of the tunnels is required to be at 25 NTUs when it comes out of the last holding pond.

According to Cote, the Stormtec system can usually clean water to the level of 10 NTUs.

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