February 13, 2010
FOCUS | Environmental engineering
Cache Creek landfill expansion is a multi-layered project
When the 40-hectare Cache Creek landfill doubles in size over the next few years, a sophisticated nine-layer system will protect the surrounding soil and water.
“Landfills used to get such a bad rap. This will not be a hole with garbage,” said Russ Black, general manager of Wastech Services, the Coquitlam company operating the landfill.
“Technology has evolved dramatically over the last 20 years. New landfills are incredibly engineered. This one will be extremely well-designed.”
While waste reduction is promoted as the long-term solution for garbage disposal, the Cache Creek landfill, which opened in 1989 (taking garbage from Greater Vancouver and B.C.’s Thompson-Nicola region), is growing by 49 hectares because of demand.
With an original closing date of about 2010, the $100-million expansion will bump up the dump’s life by 17 to 25 years, adding roughly 12.6-million tonnes of capacity.
Whistler expressed interest in sending its trash to the landfill, said Black, a UBC engineering graduate with more than 22 years of experience.
Phase one is building a seven-hectare annex, connecting to the existing landfill and adding two years of capacity.
The remaining 42 hectares will likely be built over about six years in roughly seven-hectare tracts.
Tenders will be posted for liner installation and engineering services in the final quarter of 2010, Black said.
The crucial component is the liner.
Known as a double composite liner with a leak detection system, Cache Creek’s exceeds regulatory requirements. It will cover the entire site and be more than a metre deep.
Starting from the top down, garbage will be placed atop pit run gravel.
Below that is a geotextile mat, used to prevent small soil and particles from moving down.
The third layer will be drain rock, serving to collect leachate.
Next comes another geotextile mat, followed by protective cushioning.
Below that is the first high-density polyethylene (HDPE) geomembrane liner.
Stable and strong HDPE has an estimated half-life of 350 years in a buried state, according to RAM Lining Systems.
One advantage is that HDPE is easily seamed on site using a thermal process.
Next is a geosynthetic clay liner (GCL), a thin clay liner (four to six millimetres) between two layers of a geotextile that protects the bentonite clay.
The big selling point of GCL is that if there’s a leak in the HDPE layer above, it reacts with the bentonite clay below, creating a chemical reaction which causes the liquid to harden like concrete, in effect creating a self-repairing seal, Black said.
GCL installation is quicker than traditional compacted clay liners because the material is in one big roll. Freeze-thaw cycles also have less of an impact on GCL, according to an Ohio State University study.
Below the first GCL is a second HDPE layer, bottomed-off by a second GCL.
A double composite liner system such as this one normally costs double a single liner system, Black said,
But thanks to economies of scale, he predicted that Cache Creek’s double system would cost around $35 per square metre versus about $20 per square metre for a single liner.
There will also be a separate leachate collection system that uses an electronic sensing system to detect leaks, one further safeguard for the nearby Bonaparte River.
To ensure contaminants don’t reach the aquifer, 12 new 20-metre to 100-metre-deep wells have been drilled around the Bonaparte River, augmenting the existing dozen wells, all of which are monitored.
One natural advantage is that the extension will sit on bedrock where in this case it creates a natural hydraulic capping system that dramatically slows leachate movement.
Cache Creek enjoys a second asset as a landfill - its dry climate.
If the same amount of garbage was dumped in a soggy Lower Mainland landfill, it would generate as much leachate in one day as the Cache Creek facility does in a year, Black said.
Still, Wastech, whose parent company is Vancouver-based Belkorp Industries, spends $500,000 annually on water monitoring.
Two decades of data have shown the landfill is performing well, Black said.
Additional construction over the next two to three years involves a $20-million liquid natural gas (LNG) facility.
Once operating, it will fuel the 25 heavy-duty trucks that make the four-hour, one-way, trash-toting trip from Vancouver. LNG is produced by organic landfill waste and there’s no shortage. Waste from the existing landfill will produce enough LNG for the fleet for 20 years, Black said.
When anaerobic bacteria work through food scraps, methane is a byproduct.
When collected, the gas is about 50 per cent methane with the balance CO2 and organic contaminants.
Wastech’s facility will clean the gas, producing a product that’s 99 per cent methane. Once chilled and liquified, it will fuel the trucks. Wastech has tested engines from Vancouver’s Westport Cummings to see how the fuel performs. Results have been good and two trucks have been converted to LNG.
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