Building a water treatment works for Canada's premier west coast city, Vancouver, is more troublesome than might be thought.
The area is popular and migration from the rest of the country is high. With mountains coming down almost to the shoreline there are spectacular views, but land is in short supply and property prices at a premium.
The new C$600M (£300M) Seymour-Capilano works has, therefore, been a challenge, especially as many suitable sites are located in national parks and nature reserves. In British Columbia environmental sensitivities are high.
Until recently, water was not an issue. Mountain snowmelt brought excellent tap water that, with minimal chlorine treatment, tasted 'better than bottled' and was clear and bright.
Occasionally there was a little turbidity, concedes Bob Kelly, project engineer with design and project management consortium SSBV, which includes Amec's Canadian division, US consultant Black & Veatch and his own firm, Alberta consultant Stantec.
'But it's seasonal, ' says Kelly.
'The high rainfall on the coast causes landslips and this is a fairly active seismic area too. It shakes up the water table.' A major incident involving bacterial contamination in eastern Canada in the 1990s forced changes. Canadian Federal standards for water have been raised and to bring them into line the government of British Columbia, via the Greater Vancouver Regional District, decided that filtration and disinfectant must be increased.
'Ultraviolet (UV) was selected because it helps reduce chlorination and cope with chemical resistant organisms such as cryptosporidium, ' says Stantec process engineer for the project Reno Fiorante. A bank of 24 UV dosing units will be at the core of the works, sitting in a service corridor across the centre of the site.
They are each fed by an upstream lter, also spaced laterally across the site.
'Filtration is important because you need to remove cloudiness before the UV dosing, ' says Fiorante. 'A large number of basic micro-organisms are also taken out by the filters.' These are particularly high-rate units, he says, capable of handling 75Ml/day giving maximum plant capacity of 1,080Ml/day.
Supply for works will be from two separate catchments - the Capilano and the Seymour - both with man-made mountain reservoirs, which supply about 70% of the region's water. It made economic and planning sense to merge the supplies into one new treatment works, even though to do this has meant building two 7km long parallel tunnels.
The tunnels connect the Capilano intake and outow to the works, which are located on a site about 10km downstream of the reservoir on the Seymour river. There was no room at the dam for new facilities.
Apart from the treatment itself the 16ha site has to accommodate inlet works and a 200,000m 3 clearwater holding tank for processed water.
'There is also an automated control and monitoring centre, and rainwater holding ponds and other items to t in the site, ' says Kelly. One of these is a recirculation system for the backwash water from lter cleaning, which will have its own treatment to remove solids.
The decision to process the 90Ml/day backwash rather than simply disposing of it is in line with the environmental sensitivity of the project.
The scheme is aiming to be a 'LEED Gold' project, matching the 'green' standard of the Leadership in Energy and Environmental Design programme, which has been widely adopted in North America.
'Hitting that target means fullling a range of sustainability criteria, ' says Kelly. These range from the use of materials such as pulverised fuel ash (PFA) in the concrete, to the structuring of the site shape to ensure a gravity-fed cascade throughout the processing and the creation of a complex heat pump system for the control centre.
'That will be Canada's rst use of geothermal heat from water, ' says Kelly. 'We are using a system of glycol-lled pipes in the base slab of the clearwater tank - about 47km of looped plastic pipe altogether - that will tap the temperature differential between the ground and the water.' The LEED standards have brought some bonuses. The requirement for PFA in most of the concrete has resulted in very good concrete density. 'We have found hardly any leaks in the cleanwater storage tank, ' he says.
Architectural design for the control building has equally paid attention to sustainability. It has a green, vegetated at-roof section and natural ventilation using sunlight to heat and move air in a chimney-shaped atrium.
High transmission glass ensures maximum internal daylight with external bafes for shading.
Green criteria even affected the initial site clearance in an area with old forest. 'Heritage stumps', the remains of logging the giant fir trees from decades ago, have been carefully removed and will be replaced at the end of the job as part of the landscaping. Tanks and lters will mostly be greened over too.