• Metlakatla Water Treatment Plant

  • Northern BC

Winner of the 1995 Schreyer Award, Canada's Highest Honour for Consulting Engineering Excellence

Until recently, chlorination was the only treatment used in remote communities along the north coast of British Columbia -- a less-than-satisfactory solution for areas where surface water supplies are typically very soft, highly coloured and corrosive (acidic).

The Metlakatla water treatment project was the result of three major health concerns about the quality of these waters:

  1. parasites such as Giardia, which have caused a dozen outbreaks of waterborne disease in British Columbia in recent years
  2. disinfection by-products such as trihalomethanes, which are a particular problem when chlorinating coloured waters
  3. lead contamination resulting from the corrosion of lead solder used in household plumbing.

Within the constraints of a small remote community, the objectives of this project were to: find a simple treatment process to address these problems, and produce water which meets the Canadian Drinking Water Guidelines; and, design a full-scale treatment plant in Metlakatla to demonstrate the effectiveness of the process and serve as a training centre for other communities building similar plants.

This presented several challenges. North coast communities are generally accessible only by boat or float plane and often lack trained people to look after operation and maintenance because they are small (100-1,500 in population). Consequently, any treatment facilities should be simple, reliable, and economical to operate and maintain.

New Treatment Process

Through a program of research and development into alternative treatment processes, Kerr Wood Leidal (KWL) and its affiliate CH2M - Gore & Storrie identified a unique combination of processes that is effective, yet requires virtually no electro-mechanical equipment. The treatment processes include colour precipitation, slow sand filtration, and limestone contactors. While each of these processes have been used before, this particular combination is not known to have been used previously in a full-scale water treatment plant.

An important feature of the new process is the use of limestone contactors to condition the water for colour removal and also reduce its corrosiveness (acidity). This process involves passing the water through a bed of crushed limestone (CaCO3) which slowly dissolves, adding alkalinity to the water. In essence the process simulates nature. Limestone contactors are very easy to operate since they require no feed equipment. In contrast, most plants use powdered chemicals, such as lime (CaO), which is difficult to feed and consequently quite unsuitable in small communities.

The Metlakatla plant has been in operation since February 1994. Test results show that the plant produces water which not only meets, but surpasses the latest Canadian Drinking Water Guidelines. Colour is reduced from 140 tcu (colour of tea) to 15 tcu or less (virtually colourless); trihalomethanes are reduced from a range of 0.2 to 0.5 mg/L, to 0.05 mg/L, half the recommended level in the Canadian Drinking Water Guidelines; and corrosiveness is considerably reduced, as indicated by significantly lower lead levels measured at consumers' taps. In addition, because the plant includes both filtration and chlorination, it provides effective treatment of microbiological contaminants (bacteria, viruses and giardia (cysts) to the highest North American standards.

By making effective use of hydraulic and gravity processes, theplant has virtually no electro-mechanical equipment. As a result, the plant is simple to operate and maintain. Daily operating requirements take about two hours, and are usually limited to adjusting the filter flow and measurement of a few key water quality parameters. Filter scraping, an easy manual task that takes 1 to 1.5 hours, is carried out at about two month intervals.

The plant has hosted training sessions for severalother Bands planning to proceed with similar water treatment systems.

KWL completed the project to the client's budget and schedule. The plant was put into service 18 months after the start of design. The total project cost, including design and construction, was $1,300,000. (Construction costs were about double what they would be in a central location because there is no road to Metlakatla).

Ideal Solution for Remote Communities

It is often said that "simplicity is the essence of design". The Metlakatla plant has proven to be simple and appropriate for the community, and it produces high quality water which the residents say "tastes great".

The plant is a model for other small communities with similar water quality problems. Since its completion, three other B.C. communities - Port Simpson, Bella Bella, and Hartley Bay - have built plants based on the Metlakatla process. The new process is suitable for application elsewhere in Canada, such as areas in northern Ontario and the Maritimes. In addition the new process has potential for export to other countries.