Q & A: Metro Vancouver sewage

By Leslie Young

How many sewage plants are there in Metro Vancouver?

There are five sewage treatment plants across the region. Two of these, Iona Island and Lions Gate, are primary treatment plants. The other three, Annacis Island, Lulu Island and Northwest Langley, are secondary treatment plants.

Find out where the sewage treatment plants are

How does the region treat its sewage?

Metro Vancouver uses primary treatment at two of its plants and secondary at the other three.

Primary treatment is considered the least effective form of sewage treatment. Sewage is screened to remove large objects like garbage and rags from the water, then left to settle in a large tank. Scum rises to the top and is skimmed off. Sludge sinks to the bottom and is scraped out. The water left in the middle is dumped into the ocean.

Primary treatment only removes between 40 and 60 per cent of suspended solids from the sewage and only reduces the level of fecal coliform (a harmful bacteria) by 45 to 55 per cent.

Iona Island, the region’s largest sewage plant, treats about half a billion litres of sewage a day in this manner. This facility and Lions Gate, the other primary treatment facility in Metro Vancouver, are the worst offenders for toxicity tests.

The region’s other three sewage treatment plants employ secondary treatment. After primary treatment, they expose the sewage to bacteria that devour organic matter and trap dissolved particles, resulting in a much cleaner discharge. Tertiary treatment, an even higher standard of treatment, is used by cities like Calgary and Whistler and cleans out even more dissolved chemicals and organic matter.

Watch a slideshow explaining the treatment process step-by-step

How does the region make sure that what it dumps into the ocean and Fraser River is safe?

Metro Vancouver tests the wastewater just before it is dumped out into the ocean or river. Every day, the water is tested to find the amount of suspended solids it contains, its biological oxygen demand – how much oxygen the organisms in the water suck up, its pH and how much ammonia it contains. It is also tested for a variety of metals like copper and lead. Limits on the acceptable amounts of each of these compounds are set out in the dumping permit given to each plant by the provincial government.

These certificates also require Metro Vancouver to test how toxic their water is once a month.

What is a toxicity test?

A toxicity test measures how lethal wastewater is to marine life.

The test that Metro Vancouver performs monthly at each plant is called the acute lethality of effluents to rainbow trout test, otherwise known as the LC50 acute lethality test.

It involves taking a water sample from treated wastewater just before the wastewater is dumped into a nearby river or the ocean. Rainbow trout are placed in the sampled water for 96 hours. If at the end of this period, more than half of the fish die, the test is considered a failure.

A passing grade is 100. At 100, half of the fish die after 96 hours in pure, undiluted wastewater.

The Iona Island treatment plant, just north of Vancouver airport and steps from Iona Beach Regional Park, had an average score of 91 in 2006. This means that half of the fish died in a 91 per cent concentration of wastewater after 96 hours.

Iona’s lowest score was 60. This means that on this day, the wastewater was so toxic that half the fish died in only a 60 per cent concentration. This toxic material was dumped into the Strait of Georgia.

What kind of effect is this having on the environment?

Metro Vancouver carefully monitors the environment and has so far not noticed any significant problems, even close to the pipes where wastewater is dumped. They believe that, in the ocean, the wastewater is diluted so much that it does not have a real effect on the environment.

Environmental groups disagree with this approach. They believe that chemicals or toxic materials in the wastewater eventually end up somewhere, and could build up in the environment. Even though we do not see problems at the moment, they say, we could see them in a few years.

Read the whole story on Metro Vancouver’s sewage treatment