Halifax Water declares seasonal sewage disinfection pilot a success

Skeptics, however, still aren't convinced the plan to shut down ultra-violet light disinfection over the winter is safe.

Critics still skeptical, say more testing needs to be done to ensure Halifax Harbour is safe

Halifax Water is pleased with the results of a pilot project that scaled back ultra-violet disinfection of sewage heading into Halifax Harbour. (CBC)

Halifax Water says it's buoyed by the results of a pilot program that could see the lights go out on a sewage disinfection system during the winter months, but critics still aren't convinced the plan is safe for the harbour.

On March 1, Halifax Water shut off its ultra-violet lights, which disinfect waste water in the final stage of sewage treatment, part of a two-month pilot program to test out seasonal disinfection at eight different sites.

"We're actually quite surprised, pleasantly surprised, that the numbers have stayed down as low as they are," said spokesman James Campbell.

During the pilot program, there were four instances where samples from the harbour surpassed safe Enterococcus bacteria levels for swimming. During the five months before the trial, when water was still being UV disinfected, one sample tested above safe swimming guidelines.

No tests for fecal coliform or E. coli surpassed swimming guidelines during the pilot project.

This graph shows Enterococcus bacteria levels found at eight sites tested by Halifax Water, both before and during the pilot project. (CBC)

If the Nova Scotia Department of Environment approves the program, UV lights would be shut off from Nov. 1 to March 31, saving Halifax Water $148,000 in electricity costs, and more than 1,000 tonnes — or 234 cars-worth — of greenhouse gas emissions a year.

"The benefits for us are the improved lifespan of our UV systems, to savings to ratepayers," said Campbell.

Not "the whole picture"

But not everyone is reassured by the results.

Dalhousie University assistant professor Haibo Niu, the co-author of a recent study called Prediction of Fecal Coliform Concentrations from Wastewater Discharges in Halifax Harbour, said the numbers are "not very convincing."

"You need minimum five samples," said Niu, who studies contaminants in the environment. "Here is only three."

The Halifax Water study used a "single maximum" sampling model, collecting a total of three samples per site over a two-month period.

Niu said that in order to "get the whole picture," you need to calculate the average of at least five samples from each site during a period of less than 30 days.

"We have to realize that the ocean is a highly dynamic environment," said Niu. "You can see the concentration changes all the time. The best approach is doing more samples, you get a better understanding."

Concerns about shellfish

Even with the study's small sample size, Niu said the bacterial levels make him less concerned about swimmers. But he does worry about shellfish.

In all sites but one — Dingle Beach — the limits for safe bacterial levels for shellfish were surpassed.

"If the limit is there for us to enforce, we've exceeded that," said Niu. "Based on that I would say I am not very comfortable with these numbers."

With a decades-long ban on commercial shellfish harvesting in outer Halifax Harbour still in place, Campbell said Halifax Water is instead focussing on bacterial standards for safe swimming "as required through our regulations."

Larissa Coleman, water co-ordinator at the Ecology Action Centre, said this is the wrong approach.

"These regulations are in place to protect human health for swimming in the water," she said. "But it doesn't necessarily take into consideration all the different organisms and wildlife that would be impacted by these changes in bacterial levels."

Dingle Beach was the only site tested where safe bacterial levels for shellfish were not surpassed. (Blair Rhodes/CBC)

Even where human guidelines are concerned, Coleman said adopting the seasonal disinfection program is "not in the best interest for Halifax residents."

"People use the harbour throughout the winter," said Coleman. "The ferry still runs, people are still out in the water, dogs are in the water, so even though it's occurring in the wintertime, it can negatively impact them."

Campbell said it's now up to Nova Scotia Environment to determine whether the risks, which he said are "extremely low," will be worth the benefits to the utility and the ratepayer.

"We're turning the lights back on on April 29," said Campbell, "and we expect the numbers to go down even further."