AltaGas's planned natural gas storage project will produce brine with salinity levels six times higher than what's considered harmful to fish, according to newly released documents.

The company plans to dilute that brine in a mixing zone next to the Shubenacadie River.

But according to an Environment and Climate Change Canada scientist, fish could still be exposed to unsafe salinity levels.

The documents, obtained by residents under the Freedom of Information Act and provided to CBC News, contain emails and reports dating back to 2014 about the company's discharge plan and the potential impact on fish.

South Maitland, N.S., resident Dale Poulette says the design of the Alton Gas project won't protect fish or other organisms from high salinity levels.

"There's no way for the fish, the minnows, the pinfish, anything small and big to prevent themselves from getting blasted 260 parts per thousand of undiluted brine into their gills."

In this photo taken October 2016, the mixing channel is seen mostly filled with mud. (Shawn Maloney)

Poulette was among the protesters at the project site who was recently ordered by a judge to move his protest. He lived at the site for about two years.

Alberta-based AltaGas plans to store natural gas in underground caverns near Stewiacke, N.S., about 60 kilometres north of Halifax. The caverns contain naturally occurring salt deposits, which must be removed before the gas can be stored. The company plans to dissolve the salt with water from the Shubenacadie River and then release the resulting brine back into the river.

The project has long raised concerns about the potential impact on the environment and fishing.

The documents include a 2016 report from a toxicology lab supervisor at Environment Canada's Atlantic Laboratory for Environmental Testing that says the brine will have a salinity level of up to 240 parts per thousand (ppt) before it is diluted to a maximum of 28 ppt in the mixing channel.

A level of 40 ppt has been found to be acutely toxic to three-spined stickleback fish, according to a 2017 letter from the federal department to the company included in the documents.

A rock wall will be used to reduce the likelihood that fish or larvae will enter the spot where water is drawn into the caverns, but the toxicologist said fish could get into the mixing channel at either end.

"For a short period of time, any fish in this mixing zone may be exposed to elevated salinity at levels above those considered safe for marine and estuarine organisms," the report notes.

AltaGas is considering creating a barrier to prevent fish from entering the channel but it is conceptual at this stage. (Shawn Maloney)

In an email, an AltaGas spokesperson said the company is considering creating a barrier to prevent fish from entering the channel, "but at this stage it is conceptual."

Rachael Greenland-Smith, who requested the documents, said the emails and reports show the project violates the Fisheries Act, which prohibits "deleterious substances" in water frequented by fish.

A 2017 memorandum to the deputy minister of Environment Canada confirms that when the concentrated brine is first deposited in the mixing channel, it would be deemed a deleterious substance.

Greenland-Smith said that issue should have been identified and resolved long ago.

"We see now that this project — after the pipes have been laid, the channel has been dug — that they're kind of going wait, wait, wait, wait, wait.… This should have been worked out before the channel was built, before the infrastructure was put in."

An AltaGas spokesperson said Environment Canada is developing a regulation to oversee brine release, and there will be public consultations about that regulation.

Lori MacLean said the site will be monitored, and if salinity exceeds the limit of 28 ppt within five metres of the release point, brining will be shut down.

MacLean said due to the tidal action of the brackish water, all species in the Shubenacadie River are already "well adapted to encounter quick and large salinity fluctuations."