The Dene Tha' First Nation and the Alberta NDP are questioning the effectiveness of pipeline safety measures, as Apache Canada works to clean up a massive spill of industrial wastewater near Zama City, Alta. 

The company responsible for the spill in northern Alberta says it's still assessing the damage.

Apache Canada is also trying to figure out what caused its pipeline to leak about 9.5 million litres of contaminated water from oil production.

The spill is one of the largest in Alberta's history.

The spill also includes what the company calls residual oil. On Friday, Apache Canada confirmed that 12 barrels of oil were also leaked during the spill, covering an area of about four square kilometres.

The company says the leak originated at the pipeline's oil separation battery, a pressure vessel used to separate the oil, gas and water that are part of the production fluids.

Dan Lauer, deputy incident commander for Apache, says the company is focused on the cleanup.

"We have delineated an area and there was some impact to the environment, but what we're doing is we have that area very well-contained and we're removing and recovering that water," he said.

"What we'll do is further sampling and that will determine what kind of remediation process occurs."

Lauer says more than 160 people are involved in cleaning up the spill site, which is estimated at 42 hectares.

Crews are pumping the wastewater into a large container and treating it to remove the contaminants, including salt and other minerals.

Apache refused a request by CBC News to see the pipeline from which the spill originated.

Instead, the company showed a cleanup site just over a kilometre and a half away — a brief glimpse from a moving truck of a cleanup crew working in a marsh surrounded by dead trees, beside it a 6,300-cubic-metre tank to hold the waste water being pumped out of the ground.

"We have some options on how to deal with the water," said Shawn Rimby, who is with Apache.

"We're bringing in some specialized equipment that can take the salt out of the water so that we can return the water to the environment."

Apache said there are three cleanup sites in operation at the moment.

Cleanup completion time uncertain

The spill was reported by Apache on June 1. The length of time that the pipeline was leaking isn't clear.

Company officials say they don't know how long it will take to complete their cleanup.

The Dene Tha' First Nation said Thursday in a news release that a Dene Tha' field technician who visited the site on June 6 saw that all plants and trees affected by the spill had died, and that the contamination had saturated the muskeg in the area.

It said a field technician advised Thursday that fluid is still being released from the pipe, but is now contained within in a storage pit that is pumped out into holding tanks.

The First Nation says the amount of dead vegetation in the area clearly visible from a helicopter may indicate the spill had been occurring for a long period of time.

"Given the increasing number of spills that have occurred in its territory recently, Dene Tha' hopes that the Government of Alberta will require companies to implement more effective safety measures," the release said.

Sidney Chambaud, a band councillor with the Dene Tha’ First Nation, said he was sent photos on June 6 taken by representatives of the band's land department that showed some oil had been spilled as well.

On Friday, Apache acknowledged there was oil on the ground but said it has since been removed and the soil is being remediated.

Apache called it residual oil that leaked from an oil separation battery.

Bob Curran, a representative from the Alberta Energy Resources Conservation Board, said he hadn't heard about the oil, but said if it were a big spill or if there was an operational issue with machinery, it is supposed to be reported to them by the company.

Province criticized for spill response

Nikki Booth, a spokeswoman for the Alberta environment department, said the department and the ERCB are investigating what happened.

"Alberta has some strict environmental laws," Booth said. "If we believe the law has been broken charges can be laid. But at this point in time this incident is still under investigation."

The spill prompted the New Democrats to call on the provincial government to release a report into the safety of Alberta's network of oil and natural gas pipelines.

Alberta Energy commissioned the study last summer following major breaches of oil pipelines owned by Plains Midstream Canada.

One spill last June near Sundre fouled the Red Deer River after about 475,000 litres of oil spilled.

Earlier this year, the province charged U.S.-based company over an April 2011 breach near the community of Little Buffalo in north-central Alberta following a spill of 4.5 million litres of oil.

"This government can't be trusted to protect our air and water," NDP member Rachel Notley said of the Apache Canada spill.

"It took the government and the ERCB more than 10 days to confirm the volume and affected area of the spill, and that response is simply unacceptable."

An Alberta Energy official said Thursday the pipeline safety review report will be released in the near future, but declined to elaborate.

With files from The Canadian Press