Days after crews discovered a leak along a pipeline in northern Alberta, officials with Nexen have apologized for the leak, and crews are working to clean it up.

On Thursday, officials with Nexen and the Alberta Energy Regulator (AER) went public with details on the spill. Officials said about 5 million litres of emulsion – a mixture of bitumen, water produced by the extraction process and sand – leaked into an area about 16,000 square metres in size near Nexen’s Long Lake Project.

The site is located about 35 kilometres southeast of Fort McMurray.

Officials with Nexen said Friday that the leak was found Wednesday by a worker.

“We did have a contractor actually walking the pipeline, and that’s how we discovered it,” Nexen Senior VP Ron Bailey said.

Nexen said a leak detection system was in place, but there was no warning about the spill.

AER announced late Friday that an Environmental Protection Order had been issued to Nexen.

The order requires the company to contain the spill, identify parties affected and notify them, and to test for hydrocarbons and chlorides. The company must also develop a water body management plan, a wildlife mitigation plan and detailed delineation and remediation plan.

Nexen is also required to release daily public reports and publish them to their website – and submit a final report to AER within 30 days of completion of all work in compliance with the order.

On Thursday, Nexen said the spill had been contained - steps confirmed by AER Friday.

AER officials are also investigating the spill, and AER staff remained on site to monitor the response.

Peter Murchland with AER said Friday that there is no risk to the public or wildlife.

“At this point we have no indication that there’s any risk to public health or public safety,” Murchland said.

However, Chief Allan Adam of the Athabasca Chipewyan First Nation said in a statement:

“A spill this size into the muskeg, which is an important part of the eco-system in the region and house many of our medicines, berries and habitat for species our people rely on for sustenance, is extremely serious.”

This spill is the largest in recent years – in 2011, a pipeline owned by Pails Midstream leaked about 4.5 million litres near the northern community of Little Buffalo.

With files from Susan Amerongen