Sinopec Daylight Energy is to pay $150,000 for a spill near Fox Creek in northwestern Alberta between Feb. 2 and Feb. 4, 2012.
According to an agreed statement of facts, the spill happened as a result of a contractor's attempts to restart compressors at two wells, which produced a mix of natural gas, hydrocarbon liquids and salty, contaminated water.
In order to restart compressors at the second well, the contractor had to temporarily bypass emergency shutdown devices, which stop production if internal pressure exceeds the pipeline's capacity to safely handle it.
The contractor then forgot to reset the device, leaving it in a bypass state, the statement says.
Two days later, the contractor realized that no water was flowing into a disposal well, despite the fact the well was producing.
"(He) then realized the pipeline must be leaking," the statement says. "He immediately shut the pipeline down and notified his foreman."
The spill sent 391,000 litres of contaminated, salty water into Marsh Head Creek, a tributary of the Athabasca River.
That was enough to exceed allowable levels of those contaminants 7.4 kilometres downstream of the spill.
"No dead fish were actually observed because Marsh Head Creek was covered with snow and ice at the time of the release," says the statement.
The Alberta Energy Regulator said the cleanup took until March. Final remediation wasn't complete until June 2013.
The cleanup cost nearly $10 million, the regulator said.