New environmental remediation techniques were needed to restore land after an abandoned oil well site was found to contain high levels of a long acting residual herbicide in 2006.
Cenovus Energy Inc. had found high levels of tebuthiuron during routine testing of a well site set for reclamation on Antelope Creek Ranch near Brooks, Alta. The ranch is on public land and home to wildlife, waterfowl, cattle and oil and gas production.
Companies had used tebuthiuron to control weeds on production leases and other industrial sites for more than 30 years, but it was no longer in use by the time it was discovered in the well site.
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“It is one of those historical legacies companies have to play with now, unfortunately,” said Alfred Burk, an environmental adviser and soil scientist at Cenovus.
“The difficulty with having found it was that the government didn’t have criteria for removing it.”
Vegetation and soil quality are keys to reclamation success, which means it is critical to know the concentrations that affect native plant species.
The herbicide had to be removed before reclamation could begin, which is planned for this year.
Reclamation returns land to similar production capability through decommissioning, recontouring, surface soil replacement and revegetation.
The site in Alberta consisted of an old storage battery and compressor that was used to collect oil from several locations within five kilometres.
The compound was found in high concentrations to a depth of half a metre.
Fortunately, the herbicide was confined within the lease, which was the size of two tennis courts.
Cenovus worked with the ranch manager, Alberta Environment, Sustainable Resource Development and engineering companies to form a plan to remove the herbicide from the soil rather than hauling it to a landfill.
Nelson Environmental of Spruce Grove, Alta., helped the project use a thermal desorber, which uses heat to remove the soil sterilent. The technology had been previously used to remove petroleum products but never on a herbicide.
“We were pleasantly surprised that it worked,” Burk said.
“I hate moving soils around if I don’t have to. There is always the chance of bringing in weeds and invasive species.”
Ultimately over a three month period, 15,000 tonnes of soil were cleaned on site over three years and the company is now ready to start reclamation.
A small amount of hydrocarbons at the site was also removed using the same technique.
Burk said it will be necessary to add some new soil to the site during reclamation.
“We will be working with our stakeholders and the landowner to make sure we get a compatible soil material for that location.”
The site will be recontoured to ensure it matches the landscape.
Plant regrowth should do well because there was no compaction.
The goal is to replace the native plants with a mix of grass species.
Cenovus received a 2010 Alberta Chamber of Commerce award to recognize the development of new criteria and technology to remove the herbicide from the soil.
The company has 30,000 producing oil wells in Saskatchewan and Alberta and receives reclamation certificates for 40 to 50 sites per year.
