The company addressed the seepage of the viscous form of oil from its Primrose project near the Cold Lake weapons range in Alberta in its second quarter report.
The Alberta Energy Regulator in July released results from an independent review of an assessment made by company of last year's seeps.
AER said four so-called flow-to-surface events spoiled about 50 acres of land. The company's own report said a process called cyclical steam stimulation, or CSS, may have cracked open other subsurface layers, allowing oil to leak out of control from the site.
In its second quarter report, the company said cleanup of all four sites is complete and it has confirmed there is no ongoing contamination of the groundwater aquifer at the site.
"Concurrent with the causation review, Canadian Natural has developed methods to prevent seepages for all potential failure mechanisms," it said in a report published Thursday.
The AER placed restrictions on the steam injection method at the site in June 2013.
The regulator said cleanup efforts are ongoing, though all of the released bitumen, the viscous form of oil found primarily in Alberta, has been contained.