The Adelaide City Council has been found guilty of failing to properly manage a landfill site at Wingfield Waste and Recycling Centre, where there have been a number of serious fires.
The Environment, Resources and Development Court found that the council breached its licence when it failed to cap the landfill site.
The council denied the charges, but Judge Susan Cole found the council guilty on all four counts.
Two other charges were dismissed for being out of date.
In 2008, the council agreed to a management plan, but three years after the December 2012 deadline the council had only capped 15 per cent of the site, breaching the agreement.
The series of fires at the Wingfield depot prompted investigations by the Environment Protection Authority (EPA).
The EPA and the council have been negotiating since 2000 over extending the deadline for accepting waste, licence conditions and landfill capping designs.
No penalty has been decided, but the maximum penalty for a body corporate contravening a condition of its licence is $120,000.
The case will return to court in February for sentencing submissions.
