More diesel has been discovered in the Christchurch suburb of Addington.
In July, the city council revealed a damaged fuel line at its Horncastle Arena may have been leaking for years.
Residual diesel from the damaged line has also been found in a stormwater pond at nearby Addington Park, it said.
It believes it was carried through the drainage system during heavy rain.
Both venues are managed by the council's events company, Vbase.
Its general manager, Chris Mintern, said contractors will replace the soil, which will take about two weeks.
"There's no risk to humans and there's no risk to animals that may come into the park, so there's no risk to humans or animals at all, it's a matter of now replacing that vegetation that's been affected."
Mr Mintern said they were also waiting on test results from the site near Horncastle Arena before resuming work there.