Up to a million tyres are languishing in a dump on a Huntly property, leaching toxic chemicals into the soil, but the businessman authorities say illegally dumped the tyres has left the country and might never be held to account.

The man - Auckland businessman Ross Britten - used his 61-hectare property on State Highway 22 to dump the tyres over six years.

Britten's sole-director company - Ross (Des) Britten Ltd - was this week fined $77,600 in the Hamilton District Court for dumping the tyres, having been found guilty at trial in 2011. Britten was also convicted as an individual.

But Britten was not in court when his company was fined on the six charges of discharging contaminants onto the land, and the Waikato Regional Council fears he is "living in Australia to avoid this court case".

It is not known how much Britten's company have earned from the tyres, but disposing of tyres can cost up to $3 each.

Regional council investigator Patrick Lynch described the scale of the dumping as "staggering".

"Absolutely by far and away this the largest-scale tyre dumping I have ever seen by a long way," he said.

An investigation was launched after earthworks were noticed at the property during a flyover by regional council staff in 2009.

Council staff executed a search warrant at the property, bringing in a large digger to unearth thousands of tyres, many sitting in or below groundwater.

"We kept finding more and more and more the deeper we dug," Lynch said.

Records indicated Britten had collected up to a million tyres from retail tyre outlets, with those businesses assuming he was disposing of them correctly.

Instead, the council said Britten used his own earthmoving equipment to bury the tyres, creating a possible environmental time bomb.

Lynch said that while the council was aware it might never see the fine paid, the greater concern was for the "hundreds of thousands of tyres still sitting out there."

"Some are buried above ground but there is no real way of knowing the numbers there," he said.

There are no plans to move the tyres.

"It is a difficult thing because to locate and excavate all the tyres right now would have more environmental effects associated with it than leaving the tyres where they are," Lyncg said.

But leaving them there posed its own issues with the danger of contaminants leaching into the soil and waterways if the tyres started to break down.

"I am not a scientist but suffice to say tyres are horrible things when they are exposed to water and start to break down and contaminate the groundwater,'' he said.

"What we will do is monitor the nearby water courses and if that monitoring starts to show the contamination from the tyres is elevating then we may take further action.

"But we simply don't have a clear idea at the moment what the best way to manage these tyres in the future is."

The Mangapiko Stream runs through the property, which has since been sold to an unnamed company.

Lynch said that although Britten's company involved had been fined, Britten was still to face personal liability action.

"Though he has been convicted, he left the country before he was sentenced,'' he said

"The court has issued a warrant to arrest Mr Britten that I imagine will be executed if and when he returns to New Zealand."