Officials in New Zealand's leading oil and gas region are rejecting claims that cows are being allowed to graze on land polluted by waste from mining and fracking operations.

Mining companies were permitted by the Taranaki Regional Council to dump drilling waste on some farms - known as landfarming - as long as the land was cleaned up before it was used for another purpose.

A council report showed that parts of the Schrider Landfarm exceeded acceptable levels of contaminants such as petroleum hydrocarbons and other toxic wastes.

The Green Party claimed that under current rules, livestock was allowed to graze on this land.


Energy spokesman Gareth Hughes said landowners were not required to reduce the toxicity levels on the landfarm until they surrendered the consent to do something else with the land.

"The limits for contaminants do not apply before then, meaning that these limits are not applicable when the land is being grazed by dairy cows," said Mr Hughes.

But the council said that it was "nonsense" to suggest that council allowed cows on land soon after waste had been spread onto it.

In a statement, the council's environmental quality director Gary Bedford said land could only be returned to agricultural production once extensive testing had confirmed that residues were within environmental standards.

Greens said council reports indicated that cows had been found on landfarming sites.

The council said hydrocarbons which were found in drilling waste usually degraded within three to 12 months.

Only one consent had been given to dump fracking fluids on land. That landfarm had now been closed and the council was testing the soil.

It said that most of the muds, solids and sludges dumped on landfarms was not from hydraulic fracturing and was made up of water and synthetic-based mud and rock cuttings.

Mr Hughes was concerned that the National-led Government's expansion of oil and gas exploration could create a massive waste disposal problem.

The Parliamentary Commissioner for the Environment Jan Wright said in an interim report on fracking that the industry had been mostly left to set its own rules. She found no record of fracking-related pollution or leaks into aquifers, but said the expansion of the industry increased the risks of mining-related harm.

Fracking involved the injection of large volumes of water, sand and chemicals into rocks which contained natural gas.