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Rotowaro carbonisation plant

In 1991, we cleaned up the waste storage ponds on the site of the Rotowaro Carbonisation Plant. Previously, hazardous waste had been discharged to a local stream, and the storage ponds of contaminated water and sludge were close to collapse. This part of the site now presents no significant human or environmental health risks.

Past site management

From the late 1930s until 1985, Waikato Carbonisation Limited made coke, coal tar and creosote from coal at its Rotowaro plant, near Huntly. Like many old industrial sites, there were few controls on the use of dangerous substances and waste was discharged with little or no treatment.

Wastewater from the plant was discharged into the Awaroa Stream. The wastewater contained hazardous substances such as:

  • phenols
  • ammonia
  • hydrocarbons (oil and tar residues).

This degraded the Awaroa Stream and damaged Lake Waahi downstream. Local iwi were concerned about this, particularly about the impacts on food sources such as eels.

During the 1980s, efforts were made to find other ways to dispose of the wastewater – with no success. In the meantime, two storage ponds holding contaminated water and sludges threatened to collapse. Industrial rubbish and derelict equipment, waste oils and tar littered the site, and runoff carried contaminants into the stream.

In the mid 1980s, the Waikato Valley Authority (Environment Waikato’s predecessor) declined to renew the resource consents for discharging from the site. After a fire in 1985 the company went into voluntary liquidation. The site was abandoned and presented serious human health and environmental risks.

The clean up

In 1991, we had cleaned the site with funding from the Ministry for the Environment:

  • About 11,000 cubic metres of stored liquid was incinerated at Kinleith’s pulp and paper mill.
  • The remaining 4,000 cubic metres of sludge was put into a treatment pond and bioremediated (air and extra nutrients were added to stimulate bacteria to break the contaminants down).

As a result, the amount of phenol in the sludge dropped from around 550 parts per million (ppm) to less than 10 ppm, and toxic hydrocarbon levels dropped from 630 ppm to 19 ppm.

By April 1995, all that remained of the phenol sludge was about 500 cubic metres of relatively dry, largely inert material. This sludge was:

  • mixed with clay
  • spread over land on-site
  • covered with clay
  • contoured to direct runoff away from the stream.

Some contamination in the ground water under the site and soil is still likely to exist. But only very low levels of contaminants are likely to enter the Awaroa stream. This part of the site now presents no significant human health or environmental risk.

Contributions by volunteers meant the cost of this work was kept at $900,000. A similar cleanup today would cost between four and five million dollars.

Learn about how Waikato Regional Council manages contaminated sites in the Waikato region and find out how the Hamilton Gasworks site was cleaned up.

Photograph showing sludge being removed from a storage pond.

Photograph of the site after the clean up.

Photograph of the active treatment pond.