Environment Waikato is checking out the damage after heavy rain over topped a temporary sludge storage dam at the Kinleith Pulp and Paper Mill site, sending up to 5,000 cubic metres of treated sludge into Lake Maraetai.
The area had 60 mm of rain over about five hours on Wednesday afternoon, and the company’s temporary sludge dam failed.
Environment Waikato Processing Industry Programme Manager David Stagg said a large amount of sediment from the dam itself was lost - about three quarters of the loss was dam sediment rather than sludge. It was fortunate that the company had been emptying sludge from the dam the previous week.
The company’s treatment system was not able to contain the material and it flowed into an arm of Lake Maraetai. Most was likely to settle out in the Lake arm and a relatively small amount would eventually flow into the main body of the Waikato hydro lakes and settle out there, he said. Downstream water users had been notified, although the spill was not expected to significantly harm the environment.
The sludge was organic and consisted of the ‘bodies’ of organisms that digest the waste in the treatment system. So far no fish kills had been seen and the risk of them was low, the only sign was discolouration in the lake arm.
The company was reinstating a temporary dam to contain the remaining sludge and had stopped de-sludging operations until a new system was properly installed in the new year. The company was also assessing whether adequate treatment was being achieved by the remaining ponds, he said.
Environment Waikato would evaluate how “avoidable” the incident was and investigating the effect of the additional sediment loading on the lake. A report would be made to the Council’s Regulatory Committee in the new year.