Chemicals from landfill seep into stream

20:12, Dec 13 2012

Palmerston North's old Awapuni landfill is leaking, but no traces of toxic compounds can be detected in the Manawatu River.

However, there are traces of ammonia, zinc and phosphorous leaching into the Mangaone Stream.

Horizons Regional Council has asked the city council to monitor the stream regularly and build a trench to capture the leachate. Freshwater and science manager Jon Roygard said two investigative reports on the potential for leachate from the landfill polluting the Manawatu River were triggered by concern about the dumping of coal tar, herbicides and pesticides 12 or more years ago.

The findings were presented to Horizons' environment committee yesterday.

Dr Roygard said leachate from the lined section of the closed landfill was collected and fed through the wastewater treatment plant at Totara Rd.

There were traces of coal tar in that leachate, but there was no sign of any toxic compounds in the resulting discharge to the Manawatu River after it had been through the plant.


"We monitored a total of 17 sites along the stretch of the Manawatu River and found no trace of the leachate from the lined section of the landfill.

"This indicates that somewhere through the treatment process the effect is being mitigated."

However, leachate from the unlined section cannot be collected, and was found to be seeping into the Mangaone Stream, raising levels of ammonia, zinc and phosphorus.

Traces of compounds from herbicides and pesticides were detected in the groundwater near the landfill, but could not be traced in the river itself.

The report made a series of recommendations to the Palmerston North City Council, including additional sampling of the landfill, groundwater and river to monitor any changes.

Dr Roygard said regional and city council staff were working closely to improve management of the site.

The measures Horizons was asking the city to implement went beyond the strict conditions on the resource consents, and would involve extra costs for the city.

City council water and waste services manager Rob Green said an estimate of the costs of the extra monitoring, and building a retention trench to capture leachate before it entered the Mangaone Stream, was being prepared.

He was likely to see those figures next week. "If there is not too much cost, we will do it, otherwise we will have to report to city councillors for approval."

The recommendations do not go far enough for river guardians George and Christina Paton and Bert Judd, who spoke at the start of the committee meeting. Mr Judd said a total review of the plant should have been carried out years ago.

Both referred to the recent malfunction of a wetland pond that allowed sludge to ooze into the river, drawing no punitive action from Horizons, and a series of complaints about offensive odour, which provoked only a warning letter.

Mrs Paton said Horizons was giving the city council far too much leeway.

Manawatu Standard