Experts questioned on contamination effects

Hearing commissioners have demanded to know whether a proposed sewerage scheme in Te Anau would contaminate waterways.

On the second day of a hearing for the Southland District Council's proposed Te Anau sewerage scheme yesterday, independent commissioners sought reassurance from council experts about possible environmental damage.

Senior environmental scientist Susan Bennett, speaking in support of the scheme for the council, said there was no potential for the discharged wastewater to enter any surface water like the Kepler Mire or Home creek.

Discharging the wastewater to land would result in a plume of nitrogen-enriched groundwater, which could discharge into either the Waiau River or Lake Manapouri, she said.

Environmental effects or impacts on the aquatic ecology of the Waiau were expected to be minor, while it was unlikely the groundwater plume would discharge to Lake Manapouri.

"The risk of groundwater discharge having . . . adverse effects on water quality and aquatic ecology in Lake Manapouri would be negligible," she said.

Commissioner Yvette Couch-Lewis asked Bennett for assurance the irrigation of wastewater would not mobilise contaminants towards the Waiau.

Bennett said most contaminants would be treated before irrigation and would not enter groundwater. "We are expecting minimum contamination of the groundwater."

Couch-Lewis asked what impact the groundwater plume would have on the Waiau's ecosystem, recreation at the river and food gathering.

Bennett said nitrate levels would be undetectable once groundwater had mixed with the Waiau.

"I suspect there would be no impact on the Waiau," she said.

"There would not be changes to the look and smell of this river as a result of discharge."

Further questions from commissioners focused on the possibility of the groundwater plume migrating to different areas, cumulative effects of nitrates in the groundwater over time, frequency of monitoring, and the standards of compliance.

Yesterday afternoon, the commissioners visited the current waste-water treatment plant, the Waiau River, Lake Manapouri and the proposed site for discharge.

Submitters have their chance to speak at the hearing from this morning. The hearing is expected to continue until Friday.

The Southland Times