Treated wastewater overflow into farm streams 'reeks of chemicals', samples sent for algae testing

JULIA WADE

13 Mar, 2003

Flooding was also the alleged reason why a dam on Brown Road, Hakaru – and connected to Mangawhai’s wastewater treatment plant – overflowed, causing fluoro-green water to pour into nearby streams.
 

Neighbouring farmers Paula Bygreaves and Lisa Steiner appeared on Newshub’s AM show on March 3 saying the water, which flows through their properties, is supposed to be drinkable but say it reeks of chemicals and dead duck carcasses have been found lying around the dam. Lisa also states the smell causes her to sneeze and she has had trouble breathing.

Both Paula, Lisa and Kaipara District Council [KDC] believe the unnatural looking water is the effect of a naturally growing algae and both parties have sent samples away for testing.

Treated effluent processed at the plant is pumped to a council-owned Brown Road farm and stored in a lined 170 million litre capacity dam where it is irrigated over the land in the drier months, generally from October to April. Initially, the scheme is designed to irrigate 25 hectares and can be extended when required by population growth.

The Focus put a few questions to KDC which general manager for Infrastructure Services, Anin Nama, replied to.

Mangawhai Focus: Have test results of the algae been received yet?

Anin Nama: “Our operational procedures require that we undertake regular sampling of the pond to determine the algae species. Testing to date has shown the algae not to be of concern as it is contained within the pond. The sampling undertaken on Monday was taken in the stream to understand the algae variety. As a precaution, we informed concerned farm owners not to take water from the stream for stock use. The algae testing results were estimated to take seven days, however they have not yet been received and we are following up with the lab.”

MF: It has been alleged that the dam was too full even before the flash flood of February 24 which caused the overflow.

AN: “The irrigation area covers 65 hectares and the dam can hold up to a maximum 184 million litres, but we operate the pond at a max of 170 million litres. The pond acts as a buffer and storage of treated wastewater.

“During the drier periods, we irrigate onto our farmland. Northland Regional Council’s rainfall maps show that November and December 2022 and January 2023 were all extremely wet. Normally, these months would have sufficient dry periods where irrigation to reduce the pond level would occur. Around this time last year the pond was half full. These wetter than normal months were also followed by the extraordinary February 24 storm. During this period, the surface area of the pond received 20,000 cubic metres of rainfall and at the same time our treatment plant was processing and sending three times the normal flow to the pond. This combined effect resulted in the pond overflowing.

“To manage the overflow and lower the pond level, we began irrigating onto our farmland and also started to reduce wastewater flows from the plant using sucker trucks.”

MF: As extreme weather might become a norm, are council considering any changes to the dam/plant to prevent further overflow/algae?

AN: “We are working on solutions that will minimise the algae growth. While we can limit the impact of an overflow from the pond, it’s not possible to guarantee that there would be no further overflow from the pond should there be a similar rain event.”

n Due to deadline time constraints, a follow-up story with further details will be published in a coming issue of the Focus.

An unnatural green liquid, overflow from Mangawhai’s wastewater treatment plant, oozes through a local creek, causing concerns for neighbouring farmers. PHOTO/FACEBOOK