Waikato River - wastewater discharges

Point source discharges are direct discharges from a fixed point. They include wastewater from industries, towns (for example sewage and stormwater) and dairy farms.

There are currently more than 80 point source discharges to the main stem of the Waikato River which have resource consents from Waikato Regional Council. On top of this, there are a further 1,600 discharges to the rivers and streams that drain into the Waikato River.

Of the discharges to the main Waikato River, about 30 are classed as large. These discharges are consented by Waikato Regional Council and include:

• heated water from geothermal and gas/coal-fired power stations
• geothermal waste water from a geothermal power station
• treated sewage waste water from Hamilton city and several smaller settlements
• treated waste water from a major pulp and paper mill, a major dairy factory and a large meat-works.

Wastewater treatment improved considerably in the 1970s. However, since then the amount of some contaminants, such as the nutrients in certain sewage waste waters, going into the river has increased. This is because urban populations along its banks continue to grow.

Waikato Regional Council continues to work with consent holders to improve waste treatment when resource consents are renewed.

Arsenic

Geothermal fluids from geothermal power stations are a major source of arsenic, boron and other geothermal chemicals found in the Waikato River. Since the Wairakei Power Station was built in the late 1950s, the amount of arsenic in the Waikato River has more than doubled.

Arsenic levels in the river now exceed drinking water standards. This means a high level of water treatment is needed for drinking water supply. To reduce this effect on the river the Ohaaki geothermal field re-injects waste geothermal fluid back into the ground. This is also beneficial for the geothermal systems themselves. 

Colour

Wastewater from the Kinleith Mill is a major source of dissolved colour or dark tea-coloured staining in the upper river. In 1991 when a new treatment process was introduced, the amount of dissolved colour in the mill’s waste water halved, causing levels in the river to fall. As a result, the Waikato River is now a brighter green colour than it was during the 1980s.

Bacteria levels

A recent study of bacteria levels (an indicator of health risk) in the lower river showed that discharges of wastewater are not a major source of bacteria to the river as a whole. 

The three major point sources of bacteria to the river between the Narrows and Huntly (Hamilton sewage, Ngāruawāhia sewage and a meat-works) account for only five per cent of the total bacteria levels found in the lower river. This indicates that most of the bacteria found in the river must come from non-point sources such as rural runoff.

In the upper river, since the sewage discharge from Taupō township stopped in 1995, bacteria have reduced to safe swimming levels downstream, nutrient levels have dropped and nuisance algae no longer spoils the way the river looks. Most people would be surprised but pleased to know that Huka Falls, the image of unspoilt New Zealand, is now much cleaner than it was in the 1980s!

Waste from around one-third of dairy farms in the region is treated in oxidation ponds before being disposed into waterways. Farm dairy oxidation ponds often contain high levels of bacteria. Scientists estimate that the waste from 20 farm dairy oxidation ponds contains the same amount of bacteria as the primary-treated sewage waste water from a medium-sized city.

Waikato Regional Council encourages dairy farmers to irrigate farm dairy effluent onto their land, rather than treating it in oxidation ponds and disposing of it to waterways.

In recent years there has been a major shift away from oxidation ponds to land treatment of dairy effluent. Five years ago, one third of dairy farms in the Waikato used land treatment. Today, two-thirds use land treatment, so much less farm dairy effluent now reaches waterways such as the Waikato River.