Wastewater Schemes and Treatment
Ashburton wastewater scheme
The Ashburton wastewater scheme is the largest in the district and also includes the wastewater network at the Lake Hood subdivision. The first sewer pipe reticulation was constructed in 1921 and collected wastewater from what is now the central business district. Since then the network has been greatly extended and upgraded. Information regarding the wastewater scheme:
- About 129km of pipe make up Ashburton Wastewater scheme
- The largest sewer mains are 900mm in diameter
- Most of the sewer mains are 150mm in diameter
- There are nine pump stations
Treatment system
Until 1975, all wastewater was discharged untreated directly into the Ashburton River. There was concern over the impact of this on the river environment and other river users which resulted in the construction of the oxidation ponds at Wilkins Road, below Tinwald. Treated effluent was then discharged to the Ashburton River.
In 2008, the treatment plant at Wilkins Road was upgraded and more treatment stages were added to the process. A land disposal site was also developed. The new wastewater treatment system now involves the following treatment steps:
- A screen is used to remove large solids from the wastewater when it arrives at the Wilkins Road treatment plant
- There is an 18,000m3 aeration pond that has 10 aerators. This is where the first treatment
- There is an oxidation pond and two maturation ponds which provide the next stages of treatment
- The treated wastewater (effluent) is then piped nearly 11km by gravity to the Ocean Farm disposal area
- A 9ha constructed wetland at Ocean Farm provides the final stage of treatment
- The treated effluent is then disposed to land by irrigation onto 265ha of pasture
Learn more about the Ashburton wastewater treatment and disposal upgrades
Methven wastewater scheme
The Methven wastewater scheme was first constructed in the 1930's and 1940's and originally consisted of approximately 8km of glazed earthenware pipes. Since then, the rest of the sewer network has been constructed as needed.
Information regarding the wastewater scheme:
- About 15km of pipe make up Methven Wastewater scheme
- The largest sewer mains are 225mm in diameter
- Most of the sewer mains are 150mm in diameter
- There are over 760 sewer connections to people's properties
Treatment system
With an increase in visitors during the ski season in the late 1990's, the treatment plant was not able to properly treat the increased wastewater loadings.
In 2000, the treatment plant was upgraded to include:
- a screen at the entry to the primary oxidation pond to remove large solids
- aerators in the primary pond to increase treatment capacity in winter months
- three rapid infiltration basins to replace the disposal trench
The upgraded wastewater treatment plant is now able to treat the wastewater more effectively.
Rakaia wastewater scheme
The Rakaia wastewater scheme is the newest in the district being constructed in 1999. Before the scheme was constructed every household had a septic tank. There was concern regarding groundwater contamination from these tanks and other public health risks, so in 1994 a decision was made to reticulate the wastewater and construct a treatment plant to service the town.
Information regarding the wastewater scheme:
- About 14km of pipe make up Rakaia Wastewater scheme
- The largest sewer mains are 300mm in diameter
- Most of the sewer mains are 150mm in diameter
- There is one pump station
- There are over 420 sewer connections to people's properties
Treatment system
The multi stage package treatment plant constructed in 1999 consists of the following treatment systems:
- A screen at the entry to the treatment plant to remove large solids
- A primary clarifier that provides the first stage of treatment
- A trickling filter that provides the second stage of treatment
- A Ultra-Violet disinfection unit provides the final stage of treatment
- The treated effluent is then irrigated onto pasture