Wastewater

Wai Paru

The Masterton District Council’s urban wastewater (sewage) treatment plant is located at Homebush, 4km to the east of Masterton.

A reticulated (piped) sewerage system collects wastewater from Masterton’s 20,000 residents and transports it to Homebush for treatment and disposal. The system uses a mostly gravity system that is supported by two pump stations and a siphon in low-lying areas.

Wastewater is water used from toilets, bathrooms, and kitchens. It is not stormwater which is rainwater that falls onto land and buildings, runs into gutters and downpipes, soaks into the ground or runs off hard surfaces and into waterways or to land.

Homebush Wastewater Treatment Plant

The Treatment Ponds

The wastewater treatment ponds cover around 28 hectares and are divided into two inflow or primary ponds and five linked maturation ponds. The plant is fully automated with the levels in the primary ponds and the maturation ponds controlled by a computer. The ponds have can hold 270,000 cubic meters of wastewater, have embankment heights from 2.5 to 3.2 meters, and are lined with 1.5mm thick high-density polyethylene (HDPE).

Discharge of treated wastewater to land

Treated wastewater is irrigated to 100 hectares of Council-owned land on a seven to ten-day cycle, depending on weather conditions and the time of the year. When groundwater is high after lots of rain it's not possible to irrigate to land. The grass growing on the border strips is harvested as baleage and sold for animal food. Strict conditions apply to the production and testing of the baleage to make sure it's safe for animals to eat.

Discharge of treated wastewater to river

A Greater Wellington Regional Council (GWRC) resource consent lets treated wastewater be discharged and mixed with Ruamahanga River water when river levels are high enough.

Treated wastewater is discharged through diffuser outfall pipes and turbulence in the river mixes the wastewater with the river water to achieve the water quality requirements of the resource consent.

Diffuser pipes are buried in the river bed and have mesh screens covering them to stop rocks and boulders from getting into the system.

Testing Treated Wastewater

We test treated wastewater every day to monitor dissolved oxygen, suspended solids, pH, temperature and a range of other factors. Samples are analysed in a laboratory to measure the performance of the plant and the results are measured against the resource consent criteria.

The treatment plant is monitored 24 hours a day, 365 days a year. Flows, faults, and equipment status are relayed to a central computer where they are received and logged. Alarms alert the plant operator if there are any issues that need attention.

Mākoura Stream Riparian Planting

The Mākoura Stream flows through the Homebush site and discharges into the Ruamahanga River just downstream of the diffuser outfall. Over 16,000 native trees and shrubs have been planted along the stream and the main irrigation channel that runs through the site. Exotic trees like willows, poplars, and pines have been removed.

The trees and shrubs are irrigated with treated wastewater through sub-surface drippers. Irrigation ensures a greater survival rate for the young plants, it helps in the disposal of treated wastewater and recognises that treated wastewater is a resource that can be used.

Septic Tanks

Instead of a reticulated sewerage system, rural properties generally have septic tanks – technically known as an Onsite Wastewater Management System (OWMS), commonly known as a septic tank.

A septic tank is a holding chamber for household waste. Depending on the size of your household it is recommended that you empty the tank every 3-5 years and maintain any pumps and filters over the course of the system’s life. Effluent leakages from flooding and poorly maintained septic tanks pose a major health risk to the community.

WaterNZ has produced a useful guide for OWMS owners with some key tips and information for keeping your system in good health.

Sewer Blockages

Anyone experiencing issues with their wastewater (sewerage) such as sewer blocks should call us on 06 370 6300.

We will assess and address any blockages in the sewer main or issues caused by back-up (due to excessive wet weather) at our expense.

If the blockage is in the private lateral (the pipe that connects to the Council main) and the Council main is clear, we will let the homeowner or occupant know so that they can engage their own plumber to fix any issue at their own expense.

Stormwater in our Sewerage System

The Council spends more than $1.7m every year working to stop stormwater leaking into sewer pipes including council lines and private connecting pipes. Leaking can happen during periods of heavy rain, leading to the sewer pipes being overloaded. This high flow leads to sewers backing up because it's beyond the capacity of the Homebush Wastewater Treatment Plant. Since 2006 we have been working on renewing sewer pipes, in the 2020/21 year 4.3km of sewer lines in Masterton were renewed.