The Masterton District Council’s urban wastewater (sewage) treatment facility is located at Homebush to the east of Masterton. A reticulated sewerage system collects wastewater from Masterton’s approximately 20,000 residents and transports it 4 kms to Homebush for treatment and disposal. The reticulation system uses a predominantly gravity system that is augmented in low lying areas by two pump stations and a siphon.
The Treatment Ponds
The wastewater treatment ponds cover an area of approximately 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 sufficient capacity to hold 270,000 cubic meters of wastewater, have embankments heights from 2.5 to 3.2 meters and are lined with 1.5mm thick high-density polyethylene (HDPE).
The Ruamahanga River Outfall Diffuser
The diffuser outfall to the Ruamahanga River was commissioned in June 2013 and allows treated wastewater to be discharged and mixed with river water to meet strict Resource Consent requirements. The outfall system comprises two automated pen-stocks located in Pond 6, the last of the maturation ponds. Wastewater enters the pen-stocks when either or both of the outfall gates are opened and flows 900 meters through a 1.2-meter diameter pipeline to the diffuser outfall. The diffuser outfall comprises four discharge pipes connected with, and at right angles to, the main pipeline. These pipes are buried in the river bed and have mesh screens over the end to prevent rocks and boulders entering the system.
When river conditions permit, treated wastewater is discharged through the diffuser outfall pipes and turbulence within the river mixes the wastewater with the river water to achieve the water quality requirements of the Resource Consents.
The Border Strip Irrigation System
When river conditions do not allow discharges through the diffuser, treated wastewater will be irrigated to the border strips. The border strips are a series of fields that will be irrigated with treated wastewater. They are 24 meters in width and vary in length from 150 meters to 300 meters and are separated by “borders” or “dykes” that are raised mounds of compacted earth. The borders act as small dams and contain the irrigation water within the area of each strip allowing control of application rates. The border strips will be irrigated on a 7 to 10 day cycle, depending on weather conditions and the time of the year. The grass growing on the border strips will be harvested and sold for animal food. Strict conditions apply to the production and testing of the baleage to ensure that it is safe for consumption by animals.
Makoura Stream Riparian Planting
The Makoura Stream meanders its way through the Homebush site and discharges into the Ruamahanga River just downstream of the diffuser outfall. Removal of exotic trees (willows, poplars, pines, etc) and planting of the riparian margins of the stream were undertaken as part of the upgrade of the treatment plant. In total, some 16,000 native trees and shrubs were planted along the stream and the main irrigation channel that runs through the site. The trees and shrubs are irrigated with treated wastewater via 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 in a beneficial manner.
Testing Treated Sewage
Monitoring of dissolved oxygen, suspended solids, pH, temperature and a range of other factors is undertaken on a daily basis. Laboratory analysis of samples is undertaken to determine the performance of the plant and the results are measured against Resource Consent criteria.
Flows, faults and equipment status are monitored 24 hours a day, 365 days a year and are relayed through a radio telemetry system to a central computer where they are received and logged. Alarms alert the plant operator if there are any issues needing attention.
Water & Wastewater Treatment Plant Supervisor – Kevin Godfrey
Water & Wastewater Treatment Technicians – Andrew Cutfield/Kevin Crosby
P: 06 377 4527
F: 06 378 7850
M: 0274 426 456