Why we do this
The wastewater systems focus on protecting public and environmental health by collecting and treating wastewater prior to release into receiving environments.
What we do
- Collects, treats and disposes of wastewater through sustainable, cost-effective and environmentally friendly methods.
- Owns and operates wastewater schemes for: Dargaville, Maungaturoto, Te Kopuru, Glinks Gully, Kaiwaka and Mangawhai; and
- Undertakes asset management, planning, operation and maintenance of the wastewater schemes, capital and refurbishment programmes and consent monitoring and compliance, along with responsibility of professional and physical works undertaken on the network.
How this benefits the community
- We provide and maintain infrastructure that supports the economy of the area. We will ensure that people who are able to will be connected to Council schemes;
- We are intent on lifting Kaipara district’s well-being by providing infrastructure where people live close together, which protects the health of both the community and the environment; and
- We will protect and enhance our natural assets and open spaces by ensuring we meet our compliance with the discharge consents.
Dargaville has a population of approximately 5,000 and is serviced by 40 kilometres of pipeline, 15 pump stations, 6 kilometres of rising main and a single treatment plant.
Wastewater is collected from the urban area, apart from a section of the Beach Road industrial area that has onsite treatment.
Most recent census data indicates Dargaville’s population has declined 4.6% from 2006 to 2013.
The layout and location of Dargaville’s wastewater assets are illustrated in the Asset Map below:
Dargaville Asset Map
The Sunset West development installed at Baylys (Dargaville) was originally to be vested to Council as a public system. Due to downturn in development and a change in the owner of the subdivision, as of June 2013, the scheme will be retained as a privately-owned and operated scheme.
Dargaville is served by a single WWTP situated adjacent to the Northern Wairoa and Awakino Rivers. The site comprises a 4.7 hectare (47,000m2) facultative oxidation pond, with aerators, in the western part of the site and a 20,000m2 maturation pond in the eastern part of the site. Figure 3 5 illustrates the layout of the WWTP (source: Google maps). A photograph of the oxidation pond is included as Figure 3 6.
Effluent enters the oxidation pond for initial treatment and is then pumped into the maturation pond where it circulates over a seven day period (varies according to infiltration level) for further polishing of the effluent, particularly with regard to pathogen reduction. The treated effluent discharges via a spray irrigation field onto the riparian strip bordering the Northern Wairoa River.
The Dargaville WWTP was partially upgraded in 2007 by converting the originally constructed wetlands to a maturation pond and constructing an effluent land dispersal system along the banks of the Northern Wairoa River. Then in early 2009 the maturation pond was desludged to remove an historical build-up of sludge carried over from the main oxidation pond. It is now believed that the main pond is 80% full of sludge and desludging is urgently required. An Oxidation Pond Management Study is proposed for 2018/2019 which will provide the information required to progress the desludging over two years in 2012/2021 and 2021/2022.
Dargaville WWTP layout
Maungaturoto and the Maungaturoto Rail Village have a population of 895 and are situated on State Highway 12 (SH12), approximately 10kms west of the intersection between SH1 and SH12. The main township straddles the ridgelines which fall towards the fringes of the Kaipara Harbour and the Wairau River.
Maungaturoto is serviced by 11kms of gravity reticulation pipelines, 3 pump stations and 1.2kms of rising main and a single WWTP constructed in 1992.
Most recent Census data indicates Maungaturoto’s population has growth 7.2% from 537 resident population in 2006 to 576 in 2013.
Maungaturoto asset map
In addition to the main collection and treatment system in Maungaturoto there is a small stand-alone system for seven houses in the Railway Village to the west. This system drains to a communal septic tank and drainage field. The assets are included in the main Maungaturoto valuation.
The disposal field has a new resource consent running through to 2025 and there are no specific issues with the system.
Railway Village reticulation
The Maungaturoto WWTP consists of a single 8,300m3 oxidation pond constructed in 1980 and located adjacent to the Country Club. The oxidation pond is protected by a waveband and dissolved oxygen levels are maintained by an aerator. Photographs of the oxidation pond/membrane building and the aerator and included in Figure 3-19 and Figure 3-20 respectively.
The WWTP was upgraded in 2009 to provide a higher level of effluent treatment to comply with new resource consent conditions. This work included: Installation of an influent step-screen, new membrane filtration plant and construction of a new 650m3 treated effluent storage pond and new rock discharge structure into the Wairoa River. As per the previous consent requirement, wastewater is discharged into the upper reaches of the Wairoa River via a tidal discharge immediately after high tide.
Stormwater infiltration into the Maungaturoto wastewater system is a significant issue. Present dry weather flows are around 180-250m3 per day. In heavy rainfall conditions inflows to the WWTP have exceeded 2,500m3 per day and with rainfall on the pond reached a total daily flow of nearly 3,500m3 per day. As the resource consent provides for a maximum daily discharge of only 1,200m3 per day (which is the design flow for the new membrane filtration plant), excess flows are taken into storage in the pond and released over subsequent days. The treated effluent storage pond also helps with flow buffering. The flow buffering facilities at the WWTP are however pushed to their limits during heavy rainfall events and could well be exceeded without further work completed to reduce stormwater infiltration within the reticulation system.
Since commissioning of the membrane plant in mid-2009 algal levels in the pond have tended to be higher than historically observed. This could be aggravated by dryer summers however could be related to the backwash return from the membrane plant. The main effect higher algal populations have is an increased cleaning requirement of the membrane plant, which has caused maintenance costs to be significantly higher than expected. Further work is required to understand the operation efficiency and a capacity study has been budgeted for in 2018 to 2020.
Te Kopuru lies 10km south of Dargaville on the Pouto Peninsula. The township has been built on a revetment above the Northern Wairoa River. The wastewater system uses the benefit of the elevation of the revetment to develop a reticulation network that discharges to the treatment plant without the need for pump stations or rising mains.
Te Kopuru asset map
The Te Kopuru WWTP consists of a single stage oxidation pond and wetlands area located immediately adjacent to the Northern Wairoa River, south of Makaka Creek. The oxidation pond has a surface area of 0.52 hectares and a nominal depth of 1m and is protected by a concrete waveband. The wetlands have a surface area of 1.5 hectares. A photograph of the oxidation pond is included in Figure 3-23.
The Te Kopuru network was originally designed to service a total population of 570. The Environmental Effects prepared for the resource consent renewal assessed the current population of the Te Kopuru area discharging to the scheme as 487 (including the school). This is less than the design capacity and it is considered that the scheme has sufficient capacity for the next 20 year period.
Both the oxidation pond waveband and wetland plantings are considered to be in average condition. Sampling of the effluent has indicated that there are instances of non-compliance with consent conditions. The cause of the breaches was understood to be the high level of accumulated sludge in the oxidation pond and desludging of the pond has been completed in 2013.
Te Kopuru Oxidation Pond
Glinks Gully is a small holiday community located 20km southwest of Dargaville on the west coast of Northland. The wastewater scheme servicing Glinks Gully is designed to service a peak period population of 72.
Glinks Gully asset map
The Glinks Gully WWTP is a simple 320m3 evapotranspiration soakage field located adjacent to the Glinks Gully camp ground. The soakage fields consist of 50mm uniformly graded aggregate 225mm deep, overlain with filter cloth and sand. The field consists of two equal beds that are alternatively rested. A photograph of the effluent field is included in Figure 3 10.
The soakage fields have been assessed as performing well. Their asset life is to be revisited in the next valuation planned for 2014 and a major flushing and replacement of blocked pipes together with the installation of cleaning risers and reinstatement of media is planned for 2023. The soakage fields were originally designed to service a total of 18 properties. There are now a total of 24 properties connecting to the system which is designed for a peak flow of 15m3 per day at a loading rate of 50mm per day.
While regular flow data has been intermittent due to issues with the telemetry system records indicate the peak flow has only been exceeded once over the past six years. Peak flow occurs at about New Year with approximately 20 days of the year where the flow is in double digits. The free draining soils and nature of the loading combine to reflect a low loading rate and should mean the field’s life should be approximately 50 years with no justification for a substantial reserve area.
An application to renew the Discharge Resource Consent for Glinks Gully treatment was lodged with NRC in January 2014.
A commitment to implement the conditions will be required, these include upgrading the telemetry so that appropriate flow data can be gathered and compliant reports produced. One condition the NRC is keen to see enacted that has been identified previously is the installation of effluent filters on each septic tank. This aspect will be consulted with the community with a view to arranging the upgrades in association with the desludging of the tanks.
Kaiwaka is a small community located on State Highway 1 (SH1) in the southern part of the Kaipara district. The population as of 2013 was approximately 640 and is expected to be 700 by 2018. Kaiwaka is serviced by four kilometres of gravity pipeline, 69 manholes, one pump station and a single WWTP. Most recent Census data indicates Kaiwaka’s population has grown from 537 usually resident population in 2006 to 640 in 2013. This is according to the latest revised calculations by Statistics New Zealand, published on 22 February 2017.
Kaiwaka asset map
The majority of the wastewater scheme in Mangawhai is operated by the TRILITY (formerly Water Infrastructure Group) under a Build Operate Transfer procurement scheme (named ‘EcoCare’) that commenced operation in the 2010 financial year. The operation and maintenance contract for Mangawhai will expire in 2019 although it has a renewal option. The Mangawhai Community Wastewater Scheme (MCWWS) is a state of the art collection treatment and reuse system.
The collection system is a mix of low pressure and traditional gravity system built to minimise the potential for infiltration.
As at March 2017 the Mangawhai wastewater system had 1,862 properties (including commercial) connected and 533 properties capable of connecting.
The new District Plan published in 2013 identified a new urban boundary and a study was under taken to identify what network extensions were required to maximise the number of properties classed as connectable for Mangawhai.
The WWTP utilises a CASS system with two CASS tanks followed by pressure filtration and disinfection. Sludge is dewatered via belt press and disposed of in the landfill.
The treated wastewater is sent to a Council owned farm in Browns Road some 10 km from the WWTP where the water is stored in a buffer dam and irrigated to a portion of the farm land. The farm runs drystock and the grass is managed by a contractor.
Mangawhai asset map - Mangawhai Heads
Mangawhai asset map - Mangawhai Village