Information for developers, designers and installers
All subdivisions and developments producing domestic wastewater that are unable to connect to a reticulated wastewater system will require an onsite wastewater management system (OWMS) that is appropriate for the site and the local environment.
This is a requirement of the Building Code, which is administered by the local council. Any discharge of treated wastewater will need to comply with the on-site wastewater rules in the Canterbury Land and Water Regional Plan. An application for resource consent will be required if the discharge is unable to meet the conditions of a permitted activity.
Understanding these regulatory requirements early in the process is essential to the effective discharge of wastewater.
Important considerations
Permission to connect to the public sewer system should be sought from the local authority where access is available now or new infrastructure is planned within a reasonable timeframe. This is desirable because public sewer systems are maintained and monitored and typically located away from sensitive environments.
The cumulative effect of multiple OWMS effluent discharges is of increasing concern in Canterbury because of the impact of pathogens and nitrate on the receiving environment.
Where an OWMS is the only option, the proximity to domestic and community water supply wells, rivers, streams, wetlands, and surface water drains should be carefully considered to avoid pollution.
In some sites, primary or secondary treatment systems may not be appropriate for the environment, and alternative solutions may be required.
An OWMS with an effluent disposal field should not be installed on a property less than 5000 m2.
Having a backup area for effluent disposal is considered good practice (and a requirement in some cases). Ensuring there is adequate vehicular access for proper maintenance of the system is vital.
Information for OWMS designers
It is expected that designers will provide an OWMS that considers the quantity and type of wastewater produced, the optimum treatment process, and dosing to a land application system.
There are several different types of treatment, dosing, and land application systems. A competent designer will have a sound understanding of the options and recommend the optimum design for the site.
With proper servicing and maintenance, the recommended OWMS should provide a sustainable wastewater treatment solution and mitigate risks to the environment and human health.
Designers are expected to provide a report with detailed specifications that can be interpreted and understood by technology providers, consent authorities and regulators and installers.
Information for property developers
Installation of on-site wastewater systems is not a tick-box exercise. Property developers are strongly encouraged to contact us to discuss their wastewater treatment proposals early in the planning process to confirm that OWMS are a viable option and that they understand the requirements and potential constraints.
Please seek advice by contacting customer services.
Property developers are expected to engage a suitably qualified OWMS designer. Designers are likely to be engineers, applied scientists or technicians with appropriate training, knowledge, and skills to fully assess a site and provide detailed OWMS design options that meet regulatory and environmental requirements.
Information for OWMS installers
Installers are expected to demonstrate that they have appropriate trade qualifications and practical experience to interpret the designer’s specifications and install the system in accordance with the appropriate regulations, particularly the Building Code.
Resource consent applications – additional considerations for subdivisions
Applications for resource consent will need to include (among other things) an environmental assessment that looks at the cumulative effects of subdivisions and total contaminant loads released to the environment and highlight any increases in loads.
It will need to assess any contaminants released by the systems, including pathogens, nitrogen, and greenhouse gas emissions.
In some cases, the OWMS designer may have the skills to complete the environmental assessment. In other situations, it may be necessary to engage a specialist to complete the environmental assessment.
In some cases, managed OWMS that serve a whole subdivision are more desirable than individual systems for each property.
This will generally result in better effluent treatment, reduce the number of individual discharges, and minimise the risk of system failure. It also allows for the possibility of efficiently linking in with the public sewer system when reticulation or capacity becomes available.
Selecting an on-site wastewater system
The On-site Effluent Testing National Testing Programme (OSET-NTP) undertook performance testing of on-site wastewater treatment units at its testing facility located within the Rotorua City Wastewater Treatment Plant Site. Due to several issues the site was closed indefinitely in 2021.
With the support of Water NZ, the OWMS Special Interest Group (OWMS SIG) has been tasked with establishing a replacement facility, but this will take time.
The Rotorua site provided a testing and benchmarking facility for up to seven on-site domestic wastewater treatment units annually. Units trialled at the site were issued with test certificates and detailed performance reports that are used by us (and other regional councils) to assist with decisions on resource consent applications.
View current test certificates for units which have been trialled at the facility.
Many test certificates will soon expire, and manufacturers have been invited to apply for an extension until 2026. We understand few have responded so far, in part because some manufacturers have continued to develop and improve the design of their treatment units since they were originally tested. Given this situation, we will accept other testing which is equivalent to OSET-NTP.
Training
WSP provides the following recognised training courses for OWMS designers and installers: