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Onsite Wastewater

http://www.gw.govt.nz/onsite-wastewater

Onsite Wastewater

Updated 7 November 2016 11:12am

Also available to download as PDF

Septic systems

All homes and many other buildings produce wastewater. Whether you’re a homeowner, or building your own home, this user-guide is about septic systems (also known as ‘onsite wastewater treatment systems’) which discharge wastewater from residential (urban or rural) households. Under the New Zealand Building Code, if a wastewater connection to the town sewage system is provided, such as in most urban areas, you must use it. Otherwise, your home will need its own septic treatment system.

What is a septic system ?

A septic system (also known as an ‘on-site wastewater treatment system’) treats domestic waste water and returns it to the environment within the boundaries of the property. The standard septic system has two parts – treatment and disposal. Every property and living situation is different so there are a wide variety of septic systems available. These systems have different numbers of chambers and different treatment processes. The more chambers, the more effective the treatment. Which system is appropriate for a property, is based on the number of people in the household who will use it, the intended location (soil, waterways, groundwater, bores) and accordingly the flow allowance and the expected volume for the septic system. What every system has in common is an air vent or “mushroom” located above ground, with a hatch that is buried for ease of access. This will usually be located somewhere downhill from the house and treatment system.

 

 

Source: Natural Resources Canada (n.y)

 

 

 

 

 

 

 

Airvent/Mushroom

 

 

 

 

Installation and maintenance of the septic system is the responsibility of the property owner. It is recommended that an inspection is carried out every two years, or as per the recommendations of the manufacturer. Septic systems may also need to be upgraded or replaced as individual household circumstances change. When installing a septic system it is important to think about providing enough capacity for potential future needs as well as current ones.

What you need to know about septic systems

Older systems may have trouble coping with the amount of water modern living produces. Home renovations or extensions, for example the addition of another bathroom, can also put a strain on the system. If a septic system is leaky or poorly maintained, it can contaminate water supplies and pollute the surrounding environment. Regular maintenance (including upgrades and repairs) at least once every two years improves the efficiency of septic systems and helps to protect the environment.

If your existing septic system meets the conditions in the Proposed Natural Resources Plan (PNRP), a resource consent is not required (see permitted activity Rule 74).  These conditions include:

  • The number of people in the household using the septic system has not increased since it was installed – on average this means the system discharges no more than 1,300 L/day.
  • The septic system has not been modified from its original design specifications, or if these are unknown then the system should comply with New Zealand Standards (Section 6.3 and Appendices T and U of the AS/NZS 1547:2012 On-site domestic wastewater management).
  • The septic discharge does not enter any water body and is not visible above ground.
  • The septic system is effectively and the sludge and scum layers fill no more than half of the primary tank
  • Any smells coming from the system must not affect the neighbours

If you are putting in a new system or upgrading an existing system, and it meets the conditions in the Proposed Natural Resources Plan (PNRP), a resource consent is not required (see Rule 75, for more detail).  These conditions include:  

  • The septic discharge occurs on the property where it is sited and is at least 20m from any waterway, water supply bore or neighbours boundary, and is outside of any community drinking water supply protection area (see Maps 26 – 27c) 
  • This septic system is operated and maintained according to the original design specifications, or if these are unknown, the New Zealand Standards (AS/NZS 1547:2012 – On-site Domestic Wastewater Management)
  • The discharge should not be more than 14,000L/week, and the estimated total weekly flow is based on a minimum of s 145L per day/ per person if you are on roof collection/tank water or at least 180L per day/ per person for town supply.
  • The septic discharge is dispersed evenly below ground level (minimum depth 10cm) and is not visible above ground
  • The sludge and scum layers fill no more than half of the primary tank
  • The septic system handles only domestic sewage
  • The following allowances are made for a reserve area (ie an area set aside for wastewater pipes in the future, if required):

a)      If you only have a primary treatment, you will need a reserve area along with the septic field, which is the same size as your septic field.

b)      For secondary treatment, no extra capacity is needed for drip lines with a small diameter.

c)       For all other systems (such as different pipes, aggregate used in the trench, mounded or garden bed systems) the reserve area must be at least an extra half the size of the septic field.

  • Any smells coming from the system must not affect the neighbours.

Advice

1. If you can't meet these conditions, you will need a resource consent from Greater Wellington. If you are unsure about your system, any of these conditions, or would like help to applying for a resource consent, please contact the Greater Wellington,  info@gw.govt.nz  or 0800 496 734.

2. For the detail of the rules in the Proposed Natural Resources Plan on existing on-site wastewater treatment systems (Rule R74) or new or upgraded on-site wastewater systems (Rule R75), please refer to PNRP Rules

3. If you would like information about what system to use or if you think you may need to upgrade your system, please call your local city or district council and ask to speak to a building consent officer. The local council can also give you the contact details of an authorised person to help give you more specific advice. These are people who are recognised or approved by the City or District Council as being suitably trained or qualified to undertake maintenance on, or prepare appropriate reports, designs and assessments for septic systems. An authorised person can carry-out septic tank inspections to ensure the wastewater treatment system is performing well and is adequate for the household (size) demand. Approvals from your local council may also be needed for new or upgraded systems, please contact them if in doubt.

4. More information can be found on websites such as www.lifestyleblock.co.nz, a forum for discussion between property owners who have installed onsite systems, about any of the following topics: the cost and performance of different treatment systems, reliability of companies, and the ongoing running costs.

5. Approval may also be needed from your local city or district council. Please contact them directly for further advice:

This information is intended to provide a guideline to the requirements of the Proposed Natural Resources Plan for the Wellington Region. Please also be aware of the requirements in the current operative plan as well as the provisions mentioned in this user guide.

Background sources:

http://www.mfe.govt.nz/publications/rma/proposed-national-environmental-standard-site-wastewater-discussion-document/2-what

http://www.level.org.nz/water/wastewater/on-site-wastewater-treatment/

http://www.waterboards.ca.gov/sandiego/water_issues/programs/wine_country/docs/updates081910/owts_review.pdf

http://www.aucklandcity.govt.nz/council/documents/technicalpublications/WW02%20On-site%20wastewater%20management%20systems,%20septic%20tanks.pdf

https://www.boprc.govt.nz/media/33487/Report-091015-bestManagementPracticesforseptictanks.pdf

http://www.gdc.govt.nz/assets/Files/EnvHealth/Living/Septic-Tank-Brochure.pdf