Residential wastewater systems

Home wastewater systems are used on properties that are not connected to a reticulated sewer network.

In the Gisborne district, this includes homes in all areas outside Gisborne city, Te Karaka and Te Puia townships, including Wainui Beach, Makaraka and surrounding rural and coastal areas.

When everything is working well, managing your own wastewater system is relatively straightforward.  But if something goes wrong, it can be unpleasant and costly to fix. Whether you're using or installing a septic tank, this information will help you get it right.

What are onsite wastewater systems?

Onsite wastewater systems are used to manage and dispose of all household wastewater, including everything that goes down household drains and toilets.

With an onsite system, there’s no such thing as “flush and forget.” All liquid household waste must be safely and hygienically treated and disposed of on your property. Your wastewater system is a living system that relies on natural processes to function effectively.

A well-functioning system treats and contains wastewater without contaminating groundwater or surface water and without harming the environment.

Types of systems

There are 2 main types of onsite wastewater systems:

• Septic tank systems - one or more tanks with a gravity-fed or pumped effluent disposal field.
• Home treatment systems - usually paired with a dripper-line disposal system.

Your wastewater system may include:

• Sanitary plumbing fixtures connected to drainpipes that carry sewage and sullage (wastewater from kitchens, wash basins, toilets and laundries).
• Treatment tanks – passive, aerated or filtered
• A distribution system - pump, siphon or gravity fed
• An effluent disposal system - trenches, beds, mounds or dripper lines.

How the system works

The type of onsite wastewater system you install will depend on your property. Most systems work in a similar way: wastewater is gradually separated, treated and dispersed, with help from natural organisms.

Just like our digestive systems rely on beneficial bacteria, septic tanks rely on anaerobic bacteria to partially break down solid waste. These organisms are essential to the system's performance, which is why your septic tank should be kept free from harsh chemicals wherever possible.

When you flush the toilet or use a tap, sewage and sullage flow into the septic tank. Heavier solids settle to the bottom to form sludge, while fats, oils and lighter materials float to the top and form a layer of scum.

Installing a wastewater system

If you’re installing a new onsite wastewater system, it’s important that the treatment tanks and effluent disposal area are correctly sized. This ensures the system has enough time and space to treat and disperse wastewater efficiently.

Talk to a professional

A qualified wastewater professional can help you choose the most suitable system and determine the correct size and location for your property.

Site evaluation and design

Before a building consent can be issued, your system will need a site-specific evaluation and design.

Consents for your wastewater system

Installing or upgrading an onsite wastewater system usually requires both a building consent and a resource consent.

Building consent

Before a building consent can be issued, your system must undergo a site evaluation and design assessment. You’ll need to provide:

• A scaled site plan.
• Details of the system type, size and layout.
• Evidence that the design work has been completed by a recognised wastewater engineer or approved assessor

Tip: One of the most important parts of the evaluation is assessing your soil’s soakage capacity. Sands and gravels allow water to drain quickly, while dense clay soils may have limited or no soakage capacity.

A qualified assessor will design a system that suits your site conditions. There are no shortcuts. A poorly designed system can fail, causing surface ponding, unpleasant odours, health risks and environmental contamination.

Resource consent

Onsite wastewater systems must meet environmental standards under:

• The Resource Management Act
• The Tairāwhiti Resource Management Plan

They must also comply with:

• The New Zealand Building Code
• The Building Act, including functional and durability requirements

Exempt work

Some like-for-like maintenance work may not require a building consent under exemptions provided in Schedule 1 of the Building Act. However, replacing a failed effluent line, even on a like-for-like basis, will generally still require a building consent.
Why? Because a failed system does not comply with the relevant provisions of the Tairāwhiti Resource Management Plan, the exemption is unlikely to apply.

Specialists and service agents

Some wastewater professionals carry out onsite assessment and design work specific to particular system brands. However, you can still use the information from your initial site assessment to get quotes from a range of qualified drainlayers.

You’re welcome to use any recognised wastewater site assessors and system designers listed below. Please note:

• The list is not comprehensive.
• Council does not endorse specific products or services.
• You may wish to seek quotes from other suitably qualified providers.

Looking after your system

Regular maintenance helps your wastewater system operate efficiently and can prevent costly repairs or system failure.

Key maintenance tips:

• Desludge your tank every 3 to 5 years, or when scum and sludge fill two-thirds of the tank capacity (or the first chamber of a two-chamber system).
• Keep vehicles and heavy animals, such as cattle and horses, off your tank and effluent disposal area.
• If you have a grease trap, clean it out regularly.
• Keep the vent and access cover of the septic tank exposed.
• Inspect and clean outlet filters if your system has one.

If things go wrong

A failed onsite wastewater system is a serious health and environmental hazard. It can lead to:

• Spread of infectious disease
• Increase in mosquitoes, flies and rodents
• Pollution of waterways, beaches, streams and shellfish beds
• Contamination of bores, wells and groundwater
• Air pollution and unpleasant odours

Regular cleaning and maintenance are essential to avoid these risks.

Costs to consider

Costs vary depending on the type of system, location and site conditions:

• Basic septic tank systems are generally more affordable than complex systems for sites with poor soakage or limited space
• Transport costs to remote areas can add significantly to installation and servicing fees
• Cleaning and servicing costs depend on your location - contractors often charge for time and mileage
• Systems installed since 2002 should have an outlet filter on the second tank or chamber - these must be cleaned regularly to prevent backups
• Systems with pumps, home treatment plants or low-pressure dosed effluent systems have ongoing power costs and may require maintenance twice a year.

Note: All maintenance is the homeowner’s responsibility.

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