Wastewater Dispersal Design

Where a site is not connected to the public wastewater network, on-site wastewater dispersal is required.

The on-site treatment and dispersal of wastewater has come a long way since the days of septic tanks and scoria trenches. To reduce the environmental impacts and risk to human health from on-site wastewater dispersal, a higher level of treatment is required by Council. This can be achieved by using a domestic, packaged, wastewater treatment plant which includes a septic tank, followed by a treatment tank. The treated effluent is then pumped to an irrigation field where the effluent is dispersed to the ground surface.

Wastewater design is undertaken in accordance with Auckland Council Technical Publication 58 (TP58) and NZS 1547:2012. The size of the irrigation field is based on the number of bedrooms in the dwelling and the type of soils. As part of the design of a wastewater dispersal field, subsurface exploration is undertaken to determine the nature of the subsoils as well as the groundwater level. A detailed site walkover inspection of the site is also undertaken to ensure that there are no surface features that will preclude wastewater dispersal such as surface water or unstable ground.

For most standard dwellings, wastewater dispersal field design is considered by Council to be a Permitted Activity and can be applied for at the Building Consent stage. However, for exceptionally large dwellings, or for small site or sites with a higher risk of environmental effects, Council may require a Resource Consent application for Wastewater. KGA can undertake both Permitted Activity and Resource Consent wastewater dispersal field design.