On-site wastewater systems: design and management manual

Sandy Ormiston, Robyn Floyd, Auckland Regional Council
Auckland Regional Council
Publication date:

Treatment and land disposal systems for domestic wastewater from households, commercial premises and similar facilities

A W (Sandy) Ormiston 

Robyn E Floyd

The purpose of TP58 is to provide guidance for the design and maintenance of on-site treatment and disposal systems for domestic wastewater from households and institutions. In this context, the term “institutions” refers to non-dwelling type facilities such as schools, residential accommodation facilities and commercial and public facilities.

The approach taken in the setting of design recommendations for on-site wastewater systems has been based on extensive experience in the region supported by comprehensive literature searches. Wherever practicable, these design guidelines attempt to use a pragmatic approach. However, where any uncertainty exists, ARC is obliged to take a conservative approach and to ensure some safety factor is maintained in final system designs to address uncertainties inherent in the design and operation of on-site systems. This is also to provide confidence that meeting the design recommendations as set out in TP58 gives surety that potential for adverse effects from system design alone will be minor. Maintenance is also recognised as an equally important factor, along with correct system design, installation and operation to ensure optimum performance of the system. These factors are all critical for mitigating potential adverse effects throughout the life of a system.

This document is aimed at providing guidelines applicable to existing sites in situations where there is no existing reticulation system such that on-site disposal is the only option. In the case of new developments, it applies where subdivision is of a scattered nature for example large rural lots, lifestyle blocks or developments on remote sites where reticulation for combined decentralised or centralised treatment systems is not practicable.

In the case of proposed new developments or subdivisions, that could lead to a concentration of settlement, ARC policies promote the need for consideration of all reasonable means of treating and disposing of wastewater, in addition to the immediate option of on-site disposal. There is a requirement for assessments of alternative infrastructure options to be undertaken at the early planning stage. This matter is addressed in the relevant policies in the Auckland Regional Policy Statement, which are outlined in Chapter 2. The need for alternatives to on-site disposal to be considered at the planning stages of a development is specifically discussed in Chapter 4. This outlines matters to be considered in the early Design Planning stages of a development, before any decision can be made towards on-site, off-site or a combination of on and off site treatment and disposal options.

Auckland Regional Council technical publication, TP58 TP058

Third edition, August 2004.


Last updated: 2017-09-25