- Home
- Site Analysis
- Site Use
- Passive Design
- Water
- Minimising water use
- Stormwater controls
- Rainwater Systems
- On-site Wastewater Treatment
- Septic Tanks: Overview
- Septic Tanks: Design Checklist
- Aerated Wastewater Treatment Systems
- Disposal Systems
- Care and Maintenance
- Greywater: Uses and Safety
- Greywater: System Design and Installation
- Greywater: Gravity and Pumped Systems
- Greywater: Filtering and Treatment
- Greywater: Irrigation Systems
- Composting Toilet Systems
- Material Use
- Energy
- Health and Safety
- Other Resources
Water
Designing homes to use water efficiently, reduce costs and cope with more frequent droughts or storms.
Disposal Systems
The treatment tank is only one part of an on-site sewage system. Of greater importance is efficient and effective wastewater disposal through the land application system.
The wastewater from a traditional septic tank system is disposed of by gravity in a subsoil drainage system.
If the system incorporates additional treatment such as filtration or aeration, or if the tank is multi-chambered to remove additional pollutants, the wastewater may be used for irrigation but not for vegetables for human consumption.
Site investigation
Disposal systems should be designed by an experienced person who will consider the:
- nature of the subsoil on the site including its permeability (the rate at which water can percolate through it) and stability
- characteristics of the site including slope and natural drainage characteristics, water table levels, water course location, tendency to flood, area available for land application, and vegetation and planting
- potential effects on neighbouring properties downstream, natural water courses or the sea, local ecology
- the field location – fields must not be grazed or driven over.
This will determine the characteristics and necessary length of drainage to be provided.
- Typical septic tank land application system
The effluent distribution is usually gravity-fed but may be pumped. There may be a distribution/diverter box to direct effluent into the trenches. Drainage is improved if part of the system is periodically ‘rested’ to prevent drains becoming clogged by saturated conditions.
- Typical piped land application trench system
Traditional distribution of effluent from a septic tank has been through gravity-fed perforated pipes in an aggregate bed.
Types of outfall disposal system
A typical land application system for a septic tank has: an effluent outfall which is usually gravity fed but may be pumped; a distribution/diverter box to direct effluent into the trenches (drainage is improved if part of the system is ‘rested’ to prevent drains becoming clogged by saturated conditions); and a ‘reserve’ area where additional drainage can be installed if needed in the future.
Aerated wastewater systems dispose of wastewater using a low pressure effluent distribution system where the water is periodically discharged under pressure through a drip line into the topsoil or into a mulched bed. The water is then dispersed by evapo-transpiration-seepage (ETS) where it is absorbed into the topsoil, evaporates, or is taken up by plants.
ETS systems, because they are pumped, can be used on sloping land.
- Evapo-transpiration trench
Treated effluent from an on-site domestic waste-water system may be discharged through an evapo-transpiration trench. The effluent is absorbed into the topsoil, taken up by plants, or may evaporate.
- Evapo-transpiration trenches on sloping ground
Evapo-transpiration trenches which distribute treated effluent from an on-site domestic wastewater system can be constructed on sloping ground provided the trenches run parallel to the contours. The effluent is absorbed into the topsoil, taken up by plants, or may evaporate.
For your clients
To help your clients understand onsite wastewater treatment options, safety issues, and the importance of maintenance, refer them to www.smarterhomes.org.nz/water/on-site-sewage-systems and www.smarterhomes.org.nz/water/re-using-greywater.