The use of drippers to apply treated wastewater to the land application area is an efficient method of wastewater disposal. A correctly maintained Aerated Wastewater Treatment System (AWTS) can also provide water for your garden.
However, dripper systems that are not well designed, incorrectly installed and poorly maintained can pose a significant public health risk and environmental hazard.
There are two methods of discharging wastewater through driplines to a land application area; covered surface or shallow subsurface drip irrigation systems. The choice is based on personal preferences and site constraints.
Wastewater discharged by drippers must go through secondary treatment and must meet specific standards (better than BOD5 20grams/m3 and TSS 30grams/m3). Some more rigorous parameters are set out in NZS 1547:2012 Appendix M section M2.1.
This information applies to all dripper based land application areas.
The renovated wastewater is discharged from drippers along the length of the flexible, low density polyethylene dripline. The drippers can be moulded into the dripline or mounted externally. Provision must be made in the design of the dripper to prevent root intrusion.
A disc or mesh filter must be installed on the pump discharge line to protect the dripline from any solid particles found in the wastewater which have the potential to clog drippers. The mesh/disc filter must be 130 micron in size.
The driplines should be 1m apart. The drippers shall be pressure compensated and antisiphon type. The drippers have a variety of flow rates and spacings. The dripline should be selected and spaced at sufficient intervals to ensure the Design Irrigation Rate (DIR) in mm/day is not exceeded and that effluent is distributed evenly. Where the land application area is steep or undulating a non leakage dripline should be used.
Driplines must not exceed 100m in length and shall be placed across the slope. The dripline must be coloured purple or have a purple stripe to indicate that it contains wastewater.
Provision shall be made for flushing of the lines whenever the AWTS is serviced.
The land application area should be setback at least 3m from dwellings and other buildings and 2m from boundaries. Set back distances from wells and water bodies or drains also apply.
The location of the land application area and the driplines should be shown in the as-built plan. The as-built should also show buildings and boundaries. Photos can supplement the as-built.
Covered Surface Drip Irrigation
This additional information applies only to covered surface drip irrigation land application systems.
The dripline used for surface irrigation must be pegged to the surface of the ground and covered with a mulch or granulated bark. Mulch or bark has a large surface area which assists in evaporation of the wastewater. The mulch must have a depth of at least 150mm and must be renewed at intervals to maintain the required depth. Some mulch decomposes quite quickly and will need replenishing frequently. The mulch must not be allowed to erode or decompose so that the drippers are exposed. The land application area must be planted to ensure evapo-transpiration of the effluent.
Design and Construction
This method is used when the land application area is to be planted.
Before construction, all overgrowth must be removed from the land application area. The overgrowth could be sprayed with a herbicide or cut to a low level. The ground surface should be scarified with a rake or similar, before placement of the dripline.
All pipework feeding the driplines must be buried to a depth of at least 200mm to reduce the risk of damage.