Land Application Systems
In New Zealand all wastewater systems discharge to the land via some sort of land application system. There are a handful of options with a few dependencies on council regulations. These are fully explained for your convenience below.
Low Pressure Effluent Distribution (LPED) is a low-pressure irrigation system. Lines of equal length are laid 1 – 1.5m apart on a level contour, they can either be covered with mulch or buried in the topsoil.
The laterals are fed from a manifold at the head of the field, ensuring an even distribution across the field. The irrigations lines are a 25mm lateral with holes drilled at consistent spacings. The size and number of the holes is calculated by our design technicians for each project. Innovative squirt guards developed here at Waterflow, clip over each hole to stop it spraying into the air.
Pressure Compensating Drip Irrigation (PCDI) is a flexible irrigation system that requires higher levels or wastewater treatment. PCDI has small emitters allowing a limited flow, this forces the liquid to distribute across the entire field rather than pooling in one area.
Due to the fine emitters, the treatment plant must treat to secondary level and be passed through a fine disc filter; these require more regular cleaning and maintenance than other systems. The PCDI lines can be of varying lengths and run across contour to a certain degree, giving much more flexibility to the layout and shape of the irrigation area.
Evapotranspiration Beds (ETS Beds) are a low-pressure irrigation system laid through a soakage bed. The beds can be between 0.5 – 3.0m wide and 0.45m deep.
The bed is filled with gravel, in which the LPED irrigation is put through perforated drain coil; the bed is then mounded with soil and planted on top. The mounded top helps surface water run off and the plants assist with transpiration. These can be loaded at a much higher rate than irrigation, thus reducing the land application area by up to 50%.
Conventional Soakage Bed
Much the same as an ETS bed. However, they can also be constructed with drilled 100mm PVC and trickle fed from a Septic tank. The top of a soakage bed doesn’t require mounding or planting. They are only suitable in good draining soils.
Conventional Soakage Trench
Soakage trenches are much the same as soakage beds, however they are no more than 0.5m wide. There are a few variations to these, such as sand trenches and deep trenches. These are not so commonly used and depend on council regulations as to their use.
Similar in principle to ETS beds, these are built up and constructed above ground rather than being dug in. The main reason from these is an elevated water table of flood prone area, where it is necessary is lift the height of the discharge. The purpose of raised mounds is to minimize the possibility of ground water contamination.
Deep bore holes are typically 0.6m in diameter and 6.0m deep, the number of holes is determined by a four-hour soakage test. The bore holes have a discharge pipe down the centre and are filled with coarse aggregate. These require a resource consent and aren’t a permitted activity under any council in New Zealand. They are only used on small sites with very limited options for discharge.