Drip distribution of waste water to soil percolation areas is the most efficient method of distributing treated waste water. It is the preferred method of distributing waste water to poorly soaking soils in the United States and is now beginning to be used in many counties across Ireland.
The US EPA waste water design manual 2002 describes drip as “the most efficient of all distribution methods.” The TCD draft STRIVE research/evaluation of two drip systems in low permeability was published in January 2016. The reported results were very positive for drip systems on both low permeability sites evaluated. The drip system is recommended in the report for use in the most impermeable soils with T-values up to 120 combined with a reduction of soil depth to 600mm of unsaturated soil.
Drip irrigation is a viable and cost-effective option in all low permeability soil conditions due to its installation near the ground surface (which significantly reduces the requirement for costly fill material) and also due to the small area it occupies in comparison to other distribution methods. Also, by ensuring that the water is dripped evenly across the complete infiltration area it can avoid short circuiting in limestone karst areas, preventing flows into sinkholes until it passes through surrounding soils with soil attenuation of pollutants and renovation of the water.
The treatment capacity of the soil to remove pollutants is optimised as dosing of the waste water is intermittent and controlled by a specially designed controller which allows effluent to be dispersed slowly from into the biologically active soil zones a few inches below the surface.
Benefits of Drip Sewage Systems
Often eliminates the need for a raised mound and costly fill material
Can be used in difficult sites- high water tables, tight soils, rocky areas, steep slopes around existing buildings and trees.
The system requires no gravel. It is easy to install directly into indigenous soils and the natural landscape can be maintained.
Shallow installation and maximizes use of “good or expensive” topsoil.
Consumption of nitrates by the plant material is increased.
Installations are invisible and safe for pedestrian traffic. Copper inside the drip line emitters for root intrusion.
Effluent with natural fertilisers of N and P is re-used to irrigate grass roots.
Multiple zones can be used to allow the use of different “parcels” of land.
Pedestrian or sports use of the drip field is facilitated during operation.