Percolation of Wastewater

The treated waste water from a wasterwater treatment is normally discharged by pump into a network of perforated 110mm diameter pipes laid in stone filled trenches. The extent of the irrigation system is determined by the site assessment, taking into account the soil type and percolation test results.

A typical percolation utilises an "Effluent Discharge Trench" (Gravity Feed). However where the irrigation pipes have to be above existing ground level e.g. thin topsoils and/or rock or water table close to the surface, a raised or banked up irrigation system may be suitable. The perforated pipe is laid on a 250mm bed of clean 20/30mm washed stone or gravel. The trench is then backfilled to give an overall depth of 500mm.

There are two types of raised bed percolation areas: a raised soil bed or a raised sand bed. Of these the raised sand bed is the smaller. The base of the percolation trench should be at least 600mm to 1200mm above the highest water table or fissured bedrock in accordance with EPA guidelines. The percolation piping is laid on a bed of 10/15mm pea gravel which is overlaid on a bed of sand.