A Sand filter is required if there are several factors, water, wells, size of area, permeability of the land.
A sand filter is situated after the septic tank and decolloideur ( optional extra filter )
It is a minimum of 25 meters square ( Indre is a minimum of 20 meters ) by 1.2 meters deep or more, in a plastic liner. ( A NON DRAINED SAND FILTER IS EXACTLY THE SAME EXCEPT FOR THE LINER AND BOTTOM SET OF DRAINS )
The liner is put in a pre dug hole with an exit channel as the finished treated water needs to drain away somewhere, a series of pipes are placed in the bottom connected to a regard (manhole ) and to the exit pipe. This is then covered with stones, size from 10 to 40 WASHED, and covered with GEOGRILLE, a material to allow the waste water through but retain the sand in place.
Filtrant sand is put in next, 70 cm of depth, then a layer of stone on the sand.
The final top layer of pipes are added connected to a regard, all evenly spaced with a minimum of slope, all connected at the end. After these are all in place correctly they are covered with stone pre washed, and covered with a geotextile to prevent the surface soil entering the filter and to stop roots penetrating the filter. As before the bigger the house, the bigger the septic tank, the bigger the sand filter!!!
