Il terreno fabbricabile significa semplicemente che può sostenere un sistema settico. È un terreno che può drenare e permettere all'acqua di passare attraverso di esso. Un terreno che non ha permeabilità, un terreno argilloso duro e stretto può essere così, non permetterà all'acqua di filtrare via dalle linee settiche.

Percolation tests are conducted on soils primarily to determine if they are suitable for installation of sceptic systems.
If a soil has too much clay, it has low permeability, which means it will not perk or the lines from a septic tank will not distribute the sewage supernatant into the soil and the area around the septic tank will be a stinking mess as the liquid from the tank will not soak in.
A good soil with high percolation rate with good permeability and porosity will be a sandy loam or any soil with sand and low clay. A heavy clay soil or even a silty clayey soil will have low percolation rates.
The test amounts to boring a specified diameter whole to a specified depth, and then a specified volume of water is placed in the hole and its infiltration rate is timed and measured.