(also filtration field), a plot of land on which sewage liquid undergoes natural biological decontamination as it is filtered through soil horizons.
Leach fields are established on sandy, sandy loam, and loamy soils with good filtration properties. They are flat and have an area of 0.5–2 hectares (ha). There are dividing ridges measuring 0.8–1 m high. Sewage liquid from which solid waste, fat, and worm eggs have been removed is fed past gates and through open canals onto the field in a layer of 20–30 cm (in the winter it is frozen to 75 cm). The sewage percolates through the soil and runs through drains to a collector. It then is dumped into a river. After the sewage liquid has been absorbed, the surface of the field is tilled and then flooded again.
Permissible daily norms for loads on leach fields are 70–125 cu m/ha for sand, 50–100 cu m/ha for sandy loam, and 40–70 cu m/ha for loam. Leach fields in which the waste is fed into the soil through drains are set up to decontaminate small amounts of sewage. In contrast to sewage farms, leach fields are not used for crop cultivation.
V. M. NOVIKOV