The pollutants are decomposed by aerobic bacteria that live in the upper soil layers (at depths of up to 1.2 m). Then the purified water is discharged from the facility and dumped into the pond. These options are used in the purification Where soils at the site will be impermeable or when unacceptably high level of groundwater. The most popular system, which works on the principle of the soil absorption. This field is an underground filter. They represent a network of irrigation pipes laid in underground ditches that are filled with soil with good filtration properties. At the bottom of the ditches filled layer of sand on top of it – crushed rock, gravel or slag.
In the rubble at a depth of half its diameter irrigation pipes are laid. Waste water flows to the fields of filtration by gravity or are fed by pumps. Irrigation pipes are manufactured with pyatimillimetrovymi holes through which the waste water into the filter trench. Depth of laying pipes – 0.5-1.2 m. It is impossible to have an irrigation pipe above the freezing depth of soil, because in winter the whole system can fail. If known that the upper layer of soil can freeze more than 1.2 m, while for the fields of underground filtration arranged a special insulation. And one more requirement: the distance from the bottom layer of crushed stone to the top horizon of groundwater should not be less than one meter. Otherwise treated waste water may contaminate ground water, and then, perhaps, in the well water.