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A soakaway, sometimes called a percolation pit or drainage pit, is a chamber covered by porous walls that serves to allow wastewater, previously treated, to slowly infiltrate. It can also be used to infiltrate urine into the soil when it cannot be used. The proper functioning of this technology depends on the type of soil and its permeability (HERMOSILLA 2016; TILLEY et al. 2018).
The absorption well should be 1.5 to 4 m deep; as a general rule, it should never be less than 2 m from the water table and at a safe distance from water sources (30 m). The soakaway should be kept away from high traffic areas to avoid compaction of the soil above and around it (TILLEY et al. 2018). The walls can be lined or unlined, but it should be filled with gravel and stones to avoid landslides, as well as to allow uniform distribution of urine and its proper infiltration (SALCEDO and ORE 2005). In both cases, a layer of sand and fine gravel should be spread on the bottom to disperse the flow. In order to be able to open it in the future, a removable lid (preferably made of concrete) should be used to seal the chamber until it requires maintenance. In places where large quantities of urine are produced, it is necessary to ensure that the soil has sufficient infiltration capacity, as the pit could become oversaturated and emit bad odors due to surface evaporation.
Septic Tank and Soak Pit Design
A septic tank is a device for the primary treatment of domestic wastewater. In it, the separation and physical-chemical transformation of the organic matter contained in the wastewater is carried out. It is a simple and inexpensive way to treat wastewater and is suitable (preferably) for rural areas or residences located in isolated places and is an advantageous substitute for the so-called pit latrines. However, the treatment is not as complete as in a sewage treatment plant.
This device should not be confused with the cesspool, an old system for collecting sewage, which is very imperfect since it merely stores the waste, and which is now banned in many countries because of its poor treatment.
When it has two chambers, the first one must have a volume more or less double that of the second one and the union between both will be made between two waters, so that sludge and foam do not pass from one chamber to the other. Both chambers should have manholes so that sludge can be removed periodically.
Pluvial absorption well design
According to SAGARPA, soak pits consist of generally cylindrical excavations of variable depth, which may or may not be filled with material, and are constructed to infiltrate rainwater directly into the ground in confined spaces.
Soak pits have a limited storage capacity, depending on the water table. The main function of these wells is to capture rainwater, causing the absorption of water through the perforated material and producing a natural filter between the formation and the well casing.
Excel® soakaway calculation
They are wells, ditches or trenches with a depth of between 1 to 3 meters filled with granular material. Runoff from adjacent impervious surfaces is discharged into them and the water is collected and stored while it infiltrates into the natural ground.
Infiltration trenches are narrower and shallower than wells and are more efficient from a construction standpoint. They are used primarily for quality control, but can also be used as a strategy to control the quantity of runoff flow in medium to high density residential and commercial areas. However, care must be taken with the terrain where they are to be installed, always avoiding locations near building foundations or roadways.