DIY filter well

Table of contents:

DIY filter well
DIY filter well

The design of the filter well and the principle of its operation. The basic requirements for the structure, ensuring its maximum performance. Mounting technology for structures made of reinforced concrete rings and bricks.

The filter well is an important component of the local sewerage system for summer cottages and country houses, designed for post-treatment of sewage after septic tanks. The structure is built according to certain rules that ensure its maximum performance on various soils. Information about the structure of the filter well and the technology of its installation can be found in this article.

Filter well device

The owners of private mansions, summer cottages and land plots outside the city create a local sewerage system with a septic tank for the disposal of used domestic water. The most popular device is considered to be a two- or three-chamber accumulator with the removal of the purified liquid to the site. However, in a septic tank, it is freed from impurities by only 55-60% and is considered environmentally hazardous. Therefore, from the storage tank, water flows into a special ground cleaner. Such buildings include a filter well, in which the liquid is 95% free of dirt. Its function is to trap dirt and drain water deep into the ground.

The structure is made in the form of a mine with a leaky bottom, in the lower part of which a filtering layer is formed from crushed stone, gravel, broken brick, slag fraction and other bulk material. The maximum dimensions of the elements are 3 cm. The layer thickness is about 1 m.

Passing through it, wastewater is purified from impurities. They settle on the filter fragments together with microorganisms that are capable of processing organic matter. Under the fill layer, there must be soil that is well permeable to moisture. The well is covered with an overlap with a hatch for inspection and cleaning of the device. The presence of a ventilation pipe is mandatory, which is carried out through the tank lid.

The walls of the shaft are made of different materials. The advantages and disadvantages of various designs are shown in the table:

Material Advantages disadvantages
Reinforced concrete rings Cheapness of material, ease of installation, wall tightness Large weight of the structure, the use of special equipment during installation
Brick The possibility of self-construction Quite high price, long installation time, experience in construction work
Factory made plastic structures Durable, easy to install High product cost
Improvised means (boards, tires, etc.) Low cost of consumables The inability to ensure the tightness of the walls, the fragility of the structure.

The filter well cleaner functions as follows:

  • Waste from the house sewage system goes into a septic tank (one- or two-chamber), where within several days the liquid settles and the organic matter decomposes by microorganisms.
  • In a sealed tank, anaerobic bacteria, which do not need oxygen and sunlight, process sewage to a state in which they move freely with water.
  • The decomposed elements flow by gravity into the filter well, where organic matter continues to be processed by other microorganisms - aerobic bacteria. Unlike anaerobes, these microorganisms require oxygen to function.
  • Insoluble elements fall to the bottom and, together with bacteria, create activated sludge, which must be removed periodically.
  • Clean water seeps through the filter bed of soil components at the bottom of the pit. After its passage, the water is almost completely purified from impurities.
Filter well diagram
Filter well diagram

The construction of a filtering well for drainage and its operation are regulated by the norms given in SNiP 2.04.03-85. The document specifies the requirements for such devices, which are formulated as follows:

  • The purifier can only be installed on soils with good absorbing properties - sandy and sandy loam. It is not done on clay soils, which have low filtration properties. For comparison: 1 m3 sand passes 80 liters of water per day, and a similar layer of clay - only 5. The figures indicate that dense soil cleans the liquid, but it has nowhere to go. Therefore, before starting work, find out the composition of the soil. If the clay percentage is high, the soil filter cannot be created.
  • The absorption properties of the earth can be determined independently. To do this, dig a hole 30x30 cm 15 cm deep and fill it with water. Time it for the moisture to seep completely into the ground. A good result is considered 18 seconds, which means the presence of a large amount of sand in the composition of the soil. If the water disappears after 2 minutes, the soil is clayey or loamy.
  • The depth of the mine should be within 2-5 m, and the distance to the groundwater should be 1 m. It is impossible to build a filter well for a septic tank with a high level of groundwater, because liquids have nowhere to be absorbed. The structure copes well with its functions if the groundwater is at a distance of 0.5 m from the bottom of the structure.
  • With large volumes of effluent, the structure will not cope with its duties. The permissible amount of liquid that the mine can accept is 1 m3 per day. If there are several people living in the house all year round, taking a bath, using an automatic washing machine and a dishwasher, you must choose a different cleaning system.
  • When determining the location for the filter well, observe the norms for its location on the site. If groundwater is used for cooking, the construction of the tank must be coordinated with the sanitary and epidemiological station. In any case, the pit is dug no closer than 30 m from the source of drinking water. The reservoir is located no closer than 2.5 m from the septic tank, the optimal distance is 4 m. Do not dig a hole close to the border of the site, since neighbors can also build a similar structure, and the soil will not be able to absorb a large amount of liquid

Each storage tank is connected to a drainage filtering well, which can be from 1 to 3. When determining the number and volume of the structure, consider the following:

  • The volume of the septic tank should be 3 times the daily volume of wastewater coming from the house. It has been experimentally established that a person consumes 250 liters of water per day, therefore, for a family of 4 people, the volume of the storage device should be at least 3 m3.
  • The load on the filter depends on the soil on which it is built. 1m2 the sandy bottom absorbs 80 liters per day, the clay bottom - 40 liters.
  • When the distance between the bottom of the pit and the groundwater is more than 2 m, the load increases by 20%. In summer, the rate of fluid absorption increases.
  • The size of the tank bottom is determined according to the composition of the soil. On sandy soils, it can reach 4 m2, on sandy loam - 1.5 m2.
  • The service life of the container depends on the base area: the larger the dimensions, the longer it will function. However, the owners of the plots often build a 2x2 m filter well with a 2.5 m deepening, without bothering with precise calculations.
  • If, according to calculations, several mines are needed, they are placed in different places on the site. The distance between them should be equal to twice the diameter of the tank.

Filter well installation technology

Factory-made primary polyethylene filter tanks are sold on the market, ready for installation. In the lower part of the product, crushed stone and gravel are already poured for water purification. However, the structure can be made independently from scrap materials. Everyone can build a filter well for a septic tank with their own hands. The sequence of work is shown below.

Construction of a brick well

Brick filter well
Brick filter well

It is easy to build a container of any shape out of brick, but most often the owners choose a round one. This geometry ensures an even distribution of sewage throughout the entire area of the purifier.

The work is carried out in the following sequence:

  • Start construction by digging a hole in which a 2x2 m construction with a depth of 2.5 m should fit. Increase each side of the hole by 40 mm to ensure a guaranteed gap between the walls of the mine and the ground.
  • Make sure that there is at least 1 m to the groundwater. To do this, dig a hole to a depth of 1 m and check the excavated soil. If it is wet, it is not worth continuing construction in this place, the water is too close to the surface.
  • Stand a brick wall in the pit. In the lower part of the structure, at the height of the filtering layer, make the walls with small holes from 2 to 5 cm, which are staggered. Do not leave openings above this level.
  • Fill the bottom with crushed stone or gravel with a layer of 1 m, with large elements at the top, small ones at the bottom.
  • Make the hole in the shaft through which water comes from the septic tank in such a place that the liquid pours out from a height of 40-60 cm. The sewer pipe should end in the center of the structure and be attached obliquely for water to flow independently from the storage tank.
  • Place a plastic sheet over the filter to prevent the flow from eroding the filter.
  • Cover the shaft with a reinforced concrete or wooden cover with an opening with a diameter of 70 cm. Through this opening, the shaft cavity will be inspected.
  • Close the opening with a hatch.
  • Make a hole in the lid and install a 10 cm pipe to ventilate the container. It should protrude 75-100 cm above the ground.
  • Fill the gaps between the masonry and the ground with gravel or chippings. Pour the loose mass in layers, with compulsory compaction.
  • Cover the lid with a half-meter layer of soil.
  • To keep the ventilation pipe from standing out, plant climbing plants next to it.

Construction of a well from reinforced concrete pipes

Reinforced concrete pipe filter well
Reinforced concrete pipe filter well

This design is the most popular among consumers. For construction, you will need 3 pipes with a diameter of 90-150 cm. The lower workpiece should be with 5 cm holes, made in a checkerboard pattern. Openings can be drilled or you can buy a finished perforated product. The rings are heavy, so you need a crane to mount them.

To build a filter well with your own hands, follow these steps:

  • Place the perforated ring on a level surface.
  • Check the horizontal level of the upper end of the structure with a level.
  • Choose the ground inside the ring until the product sags to its full height under its own weight.
  • Place the second ring on it.
  • Continue removing the dirt inside the structure until the top of the second piece is level with the ground.
  • Place the third on the second ring and repeat the steps.
  • Create a filtering layer of rubble and gravel as described above.
  • Lead a pipe from the septic tank to the tank.
  • Cover the well with a lid and make a ventilation hatch in the same way as above a brick shaft.
  • If the winters are harsh, insulate the upper part of the device with two covers - insulating and carrying. Fill the gap between them with heat-insulating material.

In the presence of a crane, the well construction technology is different:

  • Dig the hole completely to the specified depth. Its diameter should be 40-80 cm larger than the size of the ring.
  • At the bottom, make a concrete screed in the form of a ring so that the soil remains inside. It will serve as the foundation for the walls of the tank.
  • Punch holes with a diameter of 50-60 mm in the lower product with a puncher with a vertical and horizontal step of 100-120 mm.
  • Place the blanks in the pit one by one.
  • Further operations are carried out as in the previous case.

How to make a filter well - watch the video:

You can build a filter well for sewage in different ways, but usually an option is chosen that allows you to use your financial capabilities. The article provides examples of the manufacture of a cleaning device in the presence of a small set of materials and minimal construction experience.