Choosing a septic tank for clay soil and installing it are complex tasks that require compliance with a number of rules. Incorrect installation of such structures on loam can cause deformation of the septic tank and disruption of its operation.

It is difficult to install a septic tank on clay, because... the characteristics of this soil do not predispose to rapid disposal and treatment of wastewater. Clay does not absorb water well. Wastewater is retained in the tank. Sandy soil can absorb up to 90 liters of water per day, while loam soil can absorb only 25 liters. Pure clay is characterized by lower water absorption rates. In addition, clay soils are characterized by high density and heavy weight. When arranging an autonomous sewer system, these features must be taken into account.

Why do septic tanks installed in clay become deformed, and how to avoid this?

Most often, when installing septic tanks, large-volume plastic containers are used. They are a good option for many types of soil, but they are not ideal for clay. Possessing high density and weight, clay often deforms even thick plastic containers during seasonal temperature fluctuations. In some cases, deformation of even metal containers is possible. In addition, septic tanks in clay soil are often deformed due to soil movement. This happens especially often if groundwater lies too close to the surface.

When planning to install a septic tank in clay soil, you need to take into account the danger of possible deformation of the container. To prevent the occurrence of such a problem, it is advisable to use rigid materials for the construction of the structure, including concrete rings, slabs, etc.

If desired, you can also use plastic containers. But to protect them from soil movements, it is necessary to make a special structure made of concrete or a strong wooden sheathing. This will avoid damage to the integrity of the container due to soil pressure. If the groundwater level is low, you can use metal reinforcement or corners to make the sheathing.

What septic tanks can be used in clay?

When installing a septic tank on clay soil, it should be taken into account that it is almost impossible to create high-quality filtration fields, so classic multi-level systems should be abandoned. There are several options for autonomous sewers that can be used effectively.

Storage containers

The simplest and cheapest option for a septic tank, suitable for installation in clay soil, is a storage system. In clay soil conditions and to save money on pumping water in the future, you can use a complex storage system consisting of several containers connected to each other. Such cleaning systems can be created based on:

• concrete rings;
• wells lined with brick;
• large metal barrels;
• plastic containers, etc.

Such a septic tank for clay soil is an analogue of a cesspool and requires systematic pumping of accumulated wastewater with a sewer truck.

With soil purification

Septic tanks, consisting of several storage tanks and an artificially created filtration field, can reduce the cost of pumping wastewater. In this case, some part of the already settled wastewater will enter the filtration field and go into the soil. The design in this situation will be simple. Several containers are connected in series so that heavily contaminated wastewater remains in the first one, and the already settled water penetrates into the next container.

There doesn't have to be only 2 containers. Some owners of personal plots connect 3-4 containers together at once. This makes it possible to ensure that almost clean water enters the last cavities of the septic tank. The difficult aspects of arranging such a system are preparing the site and installing a filtration field system.

Due to the presence of clay in the place where the filtration field will be located, it is necessary to dig a pit 1 m deeper than the bottom of the hole intended for installing the system. Gravel or crushed stone, as well as a layer of sand, are poured into the bottom of the pit. Perforated pipes are laid inside such a cushion so that purified water from the last container can be discharged to the filtration field. It must be taken into account that there must be at least 50 cm of crushed stone and sand on top of the pipes.

During the shrinkage process, the filtration field can become heavily clogged with clay and cease to perform its function. To delay such an unfavorable outcome, the finished filtration field should be covered with geotextiles. Clay can be poured on top of this material. This will prevent the clay from swelling and clogging the cavities between the crushed stone.

For biological treatment

Closed septic tanks with biological treatment are very popular among owners of sites with clay soils. Such systems are autonomous sewerage stations. They provide a high degree of purification, so in the future the resulting water can be used for technical needs and for irrigation of the site.

Such autonomous sewers are multi-chamber products, where the wastewater is immediately subjected to fractional division and settled. Clarified wastewater is further purified by special bacteria that process all organic compounds present.

Design features of a septic tank for clay

The physical properties of clay soils change slightly during periods of freezing and thawing. This often causes the septic tank to gradually push to the surface. This problem especially often arises when installing septic tanks that were made of lightweight materials, including plastic and metal.

To prevent this effect from occurring, it is necessary to fix the structure in the pit. For additional fixation, metal reinforcement and concrete mortar are often used. If the surface of the container is equipped with special holes, you can use metal cables to fix it to the bottom of the pit.

In addition, to prevent the container from moving, it is recommended to install a thick substrate of gravel and sand. It is also possible to make a concrete slab that will serve as a base. When pouring it, you can make “ears”. With their help, you can later more securely attach the septic tank to the base.

When performing excavation work when installing an autonomous sewer system, all safety measures must be observed, since the clay can quickly collapse. It is best to dig a hole for the septic tank at least 1.5 m wider and longer than required. This will avoid surprises due to clay collapse.

Features of installation on clay soil

When planning to install a septic tank on clay soils, you must comply with the sanitary requirements for the location of autonomous treatment facilities. The distance to the house and other permanent buildings must be at least 20 m.

In addition, if a septic tank for clay soil has a filtration well and will purify the water not only through the operation of a sewage disposal machine, you need to take into account that the distance to the well or other water source must be at least 50 m. This will prevent contamination of drinking water by wastewater.

It is best to begin installation when the weather has been dry for a long time. This will ensure a reduction in groundwater. When digging a pit, all precautions should be taken. The height of the pit must be at least 70 cm greater than the height of the selected septic tank. A 10 cm layer of sand is placed at the bottom of the pit. After this, a 30 cm layer of gravel is poured. Laying geotextiles on top of this is recommended.

After this, a connected reinforcing mesh is laid at the bottom of the pit, which is necessary for pouring the concrete substrate. If necessary, a wooden or metal sheathing is formed to protect the septic tank from compression. After the bottom of the pit has been prepared, you can proceed to installing the septic tank structure. Be sure to secure the container with cables or metal rods. After this, you need to install all the communication pipes, fill the cavities around the septic tank and compact the soil.

Which septic tank to choose for clay soil? How realistic is it to organize soil-based wastewater treatment in this case? Is it possible to come up with some alternative use for treated wastewater?

In this article we will try to answer all these questions.

The photo shows the construction of a septic tank from reinforced concrete rings in clay soil.

Features of clays and loams

Why, in principle, should a septic tank for clay soil be different from any other?

Remember how a local treatment plant works. In a settling tank (or several settling tanks), wastewater is separated into heavy and light fractions and relatively clean water. Just “comparatively”: as a rule, it has a specific sewage smell and must undergo soil purification.

To organize the latter, a so-called filter well is dug - a structure with perforated walls and a drainage bottom. Its performance depends on depth, wall area, water level and... that's right. Type of soil.

Reference: a square meter of sand can absorb approximately 90 liters of water per day.
For sandy loam soil the volume is reduced to 50 liters, for loam - to 25.
Dense clay can absorb 5 or less liters of water per day per square surface.

It is precisely the low absorption of soil that is the problem. It’s easy to clean the drains, but there’s nowhere to dispose of them.

Solutions

Is the only solution really to be digging a cesspool and periodically removing a sewer truck? It's not that bad. On any type of soil, if you have sufficient area at your disposal, you can organize a full-fledged treatment station.

So what should a septic tank be like in clay soil?

Several solutions are possible.

Filtration

In the vast majority of cases, the clay layer has a very limited thickness - as a rule, no more than 2-3 meters. After going through it when digging a well, you may find sandy loam or even sand with excellent absorbency.

In this case, the productivity of the well will be higher than typical for the corresponding type of soil: the water column will create excess pressure.

Before looking for complex solutions, check with your neighbors how deep the clay layer is. As an option, order geological exploration work. Their price is not that high, but they will pay off handsomely: making a septic tank with your own hands in clay is much cheaper than buying and installing a biological treatment station, which may be needed in the most extreme cases.

As for the construction itself, and brick structures. The soil does not impose any restrictions on the material used.

Watering

If black soil is brought to your site and plants are planted in it, the obvious solution is to use treated wastewater for irrigation. Instead of a filter well, an ordinary sealed container (for example, a plastic tank) is buried in the ground, into which the drainage pump is immersed. With its help, water is supplied to sprayers placed along the beds.

Let us clarify: for obvious reasons, the solution is only suitable for summer cottages.
In addition, at a low degree with aeration.

Filter field

If the soil on your site is capable of absorbing at least some amount of water, the obvious solution is to maximize the absorption area. How can this be achieved?

The instructions are simple: use the filter field.

• The maximum possible area is covered with crushed stone.
• Drainage pipes are laid on it. To avoid silting, the holes in them must be large enough - at least 20 mm; as an option, pipes with a diameter of 110 mm at intervals of 2 meters are opened with tees 110 - 110 - 50. The pipe molding is based on 8-10 meters per person permanently living in the house.
• The pipes are covered with crushed stone at least 10 centimeters deep.
• Imported black soil is poured on top, on which moisture-loving plants can be safely planted. With a pipe laying depth of 40 cm, they do not freeze even at -30C (of course, provided that the sewer system is constantly used).

The solution is convenient because it is undemanding in terms of the degree of wastewater treatment: there are no odors on the surface; however, it is not suitable for dense clay, which is absolutely impermeable to water.

An important point: in order to completely get rid of odors, it is recommended that drainage pipes end with outlets to the surface equipped with deflector umbrellas.
The recommended height above ground level is 1-1.5 meters.

Dumping into a ditch

Finally, on soil with zero absorption, it is possible to discharge directly onto the terrain or, more conveniently, into a ditch to drain water. It is clear that in this case, a septic tank in clay should provide extremely high-quality wastewater treatment (at least 95%) and a complete absence of odors.

Which septic tank is better for clay soil in this case? Energy dependent, using aeration.

The operating principle of such treatment facilities:

• Air is continuously blown through the primary settling tank by a compressor. It provides the vital activity of aerobic bacteria, which devour organic matter and decompose it into water and gaseous products with a small residue of odorless sludge. Additional purification is achieved through active oxidation of organic compounds.
• The aerated wastewater enters the secondary settling tank, where the sludge precipitates and is moved into the first tank by an additional compressor - an airlift.
  
• From the third chamber, purified and clarified wastewater is lifted by a drainage pump and discharged into a ditch, which directs it into a reservoir or simply into a large area where water can evaporate.

Conclusion

The achievements of engineering in construction do not shake the imagination like discoveries in the field of high technology. Nevertheless, in terms of their significance for our lives, they are not inferior to them. A good example is a septic tank made of concrete rings for a private house, which replaced a cesspool. In this building, a process that is most important for the environment takes place – the purification of sewage by microorganisms. Dirty water that has passed through a septic tank becomes safe for humans and nature.

Unlike a cesspool, which accumulates sewage and is not able to absorb a large volume of water, a septic tank copes with this task perfectly. Three processes simultaneously occur in it: dilution of wastewater, sedimentation and decomposition of organic sediment. The rate of biological treatment in a septic tank is hundreds of times higher than in a cesspool. Thanks to the active processing of organic matter, the volume of bottom sediment in it is minimal, which allows pumping once every 2-3 years.

The question arises, what is good about the option of reinforced concrete rings, since you can use a monolithic or plastic container instead?

There are several arguments in favor of this decision:

• Installation of a prefabricated reinforced concrete structure is simpler, easier and faster than working with concrete, reinforcement and formwork;
• When using plastic containers, it becomes necessary to anchor them to a concrete slab. Otherwise, groundwater may push them out of the ground;
• A septic tank made of reinforced concrete rings is stronger and more durable than plastic.

To successfully build such a structure, you need to have an idea of ​​its calculation and the main stages of installation. You will find useful information on this topic in our article.

The volume of wastewater is a basic value taken into account when designing any treatment facility. Sanitary standards set it at 200 l/day per person. In addition, the capacity of the septic tank should be equal to the 3-day volume of sewage. Based on these two conditions, the capacity of the structure can be calculated. So, for example, a family of 4 people will need a septic tank with a volume of: 4 x 200 l/person x 3 = 2,400 l. (2.4m3).

The second issue that needs to be resolved is the number of cleaning chambers: one, two or three. If no more than 3 people permanently live at the dacha, then you can limit yourself to one camera.

With a larger number of residents (4-6 people), the sewage system in the dacha is made of concrete rings and is made of two chambers. It copes better with large sewer flows. Three cleaning tanks are used in houses where several families live.

Each septic tank chamber performs certain tasks:

• In the first, sedimentation of wastewater and anaerobic (oxygen-free) decomposition of organic matter occurs. Heavy particles settle to the bottom here, and light particles float to the top. Clarified water flows through the pipe into the second chamber;
• In the second tank, the wastewater undergoes additional bacterial purification and is discharged into a filter trench or well. Oxygen (aerobic) decomposition of organic matter occurs here.

The choice of filtration method depends on the groundwater level and type of soil. In a resorption well, water goes into the ground through perforated walls and a bottom covered with small crushed stone.

Two-chamber septic tank made of reinforced concrete rings with a filter well

When the level of soil water is high and the soil does not absorb moisture well (clay, loam), a resorption trench (filtration field) is made. A perforated pipe wrapped in geotextile is placed in it and covered with drainage material (crushed stone, gravel + sand). Due to the long length of the pipe and the presence of a filter bed, the final cleaning process proceeds normally even in heavy and wet soil.

Three-chamber septic tank with filter trench

Having determined the capacity, the number of chambers and the type of filtration structure, you can proceed to choosing a location on the site. The diagram will help you in this matter. It indicates the minimum permissible distances from the treatment plant to water sources, trees and roads.

Sanitary gaps between the septic tank, water source and other objects

From this diagram it can be seen that the greatest distance of the sewerage structure should be from the source of drinking water (50 meters). On a dacha plot of 5 acres, this requirement is impossible to fulfill. Here you will have to install a device for disinfecting drinking water with an ultraviolet lamp or use imported bottled water.

In addition to observing sanitary gaps, the septic tank must be placed so that its chambers can be reached with the hose of a sewer truck.

Construction materials

In order to make a septic tank from concrete rings with your own hands, you need to buy the following materials:

• polypropylene pipes with a diameter of 12-15 cm (the length is determined by the length of the sewerage route);
• pipes for ventilation of chambers (diameter 8-10 cm);
• plastic tees of the same diameter;
• concrete rings (diameter depends on the volume of the chambers);
• cement-sand mortar for sealing joints;
• hydrophobic impregnation for concrete or bitumen mastic for waterproofing;
• concrete cover with inspection hatch;
• plastic perforated pipes with a diameter of 10-15 cm for the drainage trench (filtration field).

The correct choice of the type and diameter of the rings is of great importance for the normal operation of the septic tank. It is best if you buy concrete rings with a bottom at a construction warehouse. This will free you from the need to fill a monolithic slab and seal the contact area.

If such products are not available, then buy standard circles, but only with a locking connection, which increases the tightness and strength of the joints. The diameter of the sections and their number are selected based on the estimated capacity of the primary and secondary chambers.

Cylinder volume formula

The number of concrete circles is determined by dividing the volume of the cleaning chambers by the volume of one circle. If the number turns out to be odd, for example, 7 pieces, then add one circle to an even number. For each container in a two-chamber septic tank, there will thus be 4 concrete circles.

The number of round concrete sections for the filter well can be taken equal to the number of chamber rings. If the groundwater is deep, then the well can be dug 1-2 meters deeper.

Construction technology

The construction of a septic tank from concrete rings begins with digging a pit. Its size should be equal to the outer diameter of the chambers plus 30-40 cm for the mounting gap on each side and 5-10 cm of space between the rings.

If circles with a bottom are purchased, then a sand cushion 15-20 cm thick is made under them. It is needed to evenly distribute the weight of the concrete onto the ground. When determining the depth of the pit, do not forget to take into account the thickness of the bedding!

When using ordinary well circles without a bottom, you will have to pour a concrete slab with a thickness of at least 10 cm under them. It must be protected from cracks with reinforcing mesh (rod diameter 10-14 mm, pitch 10-15 cm).

Installation of concrete rings for sewerage is carried out using M500 cement mortar. It is evenly distributed over the entire contact surface. Having completed the installation, holes are marked and punched in the upper part of the chambers for the passage of pipes: sewer, overflow and leading to the filter well (trench).

A plastic “tee” is put on the end of the sewer pipe entering the primary chamber. The same is done with the overflow and outlet pipes. Tees perform an important function: they prevent contaminants floating on the surface of the water from clogging the pipes and moving into other compartments of the treatment plant.

Having installed the rings, they are treated with hydrophobic impregnation on the outside and inside. Having covered the compartments with concrete covers, inspection hatches are attached to them. Holes are punched in the covers of the primary and secondary chambers and ventilation pipes are installed in them.

An important nuance is the creation of the correct slope from the exit point of the internal sewer system to the entrance to the first chamber. Its optimal value is 2% (per 1 meter of length 2 cm of height difference). In order to do this work without errors, we suggest studying the sketch of the treatment plant in the figure.

Scheme of a two-chamber septic tank with a drainage ditch

If your septic tank will work with a filtration well, then it is better to buy round sections with drainage holes.

Circles for drainage well

It should be remembered that the drainage well is made only in soil that absorbs moisture well (sand, sandy loam). In loams and clays, for final cleaning, a filtration field is set up or a drainage trench is dug.

Before laying perforated pipes, the bottom of the trench is covered with fine crushed stone (layer 20-30 cm) or gravel to create an absorbent substrate. The pipe is wrapped in geotextile. It will protect it from silting by soil particles carried by storm water.

Cost of concrete rings

Estimated prices for reinforced concrete for 2017 for a wastewater treatment plant look like this:

• An ordinary ring with a KS 10-9 lock (inner diameter 100 cm, height 90 cm) in different regions can cost from 1700 to 2300 rubles/piece;
• KS 15-9 – RUB 3,000-3,600/1 piece;
• Cover with a hole for the hatch 1PP 10-1 (diameter 100 cm, thickness 15 cm) – 1200-1700 rub./piece;
• 1PP 15-1 - 2,400-3,000 rub./piece;
• Ring with bottom KCD 10-9 (diameter 100 cm, height 90 cm) – 2600-3200 RUR/piece;
• KCD 15-9 – 4700-5700 rub./piece.

Putting the septic tank into operation

Having completed the installation and filling the pit bosoms with the excavated soil, the septic tank chambers need to be filled with clean water. Its level should be several centimeters below the bottom of the upper overflow pipe connecting the primary and secondary chambers.

Some owners make the mistake of thinking that it is better to fill the treatment plant with sewage. Let us remind them that the principle of operation of a septic tank is to dilute sewage, and not to accumulate it. Therefore, before starting work, there must be clean water in it.

There is one more important nuance. For effective cleaning, special cultures of bacteria that decompose organic matter must be introduced into the containers. They can be purchased at hardware stores in the form of a dry concentrate.

Many owners of country houses are interested in whether it is possible to make a septic tank on clay. The main problem with constructing a treatment plant on this type of soil is that pre-treated wastewater, after passing through the septic tank, is discharged into the ground, and the clay does not allow and filter water well. However, even on clay soil, an autonomous treatment plant can work effectively and for a long time if it is properly designed. In our article we will look at different types of septic tanks that can be made on clay soil, as well as the features of their design and choice.

To make it easier for you to understand what kind of septic tank is needed for clay soils, you need to study the characteristics of this soil. To create an effective sewage system, wastewater after treatment in a septic tank is discharged into the ground. The main feature of clay soils is poor absorption capacity. The earth does not absorb liquid well. This results in wastewater remaining in the treatment plant longer.

It is important to know: sandy soil absorbs 90 liters of water per day, the absorption capacity of clay soils is 25 l/day. And pure clay absorbs even less water - 20 liters.

That is why, when installing a septic tank made of concrete rings, plastic or metal containers, it is necessary to organize effective drainage. This can be a drainage well made of concrete rings without a bottom with a filter layer or a filtration field.

What septic tanks can be used in clay?

If your dacha or country house is located on an area with clay soil, then the following types of treatment facilities can be used to process wastewater coming from the house through the sewer system:

• Storage tanks. For these purposes, you can use sealed plastic containers or Eurocubes. However, stainless steel metal tanks are also suitable for clay soils. You can also make a sealed well from concrete rings if the groundwater level on the site is high. For a small private house, you can make a brick drainage well, provided you use the right technology.
• Wastewater treatment plants with soil treatment. This is a fairly effective, budget and simple option for a small country house built on clay soil. The well of such a treatment facility can be made of concrete rings, brick or metal, that is, any material can be used for such soil.
• Units with biological treatment- this is the most reliable and effective option for clay soils, suitable for a private house of any size. However, such a septic tank on clay will have the most complex design, so its choice should be made if you have the money and time to complete it.

Important: sewage from a country house on clay soil can be diverted to a septic tank of any design. It is important to properly design and install a treatment plant on such soil. In this case, the choice should be made taking into account the productivity of the structure, the required degree of wastewater treatment and groundwater treatment.

Storage containers

If you decide to equip the sewer system of a private house using a storage tank, then you need to make a sealed structure. For these purposes, you can use plastic containers, Eurocubes, steel barrels or welded cubes, structures made of concrete rings or bricks.

It is quite easy to carry out such a cleaning installation. It is enough to dig a pit, concrete the bottom and install containers or concrete rings. However, if your area has a high groundwater level or there is a well near the storage tank, then using such a design is not recommended.

Structures with soil post-treatment

These simple treatment facilities are very similar to storage tanks, but without a bottom. The structure of the well itself can be made of concrete rings, bricks or bottomless water. A drainage layer is installed at the bottom of the structure.

To make a drainage filter, you need to use geotextiles, sand and crushed stone. The thickness of the filter layer is 30-40 cm. When passing through this filter, the wastewater is cleared of large fractions and enters the soil.

If there is a well nearby on your site, then this design of the treatment plant is also not suitable. When installing this septic tank, you need to know the groundwater level, because the bottom of the filter layer cannot approach the aquifer closer than 1 m.

Units with biological purification

These are the most reliable and efficient treatment facilities that can be installed regardless of the water supply system on the site. These autonomous biological treatment stations purify wastewater so effectively that the water can then be used to water the garden, drained into open reservoirs, or taken for technical needs.

Usually these are multi-chamber products, where the wastewater directly from the sewer system is divided into heavy and light fractions. Then the clarified water undergoes a process of biological purification using bacteria (anaerobic or aerobic).

Design features

Since any septic tank design can be used on clay soil to sewer a country house, the construction scheme will be standard. However, the main feature of clay soils is that it is mobile soil. Therefore, it is worth considering some design features of the septic tank.

The thing is that when the soil begins to thaw after the winter cold, the characteristics of such soils change somewhat and they can push the septic tank to the surface. This is especially true for soils with high groundwater levels and septic tanks made of light materials. That is why, when installing a septic tank in clay, it is necessary to provide additional fasteners in the soil. If the well of the treatment plant is made of concrete rings, then it is enough to simply fill it in the pit without fixing it.

The choice of method for fixing the septic tank in the pit depends on the design of the housing. If there are no protrusions on the surface of the tank, then steel cables are more suitable. If there are loops or protrusions on the body, then reinforcement outlets can be tied to them, which will be laid in a concrete pad at the bottom of the pit.

Also, the filtration system for a septic tank on clay soil has some features. When installing a septic tank in clay, it is better to arrange double drainage, that is, two filtration fields. In this case, the drainage should take the form of a two-stage trench, in the upper part of which pipes will be laid, and in the lower part there will be a drainage layer 300 mm high of gravel.

Installation features

To make a more efficient septic tank design, it is recommended to use two chambers and a filtration field. This way you can avoid excessive overfilling of the tank and at the exit from the treatment plant you will receive the most purified water possible. After you have decided on the material of the chambers, you can begin digging a pit and further work, which is carried out in this order:

1. When choosing a place for a septic tank, you can observe the minimum recommended gaps from a residential building and sources of drinking water (7 m), since clay does not allow water to pass through well. The size of the pit for the treatment facility should be 20 cm larger than the septic tank structure itself.
2. When digging a pit, you need to know at what depth the clay layer ends. If it is more than three meters, then the work will be complicated by the fact that the drainage layer will have to be carried out at a considerable depth. It is also worth considering that the septic tank containers are connected to each other by an overflow, so they should be located at a distance of 15-20 cm from each other.
3. Together with the pit, they dig a trench for laying a sewer pipe from the house to the treatment plant. At the same time, the slope of the bottom of the trench from the house to the septic tank is observed, taking into account that for every meter of length the decrease is 2 cm.
4. Depending on the containers used, the bottom of the pit can be concreted before or after installation. If you use plastic sealed tanks, the bottom is concreted and reinforced before they are installed. And after installation, these tanks are attached with hummocks to the valve outlets. When using concrete rings, the bottom can be concreted after they are installed in the pit.
5. To make a filter layer at the bottom of the second chamber, sand and crushed stone are used. First, sand is poured and compacted in a layer of 10-15 cm, then backfill is made of crushed stone 25-30 cm high. If you use a filtration field, the bottom of the second chamber is also concreted, and the wastewater is discharged to the filtration fields.
6. Next, install an overflow pipe connecting the two containers. It should exit the first chamber 40-50 cm below the entry point of the sewer pipe. Thanks to this, heavy components of the wastewater will settle at the bottom of the first chamber, and pre-purified and clarified water will flow into the second tank.
7. Ventilation pipes from the chambers are installed.
8. After this, the plastic containers are insulated with foam. Concrete rings do not require insulation.
9. The containers are covered with lids with hatches for cleaning.
10. Now backfill the pit manually. The soil must be compacted every 15-20 cm. The manhole cover must remain above the surface of the ground.

The filtration field is made depending on the groundwater level in the area:

• at low groundwater levels, semi-buried filter cassettes or filters are used;
• at high groundwater levels, surface filtration on sand and gravel beds is used.

Important: the size of the filtration field is directly related to the daily volume of wastewater from the house.

One square meter of filtration field is capable of serving 0.5 cubic meters of wastewater. You can purchase ready-made filter wells based on geotextiles or make the field yourself:

1. After digging up soil from the field, a pipeline is laid from the last chamber of the septic tank to the filtration field. The laying depth is 70-120 cm from the ground surface, but not less than 1 m to the groundwater level.
2. A drainage mesh is laid at the bottom of the field. Then a layer of sand and crushed stone is made. The height of the layer should be such that it rises above the inlet pipe by no more than 50 mm. All pipes with holes are laid with a slope of 1 cm per meter of length.
3. The drainage pipeline is insulated using foam plastic or a wooden box.

Perhaps the first thing you should take care of when starting to build a house or cottage is the septic tank. Those owners of plots with clayey soil will find it more difficult to install a flawlessly functioning sewage drainage system. But with due diligence and knowledge of how to install a septic tank in clay, this is quite possible. In such soil, you can install both a factory-made autonomous treatment station and a homemade container with or without a bottom.

The homeowner should know that in some respects he is lucky: clay is the best soil filter.

The ability to pass water and purify it are two different things. Therefore, in such soil you can safely install a septic tank without a bottom. All sewage outlets will be effectively cleaned, but this process is quite slow. Therefore, the design of the sewer system in these conditions has its own characteristics that prevent overflow of the container.

Types for installation in clay

Storage containers

Most often, they are used as plastic containers, in particular Eurocubes of various sizes. But barrels and homemade welded cubes made of stainless steel can be installed. The storage container can be made of brick or concrete. Such septic tanks are often found in villages and towns. They are easy to install: just dig a pit of the required size, then line its bottom and walls with bricks. Or they install concrete rings with a diameter of 1 m and concrete the bottom of the pit.

For biological treatment

They are the most reliable and modern. These products are autonomous biological wastewater treatment stations capable of producing water that can be used for watering a garden or discharged into a pond with fish. The operating principle of such septic tanks is to separate fractions into heavy and light. This is facilitated by the design of the station.

The main work of wastewater treatment is performed by aerobic or anaerobic bacteria. The life activity of the former is possible only under the condition of constant air pumping. The latter live in silt or soil and do not need additional stimulation. These stations can be installed on heavy soils, including clayey ones.

With soil purification

These are the simplest wastewater storage tanks to set up. They are arranged in a similar way to storage tanks, but without concreting the bottom. That is, you can use all the same materials: brick, concrete, plastic or iron, but you need to install a drainage layer at the bottom. It is made of sand and crushed stone. Here, large fractions are filtered, after which the wastewater penetrates the clay and receives better purification.

Such septic tanks are good because the sewer truck needs to be called less often than in the case of storage tanks. However, in clayey soil the process of filtration and wastewater removal will be hardly noticeable. Therefore, you will have to pump out sewage with the same regularity as if you have a container with a concrete bottom. Such a septic tank can be built quite quickly with your own hands.

Installation technology

1. You need to decide what will be used for the storage tank device. In order to speed up cleaning and make it more effective, it is recommended to build a two-chamber structure with a filtration field. This will allow you to avoid overfilling the main tank and obtain the most purified wastewater at the output.
2. 2nd step - determining the location of sewage receivers. Here you need to focus not only on the convenience of their placement on the site, but also on sanitary and hygienic standards. Since clay does not allow water to pass through well, the risk of runoff entering a well or well is small. Therefore, it is possible to install a septic tank with your own hands at the minimum distances from water intake points and residential premises - 7 m.
3. Once the location of the tanks has been determined, excavation work begins. It would be a good idea to ask your neighbors in advance about the depth at which the clay/soil boundary lies. If it is located below 3 m from the soil surface, the work will be complicated by the need to install a drainage system at a fairly large depth. When digging pits, take into account that one container should be separated from another at a distance of no more than 2 m.
4. After installing concrete rings, plastic cubes or laying bricks along the walls of the pits, they begin to install a drainage layer directly in the containers themselves. To do this, backfill with sand and crushed stone. For the first, a layer of 10-15 cm is enough. For the second - 25-30 cm. If plastic barrels are used as tanks, then during installation it is recommended to strengthen them with chains or otherwise. This is necessary because during floods and when the soil freezes, the container can be squeezed out of the hole.
5. Both containers must be connected with a pipe so that it flows 40-50 cm below the sewer pipe, which runs from the house to the main wastewater tank. This device allows wastewater to flow into the 2nd chamber and promotes the separation of fractions. Heavier ones settle in the first container.
6. Further, if free-standing containers were used as containers, they must be insulated. This can be done using polystyrene foam. Such a septic tank, insulated with your own hands, will not freeze in the most severe frosts.

Filter field

In clay conditions, if the groundwater level (GWL) is below 1.5 m, semi-buried filters or filter cassettes are installed. At high groundwater levels, it is rational to arrange surface filtration using gravel-sand pads.

The dimensions of the post-treatment field depend on the daily water consumption in the house. If the volume of wastewater does not exceed 0.5 m³, according to established standards, a filter area of ​​1 m² will be sufficient. If the daily volume of wastewater is more than 1 m³, a field measuring 1.5-2 m² will be required. There are ready-made designs of filter wells available for sale. The price of these products is low, and installation is simple. The role of the main filter in them is played by geotextiles. But if there is no desire or opportunity to buy a ready-made structure, you can make the post-treatment field yourself.

After the soil is removed, a pipe is laid connecting the second container with the filtration field. As a rule, the laying depth is 0.7-1.2 m from the ground surface, but not lower than 1 m from the groundwater level. The bottom of the pit is leveled and a drainage mesh is installed on it. After which sand and crushed stone are poured. The height of the pillow should be such that its top rises above the inlet pipe by at least 5 cm. We should not forget that the pipes are installed taking into account the required slope. It must be at least 1* per 1 m. Pipes must be insulated using a wooden box and polystyrene foam.

Drainage device

Since such soil is not capable of good fluid permeability, a drainage system will be required to remove rain and flood water from the tanks for receiving sewage. To do this, not wall drainage, but ring drainage is performed. To install the pipeline you will need drains. You can use purchased perforated pipes or make them yourself from sewer plastic pipes with a diameter of 110 mm. Perforation is carried out with a drill 1.5-2 mm thick at a distance of 2-2.5 cm from each other. The holes should be staggered.

A trench is formed around the septic tank so that its bottom is 20-30 cm below the freezing point of the soil. Next, the bottom is leveled with a slope that should be at least 1 cm per 1 m towards the storage well. After this, they fill it with 5-7 cm of sand and 10-15 cm of gravel. Then geotextiles are laid on the bottom of the trench. A pipeline is installed inside the ditch and the pipes are wrapped with previously laid material. Then they begin backfilling.

Device Feature

Clay is a highly heaving soil. This property is especially evident if it is wet rather than dry. During seasonal freezing and thawing, such soil can easily push a plastic or other container placed in it out of the hole. Therefore, during the installation of containers for sewage drainage, provision should be made for their fastening in the pit.

This can be done using metal rods, which can be angles or small diameter pipes. The purpose of the rods is to fix the location of the container and prevent it from moving during soil heaving. For this purpose, you can also use steel chains, one end of which is firmly fixed in the soil.

For deeper wastewater treatment, two-stage trenches can be made for the filtration field. In the upper part of such a ditch there are pipes through which wastewater is discharged, and in the lower part there is a sand and gravel cushion up to 30 cm thick. Using such trenches, you can build a full-fledged filter system and remove wastewater outside the site.

The depth of the pits should be such that the liquid in the pipes does not freeze in winter, that is, below the freezing point of the soil. Each pipe will need to be perforated in the same way as a drainage pipe, but the holes should be larger, since the liquid will include small fractions. To prevent clogging of the holes with soil, each pipeline element is wrapped with geotextile.