Wastewater treatment plants in clay soils. Installing a septic tank on clay soil

When installing septic tanks, the following nuances must be taken into account:

Groundwater level and soil type.

The location of the place to install the septic tank relative to the house, well, fence.

Is there drainage from this area (ditches, drainage).

The depth at which a pipe passes from a building.

The degree of slope of the site.

In absolutely ideal conditions, the installation of a septic tank can be carried out at a depth of at least 75 cm from the surface layer of the earth, in order to protect the container from freezing in winter. For example, in some regions of Russia, the depth of ground freezing in winter according to SNiP is 140 cm, but in reality for a septic tank 75 cm will be more than enough.

Let's consider the option of installing a septic tank with clay soil and an extremely high groundwater level. In this case, the installation of a septic tank must be done so that the filtration field (drainage) made after the septic tank is slightly higher than the water level, otherwise the runoff will not be absorbed very well in the soil, which means that such a septic tank installation will not be considered correct. The septic tank should be installed shallowly and lightly sprinkled with earth on top to form a slide. It can also be insulated using polystyrene foam, insulation, for example, K-flex-ST or its analogues. When installing a septic tank in water, it is required to anchor it using concrete beams. The septic tank itself will almost always be full of water, and therefore, to prevent it from floating, too much mass is not required to strengthen the septic tank in the soil. If the installation of a septic tank is carried out in very difficult conditions, for example, in a swamp, then the installation of the septic tank must be done using a concrete slab (the septic tank in this case is attached to the slab using metal strips), with further lowering of this structure using a manipulator into the pit.

When installing septic tank in clay it is very difficult to create the necessary dispersion field, because drainage from crushed stone will begin to collect all the water from the area from rain, and therefore the drainage will be in the liquid and it will not drain well. This means that the drain can be made into a ditch, or a special well can be made at the very end of the dispersion field in order to install a drainage pump in it, with further pumping of water into the drainage ditch.

A septic tank consists of one or more separate chambers. Waste liquid passes through them. The configuration of the septic tank and the depth of its placement depend, first of all, on the performance of the structure and its overall dimensions. It is necessary to lay the septic tank on a soil that is not subject to swelling and other deformations during severe freezing or thawing.

If the soil freezes significantly in cold winter, then the container is placed in a fairly deep pit, and its bottom should be in a non-freezing layer of soil, or on a special foundation in the form of a concrete cushion. The simplest septic tanks, like the “Tank” or “Triton” system, are usually buried so that the thickness of the soil from the soil surface to the septic tank body is no less than half a meter.

For the normal stable operation of any treatment plant of this type, it is extremely important that flood waters do not stagnate in any case, and the height of groundwater is certainly more than one meter. If your site is poorly drained, then the septic tank is laid shallow and covered with soil so that a small hill about 50-70 cm high is formed. All technological openings must be left free access. It is worth considering that the angle at which the liquid flows through the chambers of this septic tank must be at least 50.

In addition, for a septic tank to work well in clay or other dense soil (heavy loam) that does not allow water to pass through well, it is necessary to install two-stage filter trenches. The first trench is equipped with a sand-gravel cushion 30 cm thick. A perforated filter pipe is laid in it at a depth of approximately 0.5-1 m, in the other trench - at a depth of 1.5-2 m.

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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 septic tank hole 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.

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Choosing a septic tank for installation on clay soil is a serious task, because the design must perform its functions efficiently and be able to purify wastewater from contamination. In addition, some designs allow the use of purified water in a second cycle. The implementation of such a project will be discussed in this article.

Features of clays and loams

The last indicator must be considered in more detail, since the efficiency of the entire structure depends on it. For example, one square meter of sandy soil can absorb about 90 liters of liquid per day.

In sandy loam soils this volume is reduced to 50 liters; loamy soils can process no more than 25 liters. In the case of dense clay soil, the situation is even worse: the soil can absorb less than 5 liters of water per day. That is why a septic tank on clay is constructed somewhat differently than conventional structures. You also need to know what to do if your septic tank stinks. There are many drugs and remedies to solve this problem.

Options for installing a septic tank in clay

Filtration in clay soil

When choosing a suitable solution, you should first study in detail the types of soil located on the site. You can find out from the old residents of the area, neighbors who have recently carried out construction work, or order a geological survey. The latter option will have maximum accuracy, and there is a point in studying the geology of the site: making a septic tank in clay is much easier and cheaper than purchasing a ready-made biological treatment station, which is only good for the most difficult situations.

Structurally, a septic tank on clay soil can be made in any way: you can install a plastic, brick, reinforced concrete or concrete system. Clay soil does not affect the choice of material at all, so this issue rests entirely on the shoulders of the homeowner, and depends on personal preferences and the amount of finance allocated for construction. Quite often, do-it-yourself installation of concrete rings for sewerage is done, which allows you to reduce costs.

Watering

This septic tank design is well suited for summer cottages, but it is not practical to use it in country houses where people permanently live. Another disadvantage is the low degree of purification, as a result of which the treated wastewater has a characteristic sewer smell. To avoid this problem, you will have to use a septic tank with aeration.

Filtration field

• first, the entire free area allocated for the structure is filled with crushed stone;
• then drains with holes of at least 2 cm in diameter are laid on it. The length of the pipeline in this case depends on the number of permanent residents: one person requires about 10 meters of pipe;
• then the pipeline is covered with at least a 10-centimeter layer of crushed stone;
• A layer of black soil is laid on top, on which moisture-loving plants can be planted.

Dumping into a ditch

Similar treatment plants operate on similar principles:

• the first tank constantly contains air, which supports the vital activity of aerobic bacteria that decompose organic substances entering the septic tank;
• Having passed the aeration stage, wastewater enters the next compartment, where the sludge sinks to the bottom and is transferred to the first container using a compressor;
• final cleaning is carried out in the third chamber, from which the purified water is pumped out and ends up in a ditch or large area from which it can evaporate.

Conclusion

As you can see from this article, a septic tank in clay soil is not a big problem. The main thing is to correctly understand the characteristics of the site and choose the most suitable design that best suits the specific situation.

Owners of country houses and summer cottages are faced with the problem of arrangement, which significantly improves the quality of life and comfort of the inhabitants. The simplest and most reliable way is to build a cesspool where all sewage will go.

There are several types of structures. For summer cottages where the amount of waste per day is small, a cesspool without a bottom is perfect. A sealed tank can solve the problem in a country house. Its disadvantage is that you need to periodically call a vacuum cleaner or clean the pit yourself. The third type of design is a storage septic tank. This is a cesspool where artificially grown microorganisms process and decompose sewage.

When choosing the type of cesspool that could handle waste from your home, you need to consider the following parameters:

• groundwater level;
• volume of waste per day;
• number of residents of the house;
• the presence of household appliances that consume water (washing machines and dishwashers);
• location of the house and other outbuildings;
• soil type.

Clay soil is one of the main problems of summer residents and owners of country houses. Urban crops grow poorly on such soil; water often stagnates on the site, especially in spring. The construction of sewage tanks on clay soil is also accompanied by some difficulties.

A cesspool in clay soil can often silt up and slowly leak liquid. The most optimal solution for such areas is to install a hermetic tank. You just have to dig a pit and install the container in the hole. But if sewerage is needed in a dacha, where the owners rarely visit, then a sealed cesspool in clay is not justified.

Sanitary standards

To avoid troubles during the operation of the drain, when constructing a cesspool in clay soil, it is necessary to comply with sanitary and hygienic requirements.

• The distance from the pit to the well or well should not be less than 20 meters.
• The distance from a residential building is at least 5 meters.
• When setting up a pit on clay soil, it is necessary to take into account the reserve, since liquids settle slowly and the container may overfill.

Important! Failure to comply with sanitary and hygienic standards during the construction of cesspools can cause a number of troubles: misunderstandings with representatives of the law, an unpleasant odor in the area, the spread of infections.

Installation Features

If you install a classic sewer system on an area with clay soil, then the efficiency of such a cesspool will decrease. Liquids seep through clay very slowly, so you need to take care of additional outlets. There are two ways to do them well.

Method No. 1

First you need to carry out the necessary earthworks and dig a pit. Now we drill holes at the bottom of the pit where plastic pipes with a large number of holes will be located. To prevent the pipe from clogging, you should install a plug on it. Thanks to this design, the absorption surface will increase, all the water will drain away faster, and solid impurities will remain at the bottom of the pit.

Method No. 2

This option will help solve the question of how to make a cesspool in loamy soils and on clay soil. It involves the installation of an overflow system, which will help prevent sewer overflow. To do this, you need to dig an additional pit next to the cesspool. To connect them, you should use an inclined trench so that the slope is towards the freshly dug pit.

Note! Various materials can be used to make the walls of a cesspool on clay soil, but they are best suited.

Most often, a cesspool is installed on clay soil using the second method. Two storage tanks can handle large amounts of wastewater faster and more efficiently. When the level of liquid waste in the main tank reaches the place where the connecting pipe is installed, the water will overflow. Solid sewage will remain in the cesspool, so there will be no need to clean the additional pit.

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 pumping of air. 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 has been 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.