How to make a septic tank in clay soil. Septic tank in clay - the right device in clay soil
Achievements of engineering thought in construction do not stagger the imagination like discoveries in the field of high technologies. Nevertheless, they are not inferior to them in their significance for our life. A good example is a septic tank made of concrete rings for a private house, which replaced a cesspool. In this structure, the most important process for the environment takes place - the cleaning of sewage by microorganisms. Dirty water that has passed the septic tank becomes safe for humans and nature.
Unlike a cesspool, which accumulates sewage and is not able to absorb a large amount of water, a septic tank does an excellent job of this task. Three processes simultaneously take place in it: dilution of effluents, their settling and decomposition of organic sediment. Speed biological treatment in a septic tank is hundreds of times higher than in a cesspool. Due to the active processing of organic matter, the volume of bottom sediment in it is minimal, which allows pumping out once every 2-3 years.
The question arises, why is the option of reinforced concrete rings good, because instead of it you can use a monolithic or plastic container?
There are several reasons for 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 can push them out of the ground;
- A septic tank made of reinforced concrete rings is stronger and more durable than plastic.
For the successful construction of such a structure, you need to have an idea about its calculation and the main stages of installation. Useful information on this topic you will find in our article.
The volume of wastewater is the basic value taken into account when designing any treatment plant. Sanitary standards set it at the level of 200 l / day per person. In addition, the capacity of the septic tank should be equal to 3 daily volumes 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 liters. (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 in the country house, then you can limit yourself to one camera.
At more residents (4-6 people), the sewerage in the country house of concrete rings is made two-chamber. It copes better with a large flow of sewage. Three cleaning tanks are used in houses where several families live.
Each chamber of the septic tank performs certain tasks:
- In the first one, sedimentation of effluents and anaerobic (oxygen-free) decomposition of organic matter takes place. Heavy particles sink to the bottom here, while light particles float to the top. The clarified water flows through the pipe into the second chamber;
- In the second tank, the effluents undergo additional bacterial treatment and are discharged into a filtering trench or well. Oxygen (aerobic) decomposition of organic matter takes place here.
The choice of filtering method depends on the level ground water and type of soil. In the absorbing well, water goes into the ground through perforated walls and a bottom covered with fine gravel.
Two-chamber septic tank from reinforced concrete rings with a filter well
With a high level of soil water and soil that does not absorb moisture well (clay, loam), an absorbable trench is made (filtration field). A perforated pipe wrapped with geotextile is laid in it and covered with drainage material (crushed stone, gravel + sand). Due to the large length of the pipe and the presence of a filter bed, the final cleaning process is normal even in heavy and wet soil.
Three-chamber septic tank with a filter trench
Having determined the capacity, the number of chambers and the type of filtration structure, you can proceed to the choice of a place on the site. A diagram will help you with this. It indicates the minimum allowable distances from the treatment plant to water sources, trees and the road.
Sanitary breaks between septic tank, water source and other facilities
From this diagram it can be seen that the largest distance of the sewer structure should be from the source drinking water(50 meters). On a summer cottage with an area of 5 acres, this requirement is not feasible. Here you will have to install a device for disinfecting drinking water with an ultraviolet lamp or use an imported bottled one.
In addition to observing sanitary breaks, the septic tank must be placed so that its chambers can be reached by the hose of the sewage 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 sewer route);
- pipes for ventilation of cells (diameter 8-10 cm);
- plastic tees of the same diameter;
- concrete rings (the diameter depends on the volume of the chambers);
- cement-sand mortar for sealing joints;
- hydrophobic impregnation for concrete or bituminous mastic for waterproofing;
- concrete cover with an inspection hatch;
- plastic perforated pipes with a diameter of 10-15 cm for a drainage trench (filtration field).
The correct choice of the type and diameter of the rings has great importance for 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 pour a monolithic slab and seal the contact area.
If such products are not available, then buy standard circles, but only with a locking joint, 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 one circle is added to an even value. For each container in a two-chamber septic tank, therefore, there will 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 device 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 concrete on 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, a concrete slab with a thickness of at least 10 cm will have to be poured under them. It must be protected from cracks with a reinforcing mesh (rod diameter 10-14 mm, step 10-15 cm).
Installation of concrete rings for sewerage is carried out on cement mortar M500. 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 passing pipes: sewer, overflow and leading to the filtering well (trench).
Finally sewer pipe entering the primary chamber put on a plastic "tee". The same is done with the overflow and outlet pipes. Tees perform an important function: they do not allow contaminants floating on the surface of the water to clog pipes and go to other compartments of the treatment plant.
Having installed the rings, they are treated with hydrophobic impregnation outside and inside. Having covered the compartments with concrete covers, revision hatches are attached to them. Holes are punched in the covers of the primary and secondary chambers and ventilation pipes are placed in them.
An important nuance is the creation of the correct slope from the exit point of the house sewer to the entrance to the first chamber. Its optimal value is 2% (for 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 for it.
Circles for a drainage well
It should be remembered that the drainage well is made only in soil that absorbs moisture well (sand, sandy loam). In loam and clay for final cleaning, a filtration field is equipped or a drainage trench is dug.
Before laying the perforated pipes, the bottom of the trench is covered with fine gravel (layer 20-30 cm) or gravel to create an absorbent substrate. The pipe is wrapped with geotextile. It will protect it from silting with soil particles carried by storm water.
The cost of concrete rings
Estimated prices of reinforced concrete products for 2017 for a treatment plant look like this:
- An ordinary ring with a lock KS 10-9 (inner diameter 100 cm, height 90 cm) in different regions can cost from 1,700 to 2,300 rubles per piece;
- KS 15-9 - 3000-3 600 rubles / 1 pc.;
- Cover with a hole for the hatch 1PP 10-1 (diameter 100 cm, thickness 15 cm) - 1200-1700 rubles / piece;
- 1PP 15-1 - 2,400-3,000 rubles / piece;
- Ring with a bottom KCD 10-9 (diameter 100 cm, height 90 cm) - 2600-3200 rubles / piece;
- KCD 15-9 - 4700-5700 rubles / piece.
Putting the septic tank into operation
After completing the installation and filling the sinuses of the pit with excavated soil, the septic tank chambers must be filled with clean water. Its level should be several centimeters below the bottom mark of the upper overflow pipe connecting the primary and secondary chambers.
Some owners do wrong, believing that it is better to fill the sewage treatment plant with sewage. We remind them that the principle of operation of the septic tank is to dilute sewage, and not to accumulate it. Therefore, by the beginning of work, it must have clean water.
There is another important nuance. For effective cleaning, special cultures of bacteria that decompose organic matter must be introduced into the containers. They can be bought in hardware stores in the form of a dry concentrate.
Which septic tank to choose for clay soil? How realistic is it in this case to organize soil post-treatment of wastewater? Is there any alternative use for treated wastewater?
In the article we will try to answer all these questions.
In the photo - 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 the local treatment plant is arranged. In a settling tank (or several settling tanks), wastewater is separated into heavy and light fractions and relatively pure water. It is “comparatively”: as a rule, it has a specific sewer smell and must undergo soil post-treatment.
To organize the latter, the so-called filter well is dug - a structure with perforated walls and a draining bottom. Its performance depends on the depth, wall area, water level and ... right. Soil type.
Reference: a square meter of sand can absorb about 90 liters of water per day.
For sandy soil, the volume is reduced to 50 liters, for loam - up to 25.
Dense clay can absorb 5 or less liters of water per day per square surface.
It is precisely in the low absorption of the soil that the problem lies. It is easy to clean the drains, but there is nowhere to dispose of them.
Solutions
Is the only way out - digging a cesspool and periodically removing a sewage truck? Everything is not so bad. On any type of soil, if you have enough space at your disposal, you can organize a full-fledged treatment plant.
So what should be a septic tank 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. Passing it when digging a well, you can find sandy loam or even sand with excellent absorbency.
In this case, the performance of the well will be higher than typical for the corresponding type of soil: the water column will create excess pressure.
Before looking difficult decisions, check with your neighbors how deep the clay layer is. Alternatively, order exploration work. Their price is not so high, while they will pay off handsomely: making a septic tank in clay with your own hands is much cheaper than buying and installing a biological treatment station, which may be needed in the most advanced cases.
As for the design itself, and brick structures. The soil does not impose any restrictions on the material used.
Watering
If you have planted black soil on your site, 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 a drainage pump is immersed. With its help, water is supplied to sprayers placed along the beds.
To clarify: for obvious reasons, the solution is only suitable for cottages with summer residence.
In addition, at a low degree with aeration.
Filter field
If the soil in your area is capable of absorbing any amount of water, the obvious solution is to maximize the soaking area. How can this be achieved?
The instruction is simple: use the filtering field.
- The maximum possible area is covered with rubble.
- Drainage pipes are laid out 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 with an interval of 2 meters are opened with tees 110 - 110 - 50. Pipe molding - at the rate of 8-10 meters per person permanently living in the house.
- Pipes are covered with rubble at least 10 centimeters.
- 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 -30 ° C (of course, subject to constant use of sewage).
The solution is convenient because it is undemanding to the degree of wastewater treatment: there are no smells on the surface; however, it is not suitable for dense clay, absolutely impervious 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 soaking, 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 (not lower than 95%) and complete absence odors.
Which septic tank is best for clay soil in this case? Energy dependent, using aeration.
The operating principle of such treatment facilities :
- Air is continuously blown through the primary sump tank by a compressor. It provides the vital activity of aerobic bacteria that devour organic matter and decompose it into water and gaseous products with a small residue of odorless sludge. Additional purification is provided by the active oxidation of organic compounds.
- The effluents that have passed aeration enter the secondary sump, where the sludge precipitates and is moved to the first tank by an additional airlift compressor.
- From the third chamber, the treated and clarified effluents are lifted by a drainage pump and discharged into a ditch, which directs them to a reservoir or simply to a large area where water can evaporate.
Conclusion
1.
2.
3.
4.
5.
6.
The choice of a septic tank for installation on clay soil is a serious task, because the design must perform its functions with high quality and be able to purify wastewater from pollution. In addition, some designs allow the use of purified water in the second cycle. The implementation of such a project will be discussed in this article.
Features of clays and loams
A septic tank for clay soil should have some design differences from conventional devices. To understand how a septic tank works in clay, you need to remember how conventional treatment plants work: first, the effluent enters the sump, separating into light and heavy fractions, and then the purified water enters the soil, where the final purification takes place. For the organization of soil cleaning, filtering wells are used, the design of which includes perforated walls and a drainage bottom. But the performance of such a system depends on several factors: the depth of the bookmark, the area of \u200b\u200bthe walls, the level of soil water and the type of soil prevailing on the site.The latter indicator has to 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 loamy 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 performed a little differently than conventional designs. You also need to know what to do if the septic tank stinks. To solve this problem, there are many drugs and means.
Clay septic tank options
Despite the fact that the task seems unsolvable, there are still methods for solving it, and for their implementation it will not be necessary to dig an ordinary cesspool, which then will have to be cleaned regularly. Regardless of the type of prevailing soil on the site, it is possible to create a high-quality local treatment plant if all the factors affecting its performance are correctly taken into account. Next will be described possible solutions allowing the use of a septic tank in clay.Filtration in clay soil
As a rule, a layer of clay soil rarely has a thickness of more than 2-3 meters. This can be seen when arranging the well: under the upper layers of the earth's surface, one can find sandy soils, or even clean sand, which has an excellent water absorption rate. In this case, the well will work much better than it could work in homogeneous soil: the water column will create a high pressure.Choosing the right solution, you should first study in detail the types of soil located on the site. You can find out from the old-timers of the area, neighbors who have recently carried out construction work, or order geological exploration. 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 plant, which is well suited only for the most difficult situations.
Structurally, a septic tank on clay soil can be made in any way: you can mount a plastic, brick, reinforced concrete or concrete system. Clay soil does not affect the choice of material at all, so this issue is 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 concrete sewer rings are installed, which reduces costs.
Watering
If there is good fertile black soil on the site, the water purified by the septic tank can be used again to provide watering for the plants. To implement such a project, it will be necessary to make the following design: the filter well must be replaced with a sealed tank, to which a drainage pump is connected. This pump will supply the purified liquid to the irrigation system.Such a septic tank device is well suited for summer cottages, but it is not advisable to use it in country houses where people constantly live. Another disadvantage is the low degree of purification, as a result of which the treated effluents have a characteristic sewer odor. To avoid this problem, you will have to use a septic tank with aeration.
Filtration field
Sometimes even the densest soils show good absorbing qualities. Of course, this does not always manifest itself, but if soil analysis has shown that it can absorb at least a small amount of water, then you can take advantage of this and increase the absorption area. Filtering fields are used to implement this idea.
- first, the entire free area allotted for the structure is covered with gravel;
- then drains are laid on it, having holes of at least 2 cm in diameter. The length of the pipeline in this case depends on the number of permanent residents: for one person, about 10 meters of pipe are required;
- 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
In the case of soils that do not absorb moisture at all, it is possible to discharge drains directly onto the site or into a special ditch. Naturally, such a system implies maximum wastewater treatment (from 95%) and no smell. To implement the design, it is best to use energy-dependent septic tanks using aeration.Such treatment facilities operate on similar principles:
- in the first tank there is always air, which supports the vital activity of aerobic bacteria that decompose those that enter the septic tank organic matter;
- after passing the aeration stage, the wastewater enters the next compartment, where the sludge goes to the bottom and is transferred to the first tank using a compressor;
- final cleaning is carried out in the third chamber, from which the purified water is pumped out and enters a ditch or a 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 appropriate design that best suits the specific situation.
The choice of a septic tank for clay soil and its installation are complex tasks that require compliance with a number of rules. Wrong installation such structures on loam can cause deformation of the septic tank and disrupt its operation.
It is difficult to install a septic tank on clay, because. the characteristics of this soil do not predispose to the rapid disposal and purification of wastewater. Clay does not absorb water well. Effluent stays in the tank. Sandy soil can absorb up to 90 liters of water per day, while loam - only 25 liters. Pure clay has lower water absorption rates. In addition, clay soils are characterized by high density and high weight. When arranging an autonomous sewage system, these features must be taken into account.
Why are septic tanks installed in clay deformed, and how to avoid this?
Most often, when arranging septic tanks, large-volume plastic containers are used. They are a good option for many types of soils, but they are not quite suitable for clay. Having a high density and weight, clay often deforms containers even from dense plastic 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 ground movements. This happens especially often if the groundwater is too close to the surface.
When planning the installation of a septic tank in clay soil, you need to consider the danger possible deformation containers. To prevent the occurrence of such a problem, it is desirable to use rigid materials for arranging the structure, including concrete rings, slabs, etc.
Plastic containers can also be used if desired. But to protect them from soil movements, it is imperative to make a special construction of concrete or a strong wooden crate. This will avoid damage to the integrity of the tank due to ground pressure. If the groundwater level is low, metal fittings or corners can be used to make the crate.
What septic tanks can be used in clay?
When arranging a septic tank on clay soil, it should be borne in mind that it is almost impossible to create high-quality filtration fields, so classical multi-level systems should be abandoned. There are several options for autonomous sewers that can be used effectively.
Storage tanks
The simplest and cheapest option for a septic tank, suitable for arrangement in clay soil, is a storage system. In conditions of clay soil and to save money on pumping water in the future, you can use a complex storage system consisting of several tanks connected to each other. Such cleaning systems can be created on the basis of:
- concrete rings;
- wells lined with bricks;
- large metal barrels;
- plastic containers, etc.
Such a septic tank for clay soil is an analogue of a cesspool and requires the systematic pumping of accumulated effluents with a sewer machine.
With soil treatment
Septic tanks, consisting of several storage tanks and an artificially created filtration field, can reduce the cost of pumping wastewater. In this case, some of the already settled effluents will enter the filtration field and go into the soil. The design in this situation will be simple. Several containers are connected in series with each other so that heavily polluted drains remain in the first of them, and the already settled water penetrates into the next container.
It does not have to be only 2 containers. Some homeowners connect 3-4 containers at once. This allows you to ensure that almost clean water enters the last cavities of the septic tank. The difficult moments of arranging such a system are the preparation of the site and the installation of the filtration field system.
Due to the presence of clay in the place where the filtration field will be located, it is required to dig a pit 1 m deeper than the bottom of the pit intended for installing the system. At the bottom of the pit, gravel or gravel is poured, as well as a layer of sand. Perforated pipes are laid inside such a pillow so that purified water from the last tank can be discharged to the filtration field. It should be borne in mind that there must be at least 50 cm of crushed stone and sand on top of the pipes.
In the process of shrinkage, 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 over this material. This will avoid inflating the clay and clogging the cavities between the rubble with it.
For biological treatment
Closed septic tanks with biological treatment are very popular with owners of sites with clay soils. Such systems are autonomous sewer stations. They give a high degree 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 effluents immediately undergo fractional division and settle. The clarified effluents are additionally treated with 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 the period of freezing and thawing. This often becomes the reason for the gradual pushing of the septic tank to the surface. Especially this problem often occurs when installing septic tanks, which were made of lightweight materials, including plastic and metal.
To prevent the occurrence of this effect, fixing the structure in the pit is required. For additional fixation, metal reinforcement and concrete mortar are often used. If the surface of the container is equipped with special holes, metal cables can be used to fix it at the bottom of the pit.
In addition, a thick bed of gravel and sand is recommended to prevent tank displacement. It is also allowed to manufacture a concrete slab, which will serve as the base. When filling it, you can make "ears". With their help, you can later more securely attach the septic tank to the base.
When performing earthworks when arranging an autonomous sewer, all safety measures must be observed, since 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 the collapse of the clay.
Features of installation on clay soil
When planning the installation of a septic tank on clay soils, it is necessary to comply with the sanitary requirements for the location of autonomous treatment facilities. The distance to the house and other capital buildings should be at least 20 m.
In addition, if a septic tank for clay soil has a filtration well and will purify water not only due to the operation of a sewage machine, it must be taken into account that the distance to a well or other source of water must be at least 50 m. This will prevent contamination by drinking water.
It is best to start installation when dry weather sets in for a long time. This will ensure the reduction of groundwater. When digging a pit, all precautions should be observed. The height of the pit must be at least 70 cm more than the height of the selected septic tank. A 10 cm layer of sand is laid at the bottom of the pit. After that, 30 cm of a layer of gravel is poured. On top of this, laying geotextiles is recommended.
After that, 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 crate is formed to protect the septic tank from being squeezed. After the bottom of the pit is prepared, you can proceed to the installation of the septic tank design. Be sure to fix the container with cables or metal rods. After that, you need to install all communication pipes, fill in the cavities around the septic tank and compact the soil.
Perhaps the first thing to take care of at the beginning of the construction of a house or cottage is a septic tank. Those owners of sites where the soil is clayey will find it more difficult to mount a flawlessly functioning sewer drainage system. But with due diligence and knowledge of how to arrange a septic tank in clay, this is quite possible. In such soil, it is possible to install both a factory autonomous treatment station and a home-made 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 fearlessly mount a septic tank without a bottom. All sewerage at the outlet will be effectively cleaned, but this process is rather slow. Therefore, the device of the sewer system in these conditions has its own characteristics that prevent overflow of the tank.
Types for installation in clay
Storage tanks
Most often, they are used as plastic containers, in particular eurocubes of various sizes. But barrels and home-made welded stainless steel cubes can be installed. The storage tank can be made of brick or concrete. Such septic tanks are often found in villages and towns. They are arranged simply: it is enough to dig a pit of the desired size, after which lay out 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 self-contained biological wastewater treatment plants capable of producing such water at the outlet that can be used for watering a garden or diverted into a pond with fish. The principle of operation 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 vital 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 clay ones.
With soil treatment
These are the simplest tanks in the device for the accumulation of wastewater. They are arranged by analogy with storage tanks, but without concreting the bottom. That is, you can use all the same materials: brick, concrete, plastic or iron, but at the bottom you need to arrange a drainage layer. It is made of sand and gravel. Here, large fractions are filtered, after which the effluents penetrate to the clay and receive better purification.
Such septic tanks are good because the sewer machine needs to be called less often than in the case of storage tanks. However, in clay soil, the process of filtering and leaving wastewater will be hardly noticeable. Therefore, sewage will have to be pumped out with the same regularity as in the presence of a container with a concrete bottom. Such a septic tank with their own hands is built quite quickly.
Mounting technology
- You should decide what will be used for the storage tank device. In order to speed up cleaning and make it more efficient, it is recommended to build a two-chamber structure with a filtration field. This will avoid overfilling the main tank and get the most purified effluent at the outlet.
- 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 pass water well, there is little risk of runoff entering a well or well. Therefore, it is possible to install a septic tank with your own hands at the most minimal distances from water intake points and residential premises - 7 m.
- When the location of the tanks is determined, earthworks begin. It would be nice to ask the neighbors in advance about the depth at which the clay / soil boundary passes. If it is located below 3 m from the soil surface, the work will be complicated by the need for a device drainage system at quite a depth. When digging pits, it is taken into account that one container should be separated from the other at a distance of no more than 2 m.
- After installing concrete rings, plastic cubes or laying bricks on the walls of the pits, they begin to install a drainage layer directly in the containers themselves. To do this, backfill with sand and gravel. For the first, a layer of 10-15 cm is sufficient. For the second, 25-30 cm. If plastic barrels are used as tanks, it is recommended to strengthen them with chains or otherwise during installation. This is necessary due to the fact that during floods and when the soil freezes, the container can squeeze out of the pit.
- Both containers must be connected with a pipe so that it hits 40-50 cm below the sewer pipe that goes from the house to the main sewage tank. Such a device allows drains to overflow into the 2nd chamber and contributes to the separation of fractions. Heavier ones settle in the 1st container.
- Further, if free-standing containers were used as containers, they must be insulated. You can do this with foam. Such a septic tank, insulated with its 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-submerged filters or filter cassettes are mounted. At high GWL, it is rational to arrange surface filtration using gravel-sand cushions.
The dimensions of the post-treatment field depend on the daily water consumption in the house. If the volume of drains 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 of 1.5-2 m² will be required. On sale there are ready-made designs of filter wells. The price of these products is low, and installation is simple. The role of the main filter in them is performed by geotextiles. But if there is no desire or opportunity to buy a finished structure, you can do the post-treatment field with your own hands.
After the soil is taken out, a pipe is laid connecting the 2nd 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, a drainage grid is installed on it. After that, sand and gravel are dumped. The height of the pillow should be such that its top rises above the inlet pipe by at least 5 cm. It should not be forgotten that the pipes are installed taking into account the required slope. It must be at least 1 * per 1 m. Pipes must be insulated with a wooden box and foam.
Drainage device
Since such a soil is not able to pass liquid well, a drainage system will be required to divert rain and flood water from the tanks for receiving sewage. For this, not wall, but ring drainage is performed. For the installation of the pipeline, drains will be needed. 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 that, backfilling is done with sand by 5-7 cm and gravel by 10-15 cm. Then geotextiles are laid on the bottom of the trench, a pipeline is mounted inside the ditch and the pipes are wrapped with previously laid material. Then they start backfilling.
Device Feature
Clay refers to strongly heaving soils. This property of hers manifests itself with particular evidence if it is wet, and not dry. During seasonal freeze-thaw, such soil can easily push a plastic or other container placed in it out of the pit. Therefore, during the installation of tanks for sewage effluents, their fastening in the pit should be provided.
This can be done using metal rods, which can be used as corners or pipes of small diameter. The purpose of the rods is to fix the location of the container and prevent it from moving during the heaving of the soil. For this purpose, steel chains can also be used, 1 end of which is firmly fixed in the soil.
For deeper sewage treatment, two-stage trenches can be made for the filtration field. In the upper part of such a ditch, pipes are placed through which drains are drained, and in the lower part there is a sand and gravel cushion up to 30 cm thick. With the help of such trenches, you can build a full-fledged filtering system and drain drains 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 by analogy with the drainage, but the holes should be larger, since the liquid will include small fractions. To prevent clogging of holes with soil, each element of the pipeline is wrapped with geotextile.