Septic tank in conditions of high groundwater. About a concrete septic tank at a high GW

The GWL (groundwater level) determines how close the groundwater comes to the surface. Well, if it passes below the bottom of the septic tank.

But what if the liquid is located at a depth of only 0.5-1m? What is the danger and how to solve the problem? A septic tank with a high groundwater level will last for many years if installed correctly.

The first thing to do is to define the GWL and understand the extent of the problem.

Important: as close as possible to the surface, the liquid comes up in spring and autumn. In the first case, the reason is the melting of snow, in the second - prolonged rains.

Here are 5 ways to identify it:

The easiest way is to ask the locals. Perhaps the neighbors already know at what depth the GWL is located or they have a well on the site.
Flora as a guide. Certain types of plants can only survive when the water comes close enough to the surface. The following table will help guide you:
Site inspection. If wetlands are present, then the GWL is located close to the surface or the soil is too clayey. Also check out the surrounding area.
grandfather's way. To do this, you need a clay pot, a tuft of wool, defatted with white spirit and an ordinary chicken egg. A small layer of turf is removed with a shovel in the place where the septic tank will be located. They put wool, on top - an egg and cover with a pot. Check in the morning. If water drops are clearly visible on the egg, the GWL is close to the surface.
Drilling pits at several points on a suburban area. This method is rather laborious. But it is 100% reliable. Step-by-step instruction:

Find a good long drill - at least two meters - and a flat pole, on which put marks every 100 mm.
Determine the points for drilling in the territory of the site. It is not necessary to drill a well only in the intended location of the sump. It is possible that it will have to be relocated, so select several points throughout the site.
Drill wells. Lay waterproof material on top so that precipitation cannot enter the shaft. Please wait 24 hours.
Using the prepared pole, determine the GWL: immerse it in the well, reaching to the bottom, pull it out and subtract the length of the wet part from the depth of the mine.

Not bad help and folk signs. This is especially true in summer, when drilling cannot 100% guarantee the accuracy of measurements. The fact is that in the heat, the liquid drains into the nearest reservoirs and the level sometimes drops - quite significantly.

Places of possible flooding will help to identify midges that feel the proximity of moisture and will swarm in this place. And you can also navigate by the abundance of dew in the morning and the density of fog in the evening. The more clearly these signs are manifested, the closer the liquid is to the surface. Obviously, when constructing any underground structures, it is desirable to avoid such places.

A similar situation with a drop in the liquid level is observed in the middle of winter. Only the reason is not in the drainage of water, but in the freezing of the upper layer of soil during severe frosts. Measurements taken during this period can easily be misleading. With heavy rainfall, the liquid mark in spring can increase by 2–3 times.

Important: if possible, it is worthwhile to determine the GWL several times a year and take the smallest value for calculations.

What could be the problems

The installation of a septic tank at a GWL closer than two meters from the surface requires additional measures.

The problems that arise during the installation of a sump on a site with WUGV can be divided into several groups:

1) When installing. First of all, this increases the complexity of the work. Digging a pit in liquid mud is not very comfortable. You will have to use a pump for pumping and organize drainage in the area. Step-by-step instruction:

deepen the pit as much as possible in one place;
organize stock;
install a vibration pump (motor pump);
when the liquid accumulates in the recess - pump out;
during pump operation, make sure that the hose does not burrow into the ground (the pump may become clogged);
meanwhile, develop the soil with a slope towards the excavation, which should also be deepened accordingly.

After the pit is dug, it is necessary to protect the walls from collapse. To do this, hammer wooden or metal tongues. During the installation of the sump, water is also collected in the recess and removed using a motor pump.

Important: it is much easier to correctly determine the level and take action in time than to deal with the consequences later.

2) Damage. As a result of excessive groundwater pressure, the soil swells and the container can be easily damaged. Sewerage, mixed with underground water veins, can enter a drinking well or come to the surface along with fecal residues. This situation can provoke infection with dangerous infections, not to mention an unpleasant smell throughout the area.

To avoid such unfortunate consequences, it is enough to choose the right material for the cleaner. Ideally, this should be a sealed container buried in the ground. Experts recommend using modern high-strength plastic.

But it is also important to properly backfill the pit after installing the sump.

Backfilling is carried out with a special composition: you need to mix 5 parts of dry sand with 1 part of cement. Layer thickness 100–150 mm. and each must be shed with water and carefully compacted.

You will have to dig out the container if the septic tank at high groundwater was nevertheless installed incorrectly and damaged, pump out the contents and find cracks. If the damage is minor, sealing can be performed.

For this, special sealants are used. In particularly difficult cases, it will be necessary to apply a patch using a special apparatus for plastic welding. In case of significant damage, the container will have to be replaced.

Important: housing damage can be indirectly diagnosed by the appearance of an unpleasant odor and soil silting at the installation site.

3) The plastic sump may float. To avoid this problem, a reinforced concrete anchor-base is provided at the bottom of the pit (it can be factory), to which the septic tank is attached. There is no other way to cope: the container will simply float.

In case of problems with the access of lifting equipment to the place of work, the slab is poured directly into the pit. Mortgages are left in the concrete body, to which the tank is attached using metal clamps. Additionally, a layer of sand, 10 cm thick, is poured onto the bottom of the tank. This design will securely hold it and prevent it from floating up.

The rise has already happened. Step-by-step instruction:

inspect the sump and make sure that it is not damaged - the container must be airtight;
pump out the contents using a pump (it is advisable to immediately call a sewage truck), in case of damage, perform the necessary repairs;
wash the sump;
completely remove it from the pit;
fasten correctly (see above).

4) Flooding . Capacity overflow can be due to many reasons. And groundwater is just one of them. First of all, it is necessary to forcibly pump out all the contents, check the operation of electrical equipment, the correct connection of hoses and infiltrates.
If, nevertheless, the reason is in excess groundwater, especially if the level is unstable, it is necessary to organize the pumping of the liquid by force. To do this, you can use another pump installed in the immediate vicinity of the outlet.

If this method does not help, you will have to use a pipe to divert clean water away to an area with dry soil. There, she can calmly soak into the soil, and the sump will not overflow.

To avoid such difficulties, it is better to provide a drainage system for draining groundwater in advance, even before installing a septic tank.

5) Waterlogging. With a high GWL, there is often a problem with the final wastewater treatment. The soil already has high moisture content. The extra moisture just won't absorb. Gradually, the place around the tank will turn into a swamp. To solve the problem, you need to mount a filter field. Simply put, an artificial embankment, which is arranged in a previously dug pit, is up to the desired level and covered with rubble and sand 1.5–1.8 m above the ground.

The step-by-step diagram of the device of such a field is as follows:

Carry out the necessary calculations. On average, 1 person drains 200 l / day into a septic tank (established empirically). The filtration coefficient is determined according to GOST 23278 “Soils. Methods for field testing of permeability” by pouring water into the pits. Based on the tests, we determine the steady flow. Let's say it was 4 l / h. Pit dimensions: diameter 250 mm, depth - 100 mm. From here we determine the wetted area: bottom - 3.14 * 0.125 2 \u003d 0.05 m 2; walls - 3.14 * 0.25 * 0.1 \u003d 0.1 m 2, S total. \u003d 0.05 + 0.1 \u003d 0.15 m 2. From here, after 1 m 2 per day, 0.15 / 1 * 4 * 24 \u003d 640 l / day will be filtered. Based on these data, we accept the required field area.
Develop a pit (necessarily dry).
Make a pillow of crushed stone 500 mm thick.
Pour 1 m of sand.
Drains are laid (plastic pipes with perforation). This design will ensure uniform distribution of liquid on the field. The length of the pipes should not exceed 20 m. The distance between the drains should not exceed 1.5 m. The supply of pretreated water to the field is provided by a pump. When laying pipes, they are protected with geotextiles. Each drain is equipped with a ventilation riser, which should be 0.5 m above the ground.
Install filter cloth.
Perform backfilling.

6) Drainage. Drainage of the sump can be done using a filter well.
Instead of a concrete well, you can use a plastic container without a bottom, the installation of which is much easier. Coarse sand is poured to the bottom, then fine gravel or crushed stone. The thickness of the layers is 200 mm. To exclude the impact on the well from the outside, it is sprinkled with expanded clay.

Requirements for a treatment device at high GWL

The case is made of durable plastic and must be sealed.
The design should have a small height.
The volume of the tank should correspond to the daily flow rate multiplied by three.
Septic tanks designed for high groundwater must be securely anchored to a concrete base.

The following types of septic tanks are ideal for the removal of sewage at VUGV:

Sealed storage container. Most often, a factory-made plastic construction is used. It is guaranteed not to leak and can have a volume of up to 300 liters. Such a system is good in a country house or in a small private house, if the owners live there periodically. But it will not solve the problems with the permanent residence of a large family. The main disadvantage of this septic tank design is the regular pumping of sewage.
Three-section anaerobic device. The first compartment (settler) serves to separate waste into fractions as a result of the separation of fats and the precipitation of solid parts. In the last two there is a preliminary treatment of effluents. The supply of waste from one compartment to another is provided by an overflow pump. It is impossible to dump waste without additional filtration through the ground, because this leads to a violation of sanitary standards.
VOC (local cleaning station). Waste goes through a full cycle of biological treatment. With the help of bacteria, wastewater breaks down into silt and water. Such devices are quite expensive, but the costs are worth it, if you equip such a system on the site, then you can forget about pumping out the sewer for many years.

Necessary tools and materials

Below we will consider in more detail the process of installing a storage sump. For self-installation, you will need the following tools:

motor pump;
shovels;
metal cable;
building level;
jigsaw.

You need to prepare the following materials:

wooden or metal sheet pile;
formwork boards, reinforcement AIII Ø12 mm, concrete B12.5 (with a monolithic foundation) or precast concrete slab;
clamps for attaching the container to the base;
sealant.

DIY installation and work plan

The installation of a sump consists of the following steps:

Development of a pit and a device for forced drainage (more details are discussed above).
Pit slopes are fastened to ensure safety and protection against collapse. During the work, there should be no liquid in the pit. It is pumped out with the help of a motor pump. But during the night it picks up again. This can lead to the collapse of the walls if they are not fixed.
Installation of a concrete slab or concreting of the base. The process is the following:

The bottom of the pit is leveled using the building level for control.
Then they arrange an underlying layer of sand 150 mm thick. Sand is poured with water and carefully compacted.
The next layer is waterproofing. Experts recommend using two layers of roofing material.
A formwork and a reinforcement frame are installed on the waterproofing, concrete is poured. It must be laid in even layers, vibrating. It is advisable not to stop work for more than 4 hours. If conditions allow the passage of equipment, you can use a ready-made reinforced concrete slab, which will significantly reduce labor intensity. With a monolithic structure in the body of concrete, it is necessary to leave mortgages for attaching the tank.
We install a ready-made plastic container on the prepared base, having previously calculated the required volume and checked its tightness. With special clamps we fasten the tank to the embedded parts of the "foundation" by welding or bolts. Now you can not be afraid that it will pop up.
We connect the supply pipe, carefully seal all joints and insulate the septic tank and all pipelines.
We carry out backfilling with protection against heaving of the soil as a result of a GWL drop (a mixture of sand and cement with layer-by-layer spillage and compaction).

Important:

A layer of expanded clay with a thickness of at least 200 mm should be covered around the tank. This will prevent freezing and reduce the negative impact of external factors.
During backfilling, it is necessary to gradually fill the container with liquid so that the water level is always above the filled level. In this way, you can protect the septic tank from damage.

Operation in the conditions of VUGV, as well as installation, requires special measures:

It is forbidden to clog the system with large debris. This will lead to clogging.
The sewer pipe and sump must be carefully insulated.
Effluent needs to be pumped out regularly. Do not allow the tank to be filled more than 2/3.
When used as a natural filter, it is worth remembering that any chemistry will kill them.

Compliance with these simple rules will make the operation of the sewer system easy and eliminate unnecessary problems and unpleasant odors.

Autonomous - the only way out at high GWL.

Useful video

Detailed and step by step:

Installation of concrete:

Hello, friends.
I want to touch on such a burning topic, I’m not afraid of this word, like self-made concrete at a high groundwater level.
Of course, we all want to save money and not buy Topas and Yubasa for crazy money. But at the same time, we want the blood bablos buried in the ground not to go to waste, that is, to work, purify, and not spread aromas.
There are a number of problems with concrete septic tanks with a high GWL:
1. It is difficult to concrete the bottom, often people do not bother with this, and bury the first well without a bottom. Then, for some reason, they still make a drain from this well in the filtration field, although a well without a bottom is already a filtration well in itself.
2. Difficult to seal rings. It is not so much important here that the concrete will let wastewater out, passing through the concrete they will be cleaned better than even reaching the last well. Worse, groundwater can get inside and change the level of liquids in the chambers. For example, if the water in the second chamber rises above the overflow with the first chamber, then the liquid in the two chambers will mix and will be of the same degree of purity. The same with the third chamber, and it turns out a single-chamber septic tank with a large chamber of a cunning shape. The degree of purification is zero.
3. And most importantly, for soil filtration, you cannot make a 3rd well. You need to make an embankment, for the same reason. So that the water does not go back into the septic tank, and does not make senseless the presence of 3 sump chambers, mixing everything together, as well as blocking the ventilation holes, and making the septic tank smell fragrant. So an extra pile on the site is inevitable.
Save for Topas? In no case!
You can save money by making two sealed chambers, and pouring into the third one through the pump and check valves!
But, in order.
1. To begin with, I would not use rings, but would fill everything myself. I would pour a monolith, in my opinion, it is easier to seal it, now there are a lot of additives and means for waterproofing concrete, and there will be no problems with the displacement of the rings. Again, it is easier to dig a hole, and most importantly, you can avoid flooding the hole with groundwater.
To do this, an auxiliary, small pit is dug next to the main pit, the pits must be communicated. The small hole should be deeper. The bottom of the main pit should be sloping towards the small one, rubble should be poured onto the bottom of the main pit so that all the water flows over the rubble into the small pit. And in this smallest hole we throw a pump for dirty water, which turns on the float, and that's it, you can fill it. Now the main pit will always be dry.
2. We put the formwork, fill in two sealed chambers, and one without a bottom. Between the first two chambers, the communication will be absolutely standard, pipes, tees ... But between the second and third chambers, we cut a check valve into the wall. There is no particular hope for gravity flow, so we hang a pump with a float from a small pit (non-waste production) in the second chamber, so that it turns on at the moment when the liquid does not reach the overflow level between the first and second chambers 5 cm.
Thus, we get the first two chambers from the bottom, sealed, in which each chamber works normally in its function, thanks to the correct levels of liquids, and a filtration well, in which the water level does not affect the operation of the first two chambers, even if it is under the surface. Also, there are no heaps.
I want to start as soon as I go on vacation, i.e. from Saturday.
Well, do you think it will work out, or is it time to give up?

For the equipment of the sewer system in country houses where it is not possible to connect to a centralized system, it is necessary to install local treatment facilities or a septic tank. The second option is the most profitable from a financial point of view, so many make a choice in its favor. However, during installation, you may encounter one serious problem - the high level of groundwater (GWL). As a result, a logical question arises - how to make a septic tank if groundwater is close?

Installation of a septic tank on the site

Why is it important to consider GWL?

If the water is near the surface of the earth, this means that when deepening the septic tank, special construction methods will be required to ensure the stability of the structure and prevent depressurization of the joints. In winter, another danger arises - freezing of the soil and, as a result, the occurrence of heaving, which can cause deformation of the drive. That is, the effluents will fall into the ground, and then into the water layer and pollute the environment, which is unacceptable.
During spring floods, reservoirs can flood the nearest territory and the septic tank can float. The result is expected to be the same as in the previous version, only sewage will also pollute the reservoir. It can also break plastic sewer pipes and have to be replaced. In the worst case, the septic tank will remain in the ground, and water will flood it from above, as a result of which sewage will go back into the house in the absence of a check valve installed.
Septic tanks with leaky structures should not be used. This is especially true for the use of cesspools or septic tanks in the form of concrete rings. Firstly, its construction will require financial costs comparable to a sealed septic tank manufactured in an industrial environment, and secondly, it is contrary to sanitary standards.
Depending on the GWL, it is necessary to apply special constructive measures to ensure maximum protection in order to prevent an environmental catastrophe.

How to accurately determine GWL?

Usually measurements are taken in the spring, when the water rises to the maximum possible height after the snow melts. They take an ordinary garden drill, make a vertical hole in the ground to the surface of the water, and then determine their depth. If the septic tank needs to be installed quickly, then you can use the data of geological exploration, which will reliably show how the water layer passes under the land. Another less informative way is to get the necessary information from the old-timers, but it is not always worth trusting.

preparation of pits for the installation of a septic tank

Is it worth it to make a septic tank yourself?

Despite the apparent simplicity of the design of a septic tank, design work on its calculation, selection of strength and performance characteristics is a task for professionals. However, their cost is several times more expensive than homemade ones. The difference in this case in them will be significant and will be as follows:

The finished design will provide maximum tightness by fitting all parts and using stiffeners that can prevent any loads within the passport specifications. It will be very difficult to evaluate a home-made system, so it is not known how it will behave in a particular situation.
An industrial septic tank is equipped with all the necessary filters, able to cope with specific loads and meet sanitary standards.
Finished septic tanks have not only a high level of protection from external mechanical, but also from internal chemical influences, while ensuring stable operation during the warranty period. A self-made design will not be able to guarantee the absence of leaks into the ground or a sufficient degree of purification when using filtration fields.

Therefore, before deciding whether to choose a septic tank of a finished design or bookmark your own, you need to weigh everything and make the only right decision.

installation of a concrete septic tank

In the absence of the necessary experience, it is worth contacting a specialist who can analyze the soil or existing data and select the most suitable design in terms of parameters.

What requirements must a septic tank meet?

have complete sealing of the chambers;
have protection against ascent;
have a high hull strength.

What device should a septic tank have with a high GWL?

The design of the septic tank must be airtight and consist of one container, divided into compartments, or several eurocubes. The system can be either gravity flow or forced injection. The second option should be used only in cases where the installation is carried out on a flooded area and it became necessary to place storage tanks above the level of the house.

A non-return valve must be installed on the inlet pipe to prevent the backflow of wastewater. The pipe for the withdrawal of purified water should be made at such a level that groundwater does not get there. Usually, a special sealed compartment or a separate sealed container is provided for this.

Rules for choosing a septic tank with a high GWL

The volume of the septic tank must be clearly calculated so that at high loads it does not have to constantly remove sewage.
The type of construction is allowed either accumulative or with pumping of purified water and its effective discharge into the ground.
It is desirable to choose the material of the septic tank based on durable plastic and steel with a protective polymer coating. A concrete septic tank at a high level of groundwater is not recommended, since the soil can freeze and there is a high probability of displacement of one ring relative to the second and sewage entering the soil is simply inevitable. An exception may be soils with a dense composition and a minimum level of heaving.
In order to increase the cleaning performance and minimize the amount of sewage removal, it is necessary to organize a multi-stage cleaning system: from mechanical impurities, chemical disinfection and filtration of purified water with discharge into the ground.

trenches for septic system

How to choose a place to install a septic tank?

The installation site must first of all meet sanitary standards:

The distance from the residential building must be at least 5 m.
From sources of drinking water, the distance should be from 50 m, and from open reservoirs - 30 m.

In this case, it is necessary to take into account the location of the buildings so that they are at a convenient distance for servicing the septic tank. Also, do not forget that the sewer pipe should go at an angle. The greater the distance from the sewage discharge points, the greater the depth required based on the condition of a slope of 2-3 degrees per meter of length, while if there is a minimum GWL up to 1 m, this is simply unacceptable.

When creating sealed containers for the removal of wastewater, it will be necessary to organize a convenient vehicle access for pumping them out.

How to properly install a septic tank?

A septic tank for a high groundwater level must not only be installed on a stable base, but also be firmly fixed to prevent its displacement or deformation of the body in weak and moving soils. The base is a compacted sand and gravel cushion, which is poured into a specially prepared trench. The size of the trench is usually selected so that its walls have a gap of at least 30 cm from the walls of the storage tank. This is required to minimize the effect of heaving soil layers.

However, when the GWL is located at a level of up to 1 m, this will not be enough and it will be necessary to additionally pour a concrete monolith or lay a finished reinforced concrete slab, after which it must be waterproofed and insulated. It will serve not only as a base, but also perform the function of fixing in case of insufficient filling of containers, preventing them from surfacing. Failure to use insulating layers can lead to cracking of concrete and loss of strength. Sometimes drainage pipes are installed at the bottom to drain water from the trench.

covering the finished septic tank after fixing with concrete

The supply pipes will also require the laying of a sand and gravel layer in order to prevent damage to it in case of possible swelling. After that, it is necessary to install a septic tank and fix it on anchor straps to a concrete base, as well as perform its waterproofing. Pipes are connected, and then a sand-gravel composition with the addition of dry cement is poured on the sides of the tank. The dimensions of the crushed stone should be up to 5 mm.

At the final stage, pipes for sewer ventilation are installed and the septic tank is covered with earth. Simultaneously with backfilling, fill the container with water by about 1/3 of its volume. The height of the ventilation pipe must be more than 60 cm above ground level.

What to do if water enters when digging a trench?

It should be noted that if there is water in the trench, installation work is strictly prohibited. Therefore, it is worth choosing one of the options for solving this problem, which are given below:

Use a drain pump to pump out the accumulated water.
Perform work during the winter. However, as a basis, use not pouring concrete mortar, but ready-made reinforced concrete slabs.
Use the method of ground installation of a septic tank with forced injection of sewage.
To make a sealed monolithic frame in the form of a box according to the size of the trench.

How to implement a soil water purification system?

Since the water level can change dramatically depending on the season, seepage field systems are not always possible to implement. Therefore, special filter cassettes are used, which are placed directly on the surface of the earth or on hills. To do this, remove a layer of soil to a depth of 30 cm and 25 cm larger on each side. A sand cushion 30 cm high is poured at the bottom with tamping and leveling.

After that, concrete blocks are placed around the perimeter, which are fixed in such a way that they are airtight. Crushed stone with small fractions is poured into the resulting box, on which the cassette will be directly installed. Then pipes for water supply are brought in, connected to the cassette and the box is closed with a concrete slab with a ventilation hole. A ventilation pipe should usually be installed in the hole so that the smell goes up under the action of the draft, and does not accumulate in the yard. The finished structure is covered with earth and decorated using various landscape design techniques.

If the soil in winter freezes to a depth greater than the height of the earthen layer of the embankment, then the cassette in the upper part should be insulated with foam boards or expanded clay, while it must be completely waterproofed.

If the central sewerage system is unavailable, the owners of houses and cottages install an autonomous system for wastewater treatment. A septic tank for high groundwater is built according to special rules, otherwise the device will quickly become unusable. If the groundwater level (GWL) in the area is less than 1 meter, the septic tank model is carefully selected and measures are taken to protect it from the harmful effects of subsoil moisture.

Problems of arranging sewerage at high GWL

The installation and operation of a septic tank at high groundwater is complicated for several reasons:

The complexity of manual earthworks. Digging a pit or backfilling while standing in the water is difficult and uncomfortable.
Difficulty in soil cleanup. It is practically impossible, since damp soil is not able to absorb water. For this reason, the construction of a filtration well or filtration fields is inefficient. To get out of the situation, the filter elements are placed above the ground, on a special platform. Such a technical solution requires additional costs - a drainage pump that pumps the contents of the septic tank into infiltration tunnels (cassettes). So that shallow cassettes are not torn apart by frost in winter, they are covered with earth: such a mound can be disguised as a flower bed.
The inefficiency of a prefabricated septic tank made of concrete rings. The most popular option for local sewerage, due to high humidity, almost always loses its tightness. As a result, runoff seeps into the soil, and external moisture enters the well. What to do if there is groundwater in the septic tank? The answer is obvious: you have to call a sewer. Otherwise, liquid from an overfilled container may flow in the opposite direction through the outer pipes.
The possibility of "floating" a plastic tank under the pressure of groundwater. The phenomenon, due to the low weight of the structure, threatens to rupture the sewer pipeline. To "anchor" the container, it is mounted on a concrete base and rigidly fixed to it. If the septic tank pops up, it will have to be pumped out of it, dismantled and flushed, and then reinstalled.

To neutralize the disadvantages of a high groundwater level will help preventive measures at the design stage of the sewerage system, the choice of the optimal model of the treatment plant.

Requirements for a septic tank and its placement

When choosing a septic tank for a summer residence or a house on a site with high groundwater, the following design characteristics are taken into account:

tightness. Since the hull will be in constant contact with wet ground, even the most thorough waterproofing will eventually deteriorate. The best option is a one-piece plastic container. If you choose a cast concrete tank, you will have to ensure the possibility of entry and work in the area of the crane and trucks. In addition, concrete gradually begins to pass water, even if its surface is treated with hydrophobic compounds.
Dimensions. When choosing a model in size, take into account the features of close ground moisture. The height of the tank should not be too large: you will have to dig a deep hole under it, and it will be filled with water all the time.
Volume. It is determined by counting the average three-day amount of wastewater entering the sewer. The number of residents and devices connected to the sewer are taken into account: a toilet bowl, a washing machine and dishwashers, a shower stall, a bath (its capacity also plays a role). A small margin is added to the calculated volume of liquid drain. It is important that the container is not empty, otherwise the microorganisms that process waste may die due to lack of nutrition.
Design. So that the septic tank does not float at high GWL , it is securely fixed with clamps or ties. In this regard, the design is more convenient, in which there are already loops or eyes for fixing.

The cleaning system is located, maintaining the generally accepted sanitary standards: at a distance of at least 5 meters from the house or road, at least 15 meters from the well or well. There must be at least 30 meters to open water.

Mounting Features

When deciding how to make a septic tank, if groundwater is close, sometimes developers install a conventional single-chamber storage tank without deepening it into the soil. Such a scheme allows you to save materials, reduce the complexity of installation and speed it up. But the accumulative autonomous sewerage is justified only when servicing a small cottage with a small number of residents and sanitary equipment. In other cases, the dimensions of the tank will turn out to be too large, but, despite this, you will often have to call a sewage truck.

The most rational with a high GWL will be one of three options:

Installation of a three-section anaerobic septic tank. In the first compartment, the effluents are settled and divided into fractions, and in the second and third, they are further purified. Thanks to infiltrators used in factory models instead of filter wells, 95% of the purified liquid is absorbed into the soil. Typically, the product is sold unassembled: its components are assembled at the installation site according to the scheme attached by the manufacturer.
Self-assembly of a sewer system with an infiltrator from suitable sealed plastic tanks or eurocubes. The resulting compartments are interconnected by pipes.
Installation of an aerobic septic tank. It is a bio-purification station, which is supplied with oxygen necessary for the activity of aerobic bacteria. To ensure a natural flow of air, a biofilter is installed - a plastic tank with expanded clay and a special ventilation system. There are volatile filter models in which air is forced in, using an air compressor for aeration.

To independently install an anaerobic wastewater treatment system in the presence of high groundwater, proceed as follows:

Dig two wells at a distance of 2 meters from each other. The dimensions of the pits are calculated so that there are 15 cm on each side between the walls of the containers and the earthen slopes. A reinforced concrete slab with special embedded loops is laid on a sand cushion. If the passage of lifting equipment for laying a massive reinforced concrete slab is difficult, the bottom of the wells is independently poured with a concrete mixture, having previously installed embedded parts to fix the tanks.
With the help of a bandage, each container is attached to a concrete base (belts are passed through its top cover). The manufactured sections are connected by a pipe for water flow. The drain from the house is brought to the first tank. Without filling the wells with earth, proceed to the next stage.
They dig a hole no more than 0.5 meters deep, along the perimeter half a meter more than the cassette. The excavation is filled to the top with sand and rammed; concrete slabs 250 mm high are placed along its contour. The resulting container is covered with crushed stone of the middle fraction (20-40 mm).
Cassettes are placed on a crushed stone pillow. They are connected to the second tank, in which a submersible drainage pump is installed (before that, electrical wiring is installed to connect the equipment). Be sure to install a float switch with a moisture-resistant cable to start the pump when the tank is full and turn it off when the minimum level is reached. It is better to play it safe and install two pumps: the float of the backup unit is set to a higher switching level so that it will work if the main one fails.
In the manufacture of sewers, the factory infiltration cassette can be replaced with a home-made device. For this purpose, they take an oblong plastic container without a bottom (similar to a pipe), make many small holes in it to let the settled liquid into the ground. The cassette is used only in conjunction with a septic tank, otherwise the holes will become clogged with untreated drains. At the outlet of the infiltration tunnel, a ventilation pipe is equipped.
Backfilling. To protect the plastic from interseasonal heaving of the soil, the wells are covered with a special composition: 5 parts of sand to 1 part of dry cement. Backfilling is carried out gradually, compacting and spilling water on each layer. To prevent flexible plastic from bending, the chambers are gradually filled with water - so that the liquid level constantly exceeds the level of the soil backfill.

Installation work is more convenient to carry out in the summer, when the GWL is the lowest. If the container is still filled with water, it is pumped out, and then the installation continues. It is recommended to equip an annular drainage around the treatment plant. They dig a trench, deepened by 20 cm in relation to the border of soil freezing. They make a sand cushion, lay perforated drainage pipes to drain groundwater in a geotextile shell, fill them with sand and gravel.

Industrial production models

If preference is given to purchased installations, the question arises: what is the best septic tank with high groundwater? There is no single answer here, since equipment is produced with different technical data, in a wide price range.

"Tank" (producer "Triton Plastic"). Universal three-chamber septic tank made of plastic. In the second section, anaerobic treatment takes place, the third one can act as a biofilter.
"Mole" (Aquamaster company). It is equipped with a body float protection and a compact biofilter.
"Multplast". Multi-chamber model equipped with a drainage pump. If desired, you can install an aerator and upgrade the installation to the level of a deep cleaning station.
"Bioton-B" (PolymerProPlus company). It consists of three sections, also includes a biofilter and a compartment in which a drainage pump can be placed.

Owners of suburban areas with high groundwater usually experience difficulties with the arrangement of autonomous sewage and drains. In wetlands, cesspools quickly fill with sewage, and the cost of sewer maintenance becomes quite high. But it is possible to arrange an effective septic tank with a high level of groundwater if the owner of the site is ready to increase the volume of construction and incur additional costs for the purchase of a finished installation. The investment of additional funds will subsequently pay off with the impeccable operation of the sewerage system and the absence of problems with its maintenance.

A septic tank, in fact, is a combination of a cesspool and a treatment plant, where wastewater enters, which is formed during the life of residents of private housing construction. As a result of the use of the toilet, bathroom, washing machines and dishwashers, a large amount of wastewater is generated, which must be disposed of without harm to the environment.

Modern septic tanks provide accumulation, biological treatment, wastewater disposal in two stages:

Contaminated effluents enter the first chamber of the reservoir, where they are settled and primary treatment takes place. Solid heavy particles quickly sink to the bottom, and the water purified from them enters the next chamber.
In the second chamber, the organic compounds that make up sewage are decomposed with the help of anaerobic microorganisms. The water becomes even purer and enters the third tank or system of special filters for final purification.

Understanding the principle of operation of a septic tank will greatly facilitate the selection and installation of the owner of a suburban area.

What problems does the high level of groundwater create?

High is the height of waters occurring at a distance of 0.5-1 m from the surface of the earth. With such a depth of occurrence, problems with sewerage inevitably appear, and difficulties arise with its maintenance.

Flooding. Devices made of bricks or concrete rings are often flooded due to the movement of groundwater and heaving of the soil. The lack of tightness in such installations facilitates the penetration of liquid into the interior, as a result of which the volume of effluents in the device quickly increases. In the best case, the owner of the house building has to call the sewage truck more often, in the worst case, sewage mixed with feces can get into the sewer and flow through it into the toilet and bathroom. If the device is overfilled, its contents may fall into the area and spoil the soil.
Ascent. The accumulation of groundwater during heavy rainfall or melting snow can push a lightweight plastic installation up if it has not been secured with a concrete pad. In the process of pushing out, the septic tank may tilt, fecal masses splash out and fall into the soil. And when the structure is shifted, a sewer breakthrough may occur, the owner of the site will incur unplanned costs for its restoration.
Drainage. According to SNiP, between groundwater and the filtration field filtering water at the last stage of purification, there must be at least 1 m of earthen layer. With a high occurrence of groundwater, this condition is simply impossible, as a result, pollution of the surrounding water bodies occurs due to insufficiently purified water entering the soil.
Destruction. Groundwater with high acidity or alkalinity gradually destroys the material from which the septic tank is made, especially concrete or brick. In addition, the housing or sewer pipes can be damaged by sharp pebbles that are brought in by moving groundwater.
Complicated installation. When installing the structure, due to the accumulation of water, the process of digging a pit and pouring a concrete pad is complicated. Installing ready-made purifiers becomes more labor intensive.

How to determine the depth of groundwater

Before installing a septic tank, it is necessary to accurately measure the height of groundwater in order to avoid errors during installation and further operation. There are several ways to do this.

There are 4 ways to self-measure GWL. Each of them allows you to accurately determine the depth of the aquifer.

Drilling rig. For this method, you will need a garden drill and a rod at least 2 m long. On the rod, markings are made along the length with an interval of 10 cm. Next, you need to drill a well to the entire depth of the drill and wait a day for moisture to accumulate. Sometimes water appears immediately after drilling, but these are rather isolated cases. The next day, the height of the water is measured with a rod. For measurement accuracy, you can make a number of wells throughout the site and measure the level for several days in a row. For tank design, the smallest value from the results obtained is taken.
By vegetation. You can determine the GWL on the site by growing wild plants on it. Below is a table of indicator plants, the presence of which can be used to judge the proximity of the aquifer. In addition to these plants, high humidity can be judged by the rich growth of sorrel and the rapid development of currant bushes.
For nearby water bodies. If there are dug wells nearby, the necessary information can be obtained by looking into them and determining how far from the surface the water mirror is located in them. It is best to do this after a heavy rainfall to get an accurate idea of the possible rise in groundwater. The presence of wetlands in the district indicates that groundwater is located close to the surface.
According to omens. There are some folk signs, based on which we can conclude about the desired parameter in the summer cottage. Morning dew and evening fog are sure signs of a shallow aquifer. The abundance of midges, mosquitoes and the absence of rodents in the local area can also tell about high humidity.

Location selection

It is necessary to start the construction of a septic tank at high groundwater by determining a suitable place, while it is important to take into account all SNiPs.

The optimal location of the sump must meet important conditions:

The distance to housing construction and other buildings on the territory of one's own and neighboring plots, as well as to the road zone, must be at least 5 m;
The distance from the sewer to the nearest water bodies is at least 30 m;
It is supposed to measure at least 50 m to a well with drinking water.

Model selection

After determining the optimal location for installation, you should decide on the type of septic tank. First of all, calculate the required volume of the device. To calculate the volume of wastewater accumulated per day, it is multiplied by 3.

The device, which will be installed in a site with a high GWL, must meet a number of requirements:

Full tightness;
Good strength;
Reliable fastenings;
Proper drainage.

To equip a septic tank in the vicinity of the aquifer, experts recommend purchasing models assembled at the factory. Such products are completely sealed, made of strong durable materials and are ready for installation.

Sometimes the owners of the sites prefer to build septic tanks from the building materials they are used to with their own hands or with the involvement of professional builders. The devices are additionally equipped with reinforced waterproofing. The device is usually built using concrete, brick, or old iron/plastic barrels.

concrete septic tank

When choosing concrete as a building material, it is undesirable to use reinforced concrete rings, since the installation of them quickly collapses and loses its tightness. A three-chamber concrete septic tank with a high level of groundwater is best done in the form of a monolith. Monolithic concrete devices are easier to give the necessary tightness, they are able to withstand high pressure, do not float, their service life will be much longer than that of a reinforced concrete ring. An additional advantage of concrete septic tanks is their low cost compared to more expensive materials.

Installation of a concrete monolith consists of the following steps:

Digging a pit;
formwork construction;
Formation of a reinforcing lattice;
Filling the bottom with concrete;
Filling of external walls and partitions;
Roof formwork construction;
Roof filling;
Ground embankment device;
Installation of ventilation and hatches.

brick septic tank

When installing a brick sump, the proximity of the aquifer will create difficulties when laying its bottom and walls. Ready-made brick installations need reinforced waterproofing to prevent fecal matter from entering the soil.

The process of building a brick septic tank is similar to installing a concrete one. Instead of the stages of construction of the formwork and pouring of concrete, the laying of the bottom, walls and roof of the device is carried out.

plastic septic tank

The material for the construction of plastic devices is usually plastic containers and eurocubes. Plastic septic tanks are not as practical as buildings made from heavier materials, but they are quite suitable for building a sewer system in the country with your own hands. The disadvantages of such materials are the risk of floating due to their low weight, the possibility of cracks in the heaving of soils.

Before installing plastic septic tanks, it is necessary to put a concrete slab at the bottom of the pit for anchoring easy installation. Plastic firmly fixed to a concrete slab will not be able to float with an increase in GWL.

Factory septic tanks

The best option for arranging an autonomous sewage system in a house adjoining area with a high level of groundwater is septic tanks made at the factory. The modern market of plumbing fixtures and devices offers products of different volumes and the most diverse modifications. The owners of suburban areas have the opportunity to choose the product that is most suitable for their sewer project.

The disadvantages of factory septic tanks are their high price and attachment to electrical networks. Cleaning tanks must be constantly supplied with fresh air, which is supplied by electrical equipment.

If the owner of the site has the skills to carry out construction work, he may well install a factory septic tank on his own, with the help of auxiliary workers. Installation is carried out in several stages:

Pit dig. When digging a pit by hand, the main problem is the water that comes in during the digging process. It is necessary to scoop out the incoming moisture at the same time as digging, sometimes you even have to connect special equipment for pumping. When using an excavator or other equipment for digging, a lot of liquid does not have time to run, and nothing interferes with the process of installing the device.
Construction of a sand cushion. At the bottom of the dug pit, sand up to 10 cm thick is poured.
Installation of a concrete base. A concrete slab with fasteners for fixing the septic tank is lowered onto the sand cushion. Sometimes, instead of a finished slab, a formwork with reinforcement is installed and concrete is poured. In the case of pouring, it is necessary to wait a week until the concrete has completely hardened.
Training. A heating cable is mounted on the septic tank and waterproofing is sprayed.
Installation. The prepared installation is lowered into the pit and installed on a concrete base.
Fixation. With the help of special fasteners, the septic tank is attached to a concrete slab.
Line of communications. Sewer pipes are connected to the device, the joints are sealed.
Sand filling. After connecting the communications, they check the operation of the heating cable and fill the septic tank with sand, immediately equipping the soil embankment on top of the cleaner.

After installing a septic tank, a filtration field or a filtration cassette is constructed next to it for the final purification of the filtrate.

TOP 10 factory cleaners

Tank. Excellent value for money. Energy independent. Rugged housing. A wide range of models with different volume and device.
Triton. Excellent service life up to 50 years. Septic tanks of this brand require anchoring during installation. A wide range of models of different sizes and shapes.
Leopard. Three-chamber cleaners with 2-level biofiltration. Consumers note strength, reliability and durability.
Tver. high throughput models. They require a constant source of electricity and regular maintenance.
Leader. 6-chamber septic tanks with airlift and aerators. Do not require biological additives for wastewater treatment.
Ecopan. Withstand heavy loads. Recommended for installation in heaving soils.
Unilos. A complex wastewater treatment process, consisting of mechanical and biological stages. Reliable, easy-to-maintain models.
Yubas. Durable septic tanks suitable for efficient operation with long breaks up to 3 months.
Poplar. Resistant to temperature extremes and loads. Equipped with airlifts, compressors and aerators. manual and mechanical sludge removal is provided.
Topas. Reliable autonomous sewage system made of high quality materials. It is in demand among Russian consumers.

Operation features

An autonomous sewage system will last a maximum period if you follow the recommendations of experts and the basic rules of use:

Do not throw large debris into the sewer;
It is good to insulate and waterproof the system;
Regularly pump out accumulated sewage from the septic tank;
Avoid the ingress of fats with the help of special grease traps;
Do not use chemicals in the case of using bio-treatment of wastewater in the septic tank chamber.

If you approach the installation of a septic tank responsibly, take the time to draw up a project, select materials, follow the rules of operation - the autonomous sewage system will function without failure for many years.

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