Calculation of the volume of the sump
According to statistics, every adult person spends about 250 liters of water per day for various household needs, such as bathing, washing hands and dishes, laundry, and so on. Those who do not have a city sewage system, use septic tanks and pits to drain the water, so an accurate calculation of the volume of the cesspool is necessary before installing an autonomous sewage system in the house.
How to calculate
Best of all, if in the calculation of the cesspool will not present approximate parameters, but certain formulas. One of them is the formula by which you can determine the volume of the pit for a private house, taking into account the interval of days from one pumping of the contents of the septic tank to the next pumping, and taking into account the number of people using this sewer system. This formula will look like this:
Vpits (m?) = n? N? Vs / h,
where N is the number of people in the house most of the time, Vs / h - is the volume of water in liters consumed by one person (150–200 l) for 24 hours, n is the interval from one pumping of the pit to another using a vacuum truck; usually this value is assumed to be 15 days. Using this formula, you can calculate the volume of the sump for your home.
We consider - for example, a family of three lives in a house. So, on average, water consumption will be about 450 liters. Now we will present everything according to the formula:
15 days) ? 3 persons) ? 150 (l) = 6750 (l). If this figure is translated into volume, then the pit should be approximately 6.75 m ?.
This calculation will not be complete if you do not provide for certain force majeure circumstances that usually occur during the operation of the sewer system. This may be a greater consumption of water, the arrival of the vacuum truck a few days after the call, or something else. Best of all, if the volume will be calculated as a family of 4 people - with a margin.
How to calculate the size of the pit
Knowing the volume of the pit, calculated by the formula presented above, you can determine the dimensions by the following formula:
V = a? b? h,
where a, b and h are the length, width and depth of the pit. For a pit with a volume of 6.75 m? The following dimensions will do: length is about 2.5 m, width is 2 m and depth is not less than 1.8 m.
Each of these parameters is also determined by several criteria. For example, the depth of the pit should not be such that no matter how the bottom of the sump reaches the groundwater. Therefore, if the depth of the pit is not allowed to be more than 1.8–2 m, then it is necessary to use plastic tanks. In this case, the required volume is achieved by increasing the length and width.
Tip! Even if the depth of the groundwater allows you to make the pit deeper, you should not dredge the bottom more than 3 m - in this case, the car with the pump cannot completely clean the pit.
In addition, the volume of the pit to be installed or the container to be mounted should be clarified with the contractor, whose duties include pumping and removal of all sewage drains. It is important to decide how often they will be taken out, and how much a car will be able to take away at once. If you do not create your own cost-effective scheme, then a situation will necessarily arise where the car will come often and leave half-empty - all this is an extra cost.
Calculations for a cesspit without bottom with sewage filtration
Such a pit, which has no bottom, is different from the usual one, completely sealed. The drains in the filter pit are cleaned with anaerobic bacteria, after which some of the content goes through the ground. You can postpone the challenge of the pumping machine if you use special biopreparations.
It is possible to calculate which volume of the cesspool will be optimal, as follows:
- We take into account that about 150 liters of water are consumed per person per day. And if you use household appliances, the drains from which will rush into the pit, the volume per day can increase even up to 500 liters.
- It is important not to forget that such a volume of waste is calculated to be as large as possible.
- When deciding which one needs to make a drain hole, one needs to take into account that its smallest volume should be three times more than the daily volume of all drains flowing into the hole.
The size of the designed sump is calculated, as well as the size of a conventional sealed pit. There are no correlations of length with width and height. True, it is better to adhere to the fact that the depth was somewhere twice as large as the length or width (or diameter, if we are talking about a cylindrical container).
Calculation of building materials for the cesspool
When deciding exactly which version of the drain hole will be applied, it is important to consider that the size of the hole itself should be slightly larger than the installed septic tank. What projects cesspools today can often be found and what kind of materials they use? Here are a few options:
- monolithic structure made of concrete with its reinforcement;
- polypropylene container;
- the design collected from several reinforced concrete rings;
- conventional brickwork on cement-sand mortar;
- septic tank of eurocubes.
Industrial method produced reinforced concrete rings with a circular or square cross section. Also for the well there are rings with a lid in which a metal hatch can be inserted. Then a hole is pulled out into which two or three rings are mounted. They are covered with a lid of concrete, and all joints are sealed on both sides. A layer of waterproofing is applied on top, and then the lid is covered with earth.
The top of the structure is able to withstand even the weight of a truck that has run over it, therefore such pits made of concrete rings are successfully used even on the roadway.
Wastewater is discharged from the house through pipes leading to the pit. Water flows by gravity, underground. Knowing the diameter of the rings, it is much easier to calculate the volume of the well. In addition, the cesspool of concrete rings is much easier to clean, and its service life, subject to compliance with the technology of construction, can be a hundred years.
Video
This video describes how to calculate the volume of a septic tank: