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Septic tanks are used as a sewage disposal system for places that cannot usually be connected to the mains sewage. They involve connecting a septic tank to the property’s sewage system, which then uses bacteria within the tank to naturally break down the waste, before disposing of the final effluent into a drainage area and collecting the sludge in the tank.
Septic tanks are normally installed underground and can be commonly manufactured from glass-reinforced plastic (GRP), or High-Density Polyethylene (HDPE).
Placing your Septic Tank
Ensuring that your septic tank system is stored in the correct place is vital to ensuring that it works properly. This applies not only to the tank itself but to the whole system.
To start with, the drainage area needs to be in the correct position and of the correct size. The drainage field disperses the wastewater (treated or untreated) into the ground in a controlled way, as well as allowing semi-treated wastewater to be further treated before it gets to the ground. Several environmental standards have been set out that you must adhere to when it comes to installing a drainage field for a septic tank.
The BS 6297:2007 regulations set out the rules around having a drainage field on your property. It is important to remember that a drainage field for a septic tank is not the same as a soakaway, which is used for storm water runoff, for example.
There are some other rules that you should adhere to that are in place to ensure that drainage areas are safe, effective, and environmentally friendly:
- It must not be a Groundwater Source Protection Zone.
- It must pass a percolation test – this ensures that the water does not soak away too quickly or too slowly. This depends on the type of soil and the presence of other materials such as gravel in the area.
- It must pass a Trial Site Assessment Hole test – this checks that the water table or bedrock is not within 1 metre of the bottom of the planned pipes.
To calculate the size of the drainage field, for a septic tank, the calculation is as follows:
Area = p x Vp x 0.25
Where p = the number of people who will be served by the septic tank and
Vp = the percolation value as determined in the percolation test
If you do not have an area that is big enough for the drainage field, you will, unfortunately, not be able to have a septic tank system installed. You could, however, consider installing a sewage treatment plant. In this system, the water is treated to a higher level, meaning that the water can then be drained safely, effectively, and legally into a watercourse like a stream or a river (unlike with a septic tank system).
Placing of your Septic Tank
Choosing the right place to put your septic tank is also an important decision. They will normally be put underground, meaning that, depending on the size of the tank, it will normally need a hole of around 2.5m of soil to be put into. It is also important to check whether any local regulations must be followed in terms of where you can place your septic tank before beginning to install it.
You will also need to have planning permission from your local planning office to be able to install your septic tank. If, however, you are replacing an old septic tank in the same property, to the same place, you may not need to get any additional planning consent.
Septic tanks are ideally situated about 7m from the building which they are servicing. Septic tanks should also be located within 30m of an access point so the tank can be emptied.
Septic tanks will normally be placed downhill from the building that it is serving, using gravity to aid with the movement of the waste. If this is not possible, a pump chamber may be required to ensure that the wastewater can adequately flow.
If you are putting a septic tank system in, it is important to check utilities such as electrical, gas, and water and where their lines into the property are to ensure that they are not damaged or disrupted by the sewage system. You should also try to avoid areas where there are trees present as roots can be especially damaging underneath the ground to septic tanks and their pipes.
