It is important to remember that the effluent discharged from a septic tank or sewage treatment plant, no matter how well it has been treated, is not clean water. It is sewage effluent and presents a risk to people and the environment.

Septic tank effluent cannot be discharged into any watercourse or ditch. In the old days, when the soakaway failed, it was much cheaper to dig an overflow pipe to the ditch than to install a new soakaway. However, this has been illegal, (even for existing systems) since 1991 when the Water Resources Act came into being to protect our ditches, streams and rivers. The max. fine is now set at £100,000, so it is not worth the risk. If your septic tank discharges into a ditch you must do something about it - fast! Any existing permissions you may have will only apply to discharge to a soakaway. Check your permit!

At the planning stage it is essential to bear in mind that establishing a practical and legal method of discharging sewage effluent is more important than the actual septic tank or sewage treatment plant that will be installed and it should not be viewed as a reserved matter. We have had cases where a building plot was sold with full planning permission, only for the buyer to find out after purchase that no sanitation is possible at all - a very expensive piece of waste ground with a mortgage attached!

Environment Agency Permits

All sewage effluent discharges, irrespective of age, volume or location, must now be registered with the Environment Agency. This also applies to the replacement of existing tanks and drainage fields.

The Environment Agency has three types of permit – Standard, Bespoke and Exemption.

Most domestic sites will fall under the exemption category however you must check that the site meets the required criteria. If it does not then a Standard or Bespoke Permit must be applied for.

Effluent Disposal Methods

discharging sewage effluent

Effluent Quality

Strong consideration should be given to the quality of effluent that you discharge.

Even though a septic tank can be discharged to ground via a drainage field, it is often preferable to install a sewage treatment plant over a septic tank because of its effluent quality.

All drainage fields will fail over time and the worse the quality of the effluent the quicker it will fail due to blocking from suspended solids and anaerobic bacterial biomass caused by the effluent BOD (Biological Oxygen Demand).

Not all sewage treatment plants are equal in terms of their effluent quality.

Effluent quality is usually described by three measures of pollutants – Biological Oxygen Demand (BOD), Suspended Solids and Ammonia. Each pollutant is measured in mg / Litre (parts per million).

Example: