Soakaways / Drainage Fields

The effluent from a packaged sewage treatment system needs to go somewhere, determined by a combination of the ground conditions, your Environment Agency zoning, the water table and access to local features such as ditches or water courses.

Once we have helped you determine what options will be compliant then you will be in a position to review the options available, which in all likelihood will include a local watercourse or drainage field.

Drainage fields typically consist of a system of irrigation pipes which allow the effluent to percolate into the surrounding soil. Biological treatment takes place naturally in the aerated layers of soil. A drainage field is used if you are installing a sewage treatment system and can not connect directly to a watercourse. The size of the drainage field again is dependent on the capacity of your sewage treatment equipment and the drainage properties of the soils at your site.

Drainage fields can take various formats, including being raised or going deep into the ground, and again depending on requirements and budgets, the MPC Install team will help with whatever is the most relevant for your requirements.

The term soakaway is no longer used to describe where effluent is discharged too. A soakaway is where rainwater from gullies and downpipes is discharged too.

To determine how the effluent from your packaged sewage treatment system can be discharged to the local environment, there is a mandated set of processes to follow that provide the necessary information about the soil conditions on your site.

Firstly you will want to know the normal water table level, or at the very least that it is not so high that it will infringe on the functioning of a drainage field. This is typically determined by digging a bore-hole down to either where you reach the water table or the maximum depth that the water table would affect the drainage field based on the general binding rules. Should a high water table be identified then this will affect the choices that are available to you when it comes to drainage field design and feasibility. Additionally this initial trial hole may identify bedrock at depths that will affect the team when it comes to digging hole for your treatment equipment and again potentially extend the project length and constraining the selection of treatment tank.

Once an understanding of the water table and any bedrock has been determined, a percolation test is needed to measure the speed at which water is dissipated through the soil. Too fast or too slow will both have an affect on the overall project design to ensure that the system is compliant to Environment Agency standards.

Our MPC Install team undertake this testing at multiple points on your site not only as this is as per guidelines laid out but also to make sure that we have a representative set of measurements. The team will provide you with all of the data collected on site as this is important when it comes to evidencing design decisions and equipment selection.

Alongside the trial holes and percolation tests are completed the team reviews the site in the context of the current weather conditions, for example recent spells of heavy rain or drought, as well as broadly assessing the soil type, e.g. clay, sandstone to help with the design process and also make sure that the project is planned well, with different soil types potentially taking different lengths of time to work on.