Soakaway | Septic Tank Drainage | Drainfield Installation

Soakaway and Drainfield design to conform with Section H of the Building Regulations - Sewage and Drainage issues and BS 6297 : 2007

Sizing of a soakaway - Length of drains

Soakaways for septic tanks and sewage treatment plants

The Environment Agency have corfirmed to us that DEEP BOREHOLE soakaway solutions are not acceptable to them.  BEWARE of adverts on the internet.

Minimum soakaway site distances

• 10m from a watercourse or ditch.
• 50m from water abstraction points.
• 15m from any building, and sufficiently distant from any other soakaway, including roof water.
• 2 metres from a boundary. 
• The soakaway or drainfield area should be downslope of groundwater sources.
• No water supply pipes or underground services should be within the soakaway area.
• No access roads, driveways or paved areas should be within the soakaway area.  This includes fields with tractor and agricultural vehiclular traffic.
• The water table or bedrock must not, at any time, be within 1.2 metres of the bottom of the soakaway trench.

Construction of Soakaways and Drainfields

• Use SOLID perforated foul drainage pipe, with the slots/holes at the bottom, laid in trenches of a uniform gradient not steeper than 1:200.  Perforated 'Flexicoil' type pipe is NOT allowed. 
• Pipes should be laid at a minimum depth of 200mm and a maximum depth of 700mm. to enable aerobic contact between the effluent and the soil particles.
• The Maximum length of a single trench is 30 metres.
• Pipes should be laid on 300mm of clean shingle, gravel or broken grade 1 stone ( 20mm – 50mm ).
• Soakaway trenches should be filled to a level of 50mm above the pipe and covered with a layer of geotextile membrane to prevent silt entry.
• The remainder of the soakaway trench can be filled with topsoil.
• Drainage trenches should be between 300mm and 900mm wide with areas of undisturbed ground of minimum 1m wide between parallel trenches.
• An inspection chamber should be installed between the septic tank and the drainfield.
• The soakaway layout should be set out as a continuous loop fed from the inspection chamber, NOT a straight pipe run with an 'end'.
• The soakaway pipes should be fed by a distribution chamber. 
• The area of the soakaway is calculated after carrying out a minimum of three percolation tests in the proposed drainfield area, over three consecutive days and applying a formula as detailed on the Percolation Test page.

Design of soakaways and drainfields

A foul water soakaway or drainfield is NOT a ‘Pit filled with stones’.  These types of soakaways are ONLY allowed for surface roof water, NOT sewage effluent.  It is not a serious matter if rainwater bubbles to the surface of the ‘pit’, but sewage effluent is an entirely different scenario.  Please visit Sewage Problems if you have soakaway issues with your current system.