The maintenance of a soakaway will likely include the periodic removal of waste sediments. This prevents the sediments from blocking the voids in the soil reducing the infiltration rate, and from collecting in the soakaway reducing the storage capacity.

Soakaway Waste Management

The quantity of sediments accumulated and therefore the frequency of maintenance required is dependent on a number of factors;

• Any sediment interception methods employed upstream such as filter strips, catchpits or separators will reduce the quantity of sediments entering the soakaway.
• The type of runoff handled by the soakaway. Soakaways handling runoff only from roofs will have a low quantity of sediments, runoffs from rural or unpaved catchments will be high in sedimentation. These can be minimised with appropriate erosion control methods and sediment interception methods.
• Size of catchment and volume of runoff. The greater the volume of runoff the greater the quantity of sediments expected.

Sediment removal should always be undertaken in a manner which minimises the risk of damaging the soakaway. A suction tanker should generally be used to empty soakaways which include a precast concrete storage area. It may be necessary to remove the sediments by hand, particularly where they have dried out. Suitable access arrangements should be made if the sediments are to removed by hand, the soakaway will be classed as a confined space.

Where large plant such as excavators or large tankers are used care should be taken to minimise the risk of damaging the soakaways structure. Care must also be taken not to compact the loose ground around the soakaway which could lead to a deterioration of the infiltration.

Filled soakaways or infiltration trenches will usually require the backfill material to be removed entirely and either cleaned or replaced. Care must be taken to avoid damage to any geotextile liners.

Sediment Testing

When the runoff comes largely from building roofs and standard roadways the sediments produced are not generally toxic or hazardous and can be disposed of by standard methods. Testing of the sediment may be required before it can be disposed of to prove that it is non-hazardous.

On industrial sites, sediment testing is essential as heavy metals, hydrocarbons and other contaminants can enter the runoff. This is particularly the case where no suitable interception methods are in place. Sometimes these sediments can be spread onsite if suitable. Otherwise the sediments may need to be disposed of as hazardous waste. Waste management legislation must be adhered to even if the sediments are being spread onsite.  A flowchart describing a sediment characterisation process is shown below.