- Asset
- Wash-bay silt trap or settlement chamber
- Typical contents
- Washwater, grit and process contamination
- Check
- Treatment arrangement and discharge permission
- Separate issue
- Whether an oil separator is suitable for the washwater
Where the washwater goes
Vehicle and equipment washing can produce water containing sediment, oil and cleaning chemicals. The drainage plan should show where that water goes and any settlement, separation, treatment or recovery stage between the wash bay and the final discharge.
A silt trap or separator does not make a discharge acceptable on its own. In England, Environment Agency guidance says contaminated water should drain to a foul sewer with the water company’s permission, while only clean water should enter a surface-water drain or soakaway. If washwater is collected or treated by another route, that route still has to meet the applicable discharge and waste controls.
Sediment and available capacity
Grit and settled material occupy the space provided for settlement or storage. Inspection should look at the depth and position of deposits as well as the inlet and outlet. A clear surface does not show that the base of the chamber is free of sediment.
Detergents and the work carried out in the wash bay affect the washwater reaching downstream equipment. The Environment Agency specifically warns that oil separators do not work properly when detergent is present in the water, so the treatment arrangement needs to suit the actual washwater.
Cleaning and safe access
Cleaning should recover sediment and washwater without pushing the contents further into the drainage system. If incoming flow would interfere with the work, the wash bay may need to stay out of use while the trap is open or unavailable.
Heavy covers, vehicle movements and contaminated liquids all affect safe access. Emptying the chamber does not make entry necessary or safe; confined-space risks still need competent assessment.
Maintenance records and repeat build-up
Record the material removed, the condition of the trap and any downstream components that were inspected or serviced separately. If the trap fills unusually quickly, the source and upstream controls should be investigated rather than treating repeated emptying as the whole answer.