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A comprehensive plan of the water drainage system should be drawn up and where all drains discharge
to and all manhole covers should be colour coded. Good knowledge of the drainage system on site and
how river pollution can be caused will help prevent water pollution incidents. On the majority of
industrial sites there will be two types of drain:
- Foul water drain: this carries trade effluent- e.g. plant cooling water, to a sewage works for
treatment. Authorisation is needed from the local water company prior to most types of effluent
being discharged to the foul sewer.
- Surface water drain: this flows directly to local rivers or streams and carries unsoiled
rainwater from roofs, and clean yards.
The majority of water pollution incidents occur when effluent or polluted water enters the surface
water drain due to incidences such as where plant cooling water is discharged to this drain and
contains chemical additives. Pollution can also occur when spillages of chemicals are allowed to
enter the drainage system, or where certain substances are spilt on the ground and over time,
contaminate the lower soil layers and then the groundwater beneath- particularly chlorinated
solvents.
Consent is required from the Environment Agency before making any discharges of effluent to
controlled waters such as streams. Consent is also required from the local water company. This is
for most discharges of effluent to the foul sewer.
Key members of personnel should be made aware of the drainage plan. Surface water drains should be
coloured blue and foul drains, red- all staff should be aware of the colour coding.
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