Managing your site's discharges and drainage
Check your site drainage
If you discharge any effluents, such as trade effluents, sewage or cooling waters, to drains on your site, you should check whether these drains are linked to the foul sewer or surface water drains.
Foul sewers carry effluents to a sewage works for treatment. If you generate trade effluent you are likely to need a consent or agreement from your sewerage undertaker to discharge to their sewers. Your business effluent may need to pass through a private sewer. If this is the case then you must get permission to discharge from both the owner of the sewer and your sewerage undertaker.
Surface water drains may discharge directly to surface waters or ground waters. You must not allow poisonous, noxious or polluting matter to enter a drain and reach surface waters or ground waters unless you have specific prior written authorisation from your environmental regulator.
Drainage plan
Have an up-to-date and accurate drainage plan available. This will identify the locations of all drains and sewers in and around your site, and where they lead. When you make a discharge to a drain or sewer, always check that you are connecting to the correct system.
- Trade effluent and sewage to the foul sewer.
- Clean uncontaminated surface water to the surface water drainage system.
Paint the drainage system manhole covers, gullies and grills on your site in the recognised colour-coding system: blue for surface water drains, red for foul water drains. This will help you identify where any spills will end up.
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Case study: Abattoir fined £25,000 for polluted surface water run-off
A beef and lamb abattoir and processing plant in Bedfordshire was fined £25,000 plus costs for polluting water with blood. Surface run-off from the site was flowing to a ditch, which runs into a brook. The Environment Agency found the discharge was over five times as damaging as raw sewage, and pollution in the ditch was 23 times more concentrated than permitted levels. Before discharging sewage, effluent or contaminated run off into waters you must have consent from your environmental regulator or you may be committing a pollution offence and could be prosecuted.
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Make sure that roof water drainpipes discharge to the surface water system via direct drain points or sealed-top entry gullies. Do not use open gullies or grates as these may allow contaminants into the system.
When constructing or surfacing external hard surfaces, such as car parks, check the requirements with respect to spills and surface water run-off with your environmental regulator. For example, you may need to use oil interceptors.
In Scotland, all new developments draining to the water environment, other than single dwellings and those that discharge to coastal waters must include sustainable urban drainage systems (SUDS).
In England, Northern Ireland and Wales you may need to include SUDS in your planning application for new developments.
It is possible to design your SUDS to degrade oil and your environmental regulator may accept this in place of an interceptor for lightly contaminated run-off.
Oil interceptors for high risk areas
Isolate run-off from refuelling areas from general yard drainage. You should cover areas at high risk of contamination, such as refuelling areas, to prevent run-off. Where this is not possible you may need to channel run-off to a collection tank. If your drainage goes to the foul sewer you may be required to install an oil separator. You may need permission from your environmental regulator or water company or authority to discharge the wastewater from your oil interceptor or other treatment system.
Interceptors are only designed to remove some oils and fuels from water. They do not remove other pollutants, such as heavy fuel oils, chemicals or dust.
To ensure your oil interceptors work effectively you should perform regular maintenance checks:
- you should inspect and remove the accumulated oil and sludge from the bottom of the tank
- you may need to dispose of sludge as hazardous/special waste if the oil content is greater than 0.1% of the total sludge weight
- you should leave interceptors partially full of water after cleaning, this will help ensure that they continue to work effectively.
You can only discharge roof water directly to the surface water system if it is clean and uncontaminated. So you must ensure that it does not pass through anything that could contaminate it, such as an oil interceptor.
