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 these sewers.

Surface water drains may discharge directly to surface waters or groundwater. You are committing an offence if you allow poisonous, noxious or polluting matter to enter a drain and reach surface waters or groundwater unless you have prior written authorisation.

Drainage Plan

Have an up to date and accurate drainage plan available at all times. This will identify the locations of all drains and sewers in and around your site, and where they lead. When making 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.

Develop and implement a system for routinely inspecting and testing any pollution prevention equipment, such as:

• oil separators
• effluent treatment plants
• storage tanks (above and below ground)
• impermeable surfaces
• drains
• bund walls.

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 with your environmental regulator to establish their requirements with respect to spills and surface water run-off, for example provision of interceptors.

In areas without mains drainage, direct your domestic sewage to a private treatment facility such as a septic tank or packaged treatment plant. Most of these require a written authorisation from your environmental regulator.

Oil interceptors

Isolate run-off from refuelling areas from general yard drainage. Drain this run-off to an oil interceptor. You may need permission from your environmental regulator, water company, water service or Scottish Water 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.

Regularly maintain all the interceptors on your site. Maintenance should include inspection and removal of the accumulated oil and removal of the sludge from the bottom of the tank. This sludge may need to be disposed of as hazardous/special waste if the oil content is greater than 0.1% w/w. Leave interceptors partially full of water after cleaning, to ensure that they continue to work effectively.

Divert clean, uncontaminated, roof water directly to the surface water system so that it does not pass through any oil interceptors.

Minimise discharges from your site

Minimise the number and quantities of effluents that you need to discharge to surface waters or groundwater. Try to find alternative means of disposal such as discharge to foul sewer (subject to a trade effluent consent or agreement from your sewerage undertaker) or disposal by a licensed waste management contractor in accordance with the duty of care.

Explore the possibilities for using alternative materials and practices that do not result in the production of effluents, for example, reuse of water for a lower grade purpose such as non-critical rinsing.

In this guideline: