Surface water from drains usually empties directly into a watercourse or indirectly into underground water (groundwater) via a soakaway. Contamination of this surface water whether by oil, chemicals or suspended solids will likely result in a significant environmental impact.
For this reason, various regulatory bodies and authorities connected with preservation of the environment (e.g. Environment Agency, Scottish Environmental Protection Agency and Department of Environment & Heritage in Northern Ireland) have produced guidelines regarding the disposal of surface water.
This guidance provides a range of methods by which pollution can be dealt with - ‘Sustainable Drainage Systems’.
It is worth remembering that pollution of the environment is a criminal offence and when substances such as oil, dissolved oil, detergents, degreasers or trade effluents are at risk of entering drainage waters then separation is a must – these infiltrations can come from a variety of sources – and can be quite unintentional e.g. leakages from vehicles, plant machinery or accidental spills from equipment or human error.
There are Four main types of Separator;
Full Retention Separator - These separators can deal with a large flow equivalent to rainfall of 65mm/hr
Bypass Separator - These separators can deal with a slower flow equivalent to rainfall of 6.5mm/hr - flows above this rate bypass the separator.
Forecourt Separators -These are effectively full retention separators, designed to retain on site the maximum spillage likely to occur at a petrol filling station. These specialised separators are mandatory for obvious safety and environmental reasons – they will handle spillages during vehicle refuelling and/or fuel tanker delivery.
Washdown & Silt Separators - This is a simple solution for use in areas such as car wash and cleaning areas which then feeds into the main drain.