Settlement tanks are increasingly becoming a necessity on many sites where environmental considerations need to be taken. They offer a degree of protection, ensuring that oil, silts and fines are not discharged back in the watercourse.
The Environment Agency’s Pollution Prevention Guidelines PPG6 states that:
Surface waters and groundwater have legal protection. It is an offence to pollute them.
Silt and oil are the most common construction site pollutants to water. Your site doesn’t need to be next to a river to cause a problem; any pollutants getting into drains can end up in a river even if it’s miles away from site, and can be traced back to their source. Drainage systems, including land drains, act as unseen pathways. If your site is near surface waters or drainage connection leading to surface waters, you’ll need to take extra care to manage your site activities to reduce the risk of pollution.
A settlement tank typically has a number of internal baffle plates or wiers which reduce the flow velocity allowing suspended particles to settle out. Since oil floats on water the baffles can be constructed in such a way that the water flows under the plate, leaving the oil trapped behind the first baffle.
The illustration below shows the flow of water through the settlement tank – entering at the top, the water then flow under the first baffle, leaving any oil floating on top and trapped in this first section, then flows over a v-notch in the second baffle before being discharged.
Maris Pumps offer a range of settlement tanks for hire.