Construction sites: 7 tips for managing surface water
With changes in regulations in Scotland and increasing financial penalties in England, Naturally Compliant Director Simon Knott offers the following advice to those responsible for the construction phase of residential, commercial and infrastructure projects.
Each project will have its own unique challenges but the following principles may help projects mitigate the risks associated with water management and pollution on construction sites regardless of scale.
1. Develop a plan
As with most things on a construction site, successfully planning how you will deal with water requires a lot thought before works start. A good plan will include the following list and address any statutory requirements placed upon the project.
2. Know what and where the receptors are
The terminology may change but the themes remain the same. Surface waters as defined by the EA or the Water Environment as referenced by SEPA includes watercourses, rivers, streams, estuaries, lakes and canals. If pollutants from your site reach any of the above you are at risk of enforcement action, so its important to know where they are in relation to your works.
3. Keep non-site water away from your construction activities.
This will obviously vary massively depending on the nature of the site, but plans should be made to isolate your works from any pre-construction surface flows. This can be in the form of impermeable bunds, upslope cut off drains or a mixture of the two. Be aware that the water you stop moving over your site will need to go somewhere, so build in plans to allow the water to move across your site in a way that maintains its non-site contaminated status. Tying your pre-construction drainage in to existing watercourses is one way of achieving this, provided all statutory paperwork and commitments are observed.
4. Keep clean water clean.
If there is water on your site that is uncontaminated, try and keep it that way. Broadly speaking, reducing the volume of contaminated water reduces the associated costs of treating it.
5. Have multiple discharge points and keep them as far as is practical from the natural water environment.
In the UK we are subject to relatively high precipitation rates, which means that even though we have installed measures to stop water flowing on to site, it is very likely that the project will have to treat water that falls on it. If possible, the installation of multiple discharge points treating surface flow close to the source of pollution is preferential. This means you are treating smaller volumes at each location and are discharging the treated water over a larger area.
As discussed, Surface waters or the Water environment are your receptors, try to discharge your treated water as far as possible from these to reduce the risks. If this is not possible robust treatment measures will be required
6. Slow silt laden site water down.
Reducing kinetic energy in silt laden waters allows sediments to settle out of the water more effectively. This is commonly achieved through check dams and settlement ponds within your treatment systems. Shallow ponds are more efficient at removing sediment from water than deeper ponds, its therefore important to understand the difference between attenuating water for flood prevention and using settlement ponds to treat silt laden water.
7. Over compensate and maintain
Where possible, it is better to overestimate the volume of water a treatment system will deal with. This will give the system a better chance to cope with any unexpectedly large downpours or other climatic variables such as; significant snow melt or precipitation falling on baked earth which can lead to an initial increase in surface flow.
The treatment systems are there to remove pollutants and so can become overwhelmed, it is therefore critical to maintain the systems so they remain effective.
Naturally compliant have a strong track record of developing water management and pollution prevention plans to meet the needs of a variety of projects. Should you wish to discuss your projects need in greater detail please don’t hesitate to get in touch.
This article was originally published in PBC Today on 3rd May 2018.