How to manage surface water drainage

   28 June 18            

The prevention of surface water and groundwater pollution from construction sites is one of the biggest issues facing construction companies nowadays. Effective surface water drainage systems are becoming increasingly vital and can help construction companies better manage their projects, while avoiding fines and damage to the environment.

What are the causes of water pollution on site?

Water pollution can come from any number of different sources, including spills or leaks from oil or chemical containers, run-off containing salt, silt and soil, fuel spills and runoff that contains concrete and grout. Excavations on a construction site can also disturb existing soil contamination.

Surface water and groundwater are protected by licensing regimes that prevent and control pollution from businesses. These exist to protect water from pollution, prevent water sources from being depleted and control interferences with the natural flow of water. Some things you need to be aware of are:

  • You must be authorised to carry out a controlled activity if you want to discharge anything into surface waters or groundwater.
  • SEPA and the NIEA can issue notices to businesses to control water pollution.
  • If your activities pose an imminent threat to the environment, you must notify the relevant enforcing authority if the threat continues and take steps to prevent environmental harm. Where pollution has already occurred, you must take action to remedy this.
  • If you intend to abstract more than 10 m3 of water per day you must contact SEPA or the NIEA. You may also require an authorisation from SEPA or the NIEA if you intend to impound (store or dam) water on an inland watercourse.
  • You must make sure you store and use hazardous substances safely to avoid causing harm to human health or the environment.

How to prevent water pollution

Manage water on site

While we know water pollution can be very damaging, there is a simple system that can prevent it. A sustainable drainage system (SuDS) can be used in all types of developments, providing a natural approach to managing surface water.

During the construction phase the use of filter strips, swales and cut off ditches, combined with settlement ponds or settlement tanks can effectively control silty runoff and protect nearby watercourses. These must be designed to cope with the volume of runoff that can be expected from the site.

You can minimise the silty runoff by maintaining a buffer strip between exposed areas and any ditches, drains or watercourses. You should also only remove vegetation from the area that you are working on, keeping exposed ground to a minimum. Channelling clean water away from your working area will also reduce the volume of contaminated water that you need to deal with.

Store and handle materials safely

Concrete and grout can be very polluting if they are carried into watercourses so take care with storage and handling. Have a separate area for mixing, and contain any drainage. Make sure that stores are secure and positioned away from vehicle movements or other potential sources of damage.

Store oil and fuels according to the Regulations on Oil Storage, in containers with secondary containment. Have designated refuelling areas, with hard standing and bunds to prevent leaks or spills escaping. Use plant nappies on any equipment such as generators which need refuelling or which could leak oil or fuel.

Completing the development

SuDS prevent water pollution and flooding and create green spaces for wildlife within towns and cities. As a natural approach to managing drainage, sustainable drainage systems are a legal requirement for all new developments in Scotland, and are often a requirement for planning permission in Northern Ireland. They work by holding back water that runs off from a site, allowing natural processes to break down the pollutants that are picked up across the site. They act to manage water quality and also to reduce peak flows during storms, reducing flood risk downstream. SuDs measures that are used in the construction phase can sometimes be incorporated into the final design of the development.

There are three types of SuDS, each one preventing different kinds of water pollution:

  • Source control measures deal with run-off at, or close to, the surface where rainfall lands.
  • Site control measures manage the surface water run-off from larger areas, such as part of a housing estate, major roads or business parks.
  • Regional control measures downstream of source and site controls deal with the gathered run-off from a large area.

Not only will having a sustainable drainage system in place help keep your project on track and to budget, but it will also help position you as a responsible and sustainable employer. By reinforcing measures on your site, such as storing hazardous substances according to the manufacturer's instructions and labelling containers clearly, you will help prevent water pollution before it even starts and could greatly decrease the chances of problems developing further into a construction.

To put these systems into practice, SEPA and NIEA encourage businesses to use the following techniques (dependent on what kind of surface water drainage is required):

  • Green roofs
  • Permeable surfaces
  • Infiltration trenches filter drains and filter strips
  • Swales - shallow drainage channels
  • Detention basins, purpose-built ponds and wetlands

Implement a sustainable surface water drainage system and ensure that your project is completed on time, that your business is following environmental best practice and that you are protecting the welfare of your staff, local residents and local wildlife in the process.

If you are looking for more information on how to put a surface water drainage system in place, have a look at our guide to SuDS