New guidance for construction site drainage to surface waters


Gravity fed silt capture channel: a series of silt mats, flocculant treated mats and silt wattles have been used to create a highly effective, low cost, silt treatment process.

Earlier this year new guidance was issued detailing the regulatory position in England and Wales, and general binding rules in Scotland, on the transfer of water from construction sites to rivers and streams.

These state that only uncontaminated water consisting of clean and clear rainwater or infiltrated groundwater may be released from a site for up to three consecutive months under exemption in England and Wales, however there is no time limit in Scotland.

In order to qualify for the exemption a series of conditions aimed to prevent pollution in the receiving water body must be met. Consequently, the discharge must not:

  • result in muddy water
  • contain any chemical agent such as a coagulant or flocculant
  • contain any contaminant such as oil
  • contain concrete wash water even if it has been treated
  • contain site drainage from surfaces such as haul roads, storage areas
  • spread invasive plants animals or diseases
  • be within or close to a sensitive ecological site
  • in Scotland be from a construction site that has an area greater than 4 hectares, a linear development greater than 5km or has an area with a slope

A method statement must document the control measures to minimise the risk of pollution such as how to:

  • minimise the level of contaminants being generated such as silt
  • minimise water entering an excavation such as from rainfall or runoff
  • prevent contaminated water moving to a river or stream
  • dispose of water that enters the excavation including any silt control interventions
  • maintenance plan for silt control interventions and water quality monitoring plan

Where any of the above cannot be complied with then a BESPOKE ENVIRONMENTAL PERMIT is required.

What does this actually mean in practice?

All sites should implement a water management plan to illustrate how they are controlling the risk of pollution, protecting the aquatic environment from the ingress of material such as soil, silt, oil, chemicals or concrete wash waters.

However, the reality is that following the new guidance, the majority of UK construction projects will need to hold a Bespoke Environmental Permit or a Controlled Activity Regulation Licence for the drainage of site waters into a stream, river or to ground.

In Scotland the minimum requirement is a pollution prevention plan that should be integrated into the method of works such as minimising soil striping and monitoring is focussed on suspended solids, turbidity and pH. No further risk assessment or water quality testing would be required unless the site has known contaminants.


Emergency silt response kit

In England and Wales there is a need to assess the risk of the discharge and the environmental permit application requires:

  • a management system including pollution prevention plan (source and pathway assessment as well as pollution control mechanisms)
  • discharge mechanism and rate from site as well as the flow rate of the receiving water
  • surface water analysis to complete the prescribed regulatory risk assessment screen tests 1 to 4

It is recommended that you engage with the local regulatory team early in the process as the determination of a permit application can be lengthy taking several months.

Sites that do not hold a permit or licence are vulnerable to regulatory action. Where pollution occurs, there is the risk of enforcement action including a fine or custodial sentence, plus the loss of reputational benefit. Equally, any unplanned remedial measures may affect the operation of a site and delay or even stop works.

Don’t panic! We can help. frog environmental specialise in water management and silt control. We are able to help you at all stages in your project including pre-tender advice.

We act for and guide construction companies of all shapes and sizes and pride ourselves on offering practical, site specific and customer focussed solutions.

We can help you at all stages in your project including pre-tender advice and can provide bespoke, practical solutions.Our services include:

  • Site Review – For numerous clients we carry out a short site review and letter reporting process. This is designed to outline risks of silt pollution from site, identify control measures and permitting requirements
  • Silt Control Products – We supply silt management products made from natural sustainable materials including Silt Mats, Wattles and Floc Mats™ to reduce and even prevent silty run-off. Bubble Curtains can be used in watercourses to limit downstream pollution whilst our WaterLynx™ flocculants designed to help remove fine clay particles from muddy water have secured regulatory approval for their use in some of the most sensitive UK environments.
  • Water Management Planning – We risk assess developments and create Pollution Risk Assessment and Pollution Control documentation, to form your site water management plan.

Contact us for expert help

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