Control in Construction & River Restoration Projects

Richard Haine Co-founder frog environmental

• Design & manufacture control and water treatment products • Related consulting services • We work with research partners to develop new techniques for silt control and improve on existing approaches Topics covered in this presentation

• Introduction: the importance of silt control • Sources, pathways & receptors • Silt control principles • Techniques & tools to control silt • Water Lynx flocculants Why is silt control important? 4 key points:

• Protecting the Environment • Protecting Reputation • Planning Efficiency (avoiding delays) • Financial (preventing prosecution)

Sediment as a pollutant

£56,000 fine handed down in 2017 for a 25 minute pumping operation with no environmental impact Environmental Sentencing

Deliberate Reckless Negligent Low/No Culpability Company Size Large £450,000 to £250,000 to £140,000 to £25,000 to £3,000,000 £1,500,000 £750,000 £130,000

Medium £170,000 to £100,000 to £55,000 to £10,000 to £1,000,000 £500,000 £300,000 £50,000

Small £45,000 to £24,000 to £13,000 to £2,500 to £400,000 £220,000 £120,000 £20,000

Micro £9,000 to £3,000 to £1,500 to £500 to £95,000 £55,000 £30,000 £5,000 What is the impact of sediment pollution?

• Sediment is probably most common pollutant from construction projects • Sediment also fulfills vital functions in fluvial systems • Impact of mobilising sediment varies depending on the function of river and downstream receptors • Site specific approach with appropriate site investigations and mitigation

Silt Pollution Sources

• Direct disturbance of the river bed or bank • De-watering of excavations • Exposed ground and material stockpiles • Roads and haul routes and river crossings • Plant washing operations Pollution Pathways Receptors Principles: Erosion control Principles: Drainage control Principles: Silt capture Principles: Sediment Size Principles: Sediment Particle Size

Stokes Law – settling velocity

2 VS = d g(DS -1)/18n The density of the particle determines the velocity at which the particle will settle Monitoring

• Consented limits? • 50 mg/l TSS is commonplace • Often a visual test can be applied • Monitoring against baseline can be low tech and easy to implement Techniques for Silt Control

• Filtration • Ground infiltration • Manage in channel • Artificial silt capture channels • Settlement tanks • Settlement • channels • Increasing particle size

Techniques: Filtration Techniques: Filtration Techniques: infiltration to Ground Techniques: Infiltration to Ground Techniques: Limitations to infiltration Techniques: in channel management Techniques: in channel management Techniques: in channel management Techniques: in channel management Limitations to in channel capture

• Short circuiting and/or scour – you may generate • Difficult to capture everything • Flood risk to site (delays) • Wider flood risk • If encouraging natural settlement where does the silt end up?

Techniques: capturing sediments Techniques: Sediment Capture Channel Techniques: Settlement Ponds Techniques: Settlement Techniques: Polishing water after settlement ponds Techniques: Increasing particle size

The use of a flocculant to increase the size of fine silt and clay particles so they may be easily taken out of suspension

Techniques: Increasing particle size

Flocculation bridges between particles to increase their mass and cause faster settling

When might you use a flocculant? Small particle size Small treatment footprint

Techniques: Increasing particle size

Anionic: negatively charged – non-ecotoxic

Cationic: positively charged – ecotoxic

4 main aspects to consider:

• Testing soil & water chemistry

• Deployment (how much, what format, where?)

• Mixing time

• Capture of flocculated particles Techniques: Increasing particle size

Release rate:

How much floc is released

What is the fate in the environment?

Peer review shows breakdown products innocuous

Water lynx: Slow release gel block – lasts up to 3 months in channel

4 frog environmental products contain flocculant: Floc mats, Treated Geo Jute, Silt Net and Water lynx floc blocks

Floc Mat Silt Net Treated Geo-Jute Pipe Reactor Pipe Reactor discharge to sediment capture channel Sediments are trapped on natural fibers reducing TSS from 550mg/l to 9mg/l

Challenges with flocculant?

• Good potential to help control sediment pollution but no regulatory position statement • How do we promote best practice? • How to prevent poor practice when applying flocculants? • We want to start a dialogue: develop working group to assess risks and develop position statement with regulator

Summary PRINCIPLES: Control at Source! Minimise mobilisation and suspension

Analyse all silt sources, pathways & receptors – different rivers have different functions: understand the relationship with sediment

Site investigation: Assess flows, particle size, topography, drainage catchment

Assess available techniques & tools: lots of products available, make sure you have the right approach (and applying correctly)

Collect baseline data: develop monitoring plan, engage early (and proactively) with the regulator…Communicate the plan!

If using a floc: sample early, to allow the blend to be matched to site chemistry Silt Control Summary

Environmental Protection Protect Reputation Planning Efficiency Managing Financial Risk

Online resource: IECA, CIRIA, SEPA, the Rivers Trusts

• Frog environmental design and manufacture silt control products • We plan to develop a working group to develop position statement on flocculants

Richard Haine follow us @frogenv 07775 755 802 www.frogenvironmental.co.uk [email protected]