Sediment

Sediment Surveying, Sampling and Characterisation

Exo Environmental is specialised in surveying and sample taking of sediments (often referred to as silts). These sediments can consist out of various particle sizes, being fine clays to course gravels. We utilise a range of different sample taking methods that are proven effective in different environments. We have cooled storage and transport facilities for the samples and work together with accredited and independent laboratory for a wide range of chemical and physical analysis. All our surveying and sampling is carried out according to the guidelines set out by the Environment Agency (EA), Marine Management Organisation (MMO) and Centre for Environment, Fisheries and Aquaculture Science (CEFAS). The analytic results can be assessed on human health risk, phytotoxicity and other thresholds to determine potential risk and beneficial reuse.

Sediment Dewatering

The dewatering of dredged sediment is an operation that is generally required subsequent to hydraulic dredging to enable the re-use or further transport of dredged sediment. There are four general processes of solid-liquid separation; natural drainage and evaporation, centrifugation, filtration and all other processes. In the dewatering or separation process modern-day flocculants and coagulants are often used to aid the dewatering. The two additives allow fine fractions to clump together, increasing the efficiency of the dewatering process and reducing the turbidity of the discharge water. A team of experts is available to provide advice on dewatering processes.

Geotube, geotextile bag, geotunnel

Sediment Treatment

There are several reasons why sediment might require treatment; the two foremost are to improve the chemical or the physical qualities of the sediment to enable re-use.

  • Chemical quality either relates to contaminations or to nutrient loads in the sediment. The treatment of dredged sediment could be a cost effective option to enable the risk free reuse of sediment. Qualitative improvements could be made to the availability of heavy metals (for example lead, mercury and nickel), organic parameters (for example herbicides, pesticides, PCB’s and hydrocarbons) and nutrients (for example nitrates, phosphates and potassium) in the sediment.
  • Improvements to the physical characteristics can be made, when dealing with physical contamination of the sediment. Physical objects, for example debris, waste, but also shells and wood can be screened out. Another important physical contamination of sediment could be asbestos.
  • Sediment can be screened to produce different grades of materials based on the fraction sizes. The physical characteristics of sediment can be improved for engineering purposes. By adding aggregates or other additives sediment can be modified physically. Sediment could be made beneficial for foundations, flood embankments or road construction.

Beneficial reuse of sediment

Under the European and UK Waste Framework Directive 2008, sediment is classified as a waste, there are two relevant waste catalogue codes:

  • 170505 “Dredging spoil containing dangerous substances”
  • 170506 “Dredging spoil other than those mentioned in 17 05 05”

Because sediment is considered a waste, clients often find dealing with arising sediment is a costly challenge. Therefore in recent years, the ‘disposal’ of sediment is no longer a feasible option because of the significant cost involved. Sediment can nearly always be beneficially reused, if it is contaminated or not. Sediment can be reused in a range of different options reuse options for example:

  • Creation of habitats: wetlands, mudflats and saltmarsh
  • In-channel applications
  • Landscaping purposes
  • Flood embankments
  • Spreading on agricultural land (SR2010 No4)
  • Side casting (D1 exemption)
  • Other infrastructure (SR2010 No7 or No8)
  • Land reclamation (SR2010 No5, No9 and No10)

Exo Environmental is a Licensed Waste Operator, and is able to manage your waste disposal or reuse.

Sediment Source Control

Sediment source control is of major importance to improve water quality and to reduce the frequency of dredging. There are several major sources of sediment, for example inputs from the tidal regime, deposition from bank erosion and agricultural run-off. Other sources can be drains, outlets and accumulation of vegetation. Source control is an activity that requires equal attention as the actual dredging process.

Exo Environmental can provide a wide range of services including:

  • Surveying and sediment sampling
  • Sediment analysis and assessment
  • Consultation of the sediment applications
  • Sediment engineering
  • Application of statutory consents
  • Waste management applications
  • Landowner consultation
  • Sediment source assessment
  • Erosion protection design
  • Feasibility studies
  • Catchment sensitive farming consultation
  • Management recommendations

For further information and advice please don’t hesitate to contact us.