Excavating the void
Site conditions can vary from entirely impermeable clays through bands of materials such as sands and gravels overlying clays to disturbed, highly variable and contaminated ground as a result of previous land use.
It is essential that you can prove the structural integrity of the proposed mooring area. To do this you will need geotechnical information on ground strength and water retention, at and below the level to be excavated to. (This is not the same as information on the material to be excavated.)
Should the basin be over excavated to allow for the construction of the liner or for the removal of any materials contained underneath it, the geotechnical investigation and supporting calculations should be based on the differential head of water in the canal as measured above the excavated floor level of the basin.
Re-using or disposing of the excavations and dealing with contamination
At most mooring schemes which require excavation, it may be possible to landscape some of the excavated material on site to avoid the costs of disposal. The condition and cleanliness of the excavated material will determine whether it can be re-used on site or must be removed. Our local team can advise on the potential for transporting the spoil by water.
Procedures for assessing and handling contaminated soil are strictly regulated. Procedures which are laid down by Defra and the Environment Agency follow a risk assessment basis. The principles of investigation and remediation of contamination are the same as for any development site but potential contaminants from the soil must be prevented from leaching into the waters which are a sensitive receptor. Contaminating materials, including excavated contaminated soils, should not be stored or placed in areas subject to flooding.
Some contaminated soil may be 'cleaned' and re-used on site. The re-use or removal of excavated material is regulated by the Environment Agency and you are advised to consult with them at an early stage. It may also be subject to approvals of the local authority (planning and/or environmental health) dependant on the nature of the re-use and is an integral component of the planning application.
The potential impacts of opening up old basins and arms as part of any development must be considered since materials originally used to fill them may be contaminated. The creation of new pathways and landscaping on contaminated soil will also need careful design.
Useful references and links
- "Site Investigation in Construction Series 1 to 4" (1993) ICE Site Investigation Steering Group, Thomas Telford, London Institution of Civil Engineering www.ice.org.uk
- Environment Agency Model Procedures for the Management of Land Contamination (CLR 11) www.environment-agency.gov.uk
- Defra (Department for Environment, Food and Rural Affairs) Assessment of risks to human health from land contamination (CLR7) www.defra.gov.uk and www.environment-agency.gov.uk
- Government Planning Portal; www.planningportal.gov.uk www.communities.gov.uk
- "Brownfields - managing the development of previously developed land. A client's guide (C578)" by DW Laidler, AJ Bryce, P Wilbourn published by CIRIA (The Construction Industry Research and Information Association) www.ciria.org.uk
- "Breaking old ground; BURA Guide to Contaminated Land Assessment & Development" (British Urban Regeneration Association) www.bura.org.uk
- "Land Contamination - Management of financial risk (C545)" by Finnamore J, Denton B and Nathanail, P. Published by CIRIA (The Construction Industry Research and Information Association) www.ciria.org.uk