"Given time, it is the ambition of every lake and pond to become dry land"
Soil washed downstream by rivers, migration of soil from the banks, organic matter from dying vegetation and leaf litter and waste from fish and wildfowl all build up in a lake or pond. Over time the lake will become eutrophic with very little oxygen at the bed to oxidise organic waste, in these circumstances the waste build up increases until emergent plants can colonise the surface. Eventually small trees and scrub will become established and eventually the lake will have fulfilled its ambition.
Periodically it is necessary to remove this build up of silt to extend the life of the water body and make it more biologically diverse supporting a greater variety of flora and fauna.
Silt removed from a lake or water body is classified as waste by the Environment Agency, and as such is subject to the waste regulations. This means that the silt disposal process is controlled by legislation. (See waste regulations section)
The first stage of the desilting process is to carry out a survey to establish the depth, and to analyse the chemical composition of the silt to characterise it for disposal, the silt may contain heavy metal contamination or hydrocarbons from road runoff that make it hazardous and so cannot be spread to land without remediation. When the quantity and quality of the silt have been established then a disposal plan can be formulated for EA permitting purposes.
We use various techniques to remove the silt and transport it to a disposal area.
Floating dredgers work on the surface of the water and either pump the silt ashore using underwater dredge pumps. Or they are excavators mounted on floating platforms to dig the silt and cast it ashore or into barges for disposal. The floating excavator can also feed a pumping system.
If the water can be drained out of the lake then the silt can be excavated and hauled in dump-trucks to the tip site or the silt can be loaded into a pumping system where it is screened and macerated before being pumped to a disposal area.
Pumping silt reduces the impact of the works because there are not dumpers running backwards and forwards to the tip area.
We have carried out various hazardous waste remediation projects where the quality of the silt has been changed to remove the pollutants, so allowing the silt to be disposed of on site.
The costs for off site disposal of silt are very high because of haulage, land fill tax and tipping fees. Before the silt can be transported off site it must be dried, this requires additional equipment and storage space. Silt can be composted by the addition of green waste to condition it, the composting process is controlled by legislation but the material that is ultimately produced is considered a product, not a waste and so can be used in different ways.
For more information or to discuss your particular requirements call Chris Keech on 01460 279200.