Landfill Settlement and Surcharge
As the waste mass decomposes, the waste infill material settles under its own weight to occupy less volume. This process is known as settlement.
Settlement in landfilled waste occurs due to loading and other processes including chemical and microbial actions. These processes are time-dependent, and are controlled by factors such as leachate composition, pH, temperature and moisture.
Settlement
As waste ages and decomposes the final landfill levels will settle to a lower level than that filled.
Settlement in landfilled waste, especially long-term settlement, is complex and difficult to predict in both magnitude and timing. Notwithstanding that, reasonably accurate estimates are commonly used.
Landfill sites operate under the terms of a Planning Permission which, amongst the matters controlled by the permission will be the final levels which the site is anticipated to meet after settlement often termed the "Settlement Contours".
Surcharge Contours
In order to ensure that the agreed final levels are achieved after the majority of the decomposition and related settlement have finished, it is common to agree that the final levels can be exceeded initially to a set of Surcharge Contours.
The degree of surcharge is termed a Landfill Surcharge Allowance.
It is conventional to have two sets of Landfill Contours agreed with the planning authority - often more commonly referred to as pre-settlement contours and post-settlement contours.
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