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An Introduction to Landfill Leachate Extraction

The subject of leachate extraction embraces:

• the wells and boreholes within the landfill into which the leachate collection system conveys the leachate;
• the pump systems which extract the leachate from the wastes;
• the systems which deliver the motive force to the pumps;
• the pipes/pipelines which convey the leachate to the collection tank, or treatment plant location;
• the monitoring and control systems.

Given the breadth of skills required to successfully achieve the extraction of leachate it is therefore not surprising that over the past 15 to 20 years since the emergence of the fully engineered landfill, a number of specialist leachate extraction contracting organisations have developed to fill the demand for these skills.

Existing technologies and products from closely from allied fields have been refined, and new products have been, and continue to be, developed in this industry. There is now a recognised range of technologies and products which are currently applied to leachate extraction.

What can be achieved in leachate extraction and progressive drawdown, was well demonstrated in a paper presented by Howard Robinson at the CIWM’s Annual Waste Management Exhibition and Conference, Torbay, June 2003. This paper (full version available on our downloads page) describes how the Arpley Landfill Site has been transformed in terms of leachate extraction and leachate level control to become a leachate management compliant site. An abridged version of Howard’s paper, which focuses on the leachate extraction aspects of the paper, is available here for downloading.

Download our paper “Best Available Techniques For Landfill Leachate Extraction And Pumping?” (Acrobat .pdf file) here.

Wells & Boreholes

The types of wells regularly utilised in leachate extraction are characterised as follows (listed in the approximate order of their first introduction):-

1. massive engineering structures in the form of rigid towers extending full height to the restored surface, and which were built during the late 1980 and early 1990’s to enable at least two dozen very deep vertical sided quarries to be infilled and continuously drained by pumping. A classic example is the Enderby Warren Quarry Landfill, Leicestershire, UK which was some 80 metres deep, and houses pumps to handle in excess of 300m³/day of leachate;
2. the most commonly used have been precast concrete chamber rings, in sizes between 600 mm and 1.8 m diameter, (sometimes larger) which were progressively raised with each lift of the waste, and into which electric pumps were most often inserted;
3. percussion driven boreholes, retrofitted into the waste, lined in drainage stone/filter textile and cased, before a pump is installed. Casings are normally steel initially but these can often be removed and replaced with plastics and stone packing may be added to act as a drainage and filter medium;
4. Proprietory HDPE well systems based upon designs developed initially in Germany, have been used on a number of UK sites. These systems are raised progressively in much the same manner as precast concrete wells, and being made from this plastic material are capable of withstanding greater settlement, and are not prone to corrosion.
5. Upslope risers are wells laid against the battered slopes which have become common to support the landfill lining. Upslope risers are assumed to suffer less from settlement damage than vertical wells, and the possibility arises for the adoption of these, that a connection may be feasible into the leachate under-drains, enabling the possibility of cleaning the leachate under-drainage system.

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