To satisfy their request we have written this post in which we have tried to answer their search by providing general information about leachate, and how it is present in landfilled waste, affects landfills, and is collected.
Leachate landfills are all landfills in areas which are not so arid as to not produce any net free liquid which becomes leachate. Very few landfills never produce leachate. Even landfills in arid areas produce leachate in wet weather conditions, although such events may be few and far between.
Leachate landfills will also continue to produce leachate for many years after they are capped, restored and closed for the acceptance of waste. In fact most landfills will be monitored for at least 30 to 40 years after closure, to ensure that no leachate (or landfill gas) escape into the environment and present a risk to the communities surrounding the landfill site.
In older landfills and those with no membrane between the waste and the underlying geology, leachate is free to egress from the waste directly into the groundwater. In such cases traces of leachate will be often found in nearby springs and streams or rivers.
As leachate first emerges it is often black in colour, anoxic and may be effervescent with dissolved and entrained gases, for a short time after it leaves the landfill. Over some hours of exposure to the air, it becomes oxygenated and it tends to turn more cloudy and brown, or yellow, because of the presence of Iron salts in solution and in suspension
Most landfills containing organic material will produce methane , some of which dissolves in the leachate. This could in theory be released in confined spaces in the treatment plant, or sewers. All plants in Europe must now be assessed under the EU ATEX Directive and “explosion risk zoned” where explosion risks are identified by doing a risk assessment. This is to prevent future accidents. However, the most important requirement is the prevention of the discharge of dissolved methane from untreated leachate, when it is discharged into public sewers. Most wastewater treatment authorities limit the permissible discharge concentration of dissolved methane to 0.14 mg/l, or 1/10th of the lower explosive limit. This usually require methane stripping from the leachate.
More modern landfills in the industrialized nations (often called sanitary landfills) have some form of low permeability liner (membrane) separating the waste from the surrounding ground to reduce leakage of leachate into the geology to very low levels. In such sites leachate must be collected.
A leachate collection system is provided comprising a series of pipes laid on the lining in the base of the site, to convey the leachate to a storage or treatment location .