If you have a problem with a substance found in leachate, we are here to help you! Our fact files, which are based on publicly published UK government research, are unique. You can save huge amounts of time hunting down this information which is otherwise spread very widely in published papers in libraries and on research databases, and is only partially accessible from the web.

What Are Trace Contaminants?

Landfill leachate invariably contains a host of different substances in addition to the major substances present (COD, BOD, Suspended solids, Metals in solution, Salinity, Ammoniacal nitrogen etc), which although only dissolved in tiny quantities (parts per million (ppm) and parts per billion (ppb)) still may represent a potential hazard to the environment and public health due to their extreme toxicity. To make a distinction between much higher concentrations of the main contaminants which are present in parts per thousand and more, and these lower concentration but much more toxic substances, the term “Trace Contaminants” is applied.

National and international standards have been set for the maximum permissible concentrations of many of these toxic (or “dangerous”) substances in drinking water, and under the EU Groundwater Directive no such substances are in principle permitted to be discharged to groundwater. In the UK these substances are often described as List 1 Substances, however since the creation of that list many more substances and species of contaminants have beeen identified which can now be analysed, and routinely reported upon within the description of “Dangerous Substances” as now applied by the environment Agency (EA).

How Does a Person Tasked With Deciding Whether a Leachate Contains Significant Quantities of Trace Contaminants Find Out About Them?

The first step is to analyse for them. Contact your water quality analytical laboratory and request a list of the subtsances they analyse when asked to complete what are variously called “List1”, “Dangerous Substances”, “or Comprehensive Prescribed List” analysis reports. Before you head off to the landfill to collect the necessary samples you will also need to await a package of special bottles which te analytical laboratory staff will prepare and send to you. Some of the se bottles wil include fixitive chemicals designed to prevent decay of some substances while en-route to the analytical test laboratory.

OK. So the Analytical Report Showed Some Dangerous Chemicals to be Present at Trace Concentrations. Does it matter? What Now?

Most leachates, especially those from older landfills, will show the presence of some of these chemicals. The next step is to decide whether they present a real hazard when the discharge route is taken into account. To do that we are writing and publishing a series of Leachate Contaminant Fact Files, each one of which will discuss the nature of a hazardous substance, or species of substances, and identify research papers written on the contaminant, to assit the reader in deciding whether the presence of the substance is significant and assist them in the decision either to treat the leachate to remove the susbtance, or to make a scientifically based case to the regulatory body or waste water treatment plant operator that negligable risk exists from the dangerous chemical at the concentration seen during water quality analysis.

Our first Leachate Contaminant Fact Files are Now Available. For more information, and purchase for immediate download, please click on the linked text below:

Leachate Trace Contaminant Fact File 1 – PCBs

Leachate Trace Contaminant Fact File 2 -Phenols

Leachate starts as rainfall.

Rain falling on the top of the landfill is the main contributor to the generation of leachate, and is by far the largest contributor for modern sanitary landfills which do not accept liquid waste. In old unlined and un-engineered landfills, some leachate is produced from groundwater entering the waste. Some, additional leachate volume is produced during waste decomposition, and some additional surface water will sometimes run onto waste from its surroundings.

The decomposition of carbonaceous material produces some additional water, and a wide range of other materials including methane, carbon dioxide and a complex mixture of organic acids, aldehydes, alcohols and simple sugars, which dissolve in the leachate cocktail.

The precipitation percolates through the waste and takes in dissolved and suspended components from the biodegrading waste, through physical and chemical reactions.

Most landfills are designed to minimise the amount of leachate they create during their lifetimes. However, there are good scientific reasons to suggest that it would be better to flush all landfills out and to do this, would produce more leachate, faster. Landfills where the latter philosophy is adopted, are called, “bio-reactor” landfills. In Europe, bioreactor landfills are effectively prohibited by EU directives, leading them to be called “dry tombs” by some, due to their rapid capping, and minimised leachate production.

The environmental risks of leachate generation arise from it escaping into the environment around landfills, particularly to watercourses and groundwater. These risks can be mitigated by properly designed and engineered landfill sites. Such sites are those that are constructed on geologically impermeable materials or sites that use impermeable liners made of  geotextiles  or engineered  clay . The use of linings is now mandatory within both the United States and the European Union, except where the waste closely controlled and genuinely inert.

Most toxic and difficult materials are now specifically excluded from landfill. However, despite much stricter statutory controls the leachates from modern sites are currently stronger than ever. They also contain a huge range of contaminants. In fact, anything soluble in the waste disposed will enter the leachate. Within the lists of substaces present in leachate are very low concentrations of “trace contaminants” which can have quite strongly contaminating effects. These are nowadays most often derived  from materials in household and domestic retail products which enter the waste stream perfectly legally.

Unfortunately, the leachate draining from most landfills will continue to reflect the contaminants of past years, when regulatory controls were less.

These substances in include extremely low concentrations of heavy metals (for example from batteries), herbicides and pesticides (as used in gardens), etc. However, leachate is becoming less contaminated with difficult substances as time goes forward, and public awareness, recycling and increased statutory control over these substances, throughout the industrialized world is making leachate less harmful in this respect.

“Leachate has a very high ammoniacal nitrogen concentration”

The concern about environmental damage from waste leachate, largely arises from its high organic contaminant concentrations and much higher ammoniacal nitrogen than commonly found in any other organic effluent.  Pathogenic   microorganisms and toxic substances that might be present in it have in the past been described as the most important. However, pathogenic organism counts reduce rapidly with time in the landfill, so this only applies to the youngest leachate and leachate is seldom removed from the landfill in this condition.

One of the most comprehensive scientific studies yet undertaken worldwide on leachate, was published by the United Kingdom, DOE., in 1995. It is titled: “A review of the composition of leachate from domestic wastes in landfill sites”; Department of Environment Research Report No. CWM 07294, and still provides much essential data on the range of contaminands present in Municipal Solid Waste, and Commercial and Industrial Waste landfill leachate.

The purpose of this section of our web site is to inform newcomers about the most common liquid referred to as, leachate – landfill leachate.

This whole web site has been written to answer the question; “What is leachate?” and how to ensure it does not cause pollution, in detail. So, we suggest that byexploring our site further you will find a more comprehensive answer to “What is leachate?, if you need it.

For now, we will give you the most concise answer to the question of what leachate is, by providing our definition of leachate below:

The Definition of Leachate

Leachate is the liquid that drains or ‘leaches’ from a landfill. It varies widely in composition regarding the age of the landfill and the type of waste that it contains. It usually contains both dissolved and suspended material.

In fact the term “leachate” is so often applied to landfill leachate, both within the waste management industry and outside, that it is easy to forget that leachate is the term used for any liquid produced by the action of “leaching”. Leaching occurs when water percolates through any permeable material.

Having Read the Answer to “What is Leachate” Most People Dislike It!

Once many people have the answer to their first question of; “What is leachate?”, they realize that it is pretty unpleasant stuff (it smells, can cause pollution etc.). Naturally,they often react by saying they would rather it was not produced. “Let’s not have any around here then”, being a common sentiment expressed!

In most temperate and tropical climates, landfills will unavoidably produce some leachate. To stop producing any leachate would in most cases entail sending “zero waste to landfill”. At the present time only a very few (probably less than a dozen) sizeable communities have been able to achieve what is known as “zero waste”. That means, for most of  us that there will still have to be actively operating landfills in our area.

No matter how hard landfill designers and operators try to avoid generating waste, through waste reduction, re-use, recycling, composting. Not to mention the many other methods of waste pre-treatment prior to landfilling. Landfilling will continue for many years yet, and thus leachate generation and its safe disposal without causing pollution, is a problem which is here to stay.

Even if all the landfills could be closed, and the creation of new leachate from rainfall falling on open (operational) landfill phase surfaces, could be stopped today, we would still have to manage the leachate from both the present operational sites,and all the old closed landfills.

There are many thousands of existing operational and closed landfill sites, which will continue to produce leachate for generations. For that reason following good practice in leachate minimisation, collection, treatment and disposal, is a very important part of the job of any landfill operator.

Steve Last BSc MICE CEng MCIWM

This website is created and maintained by Steve Last in support of his consultancy service IPPTS Associates.

IPPTS Associates have the capability (through our associate arrangements) to advise on all aspects of landfill leachate management, from leachate management option studies to leachate treatment plant design, installation supervision, and commissioning.

Our capabilities include:

• Environmental consenting (previously known as Waste Permitting (including IPPC applications))
• Best Available Techniques (BAT) assessments
• Full process design, installation, tendering, project management, specification, tendering, contract administration, construction supervision, commissioning and operation, of leachate collection and treatment systems (through associate arrangements)
• Commissioning of completed leachate treatment plants
• Troubleshooting of process problems for existing biological leachate treatment plants
• Advice on updating and refurbishing old leachate treatment facilities
• Training of biological leachate treatment plant site operators.

See more at our environmental compliance consultancy business website.

Other landfill related websites supported by this and associated authors are:

• The Landfill CQA weblog
• The Landfill Gas website – for landfill gas information and technical developments
• The Methane Stripping website – for techniques for the removal of dissolved methane from leachate extracted from gassing landfills prior to sewer discharge

Other landfill related web sites include:

• The Mechanical Biological Treatment website – to understand the new waste treatment techniques required to pre-treat the organic content of wastes and comply with the EU Landfill Directive
• The Anaerobic Digestion (AD) web site to learn about the subject of biogas digesters
• The Composting Web Site – for commercial and municipal composting.