Why is Leachate from Landfills of Concern?

OK. So you want to know why is leachate from landfills of concern. The reasons why leachate from landfills is of concern are many and are best considered by first discussing what landfills contain and the escape pathways leachate containing those substances may follow.

A leachate polluted lagoon. No wonder Leachate from Landfills is of Concern.
A leachate polluted lake – no wonder people see Leachate from Landfills as a big concern

Landfill leachate is formed when rainwater infiltrates and percolates through the degrading waste.

This highly contaminated water containing not only high levels of organic (biological) contamination, contains possibly thousands of in-organic chemicals as well.

Pathways of Leachate Escape

The pathways of escape from landfill to causing environmental damage discussed are:

  • seepage through the landfill containment liner in the ground,
  • flows which enter surface watercourses (ditches, streams, rivers and lakes).

When considering the second of these it is worth noting that the second type may occur even if the leachate is managed, if at any time the quantity treated does not keep up with the amount created. Over a period of time the excess leachate will build-up and once the leachate level exceeds the perimeter height, there will also be leachate escape.

Leachate Contaminants

A lot of the different materials that end up in landfills contain substances hazardous to the environment that are eventually released and seep into the soil and groundwater.

These substances are major hazards to the environment and they can persist for many years, before being flushed out by natural water movement.

A leachate treatment plant in operation.
A landfill leachate treatment plant in Cornwall which has been operating successfully for over 25 years.

Examples of Substances Which Are Of Concern If Found In Landfill Leachate

For example, think of electronics such as computers, batteries and televisions that get thrown out and end up in landfills. These products contain substances like arsenic, acids, lead and others which eventually end up in our environment and pose threats to public health.

Mercury is another toxic substance that frequently appears in landfills. It comes from fluorescent light bulbs and poses major health risks.

Inhaling even a small amount of mercury vapour can harm our kidneys and cause respiratory failure. via hcr-llc.com

The fact is that just about anything can end-up in landfilled waste.

The more dangerous substances are seldom thrown away in bulk into today's well-controlled landfills. But, the fact remains that small amounts do find their way in, and these “trace substances” can be highly dangerous to higher life (fish, mammals and man). This is true even if just a few parts per million are present from for example domestic battery disposal.

This is particularly of concern if these “traces” are found in drinking water. Most drinking water comes from either river abstraction. Of of groundwater from wells and boreholes.

A Recent Study Carried Out In The US Found Many Contaminants Of Concern

Sample bottles like these filled with leachate were analyzed for contaminants of emerging concern (CECs) including pharmaceuticals, industrial chemicals, household chemicals, steroid hormones, and plant/animal sterols.

In this US national-scale study, scientists provided an assessment of CECs in landfill leachate disposed offsite that has undergone treatment or storage processes (final leachate) at landfills across the United States. It was done to gain a greater understanding of this potential contaminant source to the environment.

Contaminants of concern (CECS) were found in all landfills tested, and numbers of CECs are rising as more electronic and electronic waste gets into landfills.

To better understand the composition of contaminants of emerging concern (CECs) in landfill leachate, fresh leachate from 19 landfills was sampled across the United States during 2011.

The sampled network included 12 municipal and 7 private landfills with varying landfill waste compositions, geographic and climatic settings, ages of waste, waste loads, and leachate production.

A total of 129 out of 202 CECs were detected during this study, including 62 prescription pharmaceuticals, 23 industrial chemicals, 18 nonprescription pharmaceuticals, 16 household chemicals, 6 steroid hormones. And, 4 plant/animal sterols. CECs were detected in every leachate sample. The total number of detected CECs in samples ranged from 6 to 82 (median = 31).

Scope Of The Study Re: Sampling Network Results

In the study, final leachate samples from 22 landfills were collected and analyzed for 190 CECs including pharmaceuticals, industrial chemicals, household chemicals, steroid hormones, and plant/animal sterols.

The sampling network included municipal and private landfills with varying landfill waste compositions; geographic and climatic settings; ages of waste, waste loads, and leachate production; and leachate management strategies. via usgs.gov

What Is landfill Leachate Generally Like?

Landfill leachate is characterised by high organic and inorganic pollutant concentrations, and is extremely toxic to the environment. The significant impacts of landfill leachate could be:

  • eutrophication of aquatic systems and
  • toxic effects on fauna which are caused by a variety of contaminants.

Due to its high toxicity, landfill leachate is a major threat for aquifer and surface water health status if it enters either.

Defining the Chemical Composition of Landfill Leachate

The exact chemical composition of landfill leachate depends on waste composition, climatic conditions, and the age and degradation rate of the solid waste.

Problems With High Ammonia and Organic Nitrogen

The major problem in landfill leachate treatment is the extremely high concentrations of ammonia and organic nitrogen (Bulc, 2006; Lavrova and Koumanova, 2010). via sciencedirect.com

Various treatment methods (physicochemical and biological) have been used, but [unless designed by experts with long-standing experience] they have high operational cost, or they produce dangerous by-products.

Regrettably in some cases, over ambitious designers and easily persuaded clients create leachate treatment plants which end-up being both costly and never work correctly, until later re-built or abandoned.

Landfill Leachate And Decomposition

When water percolates through waste, it promotes and assists the process of decomposition by bacteria and fungi. These processes in turn release by-products of decomposition and rapidly use up any available oxygen, creating an anoxic environment.

In actively decomposing waste, the temperature rises and the pH falls rapidly with the result that many metal ions that are relatively insoluble at neutral pH become dissolved in the developing leachate.

The decomposition processes themselves release more water, which adds to the volume of leachate.

Landfill Leachate And Normally Inert Materials

Leachate also reacts with materials that are not prone to decomposition themselves, such as fire ash, cement-based building materials and gypsum-based materials changing the chemical composition.

In sites with large volumes of building waste, especially those containing gypsum plaster, the reaction of leachate with the gypsum can generate large volumes of hydrogen sulfide. When released in the leachate it can cause odour problems.

It may also form a significant component of the landfill gas. If so, flaring must be by very efficient complete combustion or else a large odour problem can occur. A danger also exists that staff may be made ill or even killed by the toxic effects of even low concentrations of hydrogen sulfide in air.

Leachate Colour and The Difference Between Acetogenic (Fresher) and Methanogenic (Older) Leachate

The physical appearance of leachate when it emerges from a typical landfill site is a strongly odoured black, yellow or orange coloured cloudy liquid.

The back and darker leachate colours generally indicate the leachate is young leachate from the acetogenic phase of decomposition.

Leachates of a whiskey-like colour are usually older leachate which has undergone anaerobic digestion (decomposition without air (oxygen)). This type of leachate is called methanogenic leachate and often turns cloudy if shaken with air in a bottle.

Leachate Odour

The smell of acetogenic leachate is acidic and offensive and may be very pervasive because of hydrogen, nitrogen and sulfur-rich organic species such as mercaptans.

Methanogenic leachate usually has an earthy smell, not nearly as unpleasant of acetogenic leachate. However, methanogenic leachate is still highly toxic but in a different way. Methanogenic leachate usually exhibits a much higher ammonia and Chemical Oxygen Demand (COD) than the acetogenic leachate.

How Leachate Escapes Of Concern Occur At Older Landfills

In older landfills and those with no membrane between the waste and the underlying geology, leachate is free to leave the waste and flow directly into the groundwater. [If the landfill perimeter is over-topped the leachate may also drain into surface watercourses.]

In such cases, high concentrations of leachate contaminants are often found in nearby springs and flushes.

As leachate first emerges it can be black in colour, anoxic, and possibly effervescent, with dissolved and entrained gases. As it becomes oxygenated it tends to turn (cloudy)  brown or yellow because of the presence of iron salts in solution and in suspension.

Concern About Leachate If A Collection System [Or Leachate Treatment Plant] Fails

If a leachate collection system fails (or the Leachate Treatment Plant stops working), leachate levels will slowly build in a site. Eventually it may even over-top the containing membrane and flow out into the environment.

Rising leachate levels can also wet waste masses that have previously been dry, triggering further active decomposition and leachate generation.

Thus, what appears to be a stabilised and inactive site can become re-activated and restart significant gas production and exhibit significant changes in finished ground levels.

Leachate Recirculation

One method of leachate management that was more common in un-contained sites was leachate re-circulation, in which leachate was collected and re-injected into the waste mass.

This process greatly accelerated decomposition and therefore gas production and had the impact of converting some leachate volume into landfill gas and reducing the overall volume of leachate for disposal. via wikipedia.org

Approaches Taken By Landfill Designers To Limit Concerns About Landfill

Biological leachate treatment used to allay the reasons: why is landfill leachate a concern.
Successful Leachate Treatment Plant operating in Scotland for over 25 years.

Location restrictions are often imposed upon the sites chosen for landfills.

These ensure that landfills are built in suitable geological areas away from faults, wetlands, flood plains or other restricted areas.

“Composite” liners are chosen.

These include a flexible membrane (i.e., geo-membrane) overlaying at least two feet US (or 1 metre Europe) of compacted clay soil lining the bottom and sides of the landfill.

They are used to protect groundwater and the underlying soil from leachate releases.

Leachate collection and removal systems, and designed to sit on top of the composite liner and remove leachate from the landfill for treatment and disposal.

Groundwater Monitoring Requirements

Groundwater monitoring requirements are enforced in many areas, by the environmental regulatory authority (E.g. EPA in the US). The environmental regulator frequently requires testing groundwater and wells to determine whether waste materials have escaped from the landfill.

Closure and Post-Closure Care Requirements

Closure and post-closure care requirements are used to allay concern about the effects of leachate on the environment, include:

  • covering landfills and
  • providing long-term care of closed landfills.

Corrective Action Provisions

Corrective action provisions may be enforced by the environmental regulator to control and clean up landfill releases and achieve groundwater protection standards.

Financial assurance—provides funding for environmental protection during and after landfill closure (i.e., closure and post-closure care). via epa.gov

Conclusion To: Why Is Leachate From Landfills Of Concern

Landfill leachate can be contained with a  well-designed landfill for a long period of time.

It can be removed for treatment and the contaminants disposed of responsibly.

Nevertheless, there are many legitimate concerns about landfill leachate.

In fact largely due to this, EU policy, in common with support from many of the world's environmental experts, has resulted in a policy that landfill will only be used for the small amount of waste which remains after recycling. It is the final resort after failing to have recycled a material.


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