Sanitary Landfill and Leachate

I was blogging recently about sanitary landfill leachate when from a reader's query it became clear that they were not clear about what a sanitary landfill comprises. In this article I set out to put that right.

Migration Hazards at a Sanitary Landfill (Image: Masterplan
for the Aftercare of Abandoned Landfills, Van Vossen, Gravesteijn,
Kasma  and Vos; proceedings Sardinia 95, 5th Sardinia Landfill
Symposium Cagliari, Italy)

The standard definition of a Class III or "Sanitary Landfill" originates in North America and the term has spread around the world from that source. It is, as defined in the US, a landfill that accepts household garbage and is normally lined below to reduce the escape of leachate to an environmentally acceptable rate, operated to minimize leachate generation and keep the waste as dry as possible, and capped as each area of the landfill is completed - again to keep leachate to a minimum but also to allow efficient collection of the landfill gas the landfill produces. The best sanitary landfills also have a recycling center at the site or the waste passes through a recycling center before it reaches the sanitary landfill. The recycling center these days often includes processing which separate waste types and process the waste, and comprehensive centers where waste is reduced, recycled and reused are called MRFs, and some are also known as MBT Plants.

The modern sanitary landfill is lined in the US with multiple layers to protect soils and the water bearing aquifers underneath. The in the US liner is composed of multiple natural layers and an impenetrable plastic (HDPE) or similar material. The purpose of the liner is to hold the waste for as long as possible collect all the "garbage polluted rainwater" (known as leachate) so that it can be extracted and treated. In Europe and worldwide the plastic lining is usually a single layer of thicker material than is usual in the US.

The new environmental centers being built for many sanitary landfills offer the opportunity for the community to become a more sustainable community. It will not only enhance the area's management of its waste but will also provide state-of-the-art and innovative recycling and in many cases the production of renewable energy.

Sanitary Landfills in More Detail

In short sanitary landfill is simply a general description of a type of landfill, it is the commonly accepted method of controlled disposal of municipal solid waste (refuse) on land in most countries. The method was first used in England from 1912 (where it has was then called controlled tipping, and is now called controlled landfilling). Waste is deposited in thin layers (up to 1 metre, or 3 feet deep) and within hours compacted by heavy compaction machinery (known as "compactors" these are similar to bulldozers but instead of having tracks have steel cutting wheels to break up the waste). Several layers of waste are placed and compacted on top of each other over a period of a day to several days, to form a refuse cell (up to 3 metres, or 10 feet, thick).

At the end of each day the compacted refuse cell is covered with a layer of soil material (or similar) to prevent odor, keep rats out of the waste, and prevent windblown litter from being blown of the site. All modern landfill site locations are carefully selected and prepared before the waste is placed. They are sealed with impermeable synthetic bottom liners to prevent pollution of groundwater from leachate or other environmental problems.

When the landfill is completed, it is capped with a layer of low permeability material such as a clay, or a synthetic liner, in order to prevent as much water as possible from entering. A final topsoil cover is placed, compacted, and landscaped, with various forms of vegetation being planted to reclaim the surface for the planner after-use.

Traditional landfills, before sanitary landfills were introduced were referred to as “open” or “polluting” dumps, simply containing un-engineered sites with waste under the ground. Such sites potentially allow the waste by-product called leachate to enter and contaminate groundwater and other water sources. They also attract rodents, insects and other disease-carrying vermin. Other negative effects of open dumps include emission of air pollution, odors and the creation of potential fire hazards. In a sanitary landfill these risks are partly eliminated, or at least deferred thanks in part to protective liners and monitoring systems that ensure there is no harm done to the environment, for just as long as the leachate is removed and treated.