Presentation on theme: "What is a Landfill ? A secure landfill is a carefully engineered depression in the ground (or built on top of the ground) into which wastes are put. The."— Presentation transcript:
What is a Landfill ? A secure landfill is a carefully engineered depression in the ground (or built on top of the ground) into which wastes are put. The aim is to avoid any hydraulic [water- related] connection between the wastes and the surrounding environment, particularly groundwater. A landfill can be imagined as a bathtub in the ground; a double-lined landfill is one bathtub inside another. Bathtubs can leak in two ways: out the bottom or over the top.
What role does a Geotechnical Engineer play in a Landfill waste containment facility ?
WHAT IS THE COMPOSITION OF A LANDFILL? There are four critical elements in a secure landfill: a bottom liner, a leachate collection system, a cover, and the natural hydrogeologic setting. The natural setting can be selected to minimize the possibility of wastes escaping to groundwater beneath a landfill. The three other elements must be engineered. Each of these elements is critical to success.
What is Landfill Leachate ? Leachate is any liquid that, in passing through matter, extracts solutes, suspended solids or any other component of the material through which it has passed. Leachate is a widely used term in the Environmental sciences where it has the specific meaning of a liquid that has dissolved or entrained environmentally harmful substances which may then enter the environment.
A landfill is a bathtub in the ground, and a bathtub can leak two ways: it can leak through a hole in the bottom (failure of its bottom liner), or it can fill up with fluid and spill over its sides. Either way, it's bad news. The basic problem is the fluid. If a landfill begins to fill up with fluid, the weight of the fluid puts pressure on the bottom of the landfill, increasing the likelihood of bottom liner failure, so any fluid inside a landfill is a potential source of trouble.
First step is to contain the fluid from escaping into the ground. Solution The Bottom Liner System
WHAT IS A BOTTOM LINER? It may be one or more layers of clay or a synthetic flexible membrane (or a combination of these). The liner effectively creates a bathtub in the ground. If the bottom liner fails, wastes will migrate directly into the environment.
To effectively serve the purpose of containing leachate in a landfill, a liner system must possess a number of physical properties. The liner must have high tensile strength, flexibility, and elongation without failure. It is also important that the liner resists abrasion, puncture, and chemical degradation by leachate. Lastly the liner must withstand temperature variation, easily installed, and economical.
Clay Liner is mostly a sodium bentonite layer. The property of swelling also makes sodium bentonite useful as a sealant, especially for the sealing of subsurface disposal systems for spent nuclear fuel and for quarantining metal pollutants of groundwater. Similar uses include making slurry walls, waterproofing of below- grade walls, and forming other impermeable barriers, e.g., to seal off the annulus of a water well, to plug old wells, or to line the base of landfills to prevent migration of leachate.
Bentonite is an absorbent aluminium phyllosilicate, essentially impure clay consisting mostly of montmorillonite. There are different types of bentonite, each named after the respective dominant element, such as potassium (K), sodium (Na), calcium (Ca), and aluminum (Al).
Geosynthetics plays a major role in design of the landfill liner system.
Geomembranes are a kind of geosynthetic material made up of an impermeable membranes. Their use includes lining canals, ponds and also waste containment.
Geosynthetic clay liners (GCLs) are fabricated by distributing sodium bentonite in a uniform thickness between woven and non-woven geotextiles. Sodium bentonite has a low permeability which makes GCLs a suitable alternative to clay liners in a composite liner system. Geotextiles are used as separation between two different types of soils to prevent contamination of the lower layer by the upper layer. Geotextiles also act as a cushion to protect synthetic layers against puncture from underlying and overlaying rocks.
Geomembranes are made of various materials. Some common geomembrane materials are Bituminous Geomembrane (BGM), Ethylene Propylene Diene Monomer (EPDM), Low-density polyethylene (LDPE), High-density polyethylene (HDPE), Polyvinyl Chloride (PVC), Polyurea and Polypropylene (PP).
Each type of geomembrane material has different characteristics which affect installation procedures, lifespan and performance. For example, PVC geomembranes are very flexible and as a result can conform to uneven surfaces without becoming punctured. EPDM rubber is highly flexible and has excellent UV and weathering characteristics, but is not suitable for use in long term contact with oils and hydrocarbons. LDPE, on the other hand, is very susceptible to UV radiation, and therefore should not be used in applications where it will be exposed or else it will become brittle and fragile. HDPE has excellent chemical resistance, but is inflexible and suffers from environmental stress cracking and thermal stresses.
So much for just containing the landfill leachate. Second step is the collection of leachate from the landfill site by the leachate drainage system.
The leachate drainage system is responsible for the collection and transport of the leachate collected inside the liner. The pipe dimensions, type, and layout must all be planned with the weight and pressure of waste, and transport vehicles in mind. The pipes are located on the floor of the cell. Above the network, lies an enormous amount of weight and pressure.
The collection pipe network of a leachate collection system drains, collects, and transports leachate through the drainage layer to a collection sump where it is removed for treatment or disposal.
Bibliography: Wikipedia, The free encyclopedia. Introductory Geotechnical Engineering An Enviromental Perspective, Hsai-Yang Fang, John Daniels. Geotechnical Engineering, Sashi K Gulhati, Manoj Datta. Environmental Geotechnics, proceedings of the third international Congress on Enviromental Geotechnics/ Lisboa /Portugal/ 7-11 September 1998 Edited by Pedro S. Seco e Pinto