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Lesson 3: Sanitary Landfills and Leachate

Lesson 3: Sanitary Landfills and Leachate. Objectives. Students will understand that soil layers and groundwater are affected by leachate. Students will understand how geotextile fabric relates to the sanitary landfill structure. Nevada State Standards: Grades 9-12.

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Lesson 3: Sanitary Landfills and Leachate

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  1. Lesson 3: Sanitary Landfills and Leachate

  2. Objectives • Students will understand that soil layers and groundwater are affected by leachate. • Students will understand how geotextile fabric relates to the sanitary landfill structure.

  3. Nevada State Standards:Grades 9-12 • N.12.C.5 Students know soil, derived from weathered rocks and decomposed organic material, is found in layers. E/S • N.12.B Students understand the impacts of science and technology in terms of costs and benefits to society.

  4. Background* • Groundwater, the source for wells and springs, supplies drinking water to over half of the people in this country and over 90% of the residents in rural areas. • Of the population served by public water supplies, close to 40% rely on groundwater. • Geological formations which yield significant amounts of groundwater are called aquifers. • The top of the groundwater layer is called the water table. *http://cwi.css.cornell.edu/TrashGoesToSchool/Landfill.html

  5. Background • Traditionally groundwater has been assumed to be free from contamination, however, numerous discoveries in recent years of toxic chemicals in well water have proven this assumption to be false. • Groundwater contamination from chemical dumpsites tend to attract the greatest public attention. • A number of other sources including landfills, septic systems, pesticides, and underground storage tanks also can be significant sources of contamination.

  6. Leachate and Factors Affecting the Composition of Landfill Leachate Include: • Water percolating through landfills produces leachate. • Leachate may contain undesirable or toxic chemicals. • Water Characteristics: pH, temperature, and amount. • Soil characteristics under the landfill: permeability, depth and thickness of geologic strata, and mineral content.

  7. Factors Affecting the Composition of Landfill Leachate Include: • Landfill material: Is it biodegradable or non-biodegradable? Is it soluble or insoluble? Organic or inorganic? Liquid or solid? Toxic or nontoxic? • Landfill conditions: The pH, temperature, degree of ongoing decomposition, moisture content, climate, and landfill age.

  8. Sanitary Landfills and Leachate • Modern sanitary landfills are constructed to prevent leachate contamination of groundwater or surface waters. • The bottom of the landfill is lined with impermeable layers, and the leachate is collected and treated before being released to the environment.

  9. Leachate and Groundwater Contamination • The risk of groundwater contamination by any leachate that is not caught by collection systems is determined by the following factors: • Depth of the water table • Concentration of contaminations • Permeability of the geologic strata, type of geologic strata • Toxicity of contaminants • Direction of groundwater flow

  10. Leachate Containment and Collection Example

  11. Leachate Containment and Collection Example

  12. Vocabulary • Leachate: water/drainage that can pick up chemicals and microorganisms as it percolates through landfills, which may be undesirable or toxic. • Permeability: the ability to move through. • Aquifer: geologic formations which yield significant amounts of groundwater.

  13. Vocabulary • Water Table: the top of the groundwater layer. • Landfill Liner: a system of physical barriers in a landfill designed to prevent toxic leachate from reaching the groundwater.

  14. Vocabulary • Geotextile Fabric: this specially designed fabric allows moisture to pass through while filtering out soil. It allows leachate that may filter through the soil layer to reach the gravel layer. Piping within the gravel layer then pumps and removes the leachate for treatment. • Sanitary Landfill: constructed to prevent leachate contamination of groundwater or surface waters. The bottom of the landfill is lined with impermeable layers, and the leachate is collected and treated before being released to the environment.

  15. Useful Links • “Natural Attenuation and Treatment of Landfill Leachate” • http://www.bio.vu.nl/vakgroepen/mcp/research/jubhar/Jubhar.html • “How Landfills Work” • http://science.howstuffworks.com/landfill.htm/printable

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