LEACHATE CONTROL FOR SANITARY LANDFILLS

Percolated rainwater and liquefied waste materials in sanitary landfills, if not controlled, seep to the bottoms and the lateral edges of refuse piles and migrate into surrounding soil and usable groundwater. Such escape without control is now almost universally forbidden. Controls are discovered, improved, and applied; but leachate continues to form, leaching persists, and barriers or treatments are neither fool-proof nor complete.

Virtually by definition, leachate has been considered to be the waterborne, dissolved organic and inorganic pollutants seeping in liquid form through solid waste landfills into surrounding porous soil materials and potentially to nearby, down-gradient, usable groundwater. The moisture may be derived from the waste materials placed in the landfill, but predominantly the volume is contributed by infiltrating and seeping runoff from local rainstorms. Gounaris, et al., however, have learned that about 40% of the total organic carbon and 50% of the total iron in leachate are in the colloidal, solid but unsettleable particles carried in the liquid leachate (4:18).

The mechanisms of leaching -- extraction of pollutants from solid materials into a passing fluid -- have been studied in detail by Webster and Loehr (12). The principal mechanism for extraction of metals from a solid, such as concrete or Portland cement, appears to be acidic solubilization (12:72

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tailed studies of 11 landfills in Florida, a state with ubiquitously high groundwater levels and karst topography, Reddi and Scarlatos (10) have concluded that modern barriers placed in landfills to retard leachate movement and escape are extremely effective. Barriers studied include very-low-permeability soil materials, such as packed clay liners, and plastic or polyethylene-like "geomembranes" -- each used independently or in combinations with one another (10:698). In Florida, as in other places, regulations now require that a landfill have in its bottom a porous Leachate Collection System (LCS) and a Leakage Removal System (LCS), then below those a geomembrane liner (60-mils thick or more); below which there will be then a Leakage Detection System (LDS) of very porous soil material that can be monitored and sucked dry through monitoring wells (10:698-99). These authors found that leachate flow into the LCS, while on the order of 1,000 to 20,000 m3/mo., is highly controllable; and flows through or below the geomembranes into the LDS are minimal, on the order of 20-70 m3/mo. (10:705). The barrier systems are so effective, these authors argue, that monitoring well numbers and sampling frequencies now imposed by regulations cou
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Approximate Word count = 1982
Approximate Pages = 8 (250 words per page)