If leachate from a landfill is intermittently or continuously in 

 contact with groundwater or surface-water sources, the water becomes 

 polluted [121], with potentially serious consequences. For example, 

 recently landfill leachate has been identified as a major source of poly- 

 chlorinated biphenyl (PCB) pollution of coastal waters. 



Since more than 90 percent of solid wastes are disposed on land in 

 dumps and landfills, this section emphasizes the importance of location 

 and design of sanitary landfills to protect vital habitat areas and to 

 prevent water pollution. 



4.13.2 Location 



Landfilling of solid wastes at the shore, particularly in wetlands 

 areas, presents a twofold threat. First, it creates the danger of 

 polluting areas outside of the fills themselves through contamination of 

 leachates when water percolates through solid waste, and, secondly, it 

 causes a reduction in wetlands. 



Leachate : Sanitary landfills should be located in areas of suit- 

 able water characteristics and soil permeability. To avoid leachate 

 pollution, the landfill should be located well above the groundwater table, 

 where soils are of optimum permeability and texture. At the minimum, a 

 distance of 10 feet between the lowest layer of deposited refuse and the 

 seasonal high groundwater table should be maintained to provide sufficient 

 protection of groundwater quality [122]. 



Landfill sites should always be out of the path of natural drainage- 

 ways, above the lower coastal floodplain (above the 10-year flood level), 

 and away from surface water bodies. A minimum distance of 1,000 feet 

 from surface water and 1 mile from municipal wells is recommended [122]. 



The movement of leachate from a waste disposal site is governed by 

 the physical environment (Figure 39). When the wastes are deposited above 

 the water table, both chemical and biological contaminants in the leachate 

 move downward through the surficial soils (zone of aeration) at a rate 

 dependent in part on the properties of the soils. The chemical 

 contaminants, being in solution, generally tend to travel faster than 

 suspended biological contaminants. Particulate biological contaminants 

 are largely filtered from the percolating leachate. The chemical 

 contaminants, however, may be carried rapidly by the leachate water to 

 the water table. The potential for water pollution depends on the 

 mobility of the contaminant, its accessibility to the groundwater 

 reservoir, and the hydraulic characteristics of that reservoir [123]. 



In areas of high rainfall, the pollution potential from leachates is 

 greater than in less humid areas. In semiarid areas there may be little 

 or no risk of pollution because all water is either absorbed by the 

 refuse or is held as soil moisture and is ultimately evaporated. In 



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