Permeable treatment beds are also in situ treatment techniques used at sites with relatively shallow groundwater tables. The concept of a permeable treatment bed involves excavating a trench, filling the trench with a permeable treatment material, and allowing the plume to flow through the bed thus physically removing or chemically altering the contaminants. The function of a permeable treatment bed is to reduce the quantities of contaminants in the plume to acceptable levels. Potential problems with using a permeable treatment bed include saturation of the bed material, plugging of the bed with precipitates, and the short life of the treatment material (U.S. EPA 1985).
The selection of the appropriate bed material to treat the contaminants and the design of the bed are two elements that determine the effectiveness of a permeable treatment bed. The types of available treatment bed fill material include limestone, crushed shell, activated carbon, glauconitic greensands, and synthetically produced ion exchange resins. Ensuring proper physical design of the treatment bed requires a knowledge of the hydrogeology of the site (e.g., groundwater flow rate and direction, hydraulic conductivities) and the chemical characteristics of the plume (U.S. EPA 1985).
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