Chemical manipulation of soil for sealing landfills

The aim of this work was to seek a cost-effective method of limiting seepage from sanitary landfills by chemically inducing a low permeability in soil on site instead of resorting to expensive clay liners or geomembranes. The soil chemical treatment was based on the dispersion and flocculation of clay minerals, as well as the mobilisation and precipitation of humic compounds. In preliminary experiments with several contrasting soils, dispersion and subsequent flocculation were achieved by chemical treatment, and Na2CO3 and gypsum were selected as the most effective dispersant and flocculant, respectively. Soils were packed in columns in which a layer of soil with and without gypsum amendment was covered by untreated soil. The columns were then leached with Na2CO3 solution (usually 0.1 M Na) under a head of 100 cm. The characteristic result for most soils was a reduction in hydraulic conductivity to values close to and below the 10−7 cm s−1 threshold widely considered to be acceptable for clay liners. Replacement of the Na2CO3 with liquids which favour flocculation, however, led to the enhancement of hydraulic conductivity. Very sandy or structurally stable soils were highly permeable unless a small amount of humate was added. Although the technique is not claimed to be suitable as a substitute for the methods currently used to line landfills, it does offer a very much cheaper alternative in situations where the cost of conventional methods is prohibitive.