Applications of water sensitivity in situ remediation at saltwater-freshwater interface

Abstract

Based on the laboratory experiments with the saltwater and freshwater replacing each other in the level sand column, taking the kaolin, illite, smectite, bivalent hydrargyrum ion (Hg²⁺) and phenol (C₆H₅OH) as examples, this paper studies the applications of water sensitivity in situ remediation in saltwater-freshwater transition zone. In the water sensitivity process, the release and migration of clay minerals can make the hydraulic conductivity (HC) decrease and pollutants remove. A new type of low penetrable or impenetrable purdah can be built by adding clay minerals into the sand media to replace the underground concrete impenetrable wall to prevent seawater intrusion, and a number of the heavy metals and organic pollutants in the sand media can be removed by in situ remediation. The results show that the content of kaolin and illite influences the water sensitivity process slightly, and HC of the sand columns descends from 0.011 cm/s to 0.001 4 cm/s and 0.001 2 cm/s respectively even if the content reaches 12% (weight ratio, sic passim). However, for smectite, HC descends sharply to about 1×10⁻⁸ cm/s when its content reaches 4%, and no water can flow through the sand columns beyond 5%. The particle release and migration processes can remove the Hg²⁺ and C₆H₅OH out of the sand columns efficiently, the removing rate of Hg²⁺ is 31.68% when the freshwater and saltwater are filtered through the sand columns polluted by Hg²⁺, while it is 67.55% when the water sensitivity occurs. With the same method, the removing rates of C₆H₅OH under the fluid flow and water sensitivity are 55.71% and 43.43% respectively.