IMMOBILIZATION OF ARSENIC USING REACTIVE WALL TECHNIQUES

Key words: active barriers, arsenic, in-situ treatment, industrial sites, sorption, sulfides

A former dye production site near the Rhine river is highly contaminated with arsenic. A relatively small area of 2100 m2 covers about 10.000 m3 of soil mate- rial with up to 60.000 mg As /kg. Ground-water near the source of the plume contains up to 20 mg As/L and still contains 5-6 mg/L when entering the Rhine river. The site cannot be remediated by complete removal of the source because of buildings on part of the area. Therefore, subsurface treatment walls are con- sidered to immobilize arsenic in two ways: 1. an upgradient injection wall re- leasing chemicals to form co-precipitates with arsenic and 2. a downgradient funnel-and-gate system to remove residual dissolved arsenic from solution.