Effectiveness of very thin soil layers in chemical release from bed sediment

Abstract

AbstractThe chemical containment effectiveness of both the natural recovery and the “particle broadcasting” processes for remediating contaminated bed‐sediments depend upon very thin soil and/or sand layers millimeters in depth. Conventional capping for in situ chemical containment of bed‐sediment or dredged material typically involves thick layers of 30 to 90 centimeters in depth. Few studies have been conducted with thin layers of candidate natural materials. A steady‐state benzoic acid dissolution test apparatus and procedure, devised to realistically simulate bed‐sediment chemo‐dynamic conditions, was used to measure chemical flux through thin layers (1 to 8 mm) of soil, sand, and ideal porous media. The thin layers were found to be very effective. Flux reductions ranged from 81 to 96%, with fine sand being slightly better than top soil. Design algorithms developed for the thick layers used in conventional capping design will under predict the flux through very thin layers. Advective flow induced by surface roughness is proposed to explain the higher average measure d‐to‐predicted flux ratio of 1.67.