IN SITU CAPPING OF CONTAMINATED SEDIMENTS:BIOGEOCHEMICAL CHARACTERIZATION OF SEDIMENTS AND CAPS AND ITS IMPACT ON CONTAMINANT FATE AND TRANSPORT

摘要

Many United States surface waters in urban settings contain sediments that are sufficiently contaminated to cause adverse effects on aquatic life and limit their recreational and economic use.In situ capping has recently emerged as an accepted remedial method and involves placing a layer of clean material at the sediment-water interface to prevent sediment contaminants from reaching the overlying benthic community and surface water.Sand has been the traditional material employed for capping and can delay contaminant breakthrough considerably when diffusive transport dominates.Rapid breakthrough of contaminants can occur,however,when sandbased caps are subject to advective flows.This limitation precludes sand caps from use at sites subject to contaminated groundwater seeps,which are numerous considering 75% of Superfund and RCRA sites are located within a half-mile of surface water and 50% of the Superfund sites report communication between the contaminated groundwater and surface water.To address this limitation,alternative materials designed to sequester or transform contaminants(e.g.,activated carbon,Fe~0)have recently been incorporated into caps to create active caps,capable of removing contaminants from the aqueous phase during transport through the cap.