Spatial and Temporal Evolution of Biogeochemical Processes Following In Situ Capping of Contaminated Sediments

• Published in: Environmental science & technology Vol. 42; no. 11; pp. 4113 - 4120
• Main Authors: Himmelheber, David W, Taillefert, Martial, Pennell, Kurt D, Hughes, Joseph B
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01.06.2008
• Subjects: Applied sciences; Biogeochemistry; Chemical compounds; Contaminated sediments; Environmental Restoration and Remediation - methods; Exact sciences and technology; Geologic Sediments - chemistry; Iron - analysis; Manganese - analysis; Oxidation-Reduction; Oxygen - analysis; Pollution; Remediation and Control Technologies; Rivers; Silicon Dioxide; Soil contamination; Sulfides - analysis; Water Pollutants, Chemical; Sediment water interaction; Organic matter; Stratified material; Pollutant behavior; Upward flow; Sediments; Pollution; Spatial distribution; Anaerobe; Selfpurification; Microelectrode; Stratification; Interface
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es702626x

In situ capping has recently emerged as a remedial method for contaminated sediments and involves placing a layer of clean material at the sediment−water interface. The biogeochemical response of native sediment following capping, as well as the redox environments that develop within the cap, are currently unknown. Column experiments were performed using voltammetric microelectrodes to characterize spatial and temporal distributions of biogeochemical processes in capped sediments under stagnant and upflow conditions. Oxygen penetration into sand caps extended only a few centimeters, thus maintaining underlying sediment anaerobic. Chemical species indicative of heterotrophic organic matter degradation (Mn2+, Fe2+, organic−FeIII(aq), Fe x S y (aq), ∑H2S) were observed in stratified zones below the oxic layer. The majority of the overlying cap was subject to iron-reducing conditions under stagnant flow, while upflow conditions led to a compression of the redox zones toward the cap−water interface. Controls confirmed that sediment capping induced an upward, vertical shift of biogeochemical processes into the overlying cap, with redox stratification conserved. The redox conditions within the cap, specifically the predominance of iron reduction, should allow for reductive contaminant attenuation processes to extend into the overlying cap. These findings improve our understanding of the dynamics of biogeochemical processes following capping of contaminated sediments.