ABSTRACT
This chapter discusses the use of active media for in situ remediation of metal-contaminated sediments. Before choosing active media, sand caps should first be considered. Trace metal mobility can be reduced by (1) complexing with organic matter, (2) chemisorbing or co-precipitating with minerals, or (3) precipitating as insoluble sulfides, carbonates, phosphates, or oxides (McBride 1994). Most of the active media proposed for sediment capping have functional groups consisting of natural minerals or synthetic materials that utilize this chemistry. Langmuir or Freundlich parameters can be inserted into capping models to help estimate the time to breakthrough (Lampert and Reible 2009; Reible and Lampert 2014) if sorption phenomena control the performance of active cap media. In choosing active media, some understanding of the binding mechanism is important, because media can be impacted differently by competing ions, pH, redox conditions, and so on. It is also important to evaluate the biotoxicity of media toward representative organisms.
