Peggy O'Day Professor School of Natural Sciences University of California, Merced

Peggy O’Day is a Professor in the School of Natural Sciences where she teaches Earth systems science and environmental chemistry.  She received her undergraduate degree from UC Davis, her M.S. from Cornell University, and her Ph.D. from Stanford University in geological and applied Earth sciences.  Her research interests include study of the chemistry, mobility, and bioavailability of contaminants in the environment, mineral-aqueous interface geochemistry, and abiotic and biotic geochemical cycling and microbial colonization in hydrothermal systems.

Presentation Description
In Situ Precipitation and Encapsulation Technologies
Reactive amendments optimized for specific (bio)geochemical site conditions offer a promising remediation technology for high-priority metal and metalloid contaminants in sediments. If contaminants can be sequestered and stabilized in less reactive and less bioaccessible solid forms in the sediment environment, then their ability to cycle from sediments to water or biota is diminished, and bioavailability, bioaccumulation, and biomagnification is circumvented. The most popular amendment types include materials and mixtures that produce forms of cementtype, sulfate, carbonate, phosphate, or hydroxide phases. Silicate, aluminosilicate, or clay treatments, and in some applications organic residues, have also been used. Although different amendment treatments have been investigated (mostly for use with soils), molecular-chemical understanding of element sequestration mechanisms as a result of in situ reaction between the amendment and contaminated sediments is lacking in many systems. Furthermore, knowledge of the long-term fate of contaminants in amendment-reacted sediments is largely unknown, particularly for sediment cycling between oxidized and reduced conditions, which can destabilize metal-sequestering phases. The use of reactive amendments as an alternative technology for in
situ sediment remediation has been limited because of uncertainty in long-term effectiveness with changing environmental conditions, bioturbation, or microbiological alteration and degradation. Another crucial aspect for adoption of amendment technologies is effective delivery systems that react with sediment contaminants without re-suspending or spreading them. Finally, new remediation technologies must be cost-effective with respect to existing technologies that produce a similar degree of risk reduction.

This talk will review current and emerging amendment and encapsulation technologies for metal and metalloid contaminants from the perspective of molecular-chemical mechanisms of sequestration designed for compatibility with specific types of sediment environments. Reactive transport models incorporating thermodynamic and kinetic data provide an effective means to constrain biogeochemical outcomes of sediment-amendment reactions that can then be tested in laboratory and field experiments. Remediation treatments can and should be tailored to sitespecific biogeochemical and hydrologic characteristics where the existing conditions can potentially enhance the treatment method.