Thursday, 13 July 2006

Metal Speciation, Bioavailability and Remediation at Superfund Sediment Sites.

Kirk Scheckel1, Aaron Williams1, Robert Ford1, Dean Neptune2, James Ryan1, Steven Acree1, David Gratson2, Greg McDermott2, Thabet Tolaymat1, and Richard T. Wilkin1. (1) US EPA, 5995 Center Hill Ave, Cincinnati, OH 45224-4504, (2) Neptune & Company, Inc., 8962 Spruce Ridge Road, Fairfax Station, VA 22039

Remediation strategies at Superfund sites are dependent upon the prevailing speciation of metals and their impact on the environment. These sites typically have limited human contact, but the impact of metal contamination can influence biological function within the ecosystem. This presentation will outline our efforts at three contaminated sediments sites which include in-situ and monitored natural attenuation remediation strategies. The objectives of the research are to link the speciation of metals to biological availability and demonstrate effective remediation.

In-situ amendments of phosphate and biosolids have demonstrated a change in Pb and Zn speciation leading to significant decreases in phytotoxicity and bioavailability. At the Indian Head Naval Surface Warfare Center (IHNSWC) (MD), Zn-contaminated sediments are observed adjacent to a historical Zn recovery furnace leading to phytotoxicity and biologically available Zn in the sediment pore water. Surface erosion transport of Zn slag to the sediment results in Zn oxide and Zn hydroxide-like species at very high concentrations. In-situ amendments of apatite and biosolids have eliminated Zn phytotoxicity and significantly increased survivability of lower food chain organisms. Down gradient of a pre-WWI shooting range, Pb-contaminated sediments at the Quantico Marine Base (VA) have been treated with apatite in an attempt to form pyromorphite. While the range site has been removed, the persistence of Pb in the sediments remains. Galena is the primary form of Pb under saturated conditions; however, seasonal water levels may cause oxidation of galena to less stable forms such as cerussite. Conversion of sediment-Pb to pyromorphite would yield a stable species for both saturated and oxic environments.

Monitored natural attention of sediment bound As from groundwater discharged landfill leachate in contact with As-bearing bedrock shows an amazing capacity of ferrous iron to form Fe-oxides capable of sequestering labile As at the Ft. Devens Superfund Site (MA). A monitoring well network is in place to examine the groundwater flow situation and explain the distribution of As. Sediment cores have been collected and analyzed to determine As speciation and retention capacity.

Synchrotron studies, coupled with Mössbauer spectroscopy and other laboratory methods, provide overwhelming details to aid in remediation approaches at metal-contaminated sites.

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