The A-01 wetland treatment system (WTS) was designed to remove metals from the A-01 NPDES effluent at the Savannah River Site, Aiken, SC. The A-01 effluent is distributed to four pairs of treatment cells in series before discharge to a stream. Each cell is a one-acre wetland with Schoenoplectus californicus (giant bulrush) and a nominal 24 hour retention time. Our objective was to evaluate contaminant distribution and stability in the wetland sediment. The highest concentrations of Cu, Pb, and Zn were in the sediments from the first cell of each pair, suggesting that most of the Cu, Pb, and Zn in the effluent was quickly bound in the first cell. Retention of metals by the wetland sediment was evaluated by comparing data from 2001 and 2003. The spatial distribution of metals in the sediment was similar in both years, but metal concentrations were significantly higher in 2003.

Sequential extraction was used to evaluate remobilization and retention of Cu, Pb, Zn, Mn, and Fe in the wetland sediment from the A-01 WTS. Metal remobilization was determined by the Potentially Mobile Fraction (PMF) and metal retention by the Recalcitrant Factor (RF). The PMF indicates the contaminant fraction that may enter the mobile aqueous phase under changeable conditions (e.g., pH, Eh, temperature). It includes metals found in water, exchangeable, acid soluble, organic, and amorphous Mn and Fe oxide fractions. Generally, the PMF values were low (about 20%) for Cu, Zn and Pb indicating strong binding to the sediments and high (about 57-70%) for Fe and Mn indicating high desorption from the sediment. Conversely, the RF values were about 80% for Cu, Zn and Pb, indicating high retention of these elements in the sediment and 30 to above 40 for Fe and Mn indicating low retention.