Mesocosms were used to investigate the effects of Cu influx, alone and in the presence of other elements, on sediments remediated by active caps, passive caps, and in-situ treatment. Competitive interactions between Cu and other elements were investigated because contaminants often co-occur. Our hypothesis was that the sequestering agents used in active caps and in situ treatments will bind elements introduced from uncontrolled sources of ongoing contamination, thereby reducing their bioavailability and protecting underlying, previously remediated sediments from recontamination. Competitive interactions between Cu and other elements were investigated to better understand conditions occurring at actual contaminated sediment sites where several contaminants often co-occur. Tested elements in surface water remained at significantly lower concentrations in mesocosms with apatite and mixed amendment caps than in mesocosms with passive caps (sand), uncapped sediment, and spike solution throughout the 2880-hour experiment. Element concentrations were significantly higher in Lumbriculus variegatus from untreated sediment than in organisms from most active caps, and regressions of element concentrations in Lumbriculus on element concentrations in the top 2.5 cm of sediment or cap measured by DGT were strong and significant (p<0.05) for most tested elements. Our findings showed that some types of active caps can protect remediated sediments by reducing the bioavailable pool of elements from ongoing sources of contamination and that the ability of mixed amendment caps to control the bioaccumulation of Cu was not affected by the presence of other elements. This knowledge will contribute to more rigorous risk management that incorporates the resilience of remedies in the face of ongoing contamination into the criteria for remedy selection.

SRNL-L3200-2018-00181