ARSENIC CYCLING AND TRANSPORT ISSUES AT VINELAND CHEMICAL SUPERFUND SITE

Arsenical herbicides were manufactured in Vineland, NJ for more than 30 years, during which time nearby soils and groundwater became heavily contaminated with arsenic. A major treatment facility at the site has been in operation for more than four years to remove both organic and inorganic As from groundwater beneath the site. A soil washing treatment plant is also in operation. Remediation goals include (1) elimination of offsite migration of dissolved As via groundwater discharge to a small stream that flows along the site and (2) reducing the inventory of As on site. Measurements of stream discharge and dissolved arsenic concentration made in the summers of 2003 and 2004 indicated that total offsite dissolved arsenic transport was ~31 and ~22 mol arsenic per day, respectively. The offsite dissolved As transport derived from the 2003-2004 data is roughly a factor of 3 to 7 lower than that estimated for similar stream water discharge rates during 1992-1993. The 2003-2004 streamwater As was primarily derived from continued groundwater discharge since diffusion from contaminated stream sediments, based on As porewater gradients, could only account for a small fraction of the streamwater flux.

Current work focuses on optimizing pump and treat operations. Laboratory and field experiments will investigate whether manipulations of aquifer chemistry or microbiology could accelerate As mobilization from aquifer solids thus enhancing remediation of groundwater As. Preliminary characterization of the aquifer solids using sequential extractions indicates that the vast majority of the As (>95%) is released by 1M sodium phosphate. This suggests the As is in an easily mobilized form. Initial incubation experiments indicate that addition of electron donors may stimulate the growth of native microbes resulting in increased arsenic release from the sediment. After 4 weeks, concentrations of dissolved As were more than 4 times higher in samples with acetate than those without. Batch experiments will investigate the use of chemical modifications to release As from sediment and will include the addition of ligands (phosphate or oxalate) and changing pH. Further work will examine the potential for re-adsorption of mobilized As onto sediments.