Superfund Research Program
Characterizing Ground Water Contamination of a Heterogeneous Field Site: The Aberjona River Watershed
Project Leader: Charles F. Harvey
Grant Number: P42ES004675
Funding Period: 1995 - 2000
Wetland sediments adjacent to the Aberjona River near Woburn, Massachusetts contain significant amounts of arsenic and other heavy metals that may threaten human health and cause harm to the surrounding ecological community. The source of metal loading for this sediment, a peat, is thought to be the Aberjona River, whose dissolved and particulate load is contaminated by sources located within the Industri-plex area upstream. Determining the stability of arsenic in this peat is important in estimating health risks due to exposure to the peat and the waters which flow through the peat and beyond. Ongoing research is focused on developing a transport model that can predict the fate and movement of arsenic in the peat in response to varying environmental parameters, thus aiding in making determinations of the magnitude of such risks.
Researchers are determining the state(s) in which arsenic is bound in samples of the peat obtained from the wetland. In September and December 1998, peat cores to 40-cm depth were obtained within five feet of the Aberjona River near Woburn municipal wells designated "G" and "H". Preliminary peat cores taken from this area had shown elevated (parts per thousand) levels of arsenic. The cores were obtained with a novel coring device which greatly minimized exposure of the sample to atmospheric conditions, e.g., oxygen content, which may otherwise have altered the ambient sediment properties. Environmental parameters (pH, eH) were measured on site at 5-cm depth increments in the core using micro-electrodes and sampling ports incorporated into the coring device. The core was transported back to the lab and sectioned at 10-cm depth increments under a N2 atmosphere. The sections were freeze-dried to prepare them for a variety of analyses, including: (1) selective extraction techniques which specifically target surface-associated species and species incorporated into crystalline or amorphous solid phases (currently being conducted), (2) x-ray diffraction to determine the identities of any crystalline phases which may be present, and (3) electron microscopy to study the in situ associations between arsenic and the solid phases (e.g., amorphous and crystalline materials, root biomass) present in the peat, and potentially also determine the valence state of arsenic associated with individual phases.