Use of Granular Iron for Remediation of a Drinking Water Aquifer Contaminated with TCE

The Town of Wellesley Massachusetts obtains more than 50 percent of their drinking water from water-supply wells in the Rosemary Brook basin. An area of this aquifer has been contaminated with a chlorinated solvent groundwater plume, which has been slowly advancing towards the Wellesley water supply wells. In June and July 2001, the Massachusetts Department of Environmental Protection installed a permeable reactive barrier (PRB) beneath Central Avenue in the path of the plume to degrade the chlorinated solvents in situ and remediate the plume at this location. The groundwater plume was delineated to be about 535 ft wide at this location with a maximum depth of 57 feet to bedrock. The primary contaminant of concern is trichloroethene (TCE) and the maximum average concentration of TCE is approximately 300 micrograms per liter.The reactive material used in the PRB is zero-valent iron, which degrades dissolved chlorinated solvents to non-toxic end products such as ethene, ethane, methane and chloride ions. Construction was completed in June and July 2001 using biodegradable slurry to provide stability for the trench walls. Monitoring of the performance of the PRB is accomplished by collecting groundwater samples from monitoring wells immediately upgradient and downgradient of the PRB. Six months after installation, all well transect pairs show a decrease in TCE concentration between the upgradient and downgradient wells. There is a 93 percent reduction in the TCE concentration between the average upgradient concentration and the average downgradient concentration.