A chlorinated hydrocarbon (CHC) manufacturing facility in northeastern Brazil inadvertently released chlorinated hydrocarbons to the subsurface. The underlying ground water lies 60 to 70 m below the ground surface and is part of a large drinking water aquifer (Barreiras aquifer). Downgradient potential receptors include local inhabitants who draw their potable water from hand-dug wells (cacimbas), wetlands, and a large estuary.
The Barreiras aquifer is alluvial in origin and consists of interbedded clays, silts, sands, and gravels. A linear geologic structure was identified at the base of the Barreiras aquifer that resembles a paleo-channel. This channel appears to correlate with the zone of highest CHC contamination.
CHCs were subsequently detected in nearby production wells 500 m downgradient. An accelerated ground-water investigation and interim remedial action plan were implemented to contain the highest CHC concentrations and provide hydraulic control downgradient of the CHC source. Ground-water production wells were installed along the paleo-channel in the alluvial sediments. Ground-water level and quality monitoring suggest that the program has been successful although additional monitoring is required to confirm the initial results. Between April 1992 and December 1993, over 1.2 billion gallons of ground water have been pumped and over 52 tons of dissolved solvents have been removed. Future plans for the project include evaluation and optimization of the ground-water capture system and evaluation of dense nonaqueous phase liquid (DNAPL) recovery.