A pilot-scale study of an in-situ electro-heating enhanced extraction of coal tar dense non-aqueous phase liquid (DNAPL) was conducted at a former manufactured gas plant site. The DNAPL saturates up to 50 % of a water-bearing granular unit overlying a cohesive soil aquitard. The in-situ heating method involved raising the temperature of the soil, groundwater and the DNAPL, thereby reducing the viscosity of the DNAPL and increasing its mobility. The system utilized the electrical resistivity of the ground and groundwater to produce heat. The field demonstration utilized six steel electrodes configured in the shape of a hexagon that measures 20 feet in diameter to heat soil, groundwater and DNAPL around a centrally located recovery well. The heating was conducted in stages, to minimize thermal gradients within the treatment zone, and to determine the minimum operating temperature that resulted in appreciable DNAPL recovery. Soil analytical results and the volume of recovered product indicate that the technology is capable of mobilizing pooled viscous coal tar DNAPL with low operating costs.
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