LNAPL remediation using electrical resistance heating

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Courtesy of TRS Group, Inc.

An Electrical Resistance Heating (ERH) pilot test was conducted in the fall of 1998 to determine the effectiveness of using ERH in combination with soil vapor extraction (SVE) for the remediation of benzene and light nonaqueous-phase liquids (LNAPL) at an island location on a river in the Midwest.

Hydrocarbon-stained soils were discovered on an island in Ohio in May 1993 during the installation of a monitoring well. The stained soils may have resulted from a past release from a pipeline system that was formerly operated to convey petroleum products from a former refinery to a terminal on the river. The pipeline system consisted of five, six-inch diameter steel pipelines that were buried at depths ranging from two to four feet below ground surface (bgs). Each pipeline was typically dedicated to conveying a separate refined product (e.g., jet and aviation fuel, diesel fuel, and three grades of gasoline). Additional test borings and monitoring wells were installed to characterize and delineate the petroleum hydrocarbons on the island.

A soil vapor extraction (SVE) system was installed in the summer and fall of 1995. The SVE system consisted of sixteen-vapor extraction wells installed at depths ranging from nine to 19 feet bgs. The wells were connected to a 25-hp vacuum pump via a network of buried 2- to 6-inch diameter PVC collection piping. Extracted soil vapor was treated via a catalytic oxidation unit capable of handling up to approximately 700 cubic feet per minute (cfm). The vacuum pump, moisture separator, and catalytic oxidation unit were mounted on an elevated platform above the 100-year flood elevation. The SVE system has been operated seasonally during lower groundwater levels since October 1995. Seasonal operation generally has occurred between July and December.

Previous site work had shown that volatile organic compound (VOC) contamination extended from approximately six feet bgs to a depth of approximately 30 bgs. For the purpose of the pilot test, a treatment zone covering a diameter of approximately 50 feet was selected between three existing extraction wells.

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