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ELECTROKINETIC IN-SITU REMEDIATION OF A 75 TONS XYLENE CONTAMINATION IN SOIL, BEDROCK AND GROUNDWATER
Hougaard, T. and J. Rose.
NORDROCS 2018: 7th Joint Nordic Meeting on Remediation of Contaminated Sites: Poster.

In situ electrokinetic (EK) remediation of severe xylene contamination is ongoing at a former paint production facility. The contamination hot spot lies beneath a former tank farm covering ~1000 m2 to a depth of 25 m, holding some 75 tons of xylenes. The affected groundwater covers several ha. Site geology consists of sandy clay overlaying calcareous bedrock at ~6 m bgs. An unconfined groundwater table lays 20 m bgs. The aim of treatment is to lower xylene concentrations in soil, bedrock, and groundwater to levels accepted by the authorities as safe for residents and environment. The system consists of a central cathode and anodes placed ~20 m at each side of the cathode in a straight line. The electrodes, made of 160-mm mild steel pipes, are set to a depth of 30 m bgs. The electrodes are powered by a special power supply. System installation and startup began in late February 2018. After two months of operation the following results were observed: BTEX decreased by 42%, from 5.882 to 3.417 ppm; C5-C10 decreased by 35%, from 9.650 to 6.257 ppm; C10-C40 decreased by 74%, from 1.527 to 392 ppm; and C5-C40 decreased by 41%, from 11.177 to 6.649 ppm. Within the treatment area, groundwater concentrations of BTEX and TPH increased ~75%, from 207 to 356 and 332 to 596 ppm, respectively. Outside the treatment area, concentrations 30 m downstream declined some 15%, from 60 to 50 and from 81 to 63 ppm, respectively. EK proved a viable, efficient, and cost-effective method for remediation of xylenes in soil, water, and bedrock. Costs, inconveniences for residents, and carbon footprint were lower compared to traditional in situ and dig and dump methods. Depending on cleanup criteria, however, time requirements for full remediation can be a hindrance, and the use of EK in organic-rich soils might cause settlement of soil and overlying construction due to mineralization of organic matter.



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