Chlorinated Solvents & Groundwater Remediation

Roux provided consulting and engineering services for a large in situ groundwater remediation project at a former television manufacturing facility in Taoyuan, Taiwan. Working with a local consulting firm, Roux defined the nature and extent of contamination and successfully operated a full scale in situ system to treat chlorinated solvents in groundwater. The Site, located on 18 acres of land, was used for assembling and packaging computer chips and for manufacturing televisions. Various solvents (chlorinated volatile organic compounds or CVOCs), primarily tetrachloroethene (PCE), trichloroethene (TCE), and 1,1,1-trichloroethane (TCA), were used as cleaners and degreasers in the electronic assembly process. Investigations were performed to evaluate environmental conditions at the Site. The work included groundwater monitoring, soil sampling, and soil gas sampling. Results of the site investigation indicated that shallow groundwater beneath a portion of the Site contained CVOCs in the parts per million range; soil in several areas of the Site contained CVOCs.

After a thorough evaluation of the hydrogeology and geochemistry of the Site and pilot testing of two possible treatment methods, enhanced reductive dechlorination (ERD) was the technology selected to treat the Site’s groundwater. ERD is an in situ bioremediation technology that involves stimulating the growth of naturally occurring subsurface microbes. The ERD treatment system included:
• Over 2,700 meters of aboveground polyvinyl chloride (PVC) piping;
• 146 injection wells and associated appurtenances;
• Two 20,000-liter polyethylene mixing tanks; and
• Two 6-metric ton polyethylene molasses storage tanks.

The monthly injections of molasses have been successful in creating and maintaining an anaerobic subsurface environment conducive to ERD across the Site. Regular monitoring of field parameters and TOC and CVOC levels provided data that was used to optimize the ERD treatment system. As a result, after four years of operation, the mass of PCE detected in monitoring wells decreased by over 98 percent and TCE mass decreased by over 95 percent.

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