Roux Associates is providing consulting and engineering services for an in situ groundwater remediation project at a former television manufacturing facility in Taoyuan, Taiwan. Working with a local consulting firm, Roux Associates has defined the nature and extent of contamination and successfully pilot tested an in situ system to treat chlorinated solvents in groundwater.

The site, located on 18 acres of land in Taoyuan, Taiwan, 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 from 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; and 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 bacteria utilize organic carbon in the groundwater as the primary substrate for obtaining energy. Complete biodegradation of the CVOCs generates benign end products: ethene, ethane, chloride, carbon dioxide, and water. Unfavorable site conditions can cause the process to stall, leaving more toxic compounds due to incomplete degradation.

The results of a six month pilot study indicated ERD would effectively reduce CVOCs to the levels required by the new regulations. To make the system as cost effective as feasible, molasses was selected as the carbon source. A full scale ERD treatment system was then designed and constructed. Since the Site is extremely valuable for redevelopment, and since redevelopment could not start until the groundwater regulatory standards were met, a key requirement of the full scale system was to minimize the time needed to remediate the site.

The ERD treatment system includes over 2,700 meters of aboveground polyvinyl chloride (PVC) piping, 143 injection wells and associated appurtenances, two 20,000-liter polyethylene mixing tanks, and a 6-metric ton polyethylene molasses storage tank. Each month 1,000 liters of dilute molasses solution is pumped to each of the 143 injection wells via the network of aboveground piping and valving. As of the spring of 2009, over 250 tons of molasses have been injected into the subsurface.

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 were used to optimize the ERD treatment system. As a result, after one year of operation, in many of the monitoring wells PCE concentrations have decreased by over 90 percent, and TCE concentrations have decreased by over 80 percent. Corresponding increases in the concentrations of 1,2 DCE and VC were observed. In monitoring wells in which PCE and TCE have been depleted, the strongly reducing environment facilitated the further breakdown of the accumulated 1,2-DCE and VC. Compliance with Taiwan’s Class II Standards is anticipated to be achieved after an additional year of operation.