Combining In Situ Chemical Reduction and Big Diameter Vertical Soil Drill as an Alternative Solution for Thermal on a Complex Site Impacted by Chlorinated Solvents (Sao Paulo, Brazil)
Background: Groundwater in a complex hydrogeological site at an inactive manufacturing plant in Sao Paulo , SP – Brazil, was impacted with dissolved Chlorinated Volatile Organic Compounds (CVOCs) including PCE, TCE, 1,2-DCE, VC and 1,1,2,2-TCA. PCE levels in groundwater was >200,000 µg/L and in soil was around 4,000 µg/kg. With the CVOC plumes covering approximately 150,000sq ft, reaching 100ft deep, thick compact clay levels with high concentrations in the source zones and no space for big excavation pit, the obvious solution was a Thermal approach. Approach: After understanding the complex hydrogeological model of the area and considering also the Thermal limitations due to a close by subway station and occupied external areas, our remediation approach considered a synergetic combination of multiple techniques that included Big Diameter Vertical Soil Excavation and In Situ Chemical Reduction (ISCR) aiming to remediate the site within 24 months enabling a future residential occupation. The combined remediation included an excavation and off-site disposal of approximately 15,000 metric tons of contaminated soil, and in situ groundwater treatment by a customized Provect-IR® Antimethanogenic ISCR amendment and eZVI. Lessons Learned: Modifying an equipment regularly used for big foundations in the construction industry, we built an equipment able to vertically remove soil up to 250ft at a 8ft diameter, allowing us to remove the source areas highly contaminated clays and allowing the ISCR reaction to take place in the more permeable zones, including the external areas. In some external areas with DNAPL, we used eZVI for the first time in ocuntry. After 30 months following remedial activities, groundwater analytical data confirmed remediation efficiency with all Compounds of Concern (COC) below target levels calculated by Human Health Risk Assessment. The expected cost for this remediation ended up on 50% of the initial Thermal estimative.