Formatted Title
Fast Kinetics In Situ Chemical Oxidation Treatment of a PCE Source Area with Sodium Persulfate Activated with Hydrogen Peroxide
Background/Objectives
Background/Objectives. A source area pilot-scale study was completed at a former manufacturing facility located in Michigan in October 2022. Groundwater at the site was impacted with tetrachloroethylene (PCE) and its daughter products from former machine shop activities. The purpose of the pilot study was to determine if an aggressive fast kinetics in situ chemical oxidation (ISCO) program could reduce concentrations of tetrachloroethylene (PCE), trichloroethene (TCE), cis-1,2-dichloroethene (cis-1,2-DCE), and vinyl chloride (VC) below the remedial objectives (ROs) established for the site. The areal extent of the impacted groundwater plume exceeding ROs is approximately 120 feet wide and 660 feet long. The target treatment area was 900 square feet with the highest baseline concentrations at 420 micrograms per liter (µg/L) of PCE, 26 µg/L of TCE, 1,300 µg/L of cis-1,2-DCE, and 88 µg/L of VC. The groundwater flows to the north and has an average groundwater flow velocity of 0.84 feet per day or 309.7 feet per year.
Approach/Activities
Approach/Activities. Sodium persulfate activated with hydrogen peroxide was selected due to the fast kinetics needed to oxidize the contaminates before the high groundwater flow velocity transported the amendment away from the source area. The amendment was injected into nine 1-inch outer diameter polyvinyl chloride injection wells on a grid spacing of 15 feet. The target treatment depth was approximately 6 to 16 feet below ground surface (bgs) with groundwater at 7.46 feet bgs. A grid spacing of 15 feet was selected to provide adequate overlap between injection points and ensure adequate subsurface distribution assuming a targeted radius of 12 feet. The source water for the amendment mixing was municipal water distributed by a commercial trucking company to the site. The performance monitoring included 27 wells for volatile organic compounds (VOCs) with five of the wells for ISCO performance parameters.
Tetra Tech applied approximately 26,820 pounds of amendment to the impacted area. The amendment solution was mixed to manufacturer’s specifications using 980 pounds of sodium persulfate, 2,000 pounds of 34 weight hydrogen peroxide with 2,230 gallons of water to create 2,450 gallons of amendment solution per injection point. A diaphragm pump with a 550-gallon mixing tank was used to distribute the amendment solution with an average injection rate of approximately 14.3 gallons per minute. Approximately 2,450 gallons of amendment solution was injected into each injection point. Performance groundwater geochemical monitoring included sodium persulfate field test kits and geochemical parameters of pH, oxidation reduction potential (ORP), and specific conductance. The laboratory analysis included VOCs and ISCO performance parameters of dissolved sodium and sulfate. Quarterly groundwater performance monitoring began in January 2023, three months after the completion of the pilot study. The monitoring results will be used to determine if oxidation successfully decreased VOC concentrations below the ROs and confirm that back diffusion is not occurring.
Results/Lessons Learned
Results/Lessons Learned. Performance monitoring results have shown that ISCO successfully oxidized PCE and its daughter products in groundwater below the ROs. Implementation methods and performance monitoring results from the January, May, July and October 2023 groundwater monitoring will be presented.