Full-Scale Treatment of a DNAPL Source Zone through Injection of Food-Grade Vegetable Oil

摘要

Full-scale treatment of a trichloroethene (TCE) source zone began in August 2005 beneath an active manufacturing building near Portland, Oregon using food-grade vegetable oil (VO). This remedial effort targets an approximate 4,000 ft2 source zone within a shallow, unconfined, alluvial aquifer of sand and gravel that is present from 10 to 30 ft below ground surface (BGS) and is adjacent to a former vapor degreaser and TCE supply line. Dense nonaqueous-phase liquid (DNAPL) was observed during drilling activities, and the maximum baseline TCE concentration in groundwater (1,170,000 ug/L) is at the TCE solubility limit. Approximately 20,000 gallons of 23 percent VO emulsion was injected to the source zone aquifer through 17 injection wells installed on 10- to 20-ft centers.Comparison of baseline and post-injection groundwater monitoring indicates that VO injection has resulted in highly reduced aquifer conditions and enhanced RD of TCE and breakdown products within the source zone and downgradient, combined with significant partitioning/dissolution of TCE mass to VO. Post injection, elevated total organic carbon (TOC) and complete RD of TCE through end products ethene and ethane has been observed in the source zone and up to 430 ft downgradient. At 16 months, maximum TOC concentrations remain as high as 1,200 mg/L in the source zone and 32 mg/L at 270 ft downgradient, compared to baseline TOC concentrations of 10 mg/L or less. Baseline nitrate- to sulfate-reducing conditions have become more reducing as evidenced by sulfate depletion and generation of up to 14 mg/L of methane. VO collected from the source zone aquifer contains up to 37,800 (3.8 percent) TCE, reflecting significant DNAPL dissolution and partitioning.