Story

Project: EHC Treatment of Groundwater Plume Containing Chlorinated Solvents

Confidential Client - SE USA

The Challenge

Groundwater at a former manufacturing facility was impacted by chlorinated solvents, primarily carbon tetrachloride (CT) and trichloroethylene (TCE), as well as organochlorinated pesticides (OCPs). Adventus employed its EHC in situ integrated biological and chemical reduction (ISCR) technology yielding safe,rapid and effective in situ treatment.

After only 3 months of EHC application, the CT concentration decreased from 260 ppb to 7.8 ppb (97% removal) without the accumulation of catabolic intermediates. Treatment improved further at the 6-month sampling, showing a removal to 0.8 ppb (99.7% removal). All six of six monitoring wells met the groundwater clean up criteria for volatile organic compounds (VOCs).

The Solution

EHC is a patented combination of controlled-release carbon and zero valent iron (ZVI) particles used for stimulating reductive dechlorination of otherwise persistent organic compounds in groundwater. The volume requiring treatment was 110 ft (34 m) wide by approximately 190 ft (58 m) long, from 15 to 40 ft (4.6 to 12 m) below ground surface (bgs).

The approach was to create three, 10 ft (3 m) wide reactive zones: one at the upgradient edge, and two in the middle of the treatment area. The theory behind this approach is that the volatile fatty acids, hydrogen, and ferrous iron released from EHC would migrate downgradient to treat the plume. Further, contact between contaminants and the ZVI that is incorporated in the EHC product would be chemically treated. A total of 45,000 lbs (20,455 kg) of EHC were applied at the site. Within the reactive zones, the application rate was 0.5% by dry soil mass; however, the overall application rate for the total area treated was 0.08%.

The injections were completed in June of 2005 using direct injection (Figure 1). The first round of monitoring well sampling occurred in September of 2005. The Result Excellent treatment results were attained, as shown in Table 1 where the pre-treatment and 3-month post-treatment results are presented for all wells in the treatment area. The full range of analyzed chloroethenes and chloromethanes are shown in Figure 2 for the most highly contaminated well. All constituents at this well were reduced by significant amounts, with CT being reduced by 99.7%. Figure 3 shows the contoured field data for carbon tetrachloride one year prior to injection, and three and six months following the injections. All values were less than 1 ppb at the six-month sampling, and all VOC treatment goals were met. Figure 4 shows the degradation of OCPs over time due to EHC application.

The Timeline and Cost

The EHC injection was completed in twenty days. Three months following EHC additions the concentration of chlorinated solvents decreased by as much as 97%, and as much as 99.7% after 6 months. The concentrations of all VOCs were below the site clean up criteria for all sample locations.

The EHC product cost was US$0.17/ft3 (US$6/m3).