Story

Project: EHC Treatment of Chlorinated Solvents, Manufacturing Facility – Belgium

Summary

A field scale pilot test was performed to evaluate the performance of in situ biological and chemical reduction (ISCR) of chlorinated aliphatic hydrocarbons (CAHs) at a manufacturing facility in Belgium, Europe. The key CAHs found in groundwater at the site include trichloroethene (TCE) and cis 1,2- dichloroethene (DCE), as high as 1000 ppb and 450 ppb, respectively. EHC was injected along a 160 ft (50 m) line resulting in a permeable reactive barrier (PRB) that would intercept the CAH plume. The PRB consisted of two rows with sixteen injection points spaced 10 ft (3 m) apart in each row. The rows were separated by 8 ft (2.5 m).

Seven months after EHC injection, TCE remains below the groundwater standard and DCE was reduced by 50% in the PRB. No accumulation of vinyl chloride has been observed. Reducing conditions were successfully established, where other substrate applications had failed in the past.

The Challenge

The site has a history of remedial actions, including pilot tests using molassess and phytoremediation. The molasses treatment was successful in treating an offsite plume, however the onsite plume treatment resulted in the accumulation and stagnation of DCE during the usual degradation pathway for TCE (TCE, DCE, VC). This onsite plume was the target for the pilot test with the overall remedial goal to remove residential parcels from a register of contaminated lands. Access was another challenge given that the plume is located below residential houses and gardens.

The Solution:

Field-Scale Pilot Study In November of 2006, a total of 13,750 lbs (6,250 kg) of EHC was injected in 32 points to intercept the onsite plume, resulting in a PRB with dimensions of 160 ft x 8 ft and thickness of 16 ft (50m x 2.5m x 5m). The PRB was designed to target the deeper part of the aquifer at depths of 16 to 32 ft bgs (5 to 10m bgs), and the injection was performed using direct push methods. The design application rate of EHC to soil mass was 1% in the PRB.

A PRB approach was chosen over a grid approach for the pilot test to prevent interference with residential houses and gardens. The proposed full scale remediation would entail multiple PRBs along the plume.

The EHC injection was completed in 11 days; approximately three injection points were completed per day, in which each point was injected over a depth of 16 ft (5m) at 1 ft (0.25m) intervals.

The Results

• TCE was below detection limits in the PRB within 6 months following the application of EHC;

• No accumulation of vinyl chloride was observed;

• Cis-DCE was generated but shows a declining trend in the PRB and is reduced by 50%, seven months after EHC injection.

• Reducing and anaerobic conditions within the PRB have demonstrated continued performance over seven months, and are expected to continue.

• The EHC pilot test was successful in establishing reducing conditions where other substrates had failed in the past.