Fig. 1 Injection of 3DMe via direct push
Historic leakage and spillages of chlorinated hydrocarbons (CHCs) at an active manufacturing facility, had lead to high levels of contamination acting as a secondary source in the aquifer, under the building. Dual Phase Vacuum Extraction (DPVE) had effectively reduced the contaminant mass in the source area, however a 1km dissolved phase plume was found to be still migrating from the site. It was thought that residual contamination in the low permeability zones were feeding the plume via back diffusion. It was therefore determined that further remedial works would be undertaken to address the residual secondary source and reduce the mass flux within the downgradient plume.
REGENESIS worked with AECOM to create a remedial strategy using 3-D Microemulsion (3DMe) to biologically degrade the CHC contamination through Enhanced Reductive Dechlorination (ERD). The 3DMe was injected into the subsurface using three direct push rigs working simultaneously, in order to minimise the time onsite and disturbance to the busy factory; completing the application in just 15 days.
In the source area, 3DMe was injected on a grid pattern. 3DMe has the unique ability to self-distribute in the subsurface following injection, maximising the radius of influence (ROI) from each injection point. This ensures that the ROI from each injection point interlocks to provide treatment throughout the target volume. Residual contamination was located in the low permeability zones in the target areas, which was back-diffusing into the groundwater. As 3DMe provides a controlled electron donor release for approximately 4-5 years, a single injection is able to diffuse active ingredient into the low permeability zones and degrade contamination back-diffusing over a long period. This therefore remediates the contamination in the permeable and impermeable zones and prevents rebound due to back-diffusion.
In the downgradient plume, the 3Dme was installed in a series of rows, which act as barriers to the contamination flux. This is achieved by the 3DMe creating and maintaining an anaerobic treatment zone, through which the groundwater continues to flow, while the contamination influx is degraded. Because 3DMe lasts for 4-5 years, the barriers are capable of degrading contaminant influx over an extended period, allowing time for the secondary source to be degraded and preventing the residual plume migrating offsite during treatment of the residual source.
Fig. 2 Injection into downgradient plume in barrier formation, inside the factory building
Following application in the source area, the parent compound (TCE) has been reduced to very low concentrations. It is expected that back diffusion is providing an influx into the treatment zone, but the ideal degradation conditions maintained by the 3DMe ensure that the TCE is immediately degraded as it diffuses into the mobile porosity. This is evidenced by the sequential creation and degradation of the breakdown produces, with full reductive dechlorination being achieved.
Fig. 3 Long term monitoring results for well P6, located in the source zone
Validation monitoring downgradient of the barriers, show that the total chlorinated solvent mass flux has been reduced, with full reductive dechlorination occurring.
Fig. 4 Long term monitoring results for well MW12, located in the barrier (plume area)