Only 3 months of recirculation results in over 90% reduction of PCE, TCE, and DCE

At a glance

Location: Oregon

Geology: Coarse (sand/gravel), Fine (silt/clay)

Contaminant(s): Chlorinated solvent

ETEC Solution(s): CarBstrate, ISD system

Unique challenge(s): Mixed contaminant types

Site Summary

On an active industrial site contaminated with chlorinated solvents, an aggressive bioremediation solution was required to reduce concentrations quickly. The solution included a 3 month period of active groundwater recirculation and electron donor substrate delivery - followed by 1 year of post monitoring. The results indicated that a limited-time and efficient sitewide substrate delivery strategy using groundwater recirculation will create ideal enhanced reductive dechlorination (ERD) conditions that persist for years.

Site conditions and remedial goal

The site was situated across an active industrial area in the heart of a former rail yard.  The soil and groundwater contamination was primarily PCE/TCE that was co-mingled with diesel-range petroleum hydrocarbons and chlorinated ethanes (TCA and DCA).  Up to 21,000 µg/L was observed as the total concentration of contaminants.  The total volume of the saturated zone was 89,000 cubic yards.

ETEC Solution

ETEC customized and installed a 40 gpm ISD™ system enabling the re-circulation of over 2.3 million gallons of groundwater over a 3 month timeframe (~35 gpm rate).  The groundwater was amended with 8,200 lbs of CarBstrate™, selected as the electron donor due to its high solubility and low cost, as well as the fact that it poses no risk to human health.

Groundwater was extracted from 11 extraction wells, amended with CarBstrate™, and distributed into the subsurface via 20 injection wells.  Shallow groundwater was already anoxic due to the presence of diesel fuel that had promoted partial dechlorination of PCE (as indicated by the presence of TCE, DCE, and VC prior to initiating the pilot demonstration).

Remedial outcome

The results demonstrate that aggressive short-term groundwater recirculation can achieve sitewide electron donor delivery that promotes complete PCE/TCE dechlorination within months.  For months and years after the recirculation event the ERD process continued due to utilization of soluble fermentation byproducts and generated biomass.

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