Engineered Bioremediation: An Innovative Solution for Chlorinated Solvent Contamination

Elevated levels of chlorinated organic compounds, such as perchloroethene (PCE) or trichloroethene (TCE), are often present in groundwater beneath sites where manufacturing and industrial operations have occurred. An innovative technology known as Enhanced In SituBioremediation (EISB) is being used to cost-effectively treat these contaminated sites.

EISB, or engineered bioremediation, is the acceleration of microbial activities to enhance the degradation or detoxification of environmental pollutants in an anaerobic environment. EISB eliminates harmful chlorinated compounds or converts the compounds into harmless byproducts. EISB is cost-effective and efficient because it is applied in situ without major disruption to ongoing business activities.

EISB uses amendments such as oxygen, electron donors, ferrous iron, liquid-activated carbon, or microorganisms to treat groundwater impacted by chlorinated compounds. These amendments are used to create or enhance the site conditions necessary for biodegradation to take place.

3-D Microemulsion (3DME) is an example of an electron donor amendment used in EISB to aid in the anaerobic biodegradation of chlorinated compounds. 3DME is an injectable highly-distributable liquid material specifically designed for in situ remediation projects where the anaerobic biodegradation of chlorinated compounds through enhanced reductive dechlorination (ERD) processes is possible.

In some cases of EISB, a combination of amendments is used to create optimal remediation conditions. For example, 3DME can be mixed with a technology called Chemical Reducing Solution (CRS). CRS is a soluble, food-grade source of ferrous iron designed to precipitate reduced iron sulfides, oxides, and/or hydroxides.

CRS is used in conjunction with 3DME to provide the necessary iron to activate the abiotic chemical reduction of chlorinated organic groundwater contaminants, such as PCE, TCE, dichloroethene (DCE), and vinyl chloride (VC). The end products of these biogeochemical reductions are ethene and ethane.

EISB technology also addresses the issue of slow biodegradation of intermediate compounds. Bio-Dechlor INOCULUM Plus (BDI Plus) is an amendment used to accelerate the complete dechlorination of these intermediate, recalcitrant contaminants. BDI Plus is an enriched, natural microbial consortium containing species of Dehalococcoides sp (DHC) capable of completely dechlorinating contaminants during in situ anaerobic bioremediation processes.

EISB is used for remediation at a wide range of manufacturing and industrial sites with chlorinated solvent contamination. For example, at a confidential aerospace manufacturing facility located in Southern California, a combination of 3DMe, CRS, and DHC was used to treat the core of a major TCE plume measuring ½ mile long by ¼ mile wide.

Approximately 700,000 gallons of the mixed 3DME/CRS/DHC solution were injected into 75 dual-nested injection wells. Subsequent groundwater sampling results revealed that TCE was reduced in the primary observation well from as high as 40,000 micrograms per liter (µg/l) to as low as 11 µg/l. TCE concentrations in some of the other monitoring wells located within the injection area were reduced by approximately 50 to 90%.

Another example of the use of EISB technology was illustrated at a former manufacturing site in Michigan. This site was successfully treated with a combined remedy approach using 3DME, DHC, and PlumeStop, a colloidal activated carbon. At this site, former industrial manufacturing activities released chlorinated compounds into the shallow groundwater resulting in a ¼-mile-long contaminant plume.

The groundwater plume was treated with a multi-phase ERD approach using 3DME, PlumeStop, and DHC. This cost-effective approach significantly reduced the contaminant plume and created conditions for the long-term biodegradation of residual chlorinated compounds.  

A further example of the success of EISB is seen at a Santa Barbara manufacturing site. This site formerly conducted manufacturing operations leading to PCE and TCE groundwater contamination. Previous remediation attempts were unsuccessful in achieving site goals and site closure. The goals at this site included the rapid reduction of chlorinated compounds in groundwater and preventing further downgradient migration of PCE and TCE. PlumeStop, Hydrogen Release Compound (HRC), and DHC were chosen because they provided a safe and efficient solution for the site.

A pre-field remediation test was conducted to confirm the use of this technology. This test led to cost-saving adjustments in the site design, reducing project costs by 30%. The EISB approach successfully eliminated the contaminants and created conditions for sustained treatment at the site.

One of the primary advantages of EISB is that it can be performed in situ. This allows the site to be treated without removing the bulk soil, saving both time and money. In situ treatment is also beneficial because it provides safer conditions for site workers and can be completed with lower operating costs compared to conventional pump and treat methods.

EISB can be applied at a wide variety of industrial and manufacturing sites with chlorinated solvent contamination. In comparison to chemical oxidation, pump and treat, and electrical resistance heating, EISB is often both more efficient and less expensive. EISB uses amendment technology to efficiently eliminate environmental pollutants in anaerobic environments and is a proven remediation solution for chlorinated solvent contamination.

Authored by: Steve Ridenour, Daniel Nunez, and Mike Cassidy 

Steve Ridenour is Senior Project Manager/Senior Geologist III at Alta Environmental

Daniel Nunez is Southwest District Manager at REGENESIS

Mike Cassidy is Vice President, Site Assessment and Remediation, of Alta Environmental