Vinyl Chloride Bioremediation in Central Ohio

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Site Summary:

CL-Out® bioremediation removed vinyl chloride and other chlorinated  solvents found in ground water at a former automobile repair shop.  The solvents were thought to have been released from an underground storage tank (UST).    After the UST and associated contaminated soil were removed, CL-Out bioremediation was implemented to reduce the levels of contamination to site-specific cleanup goals.

Geology

The site is set in the area of central Ohio where the ground moraine is relatively thin.  The underlying bedrock is limestone with a very porous and heavily fractures surface.   While the till of the ground moraine is relatively impermeable the bottom of the UST cavity was very close to the bedrock surface.

Hydrogeology

The affected ground water was in the weathered surface of the bedrock, which is a relatively prolific formation.    The depth to the top of water was approximately 9 feet and the monitoring wells were screened to a total depth of 15 feet.

Contamination

The size of ground water plume that resulted from leaching soil contaminants was estimated to be 4,000 square feet.  The original contaminant was suspected to be PCE, but the main contaminants at the time of the remediation were cis 1,2 DCE and vinyl chloride.  There may have been naturally occurring organisms that degraded the PCE to DCE and vinyl chloride.  CL-Out bioaugmentation was implemented to accelerate the natural process to achieve timely site closure.

Remediation Design

CL-Out bioremediation was implemented through temporary injection wells in the source area.  Two applications of CL-Out were made between February and August 2008.    Monitoring wells were sampled in the treatment area to assess the progress of the remediation.  The following table shows the contaminant concentration treads in the monitoring well with the highest pre-treatment contaminant concentrations.

  Contaminant Concentrations (µg/L)
PCE TCE DCE Vinyl Chloride
Pre-Treatment  11/13/07 BDL BDL 10.0 80.0
First Injection 2/29/08 – 1 Drum of CL-Out
Post-Treatment 6/16/08 BDL BDL 7.7 27.0
Second Injection 8/12/08 – 2 Drums of CL-Out
Post-Treatment 9/4/08 BDL BDL 1.6 4.6
Post-Treatment 12/9/08 BDL BDL 1.3 BDL

Maintaining Aerobic Conditions

CL-Out bioremediation is aerobic cometabolism that uses dextrose as the growth substrate.  Oxygen is required for the metabolism of the dextrose and to supply oxygen for the oxygenase enzyme that is responsible for the destruction of the DCE and vinyl chloride molecules.  During the project dissolved oxygen levels (DO) and redox conditions (ORP) were monitored.   Prior to CL-Out remediation the DO average was 1.4 mg/L and the ORP was -62.  With clearly anoxic site conditions, CL-Out bioremediation was selected, but the redox conditions were monitored to be sure the conditions did not fall out of the effective range for CL-Out bioremediation.

As the remediation progressed, the DO and ORP decreased to 0.42 and -225 respectively.  During the August 12, 2008 CL-Out application, ORP socks were installed in two monitoring wells to maintain aerobic conditions for the remainder of the project.

Microbial Population

CL-Out consists of naturally-occurring Pseudomonas sp. organisms.  The background population of Pseudomonas sp.  was tested prior to CL-Out bioaugmentation.  The background population was 19,000 cfu/ml.  The target population for effective remediation is 1,000,000 cfu/ml.  Thirty days after CL-Out bioaugmentation the population of Pseudomonas sp.  was 840,000 cfu/ml in a down gradient monitoring well.

 Results

After two small treatments, the contaminant concentrations in the source area were reduced to acceptable levels.  There was no rebound in the four months of post treatment monitoring.

 

CL-Out Bioremediation of Groundwater in Clay Soils

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CL-Out bioremediation of groundwater in clay soils reduced concentrations of PCE and TCE at a former dry cleaners in Illinois.  In just over 2 weeks after injection, CL-Out microbes cut the contaminant concentrations in half.

  • PCE from 62.2 to 25.6 mg/L
  • TCE from 11.2 to 6.0 mg/L
  • Cis 1,2-DCE from 3.8 to 1.2 mg/L
  • Vinyl chloride less than 0.001 mg/L before and after treatment

The remediation continues as the microbes grow and cometabolize the residual contamination.  Even in tight clay soils the aerobic cometabolism remediates dry cleaning solvents without producing vinyl chloride or other dangerous by products.

Aerobic PCE Bioremediation

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CL-Out Aerobic PCE Bioremediation Pilot Study Results

A CL-Out bioremediation pilot study confirmed that aerobic PCE cometabolism removed dry cleaning solvent contamination from ground water.  The pilot study was located at a former dry cleaners.  At the site, the PCE in ground water was 27 parts per billion (ppb).  Bioaugmentation introduced CL-Out microbes and dextrose as the metabolic substrate by injected into the ground water up gradient from the sentinal monitoring well.  After 30 days the PCE concentration decreased to 20 ppb.  After 6 months the PCE concentration decreased to 16 ppb.

As the PCE was decreasing, the site conditions stayed aerobic.  The dissolved oxygen level in ground water decreased from 1.07 to 0.71 mg/l.  Meanwhile,  the ORP decreased from 99 to 45 mv.  These aerobic aquifer conditions support the conclusion that the PCE removal was through aerobic bioremediation.

CL-Out cometabolism uses a dioxygenase enzyme that is produced constituatively as the metabolic substrate is consumed.  The dioxygenase enzyme destabilizes the carbon bond in the PCE to convert the molecule to an organic acid that leads to complete mineralization. Click here to view the PCE and TCE cometabolic degradation pathways.

CL-Out is a consortium of naturally-occurring microbes.  The microbes have the benefits of metabolic diversity and environmental stability.  They are non-pathogenic and safe for human health and the environment. Click here to find out more about CL-Out bioremediation.

 

 

Brownfield Plan Included CL-Out Bioremediation

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A brownfield plan included Cl-Out bioremediation to reduce high concentrations of TCE and other contaminants in ground water at an industrial site near Newark, New Jersey. Using a dynamic remediation plan, three applications of CL-Out microbes followed remediation progress sampling during the site preparation for construction. After reducing the maximum CVOC concentrations from over 8,000 ug/L to less than 20 ug/L, the site met the remediation goals and received a No Further Action Letter from NJDEP. For more information and a detailed case study, click here.

Aerobic Cometabolism of Chlorinated Solvents

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CL-Out® aerobic cometabolism successfully remediated solvents in ground water at an operating industrial site in central New Jersey.  The manufacturing and plating facility had historical petroleum and solvent releases.

Chlorinated solvents found in the ground water in two plumes covered a combined area of about one half acre.  A mix of chlorinated solvents including 1,1,1-TCA, 1,1-DCE and PCE in low concentrations icontaminated the ground water.    The remediation goal was to reduce the mass of contamination in the ground water plume to prevent mitigate off-site risks.

After the CL-Out aerobic cometabolism, ground water concentrations in all monitoring wells decreased by more than 80%, which was sufficient to meet the remediation standards.  Click here to download a complete case study.