Edible Oil Barriers for Treatment of Perchlorate Contaminated Groundwater

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An EOS® biobarrier was designed and implemented to remediate perchlorate contaminated groundwater. The report describes the site characterization, design steps, implementation, monitoring results and lessons learned from this effective remedial approach.

EXECUTIVE SUMMARY
This final technical report documents the demonstration of emulsified edible oils for remediation of perchlorate in groundwater. The demonstration was conducted at a confidential site in Maryland with a mixed perchlorate and 1,1,1-TCA groundwater plume. The primary objective of this project was to evaluate the cost and performance of an emulsified oil permeable reactive barrier (PRB) to control the migration of perchlorate plumes at DoD installations. The performance of the PRB was evaluated by monitoring the distribution of the oil emulsion in the aquifer, the impact of the oil injection on the aquifer permeability and groundwater flow paths, and the changes in contaminant concentrations and biodegradation indicator parameters both upgradient and downgradient of the PRB. Data obtained during the pilot test were used to demonstrate the cost-effectiveness of emulsified edible oils for remediation of perchlorate and chlorinated ethanes in groundwater through enhanced biodegradation.

The primary advantages of emulsified oils for groundwater remediation are:
  • No aboveground remediation equipment
  • Rapid conversion of aquifer to reducing conditions
  • Low operation and maintenance costs
  • Long-lasting (est. 5 years) in situ treatment
  • Cost-effective

The cost-effective use of emulsified oils may be limited by the potential impacts on groundwater geochemistry, the absence of the appropriate microorganisms, and the depth to groundwater. However, proper design can account for many of these issues.

Demonstration Design
The demonstration was conducted at a site in Maryland with a mixed perchlorate and 1,1,1-TCA groundwater plume. The shallow aquifer at the site consists of silty sand and gravel to a depth of approximately 15 feet below ground surface (bgs) and has been impacted by a former lagoon that received ammonium perchlorate and waste solvent. The water table is approximately 5 feet bgs with a groundwater velocity of approximately 100 feet/year. The demonstration activities included both laboratory studies using site soils and a field pilot test involving injection of emulsified oil substrate (EOS®) to form a PRB.

A laboratory microcosm study was conducted to evaluate the effectiveness of EOS® for remediating perchlorate and 1,1,1-TCA, and a column study was performed to assess EOS® distribution in site sediments. The microcosm study demonstrated that EOS® addition was effective in stimulating anaerobic biodegradation of perchlorate and 1,1,1-TCA in site sediments and that bioaugmentation was not required to achieve complete dechlorination of 1,1,1-TCA and other chlorinated compounds to non-toxic and products. These column study results indicated that EOS® could be effectively distributed in aquifer material from the Maryland site.

The field demonstration consisted of a one-time injection of EOS® and chase water to create a 50-ft long PRB. In October 2003, approximately 110 gallons of EOS® and 2,070 gallons of water were injected into the subsurface. Monitoring activities were conducted over an 18-month period to evaluate performance of the PRB. The PRB was located approximately 50 feet upgradient of an existing interceptor trench. Groundwater is extracted from the interceptor trench, treated via an air stripper, and re-injected via an upgradient infiltration gallery.

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