Bioaugmentation, using emulsified edible oil was tested in two field demonstrations for the in situ remediation of groundwater impacted with perchlorate and/or chlorinated solvents. Details about each demonstration are provided below:
The first demonstration was conducted at a confidential industrial site in eastern Maryland, using an emulsified oil substrate (EOS®) permeable reactive barrier (PRB) to treat a commingled perchlorate/chlorinated solvent plume. The design of the system is detailed below:
- Seven monitoring wells, four soil gas monitoring points, and two tracer test wells were installed as part of the site characterization activities.
- A 50-foot (ft) long by 10-ft wide by 10-ft deep EOS® PRB was installed perpendicular to groundwater flow.
- The optimal screen interval of the injection wells was determined to be 5 to 15 feet below ground surface (bgs).
- Due to uncertainties regarding the permeability of the aquifer, a conservative injection well spacing of 5 feet on-center (OC) was utilized.
- Nearly 2,200 gallons of EOS® were injected evenly into the 10 injection wells to create the PRB.
Source Area Demonstration
The second demonstration used EOS® to treat a small, simulated trichloroethene (TCE) source area test cell within a chlorinated solvent-contaminated solid waste management unit (SWMU) at the Charleston NWS in Goose Creek, South Carolina. A tightly-spaced grid of injection wells was used to distribute EOS® in the 20-ft by 20-ft by 10-ft deep pilot treatment test cell. The injection design consisted of a grid of 16 temporary, 1- inch diameter injection/extraction wells installed using direct-push methods, approximately 5 feet OC across the test cell.
The project was conducted in two phases within a small area within SWMU 17 at the site. Phase I included site characterization, baseline sampling, injection of EOS® and performance monitoring for 28 months. Phase II was performed after Phase I results indicated that low pH was limiting further biodegradation of the target contaminants. Phase II included a bench-scale treatability study, development and injection of a newly formulated pH-buffered substrate to overcome the pH problem, and an additional 11 months of monitoring.
Department of Defense (DoD)
Robert C. Borden
1101 Nowell Road
Raleigh, NC 27607
1101 Nowell Road
Raleigh, NC 27607
Environmental Restoration Program Manager
901 Stuart Street, Suite 303
Arlington, VA 22203
Contracting Officer Representative
Naval Facilities Engineering Service Center
1100 23rd Avenue, Code 411
Port Hueneme, CA 93043
Perchlorate, Trichloroethene (TCE)
PRB Demonstration: A defective rubber liner at a former impoundment used to store an aqueous solution of ammonium perchlorate and waste solvents resulted in groundwater contamination at the site.
Source Area Demonstration: EOS® was tested in a simulated TCE treatment zone located in a shallow, low-permeability aquifer where the geochemistry of the groundwater was not optimal for biodegradation to occur.
Type/Quantity of Media Treated:
PRB Demonstration: Groundwater (quantity not documented)
Source Area Demonstration: Groundwater (4,000 cubic feet)
Purpose/Significance of Application:
Purpose/Significance of Application: The project goals were to: (1) demonstrate and evaluate use of EOS® as the substrate for stimulating in situ biodegradation of perchlorate and chlorinated volatile organic compounds (CVOC) in groundwater and (2) develop a protocol for its implementation. The pilot tests evaluated the distribution of the emulsion in the aquifer, the impact of substrate injection on permeability and groundwater flow paths, and the changes in contaminant concentrations and biodegradation indicator parameters.
The overall goal of the PRB demonstration project in Maryland was to evaluate the cost and performance of an EOS® PRB for remediating perchlorate and chlorinated solvents in groundwater. The source area demonstration was designed as a pilot test to evaluate the effectiveness of EOS® for enhancing the biodegradation of CVOCs in a simulated source area.
Regulatory Requirements/Cleanup Goals:
Performance objectives for each demonstration are detailed below:
Source Area Demonstration:
- Reduce perchlorate concentrations by over 90% in one or more downgradient wells and achieve reductions that will meet the assumed 4 microgram per liter (ug/L) regulatory standard (effectively, the detection limit, which is greater than the two MDE standards and is accepted as demonstration of compliance.
- Reduce 1,1,1-TCA concentrations by over 75% in average 1,1,1-TCA concentration in downgradient wells.
- Reduce mass flux of perchlorate by over 75%.
- Reduce mass flux of total chlorinated ethanes by over 75%.
- Reduce TCE levels by over 90% in monitoring wells in treatment zone.
- Convert over 50% of TCE to nontoxic to ethene or ethane.
- Reduce mass flux of chlorinated ethenes by over 75%.
- Reduce average TCE concentration in treatment zone by over 80%.
Performance monitoring was initiated after the EOS® was injected (October 13-14, 2003) and then approximately 1 month, 2 months, 4 months, 11 months, and 18 months thereafter. Four additional semi-annual monitoring events were conducted in the 24 months following the initial performance period to evaluate the long-term effectiveness of the PRB.
- The EOS® PRB was very effective at degrading perchlorate throughout the duration of the pilot study with perchlorate concentrations below non-detect (<4 µg/L) in all injection wells within 5 days of injection. Perchlorate removal efficiency remained greater than 93% for 133 days in groundwater from the five injection wells that were measured.
- Additional contact time was needed to achieve the same results for 1,1,1-TCA and TCE. After 42 months, 1,1,1-TCA was reduced by 91% at a distance of 20 feet downgradient of the barrier. However, the lowest concentrations achieved did not meet the federal MCL of 200 µg/L. Increasing contact time allowed 1,1,1-TCA concentrations to get close enough to the MCL.
- The mass flux calculations indicated approximately 61 pounds (lb) of perchlorate was removed over the entire 42-month demonstration.
- No changes were observed in hydraulic conductivity or pH due to introduction of emulsified oil.
Source Area Demonstration:
- Almost 6 months after the Phase I injection of EOS® substrate, evidence of enhanced reductive dechlorination was noted in the test cell compared to the surrounding environment. By 28 months, the TCE concentrations were routinely 76 to 86% lower throughout the test cell groundwater than in the background groundwater.
- After the aquifer was neutralized, TCE was rapidly reduced to cis-1,2-dichloroethene (cDCE) and vinyl chloride (VC). However, the absence of appropriate microorganisms may have limited further biodegradation.
The unit cost to install the 50-ft long PRB was $226/ cubic yard (yd3). The cost to create a 20 x 20-ft source area treatment cell ranged from $325/yd3 for direct injection to $428/yd3 for a recirculation design. The mass of contaminant treated in the PRB was much higher due to the rapid flow of contaminated groundwater through the barrier. Consequently, the cost per gram of contaminant treated was also less in the PRB.
The total cost of the PRB pilot test demonstration was approximately $264,700. Primary cost elements included:
- Site characterization and design: ~$54,750 (21%)
- Laboratory treatability study: ~$30,000 (11%)
- PRB construction: ~$8900 (3%)
- Monitoring well network consisting of 14 additional wells: ~$10,130 (4%)
- Substrate and shipping: $2870 (1%)
- Labor and equipment to inject PRB: ~$20,000 (8%)
- Performance monitoring: ~$124,500 (~47%)
- Additional specialized analyses: $13,550 (5%)
The combined cost to install the PRB and the monitoring network and to manage the one-time injection of substrate to create the PRB (items c, d, e, and f) was $41,900, which calculates to $8.39/cubic feet (ft3) or $226/yd3.
Source Area Demonstration:
The total cost of the source area treatment demonstration was approximately $377,800. Primary cost elements included:
- Site characterization and design: ~$37,900 (10%)
- Treatment cell construction with monitoring wells: ~$27,800 (8%)
- Phase I substrate and shipping: ~$3100 (1%)
- Labor and equipment to inject Treatment Cell — Phase I: ~$38,400 (10%)
- Laboratory treatability study: ~$43,100 (11%)
- Phase II substrate and shipping: ~$10,500 (3%)
- Labor and equipment to inject treatment cell — Phase II: ~37,650 (10%)
- Performance monitoring: ~$128,250 (34%)
- Extra specialized analyses: ~$51,100 (14%)
The combined cost to install the treatment grid, the monitoring network, and manage the injection of substrate using the temporary injection/recovery recirculation approach was $69,300 (items b, c and d), which calculates to $17/ft3 or $468/yd3 to impact the 4000 ft3 (148 yd3) treatment zone.
The PRB demonstration was conducted at a confidential industrial site in eastern Maryland to treat a plume that extended downgradient of a closed surface impoundment. The former impoundment which operated at the site from 1976 through 1988 was used to store aqueous solution of ammonium perchlorate and waste solvents. A defective rubber liner leaked and led to groundwater contamination.
Site characterization activities revealed high perchlorate concentrations that were comingled with elevated levels of 1,1,1-trichloroethane (1,1,1- TCA) and low concentrations of trichloroethene (TCE) in the shallow groundwater. Perchlorate concentrations ranged from 3,100 to 20,000 µg/L, 1,1,1-TCA ranged from 5,700 to 17,000 µg/L, and TCE ranged from 28 to 210 µg/L. In October 2003, the PRB was constructed in an open grassy area approximately 150 feet downgradient from the former impoundment. EOS® injections occurred from October 13 through 14, 2003. Following the injection, performance monitoring occurred for a period of 18 months to test the effectiveness of the PRB to intercept and treat contamination and prevent further downgradient migration. Monitoring was prolonged by an additional 24 months to evaluate the longevity of the substrate in the subsurface. Sample results indicated that the PRB reduced perchlorate to below the regulatory target, but additional contact time was needed to achieve the same results for 1,1,1-TCA and TCE. There was no adverse change in pH and no evidence of flow by-passing around the PRB.
Source Area Demonstration:
The Source Area demonstration was performed within a TCE plume in an area designated as SWMU 17 at the Charleston NWS in Goose Creek (near Charleston), South Carolina. Previous site characterization activities indicated that the geochemistry of the groundwater was not optimal for biodegradation to occur. For the purposes of the demonstration, EOS® was tested in a simulated TCE 20 x 20 ft test cell at the Charleston on NWS. The concentrations of TCE within the test cell ranged from 9,800 to 28,000 µg/L, with very little cis-dichloroethane (cDCE) and no vinyl chloride or ethene detected. Contaminant concentrations were highest at between 8 and 16 feet bgs in this cell, in a moderate to lower permeability silty sand layer. The volume of contaminated aquifer material within the test cell was 4,000 ft3 (148 yd3).
The demonstration at the site was designed to evaluate the effectiveness of EOS® for enhancing the biodegradation of CVOCs in the simulated TCE source area. EOS was injected in a small grid configuration within the treatment cell in two separate phases. Phase I included site characterization, baseline sampling, injection of EOS® and performance monitoring for 28 months. The project was expanded to include Phase II after the performance monitoring results from Phase I indicated that low pH was limiting further biodegradation of the target CVOCs. Phase II included a bench-scale treatability study, development and injection of a newly formulated pH-buffered substrate to adjust the pH in the aquifer, and an additional 11 months of performance monitoring in the field to measure the effect of the second substrate on enhanced reductive dechlorination. After the aquifer was neutralized, TCE was rapidly reduced to cis-1,2-dichloroethene (cDCE) and vinyl chloride (VC) with some measurable ethene production. However, the absence of microorganisms with the VC-reductase enzyme appeared to limit further biodegradation.