Methane Enhanced Bioremediation Using Horizontal Wells at the Savannah River Site, Aiken, South Carolina

Site Name:

Savannah River Site

Location:

Aiken, South Carolina

Period of
Operation:

February 26, 1992 to April 30, 1993

Cleanup
Type:

Field demonstration

Vendor:

Not Provided

DOE Integrated
Demonstration
Manager:

Kurt Gerdes
U.S. DOE
Office of Environmental Management
Science & Technology Development
Office of Technology Systems
Cloverleaf Room 1135
Germantown, MD 20874
Telephone: (301) 903-7289
Fax: (301) 903- 7457

Technology:
In Situ Bioremediation
- Methane enhanced bioremediation
- Two horizontal wells used for the demonstration:
- "lower" horizontal injection well - depth of 175 feet (below the water table); screen length of 310 feet; "upper" horizontal extraction well - depth of 80 feet (in the vadose zone); screen length of 205 feet
- Air and gas injection rate - 200 scfm; air and contaminant extraction rate - 240 scfm
- Catalytic oxidizer used to treat the extracted vapors
- Demonstration performed in six different operational modes:
- baseline tests of the vapor extraction and injection systems (with and without air sparging)
- a series of nutrient additions (addition of 1% methane, 4% methane, pulsed 4% methane; and combination of nitrous oxide at 0.007% and triethyl phosphate at 0.07% in air in combination with pulses of 4% methane)
- a helium tracer test
- an assessment of microbiological assays for monitoring performance

Cleanup Authority:
CERCLA

Regulatory Contact:
Not Provided
Principal Investigators:
Dr. Terry C. Hazen
Lawrence Berkeley National Laboratory
Center for Environmental Biotechnology
MS 70A-3317
One Cyclotron Road
Berkeley, CA
(510) 486-6223
Fax: (510) 486-7152
tchazen@lbl.gov

Brian Looney
Westinghouse Savannah River Company
PO Box 616
Aiken, SC 29802
(803) 725-6413/(803) 725-3692

Contaminants:
Chlorinated Solvents
- TCE and PCE concentrations in groundwater ranged from 10 to 1,031 µg/L and 3 to 124 µg/l, respectively
- TCE and PCE concentrations in sediment ranged from 0.67 to 6.29 mg/kg and 0.44 to 1.05 mg/kg, respectively

Waste Source:
Wastewater discharges from aluminum forming and metal finishing operations

Type/Quantity of Media Treated:
Groundwater and sediment
- VOC plume was estimated to cover about 1200 acres and to be about 150-ft thick
- Dense nonaqueous phase liquids (DNAPLs) have also been observed
- Depth to groundwater - 120 to 135 feet bgs
- Groundwater velocity - 15 to 100 feet/year

Purpose/Significance of Application:
Field demonstration of in situ bioremediation system using horizontal wells and methane injection

Regulatory Requirements/Cleanup Goals:
- Cleanup goals for groundwater included TCE (5 ppb) and PCE (5 ppb)
- Information was not provided about cleanup goals for sediment

Results:
- After 384 days of operation, the system removed about 17,000 lbs of VOCs through a combination of vacuum extraction and biodegradation - the vacuum component of the system removed 12,096 lbs of VOCs and the biological component degraded 4,838 lbs of VOCs
- After treatment, the total sediment inventory for both TCE and PCE decreased by 24%, with the concentrations of VOCs in most sediment samples reported to be below the detection limits; concentrations of TCE and PCE in groundwater were reported to be less than 5 ppb; soil gas concentrations reportedly decreased by more than 99%
- The addition of methane stimulated the growth of methanotrophs - 1% methane addition increased the population of methanotrophs by several orders of magnitude, to levels close to 100,000 MPN/ml; 4% methane addition initially increased the population of methanotrophs, which then decreased as a result of nutrient depletion
- The addition of nitrogen and phosphorous nutrients with pulsed methane stimulated microbial activity. This phase was reported to optimize bioremediation and mineralization of TCE and PCE in groundwater and sediments
- Helium tracer tests indicated that more than 50% of the injected methane was consumed by indigenous microbes before it reached the extraction well; results were not provided from the microbiological assays

Cost Factors:
- Projected costs for full-scale application at this site were $452,407 for total capital costs (including equipment amortized over 10 years, well installation, and mobilization) and $236,465 for operation and maintenance (including monitoring, consumables, and demobilization)

Description:
The U.S. Department of Energy (DOE) Savannah River Site (SRS) is a 300 square mile facility located in Aiken, South Carolina that has been used for the research and production of nuclear materials. Area M at the facility was used for aluminum forming and metal finishing operations. Wastewaters from this area containing an estimated 3.5 million pounds of solvents were discharged to an unlined settling basin, a process sewer line, and a nearby stream from the 1950's to the 1980's. High levels of chlorinated solvents, primarily TCE (up to 1,031 ug/L in groundwater and 6.29 mg/kg im sediment) and PCE (up to 124 ug/L in groundwater and 1.05 mg/kg in sediment), were found at the site and DNAPLs were observed. The VOC groundwater plume was estimated to cover about 1200 acres and to be about 150-ft thick.

From February 1992 to April 1993, DOE conducted a field demonstration of in situ methane enhanced bioremediation using two horizontal wells - one located below the water table and used for injection and one located in the vadose zone and used for extraction. A catalytic oxidizer was used to treat the extracted vapors. The demonstration was performed in six different operational modes, varying the type and concentration of nutrients added and the use of pulsing. During the demonstration, about 17,000 lbs of VOCs were removed through a combination of vacuum extraction and biodegradation. The addition of methane stimulated the growth of methanotrophs, with the addition of 1% methane increasing the population of methanotrophs by several orders of magnitude. Results of a tracer test showed that more than 50% of the injected methane was consumed by indigenous microbes before it reached the extraction well.