In Situ Bioremediation Using Horizontal Wells at the U.S. Department of Energy's Savannah River Site, M Area, Aiken, South Carolina

Site Name:

Savannah River Site

Location:

Aiken, South Carolina

Period of
Operation:

February 1992 to April 1993

Cleanup
Type:

Field demonstration

Vendor:

Terry Hazen and Brian Looney, Prin. Inv.,WSRC,
(803) 725-6413, (803) 725-3692

Caroline Teelon, (Licensing Information), WSRC
(803) 725-5540

Technology:
In Situ Bioremediation (ISB)

- Combines gaseous injection of air and nutrients (N, P, CH4) into ground water with soil vacuum extraction
- Provides for sparging/biodegradation of VOCs in the ground water
- Uses horizontal wells to provide more effective access to subsurface contamination
- Horizontal wells installed at 176 ft below ground surface (bgs) (saturated zone - used for injection) and 75 ft bgs (vadose zone - used for extraction)

Cleanup Authority:
State: Air discharge and underground injection control (UIC) permits for the SRS are in place with the South Carolina Department of Health and Environmental Control (SCDHEC).

SIC Code:
9711 (National Security)
3355 (Aluminum Forming)
3471 (Metal Finishing)
Point of Contact:
Kurt Gerdes, DOE
(301) 903-7289
Jim Wright, DOE
(803) 725-5608

Contaminants:
Chlorinated Aliphatics

- Trichloroethene (TCE) and tetrachloroethene (PCE)
- TCE concentrations in the ground water ranged from 10 to 1031 mcg/L, and PCE from 3 to 124 mcg/L
- TCE concentrations in the sediments ranged from 0.67 to 6.29 mg/kg, and PCE from 0.44 to 1.05 mg/kg.

Waste Source:
Surface impoundment (unlined settling basin)

Type/Quantity of Media Treated:
Soil (sediment) and Ground Water
- Water table located at 120 ft bgs
- Vadose zone well radius of influence estimated to be greater than 200 ft
- Saturated zone well influence extended as far as 100 ft from well
- Vadose zone soils consists of sand, silt, clay, and gravel, with layers ranging up to 18% silt and clay
- Saturated zones consist of several layers of sand with silt and clay beds

Purpose/Significance of Application:
ISB combines biodegradation (sparging and biostimulation) with SVE to remediate both soil and ground water contaminated with VOCs

Regulatory Requirements/Cleanup Goals:
The demonstration was covered by permits issued by the SCDHEC, including an air quality permit and a UIC permit (because of the addition of methane and nutrients).
Groundwater protection standards of 5 ppb for TCE and PCE, and 200 ppb for TCA, were identified for Area M

Results:
- Almost 17,000 lbs of VOCs were removed or degraded over 384 days of operation (12,096 lbs extracted and 4,838 lbs biodegraded)
- Mass balance data showed that bioremediation destroyed 40% more VOCs than simple air sparging
- ISB reduced VOC concentrations in the ground water below the 5 ppb cleanup goals for TCE and PCE; overall groundwater concentrations were reduced by up to 95%
- VOC concentrations in most sediments were nondetectable; soil gas concentrations decreased by more than 99%

Cost Factors:
- No information is provided on the capital or operating costs for the ISB demonstration at SRS
- An analysis of capital and operating costs for an ISB application was made by LANL in a comparison with conventional pump and treat with SVE
- The LANL analysis showed that ISB had capital costs approximately 30% greater than PT/SVE, operating costs 10% lower, and would require 3 yrs instead of 10 yrs to remediate the demonstration site

Description:
From 1958 to 1985, Savannah River Area M conducted manufacturing operations including aluminum forming and metal finishing. Process wastewater from these operations containing solvents (TCE, PCE, and TCA) was discharged to an unlined settling basin at Savannah River, which lead to contamination of ground water and vadose zone soils. Full-scale treatment of groundwater began in 1985. Treatment of vadose and saturated zones has been the subject of several demonstrations (e.g., in situ air stripping), including this investigation of the technical and economic feasibility of in situ bioremediation (ISB) technology.

ISB combines gaseous injection of air and nutrients (N, P, CH4) into ground water with soil vacuum extraction technology. This provides for sparging and biodegradation of VOCs in the ground water, and extraction of VOCs from the vadose zone. At SRS, two horizontal wells were used to provide more effective access to subsurface contamination. Horizontal wells were installed at 176 ft bgs (in the saturated zone - used for injection) and 75 ft bgs (in the vadose zone - used for extraction).

Almost 17,000 lbs of VOCs were removed or degraded at SRS over 384 days of ISB operation. This total consists of 12,096 lbs of VOCs extracted and 4,838 lbs biodegraded. Mass balance data showed that bioremediation destroyed 40% more VOCs than simple air sparging, and that it reduced VOC concentrations in the ground water below the 5 ppb cleanup goals for TCE and PCE. Overall TCE and PCE groundwater concentrations were reduced by up to 95%. In addition, VOC concentrations in most sediments were nondetectable, with soil gas concentrations decreased by more than 99%.