In Situ Air Stripping of Contaminated Groundwater at the U.S. Department of Energy's Savannah River Site, A/M Area, Aiken, South Carolina

Site Name:

Savannah River Site

Location:

Aiken, South Carolina

Period of
Operation:

July 1990 to September 1993

Cleanup
Type:

Field Demonstration

Vendor:

C.L. Bergen Westinghouse Savannah River Co. Aiken, SC

Technology:
In Situ Air Stripping - 7 horizontal wells installed; only 2 wells used in field demonstration - Demonstration wells: 1 installed in saturated zone; 1 installed in vadose zone; targeted contaminated sands - Air injected through lower horizontal well, below the water table - Demonstration focused on supplementing pump and treat efforts - Demonstration did not include offgas treatment

Cleanup Authority:
RCRA Corrective Action and State: South Carolina Dept. of Health and Environmental Control, Air Quality Control, and Underground Injection Control

SIC Code:
9711 (National Security) 3355 (Aluminum forming) 3471 (Metal finishing)
Point of Contact:
G.E. Turner, DOE Savannah River Oper. Office Environmental Restoration Div. Aiken, SC

Contaminants:
Chlorinated Aliphatics - Trichloroethene (TCE), Tetrachloroethene (PCE), 1,1,1-Trichloroethane (TCA) - Concentrations of volatile organic compounds (VOCs) in groundwater reported as high as 500 ppm - Groundwater TCE concentrations over 48 ppm - Groundwater contains 260,000-450,000 pounds of dissolved organic solvents in concentrations greater than 0.01 ppm, estimated to be 75% TCE - Soil TCE concentrations over 10,000 ~g/L (1991) - Dense nonaqueous phase liquids (DNAPLs) are present in groundwater

Waste Source:
Surface Impoundment

Type/Quantity of Media Treated:
Groundwater and Soil - Area of VOC-contaminated groundwater has an approximate thickness of 150 feet and covers about 1,200 acres - Aquifer units characterized to 180 feet below ground surface (9 separate units), showing complex hydrogeology and discontinuous sand and clay layers - Hydraulic conductivity 9 - 73 ft/day - Transmissivity 175 - 12,500 gpd/day

Purpose/Significance of Application:
Field demonstration of in situ air stripping using horizontal wells to supplement groundwater pump and treat technology.

Regulatory Requirements/Cleanup Goals:
- No specific cleanup goals identified for the field demonstration - Demonstrations permitted by the South Carolina Department of Health and Environmental Control (SCDHEC) Air Quality Control (AQC) and Underground Injection Control (UIC)

Results:
- Substantial changes in groundwater VOC concentrations measured during demonstration - Increased microbial numbers and metabolic activity exhibited during air injection period - 139 day demonstration (July-December 1990) removed nearly 16,000 pounds of VOCs - Vacuum extraction removed an estimated 109 lbs VOC/day while air injection resulted in an additional 20 lbs/day VOC removal

Cost Factors:
- Costs for conducting field demonstration not provided Cost study for in situ air stripping provided the following projected

Costs:
- Total equipment costs - $253,525 (including design and engineering, well installation, air injection and extraction system, piping, and electrical) - Site costs - $5,000 (setup and level area) - Total Annual Labor Costs - $62,620 (including mobilization/demobilization, monitoring, and maintenance) - Total Annual Consumable Costs $157,761 (including carbon recharge, fuel, and chemical additives)

Description:
At the U.S. Department of Energy Savannah River Site, administrative buildings are located within the A area and aluminum forming and metal finishing operations have been performed within the "M" area. An estimated 3.5 million pounds of solvents were discharged from these operations between 1958 and 1985, with over 2 million pounds sent to an unlined settling basin. Groundwater contamination beneath the settling basin was discovered in 1981. A pump and treat program has been ongoing since 1985 for removal of VOCs from the groundwater.

A field demonstration using in situ air stripping with horizontal wells in the A/M Area was conducted from July 1990 to September 1993. The demonstration was part of a program at Savannah River to investigate the use of several technologies to enhance the pump and treat system. In the air stripping demonstration, air was injected into a lower horizontal well in the saturated zone and extracted through the horizontal well in the vadose zone. The demonstration did not include treatment of offgases. The in situ air stripping process increased VOC removal over conventional vacuum extraction from 109 pounds per day to 129 pounds per day. Nearly 16,000 pounds of VOCs were removed during the 139 day demonstration period.

A cost analysis performed as part of this demonstration showed that in situ air stripping would reduce costs by 40% over a conventional pump and treat with soil vapor extraction system. Installation costs for horizontal wells is greater than for vertical wells. At depths greater than 40 to 50 feet, horizontal well installation costs are approximately $200/ft; at less than 40 to 50 ft, costs are as low as $50/ft. Several implementation concerns were identified for installing horizontal wells at Savannah River.

can remove VOCs for approximately 69% of the cost for conventional methods. Installation costs for horizontal wells is greater than for vertical wells. For deeper horizontal wells (over 40-50 feet), costs range from $360 to $700 per foot. Several implementation concerns were identified for installing horizontal wells at Savannah River.