Dynamic Underground Stripping-Hydrous Pyrolysis Oxidation at the Savannah River Site 321-M Solvent Storage Tank Area, Aiken, Georgia

Site Name:

Savannah River Site 321-M Solvent Storage Tank Area

Location:

Aiken, Georgia

Period of
Operation:

September 9, 2000 to September 28, 2001

Cleanup
Type:

Field demonstration

Technology:
Dynamic Underground Stripping-Hydrous Pyrolysis Oxidation (DUS/HPO)
- 3 steam-injection well clusters installed around the perimeter of the 100 ft by 100 ft treatment area; each well cluster consisted of 3 injection wells with screen intervals at 50-70 ft bgs, 110-130 ft bgs , and 150-160 ft bgs
- One dual-phase groundwater and vapor extraction well installed in the center of the target zone with a screen interval from 20-160 ft; this well was operated using a high-temperature electric-submersible pump, located 15 ft below the static groundwater elevation (143 ft bgs)
- 3 vadose zone soil vapor extraction wells along the perimeter of the target zone vapors
- Steam for the system supplied from other industrial operations at the site
- Extracted vapors sent through a heat exchanger, DNAPL-water separator; SVE operated at level that kept contaminant vapor discharge below permitted levels
- Air was injected into the deep saturated zone injection wells to enhance the HPO process
- Initial steam injection to the deep vadose zone was at a maximum design pressure of 60 psig and a temperature of 152°C; and 40 psig and 143°C for the intermediate vadose zone
- 14 downhole thermocouple arrays and electrical resistance tomography (ERT) images which displayed changes in subsurface resistance caused by differences in temperature
- Groundwater was heated to a temperature of approximately 100°C, while the source zone reached a temperature of approximately 100°C

Cleanup Authority:
RCRA

Contacts:

Technical Contacts:
Jerry “Bull” Bullard
Site Technical Representative
Westinghouse Savannah River Company
Building 730-2B
Aiken, SC 29808
Telephone: (803) 592-6359

Technology System Vendor:
Dr. David Parkinson
Project Manager
Integrated Water Resources
P.O. Box 2610
Santa Barbara, CA 93120
Telephone: (805) 966-7757
E-mail: dave@integratedwater.com
State Regulator:
Mair DePratter, P.G.
Hydrogeologist
South Carolina Department of Health and Environmental Control (SC DHEC)
2600 Bull Street
Columbia, SC 29201
Telephone: (803) 898-3432

Contaminants:
Chlorinated Solvents
- Tetrachloroethene (PCE) and trichloroethene (TCE)
- DNAPL contamination - 90% PCE and 10% TCE

Waste Source:
Spills and leaks from storage areas, sewer lines, and settling basins

Type/Quantity of Media Treated:
Source zone
- Total volume of 52,000 cubic yards based on a surface area of 100 ft by 100 ft and a depth of 160 ft

Purpose/Significance of Application:
Field demonstration of DUS/HPO to treat DNAPL contamination in the source zone

Regulatory Requirements/Cleanup Goals:
- The performance objectives for the pilot demonstration were: (1) contaminants must be extracted from the target source zone; (2) the target source zone must be heated to the applied boiling point; and (3) air to support HPO must be injected into the treatment area
- The system must meet discharge limits for vapor emissions and water discharge; however, specific values were not provided

Results:
- From September 2000 through September 2000, a total of 31,000 kg of contaminant were removed (30,000 kg of PCE and 1,000 kg of TCE)
- By March 2001, more than 62% of the TCE mass had been removed compared to 26% of PCE mass; attributed to the lower boiling point of TCE; after March 2001, concentrations and daily removal rates decreased more rapidly for TCE than for PCE, likely due to removing the majority of TCE during initial heating and the relatively higher rate of destruction of TCE by HPO
- Performance objectives were met on March 8, 2001; however system operation was continued until September 26, 2001 for additional contaminant mass removal
- The mass of contaminants destroyed in the subsurface by HPO was not quantified. However, based on estimates from other projects and experimental work at Lawrence Livermore National Laboratory, the vendor indicated that the amount of dissolved phase contaminants expected to be destroyed by HPO would be at least 10% (6,800 lbs) and could be as high as 30% (20,000 lbs) of the contaminant removed by DUS.

Cost Factors:
- The Interstate Technology Regulatory Council (ITRC) reported a project cost of $29/cu yd for the pilot system not including the cost for steam generation and treatment of vapor and dissolved phase contaminants
- No additional information was provided

Description:
The Solvent Storage Tank Area (SSTA) is located west of Building 321M in the M-Area of the U.S. DOE Savannah River Site (SRS), in Aiken, S.C. Building 321M operated as a target fabrication facility, primarily housing metallurgical and mechanical processes such as casting, extrusion, hot-die-sizing and welding. The SSTA included a 17,000 gallon storage tank for chlorinated solvents including PCE and TCE. Numerous spills and leaks were suspected to have occurred in this area. Results of site investigations indicated that DNAPL was present in silts and clays in the vadose zone above the water table at depths ranging from 20 to 35 feet bgs. A pilot-scale demonstration of DUS/HPO was performed from September 9, 2000 to September 28, 2001 to treat DNAPL in the source zone.

A treatment area of 100 ft by 100 ft by 160 ft (52,000 cubic yards) was used for the demonstration. The pilot-scale system included 3 steam-injection well clusters installed around the perimeter of the treatment area; one dual-phase groundwater and vapor extraction well installed in the center of the target zone; 3 vadose zone soil vapor extraction wells along the perimeter of the target zone vapors; and vapor and effluent treatment. Air was injected into the deep saturated zone injection wells to enhance the HPO process. Groundwater was heated to a temperature of approximately 100°C, while the source zone reached a temperature of approximately 100°C. By March 2001, the performance objectives for the pilot-scale demonstration had been met. System operation was continued until September 26, 2001 to remove additional contaminant mass. A total of 31,000 kg of contaminant were removed, including 30,000 kg of PCE and 1,000 kg of TCE. The reported cost for the pilot-scale demonstration was $29/cu yd for the pilot system not including the cost for steam generation and treatment of vapor and dissolved phase contaminants. According to the vendor, the most difficult region of the target zone to heat was the shallow portions at the center of the treatment area. The most likely reason for this was the circulation of air from the surface to the shallow zone. Restricting vapor extraction and continuous long-term steam injection sufficiently heated this portion after five months of steam injection.