In Situ Enhanced Soil Mixing at the U.S. Department of Energy's Portsmouth Gaseous Diffusion Plant, X-231B Unit, Piketon, Ohio

Site Name:

Portsmouth Gaseous Diffusion Plant

Location:

Piketon, Ohio

Period of
Operation:

June 1992

Cleanup
Type:

Field demonstration

Vendor:

Jim Brannigan, Millgard, (313) 261-9760
Steve Day, Geo-Con, (916) 858-0480

Technology:
In Situ Enhanced Soil Mixing (ISESM)

- ISESM consists of soil mixing combined with additional technology
- Four additional technologies were demonstrated at PGDP: vapor extraction with ambient air injection (stripping); vapor extraction with hot air injection (stripping); hydrogen peroxide injection; and grout injection for solidification/stabilization
- 12 soil columns, each 10 ft in diameter and 15 ft deep, were treated in the demonstration
- One additional column was treated by hot air stripping to a depth of 22 ft
- Another additional column was used for a tracer study

Cleanup Authority:
State: Ohio EPA

SIC Code:
9711 (National Security)
Others - information not provided
Points of Contact:
Dave Biancosino, DOE, (301) 903-7961
Jim Wright, DOE, (803) 725-5608

Contaminants:
Chlorinated Aliphatics

- 13 VOCs were identified in the soil at PGDP
- Most prevalent VOCs were Trichloroethene (TCE), 1,1,1-Trichloroethane (TCA), 1,1-Dichloroethene (DCE), and methylene chloride
- Concentrations ranged from several hundred to several thousand mcg/kg

Waste Source:
Waste Treatment Plant/Disposal Pit (waste oil biodegradation units)

Type/Quantity of Media Treated:
Soil

Purpose/Significance of Application:
Application of ISESM to remediate fine-grained soils that are difficult to treat with other technologies alone; technology is particularly suited to shallow applications, above the water table.

Regulatory Requirements/Cleanup Goals:
- Closure plan required 70% mass removal
- No RD&D permit was required

Results:
- Soil mixing with each of the 4 additional technologies performed better than the 70% VOC mass removal requirement
- Soil mixing with ambient air stripping achieved >90% removal after 3.75 hrs of treatment
- Soil mixing with hot air stripping achieved >95% removal after 3.75 hrs of treatment
- Soil mixing with peroxidation achieved >70% removal after 1 hr of treatment
- Soil mixing with solidification achieved >90% capture after 1 hr of treatment
- Soil mixing with hot air (thermal) stripping was selected as the remedial option for the site, with cleanup and closure completed in 1994; 628 soil columns at a depth of 22 ft were treated in remediation

Cost Factors:
- Actual capital costs of $1,956,000 were expended for the demonstration, including $481,000 for labor and $500,000 for vendor subcontracts
- Equipment operating costs during demonstration were estimated at $20,000 per day
- Demonstration costs for all four technologies reported as ranging from $150-200/yd3
- Hot air stripping costs were 5% greater than for ambient air stripping, but achieved cleanup goals faster

Description:
The X-231B waste management unit at the DOE Portsmouth Gaseous Diffusion Plant (PGDP) consists of two waste oil biodegradation areas. The unit was used from 1976 to 1983 for treatment and disposal of waste oils and degreasing solvents, and contributed to contamination of soil and shallow ground water with VOCs. Thirteen VOCs were identified in the soil, including TCE, TCA, DCE, and methylene chloride, at concentrations ranging from several hundred to several thousand g/kg. The site consists of relatively low permeability soils with elevated clay content.

In situ enhanced soil mixing (ISESM) was demonstrated at the site in 1992. ISESM consists of soil mixing combined with an additional technology. The following four additional technologies were demonstrated at PGDP: vapor extraction with ambient air stripping; vapor extraction with hot air stripping; hydrogen peroxide injection; and grout injection for solidification/stabilization. Three demonstration soil columns were completed for each of the four technologies (12 total). The 12 soil columns were each 10 ft in diameter and 15 ft deep. One additional column was treated by hot air stripping to a depth of 22 ft, and a second additional column was used for a tracer study.

Performance results showed that all four technologies performed better than the 70% VOC mass removal requirement specified by the Ohio EPA. Removals ranged from >70% (for peroxidation) to >95% (for hot air stripping). Based on the results of the demonstration, hot air stripping was selected for site remediation, which was completed in 1994. In situ solidification was more complicated than originally anticipated due in part to difficulty in effectively mixing the dense clay soil in situ and delivering the proper volume of grout. In addition, the solidification process generated secondary liquid wastes from grout delivery trucks and equipment cleanup. An improved "grout-on-demand" system has been developed to minimize waste.