Soil Vapor Extraction at the Sacramento Army Depot Superfund Site, Burn Pits Operable Unit, Sacramento, California

Site Name:

Sacramento Army Depot Superfund Site


Sacramento, California

Period of

May 1994 - September 1995


Full-scale cleanup


Ashok Gopinath
OHM Remediation Services Corp.
5731 W. Las Positas Blvd.
Pleasanton, CA 94588
(510) 227-1100

Soil Vapor Extraction

- System was OHM's patented Fluid Injection-Vacuum Extraction (FIVE) technology
- Included 10 shallow extraction/injection wells, 12 deep wells, 1 horizontal well, HEPA filters, and 2 trains of GAC units
- Shallow wells screened 10-25 ft below ground surface (bgs)
- Deep wells screened 50-80 and 17-47 ft bgs
- Some wells operated as injection wells and others as extraction wells

Cleanup Authority:
- Record of Decision Date 2/26/93
- U.S. Army Lead

Point of Contact:
Marlin Mezquita
USEPA Region 9
75 Hawthorne Street
San Francisco, CA 94105
(415) 744-2393

Organic Compounds; Volatiles-Halogenated

- Trichloroethene (TCE), tetrachloroethene (PCE), and 1,2-dichloroethene (DCE) each less than 0.01 mg/kg

Waste Source:
Disposal Pit; Incineration Residuals Handling

Type/Quantity of Media Treated:

- 247,900 cubic yards
- Subsurface consists of interbedded sands, silts, and clays, with some coarse gravels
- Six facies identified during site investigation

Purpose/Significance of Application:
Full-scale application combining fluid injection and vacuum extraction wells in a complex subsurface environment

Regulatory Requirements/Cleanup Goals:
- Soil cleanup standards for TCE, PCE, and DCE of 0.005 mg/kg
- Air emission limits identified for TCE, PCE, and DCE

- Soil cleanup goals met within 14 months of system operation
- Concentrations in treated soil were: TCE - 0.0021 mg/kg; PCE - 0.0013 mg/kg; and DCE - 0.0027 mg/kg
- Approximately 138 lbs of TCE, PCE, and DCE extracted

Cost Factors:
- Actual costs of $865,873 included $195,000 for before-treatment activities (drilling, soil gas survey, confirmatory borings, and chemical testing), and $670,500 for activities directly attributed to treatment (design, mobilization, construction, start-up/testing/permitting, SVE operations and maintenance, and demobilization)
- The unit cost for activities directly attributed to treatment was $2.70/yd3 of soil treated, and $4,858/lb of VOC removed

The Burn Pits Operable Unit at SAAD was the location of two rectangular trenches constructed in the late 1950s and used intermittently as incineration pits until 1966. Materials reportedly buried and/or burned in the pits included plating shop wastes, oil and grease, batteries, and construction debris. Remedial investigations conducted from 1990 to 1993 showed average soil contaminant concentrations for TCE ranging from 0.0029 to 0.0069 mg/kg, PCE from 0.0029 to 0.0079 mg/kg, and DCE from 0.0038 to 0.0055 mg/kg. In addition, the Army's basewide contractor estimated the total mass of selected contaminants in the operable unit as follows: TCE - 22.3 lbs; PCE - 7.1 lbs; and DCE - 39.3 lbs.

A Record of Decision (ROD) addressing the Burn Pits O.U. was signed in March 1993. OHM's patented fluid injection/vapor extraction (FIVE) system was used to remediate the Burn Pits O.U. In the FIVE technology, pressurized air is injected into vadose zone soils to produce relatively larger subsurface pressure gradients and higher flow rates of extracted vapors than would be achieved solely with using vapor extraction technology. The vendor stated that this system "enhanced subsurface volatilization and shortened the period of remediation," however, no data were provided to support this statement. The FIVE system used at the SAAD Burn Pits consisted of 10 shallow extraction/injection wells, 12 deep extraction/injection wells, 1 horizontal extraction/injection well, air injection piping, vapor monitoring wells, liquid/vapor separators, high efficiency particulate filters, vapor phase granular activated carbon, and positive displacement blowers. The wells were screened up to 80 feet below ground surface.

Confirmatory soil borings showed that the average concentrations for each of the three target contaminants was less than the cleanup standards set in the ROD. TCE was reduced to an average concentration of 0.0021 mg/kg, PCE to 0.0013 mg/kg, and DCE to 0.0027 mg/kg. Approximately 138 lbs of TCE, PCE, and DCE were extracted during this application, or roughly two times as much VOCs as originally estimated to be present at the operable unit. Possible reasons for the discrepancy between the original estimate and the actual amount recovered identified by the treatment vendor include inaccuracies in the original estimate and for 1,2-DCE, a reductive dehalogenation mechanism that occurred in situ. According to the vendor, the use of the FIVE technology "enhanced subsurface volatilization and shortened the period of remediation"; however, no additional information comparing this technology to other SVE systems was provided.