In Situ Soil Vapor Extraction at McClellan Air Force Base, California

Site Name:

McClellan Air Force Base


Sacramento, California

Period of

Status - Ongoing
Report covers - 1993 to 5/94


Field Demonstration


CH2M Hill

Soil Vapor Extraction - 17 vapor extraction wells in three contamination zones - 5 vacuum blowers, 2 vapor/liquid separators - Catalytic oxidizer and scrubber used to control air emissions - Total system average air flow rate was 2,500 scfm

Cleanup Authority:
CERCLA and State: California
- ROD Date: pending
(scheduled for issuance mid-1995)

SIC Code:
9711 (National Security)
Point of Contact:
Kendall Tanner
Remedial Project Manager
McClellan, AFB

Chlorinated Aliphatics Tetrachloroethene (PCE), Trichloroethene (TCE), 1,1-Dichloroethene (1,1- DCE), Vinyl Chloride, 1,1,1-Trichloroethane (TCA), 1,2-Dichloroethene (1,2- DCA), Freon 113 - PCE, TCE, 1,1-DCE, TCA, and Freon 113 account for over 99% of the speciated VOC mass in the vadose zone - Maximum borehole concentration of VOCs in vadose zone reported up to 2,975,000 ~g/kg

Waste Source:
Disposal Pit (for fuel and solvents)

Type/Quantity of Media Treated:
Soil - Three zones of contamination - waste pit (landfilled silty sands and sandy silt with oily material, wire wood, debris, etc.); intermediate alluvium; and deep alluvium - Permeability ranged from 0.001 (for silty clay) to 1.7 (for sand) darcies

Purpose/Significance of Application:
A demonstration of soil vapor extraction to remediate VOCs in waste pit materials and vadose zone soils, and to assess performance of catalytic oxidation and scrubbing.

Regulatory Requirements/Cleanup Goals:
- Cleanup criteria not yet established for this site at McClellan - Air Emissions - 95% destruction of total VOCs, required by the Sacramento Air Quality Management District

- Demonstration not complete at time of report; no soil samples to characterize post-treatment vadose zone were collected at time of report - Approximately 46,000 lbs of speciated VOCs were extracted and treated during initial 6 weeks of operation; 113,000 lbs during initial 15 weeks of operation - TCE, 1,1-DCE, and TCA accounted for more than 90% of the mass of contaminants removed - Up to 150,000 lbs of contaminants (hexane-equivalents) believed to have been biodegraded in situ during initial 6 weeks of operation - Overall DRE averaged 99% for total VOCs during second and third months of demonstration; lower DRE in first month attributed to operational concerns

Cost Factors:
- Field demonstration budget - $1.8 million for 1993 and $2.0 million for 1994 (including site characterization; air permeability testing; installation and operation of SVE wells; vapor probes and manifold; air/water separators; blowers; scrubber; catalytic oxidizer (rented); resin adsorption (rented); electronic beam technology testing; laboratory analysis; and engineering support)

The McClellan Air Force Base in Sacramento, California is an Air Force Command Logistics Center that has been in operation since 1943. The base was placed on the National Priorities List in 1987 and Site S within Operable Unit D is one of the areas of confirmed contamination at the base.

Site S is the location of a former fuel and solvent disposal pit, used from the early 1940s to mid-1970s. Soil at Site S has been contaminated with chlorinated and petroleum-based volatile organic constituents (VOCs). No cleanup goals had been established for Site S at the time of this report. The report indicates that a Record of Decision for Operable Unit D (which includes the disposal pit site) is scheduled to be issued in mid-1995. A 95% destruction and removal efficiency (DRE) for total VOCs in the extracted vapors was required by the Sacramento Air Quality Management District.

A field demonstration of soil vapor extraction (SVE) at Site S began in mid-1993. This demonstration is being conducted as part of a series of field programs designed to optimize remedial technologies to be used in a full-scale cleanup at McClellan. This SVE system includes 17 vapor extraction wells, vapor/liquid separators, a catalytic oxidizer, and a scrubber. Results from the field demonstration of SVE to date showed that approximately 113,000 pounds of VOCs were extracted in 15 weeks of operation; mostly consisting of TCE, 1,1-DCE, and TCA. In addition, up to 150,000 pounds of contaminants (hexane-equivalents) were believed to have been biodegraded in situ during the initial 6 weeks of the SVE demonstration. The average DRE for total VOCs during the second and third months of the demonstration was 99 percent.

It was noted during this application that the heterogeneity of the soils at this site caused the radius of influence for the extraction wells to vary from 15 to 60 feet for a single well. The calculated mass of contaminants was almost two orders of magnitude less than the mass extracted in the first six weeks of system operation. It was also noted that SVE air pollution control systems should be designed with sufficient capacity to provide for operational flexibility.