Soil Vapor Extraction at Site ST-35, Davis-Monthan AFB, Arizona

Site Name:

Davis-Monthan Air Force Base

Location:

Arizona

Period of
Operation:

September 1995 - July 1997

Cleanup
Type:

Full-scale cleanup

Vendor:

Montgomery Watson JMM
Consulting Engineers

Technology:
Soil Vapor Extraction (SVE)

- Six vapor extraction wells, a blower system, moisture separator, thermal oxidizer, and air treatment system
- Two 460 cubic inch internal combustion engines (ICE) were used to create the vacuum. The extracted vapors were burned as fuel in the ICEs, with supplemental fuel added as contaminant concentrations were reduced.
- System operated at an average flow rate of 123 scfm - System removed about 1,200 lb/day of contaminant

Cleanup Authority:
Installation Restoration Program

Additional Point of Contact:
U.S. Air Force
Air Combat Command
Regulatory Point of Contact:
Information Not Provided

Contaminants:
Petroleum Hydrocarbons
- Total petroleum hydrocarbon (TPH) was detected in soil at levels up to 320,000 ppm
- Benzene was detected in soil at levels up to 110 ppm

Waste Source:
Fuel Spill

Type/Quantity of Media Treated:
Soil
- 63,000 cubic yards
- Contamination extended to a depth of about 260 feet (ft) below ground surface (bgs)
- Sandy clay with interbedded gravels and sands in upper 260 ft
- Caliche (cemented silts and clays) layer at about 240 ft bgs impeded vertical migration of contamination

Purpose/Significance of Application:
SVE application to remove TPH from soil; extracted vapors used as fuel for ICEs.

Regulatory Requirements/Cleanup Goals:
The objective of the SVE system was to remove contamination in the soil as cost-effectively as possible to prevent contamination of surrounding soil and groundwater.

Results:
- Performance results for the system were reported for the first 16 months of operation (through December 1996)
- After 16 months of operations, the system had removed 585,700 pounds (lbs) of total volatile hydrocarbons (TVH); monthly contaminant removal rates ranged from 14,700 to 67,800 lbs.
- No concentration data for contaminants was reported.

Cost Factors:
- Total capital cost (estimated) - $162,000
- Total O&M cost after 22 months of operation - September 1995 through July 1997 - $45,000
- Report also includes monthly O&M costs for the first 16 months of operation - ranged from $1,818 to $2,602/month for a total of $32,700 through December 1996
- Data on cumulative O&M costs versus cumulative total volatile hydrocarbons removed showed that the cost per unit of contaminant began to increase in October 1996. The ICE engine was reconfigured with a smaller engine to reduce the need for supplemental fuel and thereby reduced the overall operating costs.
- The average O&M cost per unit of contaminant removed after 16 months of operation was $0.06/lb.

Description:
Site ST-35 at the Davis-Monthan Air Force Base (AFB), located in Arizona, was the site of a spill of JP-4 fuel. An estimated 63,000 cubic yards of soil were contaminated to a depth of about 260 ft bgs. TPH and benzene were detected in the soils at levels as high as 320,000 ppm and 110 ppm, respectively. In addition, benzene was detected in groundwater at levels as high as 510 ppb, and there was a 1 to 3 inch layer of free product floating on the groundwater. An SVE system was used to remediate the soil contamination at the site. The SVE operational objectives were to remove contamination at the site as cost-effectively as possible to prevent contamination of the surrounding soil and groundwater. No specific contaminant goals were identified in the report.

The SVE system consisted of six vapor extraction wells, a blower system, moisture separator, thermal oxidizer, and air treatment system. Vacuum was created using two 460 cubic inch ICEs. Extracted soil gas was burned as fuel in the ICEs; when contaminant concentrations in the soil gas were reduced, supplemental fuel was used to operate the ICEs. The SVE system was operated from September 1995 through July 1997. Performance data on amount of contaminant removed were available through December 1996. After 16 months of operation, a total of 585,700 lbs of TVH were removed. Monthly TVH removal rates ranged from 14,700 lbs to 67,800 lbs. In October 1996, the contaminant removal rate began to level off. The ICE was then reconfigured to reduce the need for supplemental fuel. System performance was reported to have improved following the reconfiguration, and the system was reported to be meeting its operational objectives.

The total capital cost for the system was $162,000. O&M costs through July 1997 were $45,000. Monthly O&M data were provided for the first 16 months of operation (through December 1996) and ranged from $1,818 to $2,602/month for a total of $32,700. Monthly O&M costs per unit of contaminant removed ranged from about $0.03/lb to $0.16/lb. From July to October 1996, there was a steady decrease in the O&M cost per lb of contaminant removed. However, the O&M cost began to increase in October 1996 at which time the ICE engine was reconfigured to reduce the need for supplemental fuel. The average O&M cost per unit of contaminant removed after 16 months of operation was $0.06/lb.