U.S. EPA Contaminated Site Cleanup Information (CLU-IN)


U.S. Environmental Protection Agency
U.S. EPA Technology Innovation and Field Services Division

Fractured Bedrock Project Profiles

Last Updated: February 3, 2006

Point of Contact:
Gorm Heron
TerraTherm, Inc.
28900 Indian Point
Keene CA 93531 
Tel: 661-823-1620 
Email: gheron@
terratherm.com

Edwards AFB - Site 61
Edwards AFB, CA


Hydrogeology:

The site geology consists of a thin layer of alluvium resting on 30 to 40 ft of weathered bedrock,which grades downwards into unweathered fractured granitic bedrock with enclaves of weathered diorite. the water table is 32 bgs. The ground water flow is towards the east-southeast, and has led to the creation of an elongated plume of chlorinated solvents, pricipally TCE.

Targeted Environmental Media:
  • - Fractured Bedrock

Contaminants:

Dissolved-phased TCE contaminatio was present to depths of at least 100 ft, with high levels indicating potential DNAPL presence, mainly in the upper 60 ft.

Major Contaminants and Maximum Concentrations:
  • - Trichloroethene (var)

Site Characterization Technologies:

  • - Vertical Chemical Profiling
    • Packer Isolation

Remedial Technologies:

  • - Chemical Oxidation (In Situ)
    • O2
  • - Thermal Treatment (In Situ)
    • Steam Enhanced Extraction
  • - Soil Vapor Extraction
    • In Fractured Bedrock Vadose Zone
Comments:
The treatability study was designed to evaluate the applicability of steam enhanced remediation for restoration of fractured rock source zones and aquifers impacted by volatile organic compounds. Steam was injected, in the summer of 2002, in three discrete intervals within one nested well to a target depth range from 12 to 60 bt bgs. Contaminant vapors and liquids were extracted from four surrounding wells. The upper 40 ft. of the treatment zone was heated within 20 to 30 days of steam injection. The initial high-vacuum extraction resulted in high concentrations of TCE and other VOCs in the extracted vapor. After 30 days of heating, pressure cycling was initiated, resulting in increased mass removal.After heating one of the extraction wells to over 140 degrees (F) LNAPL was recovered in a liquid form. The total mass of contaminants removed was approximately 2,000 to 3,000 lbs, including 250 lbs of LNAPL. After cool-down, soil, rock and water samples were collected to assess the remedial success. Soil and rock concentrations were below the detection limit in all samples from the surface to a dept of 32 ft. In the upper part of the saturated area (from 32 to 45 ft. below grade), TCE concentrations were lowered from 500 - 2,200 ug/L to 0.8 - 200 ug/L (approximately 90% reduction). In the deeper intervals, TCE remained in the 97 - 1,800 ug/L range. This was explained by the relatively cool temperatures achieved at the deeper zones. Treating the ground water to lower levels would have required more time for operation, and potentially deeper injection intervals.Air-coinjection was part of the pilot.


Remediation Goals:

This was a treatability study.


Status:

Steam enhanced remediation was recommended as a source zone remediation technology in combination with plume control.


Lessons Learned:

Data suggests that the air injection may have a beneficial effect of opening fractures to steam flow. Electrical Resistance Tomography (ERT) proved useful as a process monitoring tool as heated zones showed significant decreases in electrical resistivity.

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