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: July 12, 2010

Point of Contact:
Matthew Hansen
300 Oceangate Suite 700
Long Beach CA 90802 
Tel: 562-951-2000 
Fax: 562-951-2100
Email: matthew.hansen@
earthtech.com

Site 49 Operable Unit 1 Edwards Air Force Base
Los Angeles County , CA


Hydrogeology:

The site is located on a flat area with a gradual slope to the southeast. Geology of the site consists of alluvium on top of granite bedrock. The alluvium is comprised of quartz and feldspar sands and silty sands. Occasional seams of clay were also noted, as was tough bedrock from 40 to 45 feet below ground surface (bgs). The depth to ground water at the site was 40 feet bgs. Ground water is found in the alluvium and bedrock and flows toward the southeast.

Targeted Environmental Media:
  • - Fractured Bedrock

Contaminants:

This information was not provided by the sources sited.

Major Contaminants and Maximum Concentrations:
  • - Trichloroethene (94 µg/L)
  • - 1,2-Dichloroethene (82 µg/L)
  • - Benzene (1 µg/L)
  • - Trichloroethene (94 µg/L)

Site Characterization Technologies:

  • - Other (TVA 1000, Photo Ionization, Flame Ionization)

Comments:
The Bubblex SM two-phase extraction (BTPE) remedial system was comprised of a 500-cubic feet per minute (cfm) vapor destruction system with a liquid ring pump. Groundwater and vapor were removed from the monitoring wells as a two-phase flow through an extraction pipe. Vapor and water were drawn to the remediation system using a high-powered vacuum. In all, 99 percent of volatile organic compounds (VOCs) were removed from the ground water during the extraction process through the BTPE pipes. Extracted water was pumped through four 200-pound tanks of granular activated carbon. The water was then pushed through the sewer, and the vapor was removed from the tanks and contaminants were destroyed by use of a thermal/catalytic oxidizer. Monitoring occurred daily for the first week, when the system was implemented, and then weekly thereafter. Ground water concentrations and vacuum readings were collected during monitoring.


Remedial Technologies:

  • - Soil Vapor Extraction
    • With Air Stripping
Comments:
Vapor was removed from ground water through a thermal/catalytic oxidizer.
Remediation Goals:

The objectives of the pilot test were to evalute whether the Bubblex SM two-phase extraction (BTPE) is a usable option for groundwater remediation for low-level VOCs and whether prolonging the use of BTPE will be effective in remediating the source area.


Status:

Results from September 2003 reported trichloroethene (TCE) at a concentration of 30 micrograms per liter (g/L) in Well 49-DEW01 only. There was a reduction in TCE concentrations by more than 50 percent in most wells where initial concentrations had been above 30 g/L. Cis-1,2-dichloroethene (cis-1,2-DCE) and benzene were at concentrations below laboratory detection limits. The concentrations of TCE in the vapor were also reduced by more than 50 percent in most wells.


Lessons Learned:

The pilot period consisted of three months from July 2003 to September 2003. A second round of treatment planned six months after the BTPE test was cancelled due to follow up monitoring that did not indicate any rebound in TCE concentrations. A longer period for extraction would likely decrease the concentration of TCE in soil to below action levels and help reduce the concentrations in groundwater to the background level.

References:
Hansen, Matthew W., Tara MacHarg, James Specht, and Mehmet Pehlivan. 2004. Paper 3C-14. Results from a Two-phase Extraction Pilot Study with Low-level Chlorinated Hydrocarbons and Aromatics. The Fourth International Conference on Remediation of Chlorinated and Recalcitrant Compounds (Monterey, California). May 24-27.

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For more information on Fractured Bedrock, please contact:

Ed Gilbert
Technology Assessment Branch

PH: (703) 603-8883 | Email: gilbert.edward@epa.gov