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: March 22, 2010

Point of Contact:
Tara MacHarg
100 West Broadway
Suite 5000
Long Beach CA 90802-4443 
Tel: 562-951-2245 
Email: Tara.macharg@
earthtech.com

Edwards Air Force Base, Operable Unit 1, Site 18
Edwards Air Force Base, CA


Hydrogeology:

Within the fractured granite bedrock, groundwater occurs at approximately 25 feet below ground surface (bgs).

Targeted Environmental Media:
  • - Fractured Bedrock

Contaminants:

The groundwater plume extends laterally more than one mile from the source. The greatest concentration of contamination occurs at approximately 80 feet bgs and the contamination extends to more than 150 feet bgs.

Major Contaminants and Maximum Concentrations:
  • - Trichloroethene (53,000 µg/L)
  • - Tetrachloroethene (0 µg/L)
  • - 1,2-Dichloroethane (0 µg/L)
  • - 1,1-Dichloroethene (0 µg/L)
  • - 1,1,2,2-Tetrachloroethane (0 µg/L)

Site Characterization Technologies:

No technologies selected.


Remedial Technologies:

  • - Chemical Oxidation (In Situ)
    • O2
Comments:
In situ chemical oxidation was performed to treat chlorinated ethenes and ethanes. A single injection of sodium persulfate activated with sodium hydroxide was injected in May 2007 via two wells screened from 20 to 100 feet bgs. Post injection groundwater monitoring took place for nine months after the injection. Three multi-level monitoring wells were installed at various depths to evaluate treatment.
Remediation Goals:

None provided


Status:

Three post-injection sampling events took place between July 2007 and January 2008. The extent to which contaminants were affected varied: TCE showed significant reduction; 1,4-dioxane decreased in all study wells; and persulfate was not as effective in oxidizing PCE and 1,2-DCA. Based on monitoring results, the radius of influence was at least 80 feet.


Lessons Learned:

Monitoring of the site after ISCO treatment was logistically challenging, mainly due to the unanticipated persistence of persulfate and oxidizing conditions (primarily in the deeper intervals). After nine months, these conditions still existed in some locations.

References:
MacHarg, Tara, Holly Holbrook, Greg Tessier, and Paul Schiff. Activated Persulfate Injection to Treat Chlorinated Solvents within a Fractured Granitic Aquifer, Platform Abstract Session A4. Presented at the Sixth International Conference on Remediation of Chlorinated and Recalcitrant Compounds. Monterey, CA. May 19-22, 2008.

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