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:
Brian R. Hitchens
GeoSyntec Consultants
11305 Rancho Bernardo Rd. Suite 101
San Diego CA 92127 
Tel: 858-674-6559 
Fax: 858-674-6586
Email: bhitchens@
geosyntec.com

Inactive Landfill
Southern, CA


Hydrogeology:

The pilot test area is characterized by a 20 to 60 foot veneer of alluvium and grus overlying fractured tonalite. Ground-water beneath the site is unconfined within the alluvium and fractured bedrock and flows from the landfill through the pilot test area toward the river.

Targeted Environmental Media:
  • - Fractured Bedrock

Contaminants:

Chlorinated volatile organic compounds (VOCs) have been detected in monitoring wells screened in both the alluvium and bedrock zones, at depths of up to 300 feet below ground surface (bgs). To date, VOCs have not been detected in surface water of shallow ground-water samples along the margin of the river.

Major Contaminants and Maximum Concentrations:
  • - Tetrachloroethene (300 µg/L)
  • - Trichloroethene (300 µg/L)
  • - 1,1-Dichloroethene (300 µg/L)
  • - 1,1-Dichloroethane (0 µg/L)
  • - cis-1,2-Dichloroethene (0 µg/L)
  • - Vinyl chloride (0 µg/L)

Site Characterization Technologies:

  • - Borehole Geophysics
    • Caliper
    • Acoustic Televiewer
  • - Pumping Tests
  • - Tracer (dye) Test
  • - Other (Lineament Analyses; Geophysical Surveys; Thermal Flow Meter Testing; Hydrophysics )

Comments:
A hydrogeologic characterization was performed to evaluate the nature of ground-water flow in the alluvial and underlying fractured bedrock aquifer.

Aquifer test analyses indicated that hydraulic conductivities ranged from 25 to 40 feet per day (ft/day) in the fractured aquifer and 13 to 17 ft/day in the alluvium.

Results of the dye tracer studies confirmed that ground-water within the fractured rock aquifer was moving rapidly under passive conditions, and confirmed communication between the upgradient and downgradient wells within the pilot test area.


Remedial Technologies:

  • - Bioremediation (In Situ)
    • Reductive Dechlorination (In Situ Bioremediation)
Comments:
Initial deoxyribonucleic acid (DNA) testing of site ground-water confirmed the native presence of members of the Dehalococcoides group in both the alluvial and bedrock zones. The DNA signal analyzed to determine the presence of Dehalococcoides bacteria increases with depth. Bench scale microcosm studies were performed to determine if native populations could satisfactorily remediate ground-water if provided with an electron donor source such as MEAL (methanol, ethanol, acetate, and lactate), or if a specialized culture such as KB-1, would be necessary for complete degradation. After 50 days, the microcosm spiked with the electron donor additive had little change, and did not show complete degradation to ethene. Although Dehalococcoides had been shown to be present at the site, some strains of the bacteria are more efficient at degrading VOCs than others, and the native strain appeared to be inadequate for site remedial goals. The microcosm spiked with the KB-1 culture demonstrated rapid, complete degradation of PCE to ethene.
Remediation Goals:

This is a pilot test and the goal is to stimulate and augment naturally occurring biologic degradation to increase degradation rates such that chlorinated VOCs are destroyed prior to migrating off-site and interacting with a river system downgradient of the landfill.


Status:

Following regulatory approval in August 2004, an electron donor will be injected into the pilot test area. The donor will be tagged with a sodium bromide solution, which will be monitored downgradient with ion specific probes, to determine nutrient delivery concentration. KB-1 will be injected after donor addition has allowed for the development of appropriate redox conditions in the pilot test area.


Lessons Learned:

References:
Hitchens, Brian; Barry Pulver; Brian McDaniel; David Major; Suzanne OHara. 2005. Remediation of Chlorinated VOCs in Fractured Bedrock Through In Situ Bioaugmentation. The Fifteenth Annual AEHS Meeting and West Coast Conference on Soils, Sediments and Water, San Diego, California. March 14-17.

Hitchens, Brian; Suzanne OHara; David Major; Candace Gibson; Barry Pulver. 2005. Remediation of Chlorinated VOCs in Fractured Bedrock Through In Situ Bioaugmentation. The Fourth International Remediation of Chlorinated and Recalcitrant Compounds Conference, Monterey, California. May 24-27.

Witting, Veryl; Sean McClain; Candace Gibson. 2004. Fractured Bedrock Aquifer Hydrogeologic Characterization for a Bioaugmentation Pilot Study. The Fourth International Remediation of Chlorinated and Recalcitrant Compounds Conference, Monterey, California. May 24-27.

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