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: December 15, 2004

Point of Contact:
Jim Warner
ERM
1777 Botelho Dr. Ste.260
Walnut Creek CA 94596 
Tel: 925-946-0455 
Email: jim.warner@
ermwest.com

DNAPL Site
Northern Area, CA


Hydrogeology:

The investigation involved drilling numerous deep wells and performing geophysics, a seismic reflection survey, aquifer testing, and extensive monitoring. Optical and acoustic televiewer logging were used to map fracture depth and orientation. The seismic reflection survey identified two primary SE dipping normal faults and one proimary NE dipping reverse fault, each with secondary antithetic faults. The seismic data reliably predict fracture density across the site. Sonic wave-form, temperature, conductivy, and flow meter logging were used with slug tests to establish that ground water flow is primarily through the lower alluvium, weathered rock, and fractured rock intervals. These data were used to install an effective multilevel well network, establish a southward ground water flow pattern that reflects the regional gradient and possibly geologic controls and perform MNA monitoring. The MNA results include contaminant, electron acceptor, metabolic gas and other inorganic parameter distributions indicating abiotic and biotic degradation. Three years of monitoring suggest that the plume extent may be stable.

Targeted Environmental Media:
  • - Dense Non-aqueous Phase Liquids (DNAPLs)
  • - Fractured Bedrock

Contaminants:

The dissolved plume extends south from the source approximately 1,000 feet through an extensive fracture network.

Major Contaminants and Maximum Concentrations:
  • - 1,1,2-Trichloroethane (DNAPL)
  • - 1,1-Dichloroethane (DNAPL)

Site Characterization Technologies:

  • - Borehole Geophysics
    • Acoustic Televiewer
    • Video Camera Televiewer
  • - Fluid Loggings
    • Temperature
    • Conductivity/Resistivity
  • - Flow
    • Heat Pulse Flowmeter
  • - Surface Seismic Surveys
    • Reflection
  • - Downhole Seismic Surveys

Remedial Technologies:

  • - Pump and Treat
Comments:
DNAPL has been periodically recovered from fractured bedrock for three years and a pilot test was performed to evaluate the potential to enhance recovery. Prior to the pilot test, DNAPLrecovery was performed initially by bailing and later by evacuating all fluids in the well to increase recovery. Recovery rates declined over time except immediately following a 5.3 Richter magnitude earthquake, which apparently caused a temporary increase. The pilot test involved well evacuation for 4 days (with and without a low vacuum), which increased the DNAPL recovery rate by approximately 25 times over rates prior to pilot testing. The results indicate that sustained dewatering is the most significant influence on enhancing DNAPL recovery, and 70 gallons of 1,1,1-TCA have been removed to date.
Remediation Goals:

None provided


Status:

Information to date suggests that the plume will not migrate to potential receptors under current conditions. The remedial strategy is being developed and may include periodic DNAPL recovery, where practical, and MNA for the dissolved plume. Contingency measures, to be implemented if the plume expands or accelerated remediation becomes necessary, may include in-situ dissolved phase remediation and/or hydraulic containment. This strategy represents a cost effective and protective risk management approach that is well supported by the investigation results.

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