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: January 17, 2011

Point of Contact:
Kymberlee Keckler
USEPA 5 Post Office Square, Suite 100
Mail Code OSRR07-3
Boston MA 02109-3912 
Tel: 617-918-1385 
Email: keckler.kymberlee@
epa.gov

Weymouth NAS
South Weymouth, MA


Hydrogeology:

A thin veneer of glacially-derived sediments, including glacial outwash and till deposits underlies granitic bedrock. Overburden units have been most commonly logged as sandy till, but fine sandy materials with a variable silt content, interpreted to be outwash, are also locally described. On the basis of injection tests, hydraulic conductivity values of 1.4E-04 cm/sec to 9.2E-05 cm/sec were found in the fractured bedrock. Fracture spacings from cores rarely exceeded one ft. with most fractures spaced from 2 inches to one ft.. Many of the high angled fractures exhibited water-bearing characteristics such as iron staining. Borehole geophysical data suggests that hydraulically significant fractures are more widely spaced.

Targeted Environmental Media:
  • - Fractured Bedrock

Contaminants:

The plume was approximately 90m long by 45 m wide with a vertical depth between 3 and 35 m.

Major Contaminants and Maximum Concentrations:
  • - Tetrachloroethene (1,600 µg/L)

Site Characterization Technologies:

  • - Borehole Geophysics
    • Natural Gamma
    • Caliper
  • - Fluid Loggings
    • Temperature
    • Conductivity/Resistivity
  • - Flow
    • Heat Pulse Flowmeter
  • - Vertical Chemical Profiling
    • Packer Isolation
  • - Coring

Remedial Technologies:

  • - Chemical Oxidation (In Situ)
    • Fenton's Reagent
Comments:
During September/October 2000, 28,000 lbs of oxident was injected in 28 wells in the bedrock. Sample results after ten days showed an 85% reduction in concentrations of VOCs in most wells, but the results from 60 day post treatment sampling showed significant rebounding in the central area of the plume. A follow up primary treatment was conducted during March/April 2001, when another 40,000 lb. of Fenton's reagent were injected. Post-treatment sampling was conducted 45 and 100 days following re-injection.
Remediation Goals:

This was a pilot test.


Status:

VOC concentrations appear to rebound in at least some domains of the plume following each injection event. After two injection events and aproximately nine months elapsed time, total VOC concentrations at a number of monitoring points returned to levels comparable to those observed in the pre-test baseline sampling.

The pilot study is complete. A draft RI was submitted on May 15, 2008. Additional field studies are currently underway and remedy selection is planned for September 2012.


Lessons Learned:

An assessment of the results suggests that the injected oxidents primarly influenced the more tranmissive fractures in the treatment zone, whereas the less transmissive fractures were less influenced. Geochemical data and calculations indicate that the peroxide and catalyst may persist in the subsurfacefor prolonged periods (>200 days), thus complicating the assessment of rebound and the actual effectiveness of the technology.

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