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 4, 2011

Point of Contact:
Mark Ripperda
Mail Code SFD83
75 Hawthorne Street
San Francisco CA 94105 
Tel: 415-972-3028 
Email: Ripperda.Mark@
epa.gov

Andersen Air Force Base MARBO Annex
Yigo, GU


Hydrogeology:

The geology underlying the MARBO Annex consists of limestone reef deposits underlain by volcanic rocks. The volcanically derived Alutom formation consists of thick sequences of water-laid tuffaceous shales containing pyroclastic deposits of ash, dust, sandstones, and conglomerates. Interlayered within this formation are lava flows, breccia, and fragments of reef limestones. The MARBO Annex is underlain by the Barrigada and Mariana limestone formations.

Groundwater resources are primarily found in the northern half of the island in porous limestone deposits of the Barrigada and Mariana formations. The groundwater is encountered
approximately 300-500 feet bgs. The groundwater surface generally coincides with sea level and the depth to water depends on surface elevation. The thickness of the lens is generally around 90 to 120 feet.

Spatial variation in porosity of the Barrigada and Mariana limestone formations varies considerably depending on the depositional settings in the vicinity of the Northern Plateau.
Openings can range in size from microscopic to large, well-developed cavern systems, but are generally about 1/8 to 1/4 inches in diameter and are the result of dissolution of the
limestone.

The estimated sustainable yield of the aquifer is reported to be 59 mgd, and
an estimated 37 mgd is considered available for future development.

Targeted Environmental Media:
  • - Fractured Bedrock

Contaminants:

Not identified in the documents reviewed.

Major Contaminants and Maximum Concentrations:
  • - Tetrachloroethene (28 µg/L)
  • - Trichloroethene (210 µg/L)

Site Characterization Technologies:

  • - Tracer (dye) Test

Remedial Technologies:

  • - Pump and Treat
  • - Other (Monitored Natural Attenuation)
Comments:
The groundwater remedy was to continue treating production well water at the wellheads and allow for monitored natural attenuation in the aquifer in general. Note the 1998 ROD states that degradation products of PCE and TCE are generally not detected and the MNA will be due to dilution and dispersion.
Remediation Goals:

Cleanup goals are MCLs for TCE and PCE.


Status:

The treatment at the wellheads continues. However, the MNA aspect of the ROD is not working and a finding of technical impracticability will be made (2009 Five Year Review).

http://cfpub.epa.gov/supercpad/cursites/csitinfo.cfm?id=0902825

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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