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 23, 2004

Point of Contact:
Andrew Kendrick
Tetra Tech NUS, Inc.
661 Andersen Dr.
Pittsburgh PA 15220 
Tel: 412-921-8623 
Fax: 412-921-4040
Email: kendricka@
ttnus.com

TBS Gas Station Site
Quantico, VA


Hydrogeology:

Fill material of silts and silty sand underlie the site. Bedrock grades from saprolite to medium hard, micaceous schist with a high percentage of quartz. The percent rock quality designation (%RQD) ranged from approximately 10% in the highly weathered zones to 70% in the deeper less fractured zones. Fracture orientaions were moderate to high angle and evidence of oxidation (iron staining) was present on the fractures to a depth of approximately 28 feet bgs. Below 28 ft. the fractures were no longer stained, indicating decreased contact with an oxygenated surficial supply.

Ground water is within the top 10 ft. of bedrock.

Targeted Environmental Media:
  • - Fractured Bedrock

Contaminants:

Major Contaminants and Maximum Concentrations:
  • - Benzene-toluene-ethylbenzene-xylene (BTEX) (2,600 µg/L)

Site Characterization Technologies:

No technologies selected.


Remedial Technologies:

  • - Bioremediation (In Situ)
    • Aerobic Oxidation
Comments:
Two phases of ORC were tested. First, ORC was injected into five wells in a small portion of the plume (approximately 25'). Second, an ORC barrier, consisting of 28 injection wells was extended across the plume to cover an approximately 150-foot treatment zone.
Remediation Goals:

None provided


Status:

The results of both phases indicated that these applications were successful at enhancing the aerobic conditions at the site and ultimately reducing the offsite flux. However, several limitations were realized in the fractured bedrock, which are not normally encountered in unconsolidated deposits. First, despite extensive site characterization, the true interconnectivity of fractures remains unknown. Thus, accessibility to all contamination is believed to be limited. Second, in some fracture zones, the hydraulic conductivity is higher then expected, causing increased velocities which limit residence time and microbe degradation. Third, it is expected that a large percentage of flow occurs through preferential pathways (i.e., a small percentage of the contaminated mass). As a result, the available matrix for microbial growth is reduced.

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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