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 25, 2011

Point of Contact:
David Keefer
USEPA 61 Forsyth Street, S.W.
Mail Code: 9T25
Atlanta 30303-8960 
Tel: 404-562-8932 
Email: keefer.david@
pa.gov

Anniston Army Depot (Southeast Industrial Area)
Anniston, AL


Hydrogeology:

The site lies within the fold-and-thrust belt of the Appalachian Valley and Ridge physiographic province. The fold-and-thrust belt is characterized by Paleozoic rock formations that were repeatedly folded and thrust faulted by northwestward-directed tectonic stresses during the Appalachian orogenesis that occurred in the Ordovician through Permian periods more than 250 million years ago. As a result of this structural deformation, major geomorphic and geologic features, including topographic ridges and
valleys, fold axes, fault traces, and lithologic boundaries, are commonly oriented in a northeast-southwest direction. Northwestward transport of the Paleozoic rock sequence along thrust faults has resulted in the imbricate stacking of large slabs of rock referred to as thrust sheets. Within an individual thrust sheet, smaller faults may splay off the larger
basal thrust fault, resulting in stacking and overlap of rock units. Geologic contacts in the region are generally oriented parallel to mapped faults, and repetition of lithologic units is common in vertical sequences. ANAD lies on the Pell City thrust sheet within the fold and thrust belt.

The current conceptual model of groundwater flow includes the following:

The residuum, weathered bedrock, and competent bedrock comprise an
interconnected aquifer.

The transition from weathered bedrock to unweathered bedrock is gradational and variable with some areas having severely weathered intervals within more
competent rock.

On a borehole scale, it is evident that a rock interval can exhibit a high frequency of fracturing, yet the connectivity of the fractures can be limited in the immediate area of the borehole.

The fractures in the Knox Group boreholes exhibit a trend of decreasing fracture frequency with depth, although fracturing was present in the deepest boreholes.

Faults are not prime intervals of flow, yet are connected to adjacent fracture sets. The visible faults are indicators of mechanical breakage, but do not always correlate to flow intervals.

The aquifer rock in the site area is highly variable, with intervals of
completely fractured rock; dense, tight rock; and cavernous sections, creating a
heterogeneous, complex flow network.

In general, ground water flow is toward the south, with both eastern and western
components. On a regional scale, ground water flow follows the topography, although there are significant exceptions on local scales. Even though the bedrock has numerous karst features, there are few high yielding wells. The site monitoring wells have no sustainable yields above 2.5 gpm and most wells yield less than one gpm. Extraction wells in the remediation system yield between 1.5 and 16.3 gpm.

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

Contaminants:

There are multiple plumes at the site.

Major Contaminants and Maximum Concentrations:
  • - Chromium (583 µg/L)
  • - Chloroform (23,466 µg/L)
  • - Carbon tetrachloride (4 µg/L)
  • - Methylene chloride (6,631,300 µg/L)
  • - Tetrachloroethene (342,847 µg/L)
  • - Trichloroethene (344,827 µg/L)
  • - 1,2-Dichloroethene (9,966 µg/L)
  • - 1,1-Dichloroethene (27,397 µg/L)
  • - 1,1,1-Trichloroethane (225,733 µg/L)
  • - Phenols (117,878 µg/L)

Site Characterization Technologies:

  • - Tracer (dye) Test

Remedial Technologies:

  • - Pump and Treat
Comments:
A ground water pump and treat system was installed in 1990.
Remediation Goals:

Original cleanup goals were MCLs. The army is pursuing a technical impracticability finding for the site.


Status:

The pump and treat system continues. Contaminant concentrations have shown erratic trends. A final ROD for the ground water has not been issued.

http://cfpub.epa.gov/supercpad/cursites/csitinfo.cfm?id=0400443

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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