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 14, 2004

Point of Contact:
Paul Blood
Maine DEP
106 Hogan Rd.
Bangor ME 04401 
Tel: 207-941-4570 
Fax: 207-941-4584
Email: paul.s.blood@
state.me.us

Leaking Gasoline Storage Tank
New Sweden, ME


Hydrogeology:

Low grade, meta-sedimentary, fractured, calcarous pelite beneath 1-3m of overburden. The attitude of the slaty cleavage is 50 degrees.

Targeted Environmental Media:
  • - Fractured Bedrock

Contaminants:

The dissolved gasoline, BTEX and MTBE plumes stabilized at 200m long and 50m wide. Contaminated monitoring wells and residual water supplies both up-and down gradient from the site fall along the strike of the slaty cleavage, whereas monitoring wells directly down gradient but oblique to strike were never contaminated. The plume followed the strike of cleavage rather than the direction expected from head gradient.

Major Contaminants and Maximum Concentrations:
  • - Benzene-toluene-ethylbenzene-xylene (BTEX) (var)

Site Characterization Technologies:

  • - Coring

Comments:
Shallow bedrock fracture zone flow paterns differ from overburden and from deeper bedrock and can be recognized using test pits, direct-push sampling, and coring. Understanding the relationship of these zones of weather-enhancing, preferential permeability to water table elevation makes efficient free product recovery.


Remedial Technologies:

  • - Pump and Treat
  • - Other
Comments:
Remediation included overburden pump-and-treat to recover 35 gallons of free product in 1991 followed by excavation of 800 square meters of petroleum contaminated soil and weathered bedrock in 1994. In 1995 horizontal soil vapor extraction (SVE) extracted approximately 100 gallons of gasoline from unsaturated weathered bedrock. A bedrock ground water pump and treat system ran from 1992 to 1997.
Remediation Goals:

None provided


Status:

Prior to the 1994 excavation, a key monitoring well showed up to 4000 ppb of gasoline range organics (GRO) but dropped to <100 ppb within six months of excavation. Annual monitoring from 1995-1999 showed that low levels of GRO persisted across the site but no more drinking water wells became contaminated. Natural attenuation will be a final remedy.

In January, 2004 the state was in the process of dismantling the remediation equipment and will initiate closeout procedures

The lesson learned at this site was to first place bedrock monitoring wells along strike of predominant fractures then to place sentinel wells across-strike to monitor seasonal variation in head gradient and contaminant migration.

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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