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: November 8, 2005

Point of Contact:
Paula Chang
289 Great Road, Suite 105
Acton MA 01720-4766 
Tel: 978-263-9588 
Fax: 978-263-9594
Email: Pchang@
GeoSyntec.com

Boston Industrial Facility
Boston, MA


Hydrogeology:

A saline and fractured bedrock aquifer is contaminated below an industrial facility in Boston, Massachusetts. The site is adjacent to a 240,000-square-foot excavation that is intermittently dewatered by 60 feet using 10 dewatering wells. Extracted groundwater is recharged to the bedrock between the industrial building and the excavation to prevent consolidation settlement of the building piles, which are founded in overburden clay. The site is located 650 feet from the excavation and experiences a 90-degree change in hydraulic gradient as a result of dewatering.

Targeted Environmental Media:
  • - Fractured Bedrock

Contaminants:

Major Contaminants and Maximum Concentrations:
  • - Trichloroethene (0 µg/L)
  • - Vinyl chloride (0 µg/L)
  • - cis-1,2-Dichloroethene (0 µg/L)

Site Characterization Technologies:

No technologies selected.


Remedial Technologies:

  • - Bioremediation (In Situ)
    • Reductive Dechlorination (In Situ Bioremediation)
Comments:
The pilot test has been operating for more than 16 months. Methanol and acetate are added to the aquifer three times per week to promote complete reductive dechlorination of trichloroethene (TCE) by the indigenous community of halorespiring microorganisms. Performance is assessed using geochemical and microbiological parameters. The geochemical parameters include production of vinyl chloride and ethene. The microbiological assessment includes analysis of microbial communities upgradient of the pilot treatment area.
Remediation Goals:

The pilot test will evaluate the efficacy of enhanced bioremediation of chlorinated ethenes in a saline and fractured bedrock aquifer.


Status:

Within the zone of most active remediation, ethene has increased to levels of 35 micromolars and methane has increased to above 400 micromolars. Methane has continuously increased despite the presence of 2 millimolar sulfate, indicating that the methanol that is added for remediation is directly metabolized by methanogens.

TCE is no longer detected in the pilot test area despite as much as 85% leakage of groundwater containing background levels of 1,500 micromolar TCE. Concentrations of cis-dichloroethene (cis-DCE) and vinyl chloride (VC) fluctuate over time.

Complete dechlorination of TCE by indigenous bacteria without the addition of electron donors is observed at a location upgradient of the pilot treatment area. Analysis of the microbial community indicates that the organisms in this area are closely related to well-characterized complete dechlorinators. However, the source of electrons for the upgradient dechlorination is unknown.


Lessons Learned:

Data for iron II (Fe[II]), volatile organic compounds (VOCs), and methane along one edge of the pilot test area indicate that oxidizing groundwater may be leaking into the treatment zone. In this area, Fe(II) is decreasing, TCE is present, and methane is between 100 and 225 micromolars. These trends indicate that higher redox potential electron acceptors are present, which reduces methanogenic activity.

Compound-specific stable carbon isotopes are being analyzed upgradient and in the pilot test area to provide insight on sources of cis-DCE, VC, and ethene. The possibility that the bedrock environment at this site has a diverse community of indigenous halorespiring microorganisms also is being investigated. However, this possibility contradicts the common opinion that there is limited microbial diversity in fractured rock aquifers.

Reference:
Chang, Paula; Carl Elder; Kevin Finneran; Dave Major; Peter Zeeb; Duane Wanty. 2003. Geochemical and microbiological characterization of in situ reductive dechlorination in fractured bedrock. The Seventh International In Situ and On-Site Bioremediation Symposium, Orlando, Florida. June 2-5.

Top of Page

For more information on Fractured Bedrock, please contact:

Ed Gilbert
Technology Assessment Branch

PH: (703) 603-8883 | Email: gilbert.edward@epa.gov