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: December 15, 2005

Point of Contact:
Christopher Voci
512 Township Line Road
Two Valley Square, Suite 210
Blue Bell PA 19422 
Tel: 215-628-9107 
Fax: 215-628-9953
Email: info@obg.com

Former Manufacturing Facility
Lancaster, PA


Hydrogeology:

Lancaster is located in the Conestoga Valley of the Piedmont Province in south-central Pennsylvania. The site is underlain by the Conestoga formation, consisting of blue to gray argillaceous limestone and limestone conglomerated with varying amounts of pyrite and calcite crystallization. Groundwater in the vicinity occurs in fractures and solution openings in the limestone. Shallow groundwater generally flows easterly, following the topography of the stream valley and discharging to McGrann Run and the Conestoga River. Deep groundwater flows through fractures and along bedding planes of the bedrock and discharges into the Conestoga River. Site wells generally have low specific capacity, as they intercept a small percentage of fractures and the carbonate bedrock aquifer is of low permeability.

Targeted Environmental Media:
  • - Fractured Bedrock

Contaminants:

The highest concentrations of volatile organic compounds (VOC) in groundwater were measured in fractures 100 to 200 feet below ground surface (bgs). The treatment area was 7,850 square feet.

Major Contaminants and Maximum Concentrations:
  • - Trichloroethene (1,800 µg/L)
  • - cis-1,2-Dichloroethene (165 µg/L)
  • - Vinyl chloride (10 µg/L)

Site Characterization Technologies:

  • - Borehole Geophysics
    • Single Point Resistance
    • Natural Gamma
    • Caliper
    • Acoustic Televiewer
  • - Fluid Loggings
    • Temperature
  • - Vertical Chemical Profiling
    • Packer Isolation
  • - Other (Spontaneous Potential)

Comments:
Hydraulic communication between injection wells and groundwater recovery well GW-9001 was verified with hydraulic packer testing conducted after the injection wells had been installed. Specific intervals for ethanol injection were identified using a combination of geophysical tools and the packer testing. Fracture intervals with direct communication to recovery well GW-9001 were isolated by installing permanent packers.


Remedial Technologies:

  • - Bioremediation (In Situ)
    • Reductive Dechlorination (In Situ Bioremediation)
Comments:
This study was a pilot test designed to target remediation of groundwater within bedrock fractures where prior groundwater investigations had identified elevated concentrations of VOCs. A recirculation approach was employed using three 220-foot deep bedrock injection wells located updip, downdip, and along strike from the existing groundwater recovery and treatment system (GWRTS) recovery well GW-9001. An ethanol mixing system was designed and installed to meter ethanol at a time-weighted average concentration of 152 mg/L (three times the calculated stoichiometric demand) in a stream of effluent from recovery well GW-9001. The solution of ethanol and treated effluent was injected through the three injection wells at 6-hour intervals twice daily at a combined rate of 2.0 gallons per minute (gpm). The Lower Lagoon aquifer area was bioaugmented after 8 weeks of biostimulation using the halorespiring microbial consortia KB-1. Biostimulation was performed after bioaugmentation to sustain anaerobic conditions. Regular monitoring was conducted at the recovery wells to demonstrate reductive dechlorination of VOCs in the treatment area. Monitoring was conducted at five locations. One location, Spring 1, is a surface discharge point for both the overburden and bedrock aquifers. Two wells, GW-9004, Well-18, are located downgradient and outside of the test plot. No location is listed for the remaining two monitoring wells, AW-3 and GW-9001. The pilot test was conducted for 40 weeks.
Remediation Goals:

The site is a Resource Conservation and Recovery Act (RCRA)-regulated former manufacturing facility. It consists of a closed and capped RCRA surface impoundment, the Lower Lagoon, and a closed and capped landfill, the Upper Quarry, that formerly contained sludge from the Lower Lagoon. The goal of this pilot test is to demonstrate the efficacy of enhanced in situ bioremediation (EISB) in the fractured bedrock system and eventually transition from a pump-and-treat remedy to EISB under natural flow gradient.


Status:

Concentrations of trichloroethene (TCE) ranged from a baseline maximum of 1,800 g/L at week 14 to a minimum of 680 g/L at week 16. Continued monitoring after the pilot test has indicated that concentrations are dropping significantly. Concentrations of cis-1,2-dichloroethene (cis-1,2DCE) exhibited an increasing trend, from 165 g/L at baseline to 1,500 g/L at week 20. Post-pilot test monitoring indicated that concentrations reached a maximum of 2,500 g/L at week 25. Concentrations of vinyl chloride concentrations also exhibited an increasing trend, from less than 10 g/L at baseline to 73 g/L at week 20. Ethene concentrations increased over the pilot test period as much as four orders of magnitude. The VOC data indicate that reductive dechlorination was occurring as early as week 5, several weeks before bioaugmentation. These data suggest that indigenous dehalogenating bacteria were present in site groundwater.

Concentrations of ethanol in monitoring well AW-3 ranged from 10 mg/L to 260 mg/L and represent near-injection point conditions. Ethanol concentrations in samples from well GW-9001 ranged from less than 0.05 mg/L to 89 mg/L and represent average contaminant concentrations present in groundwater in the extraction well. Ethanol was not detected in off-site wells, suggesting that either migration to the wells was not possible under the induced gradient or that the ethanol was consumed before it reached the monitoring point.

Measurements from wells GW-9001 and AW-3 indicated that reducing conditions were achieved from the first post-baseline event through week 40. Monitoring well points outside of the study area exhibited oxidizing conditions throughout the pilot test.

Terminal electron acceptors (TEA), including nitrate and sulfate, were periodically monitored throughout the pilot test. Sulfate concentrations ranged from 200 mg/L at week 1 to 34 mg/L at week 24. Nitrate concentrations decreased from 5.0 mg/L to below 0.4 mg/L from baseline sampling through week 12. Decreasing concentrations of TEAs indicate a thriving microorganism population.

Volatile fatty acids (VFA) indicate that biodegradation through oxidation has occurred. Acetic acid is the primary VFA breakdown product of ethanol. Maximum concentrations of acetic acid were up to 680 mg/L in week 14. Methane is also an indicator of biological metabolism. Methane increased steadily in the groundwater over the pilot test period.


Lessons Learned:

The ethanol concentrations were sufficient to sustain KB-1 in the pilot test area. This conclusion is supported by changes in VOC concentration, increasing VOC daughter products ratios, presence of VFAs and methane, and decreasing nitrate and sulfate concentrations.

The recirculation approach was effective in demonstrating the efficacy of EISB in the site aquifer. However, persistent sulfate concentrations, higher oxidation-reduction potential measurements, and lower VFA concentrations may have slowed the biodegradation rate in the pilot test area through electron competition. This slowed rate may have been caused when recovery well pumping formed a capture zone that extended beyond the biologically active zone created through ethanol injection. Groundwater extraction at the recovery well has been suspended to test whether expansion of the biologically active zone downgradient of the pilot test area can occur in the absence of recirculation.

Reference:
Voci, Christopher J.; Michael S. Kozar; Roy S. Blickwedel. 2004. Ethanol biostimulation and bioaugmentation of a VOC-impacted deep bedrock aquifer. The Fourth International Remediation of Chlorinated and Recalcitrant Compounds Conference, Monterey, California. May 24-27.

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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