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.

• Fractured Bedrock

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.

• Trichloroethene (1,800 µg/L)
• cis-1,2-Dichloroethene (165 µg/L)
• Vinyl chloride (10 µg/L)

• 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.

• Bioremediation (In Situ)
  • Reductive Dechlorination (In Situ Bioremediation)

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.

Concentrations of trichloroethene (TCE) ranged from a baseline maximum of 1,800 µg/L at week 14 to a minimum of 680 µg/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 µg/L at baseline to 1,500 µg/L at week 20. Post-pilot test monitoring indicated that concentrations reached a maximum of 2,500 µg/L at week 25. Concentrations of vinyl chloride concentrations also exhibited an increasing trend, from less than 10 µg/L at baseline to 73 µg/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.

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.