Formatted Title
Karst Formation Bioaugmentation Pilot Study for a Trichloroethylene Source at an Electronics Manufacturer in New York
Background/Objectives
The site has had several historical manufacturing uses, with a primary focus on electrical components for the last half century. Operations included the use of trichloroethylene (TCE) and 1,1,1-trichlorethane (1,1,1-TCA) as degreasing solvents, with the associated site contamination present in a source located beneath the main manufacturing building and a potential secondary source related to activity from historical construction. The site is located in the Finger Lakes region of New York and is underlain by the karst Onondaga Formation consisting of mudstone and packstones, overlain by glacial till and sand and gravel backfill, with competent bedrock ranging from more than 40 to less than three feet below grade across the 27-acre property. Contamination is present in soils, overburden and shallow bedrock groundwater and associated soil vapors. All potential receptor pathways are incomplete and managed through the use of institutional controls and engineering controls such as capping and groundwater treatment systems.
A prior microbiological census provided that Dehalococcoides (DHC) bacteria, that can degrade TCE to ethene, are present, however inconsistently, along the groundwater flow path with greatest populations downgradient from the source. Additionally, the compound specific isotope analysis demonstrated that degradation of TCE to daughter products is occurring along the plume and also suggested the existence of a secondary source area, with downgradient mixing. Data indicate that sulfate associated with the karst formation and dissolved oxygen concentrations will need to be monitored to verify reductive dechlorinating conditions.
The objective of the pilot study is to confirm the feasibility of bioremediation of a karst source area through the combined use of emulsified vegetable oil (EVO) to facilitate reductive conditions and the introduction of DHC predominant bacterial cultures with desirable functional genes for complete degradation to enhance existing native bacterial populations.
Approach/Activities
The pilot study is ongoing and planned to occur over a 12-month interval, with initial activities inclusive of injection of EVO at four wells at adjustable dilution ratios, coupled with transducers at adjacent and downgradient wells for hydrogeological evaluation. Planned groundwater sampling and aquifer characterization milestone events occurring prior to injection and at one, three, six, nine and 12 months thereafter. Groundwater elevations, chlorinated compound concentrations, and groundwater quality parameters, including pH, specific conductivity, oxidation-reduction potential, and dissolved oxygen, are measured at each event. Monitoring of dissolved gases is planned for the six- and 12-month events. The bacterial culture was introduced after confirmation of acceptable reducing conditions.
Results/Lessons Learned
The pilot study is in progress, and data from up to the nine-month monitoring event will be available by the conference presentation date. The hydrogeological assessment at the injection event demonstrated observable communication among the treatment wells and monitoring points in both the overburden and bedrock, with a promising corollary being the potential to inject from outside the building footprint to treat a karst source area found underneath. Following the 30-day event, field data confirmed acceptable reducing conditions were present. Further, characterization data from this event suggests a modest decrease in TCE concentrations prior to the bacterial injection. Additional monitoring data from future pilot study events will help determine the treatment radius of influence and coupled with the hydrogeological data to determine feasibility of bioremediation of a karst source area.