Topic Area: 1h. Optimization of Classical Bioremediation Technologies

Formatted Title:

Optimization of Enhanced In Situ Bioremediation of CVOCs Using Real-Time Conductivity Monitoring and Compound Specific Isotope Analysis

Background/Objectives:

Enhanced in situ bioremediation (EISB) is a common remedial technology employed for treating sites with chlorinated volatile organic compounds (CVOCs) impacts. At the site presented here, there are chlorinated solvent impacts, including tetrachloroethene (PCE) and trichloroethene (TCE), as well as their degradation products, cis-1,2-dichloroethene (cDCE), and vinyl chloride (VC). Prior interim measures included multiple source area soil excavations, however, some localized impacts of the CVOCs remain. The site is located on a peninsula surrounded by surface water. The geologic setting of the site is complex, including weathered bedrock and bedrock fractures that run through the site. Pilot EISB test implementation was performed to evaluate the effectiveness of the injections for treating overburden and bedrock, as well as to protect an adjoining surface water body. A concern with injections included potential impact to the surface water by way of substrate daylighting via preferential pathways, thus injection radius of influence needed to be monitored closely.

Approach/Activities:

In the pilot test area, the overburden is fairly shallow (5-15 ft. in thickness), and bedrock outcroppings are present around the site. A total of 14 injection wells were installed in the overburden to the top of rock in two rows – an upgradient row and a downgradient row closer to the lake. The pilot test utilized the upgradient row of injection wells for substrate injections, and the downgradient wells were monitored for substrate breakthrough. One objective of the pilot test was to evaluate if injecting in the upgradient wells would influence the entire pilot test area. Bluetooth enabled transducers were deployed to wells to monitor for signs of substrate breakthrough via changes in conductivity to determine precisely when the intended radius of influence had been achieved. Mechanical methods were also used to visually identify breakthrough in nearby wells. Additional field monitoring to optimize the injections included monitoring for breakthrough of fluorescein dye included in the substrate mixture, used as a tracer, to determine the extent of injection impacts several weeks after the injections. Additional field parameters were monitored to ensure the longevity of the substrate in the pilot test area prior to bioaugmentation, as well. The weathered bedrock and fracture system at the site is complex, and it was unclear the extent of connectivity with the pilot test area. Compound specific isotope analysis (CSIA) samples were collected at baseline and will be collected again in first quarter 2025 to evaluate the influence of overburden substrate injections for treating the bedrock underlying the pilot test area.

Hannah Annunziata

Affiliation

Refine Results

(Group 2, Poster Board #81) Optimization of Enhanced In Situ Bioremediation of CVOCs Using Real-Time Conductivity Monitoring and Compound Specific Isotope Analysis