Formatted Title

Innovative Permeability Enhancement and Delivery Methods Achieve Accelerated BTEX, PAHs and VOCs Bioremediation in Clay 

Background/Objectives

A former gasoline station with petroleum hydrocarbons (PHCs), polycyclic aromatic hydrocarbons (PAHs), and chlorinated solvents identified four in situ treatment areas totalling approximately 14,750 m³ of contaminated soils, from the surface down to 46 ft depth. Site geology comprises predominantly clay with low hydraulic conductivity calculated to require more than three decades of back diffusion of residual mass if traditional injection/remediation methods were employed. 

Approach/Activities

Permeability enhancement was employed to increase localized hydraulic conductivity within the target treatment zones by combining silica sand proppants with powder activated carbon along with bioremediation reagents and bioaugmentation.  The in situ injection methods used were hydraulic fracturing and permeation injection for the emplacement of bioremediation amendments. Sand proppant was incorporated into the injection slurry following by installation of injection wells. Injection wells were perforated to overlap with the sand proppants at heavily contaminated areas anticipated to require three rounds of biostimulation reagent injections. 

Results/Lessons Learned

The third and final biostimulation event was completed in the summer of 2023. Significant reductions in all target contaminants demonstrate accelerated performance through the use of permeability enhancement and combined remediation technologies. Two of the four treatment zones had achieved remediation targets within the first year of injections. The remaining two areas receiving additional biostimulation showed further reduction after the second phase. Final performance results from all four treatment areas will be available and presented in early 2024. Permeability enhancement with combined remediation methods has overcome diffusion rate limitations estimated to take more than 30 years has been reduced to what is expected to be 3 to 4 years.