IN001 – Pneumatic Fracturing, Enhanced Soil Vapor Extraction
Active Manufacturing Facility – Northern Indiana
This case study presents a successful application of Pneumatic Fracturing (PF)-enhanced soil vapor extraction system in an active manufacturing facility in Indiana. The site was contaminated with trichloroethylene (TCE) resulting from historic plant activities. TCE had been detected at concentrations as high as 17,000 µg/L and 25 mg/kg in the groundwater and soils, respectively. The site is underlain by low-permeability glacial till consisting mainly of sand, silt and clay.
Figure 1: Source Area 1 – Degreaser Pit Inside Facility.
Pneumatic Fracturing of “tight” subsurface soils serves to increase the bulk air permeability by creating a dense inter-connected fracture network. The technology can effectively enhance (or, in many cases, enable the implementation of) conventional remediation practices such as soil vapor extraction, multi-phase extraction and air sparging by improving the induced airflow and mass transfer rate of the contaminants.
Prior to the full-scale implementation, ARS conducted a PF/SVE pilot test at the site to evaluate the effect of the PF by comparing the results of the post-fracturing SVE test to that of a previously performed and unsuccessful extraction test prior to ARS’ involvement. Throughout the post-fracturing SVE pilot test, significant vacuum radius of influence was observed in the majority of the monitoring points in the area. Vacuum was observed in monitoring wells as far as 35 ft. from the extraction point.
Figure 2: Source Area 2 – Aboveground Storage Area
The pilot test provided data and operational parameters for the design of a full-scale system later installed in two source areas at the facility (one inside the facility and the other outside the facility). The photographs on this page show the two source areas. The full-scale system was installed in 1997 and was comprised of 8 soil vapor extraction and 3 dual-phase extraction wells. During its first year of operation, the system recovered more than 1,330 lbs. of TCE. It should be noted that design calculations based on soil and soil gas sampling results estimated only 1,100 lbs. of VOC to be present at the site.
The graph below shows the TCE removal rate versus time during the first 6 months of the full-scale implementation. The shape of the curve and the significant initial mass reduction are typical of an SVE system within a formation that experienced efficient mass transfer of contaminants from the adsorbed phase to vapor phase. It is indicative of sufficient contact between the induced air flow and the soil matrix, benefited from the application of Pneumatic Fracturing technology as a system enhancement.
Figure 3: System TCE Mass Removal Vs. Time