Case Studies - CAN003

Multi-Reactive Treatment Barrier Installed to address TCE Contamination

ARS Technologies and Adventus Group announce the completion of their first joint project integrating the firms’ environmental treatment technologies. The joint project, completed for a governmental agency consisted of the installation of a multi-reactive treatment barrier at a facility in Quebec, Canada.

The project site is an active facility that has a TCE plume that is migrating to a local river. The plume is about 2.2 km (1.5 miles) long and has three large source areas and a few smaller source areas. The three source areas co-mingle to form one large plume. The geology is comprised of sands and gravels over bedrock with small localized inclusions of silts and clays. Groundwater (GW) travel times are estimated at 1.0 to 3 ft per day. Depth to bedrock varies but is 95 to 130 ft bgs and water table is about 30 ft bgs. Concentrations in the pilot test areas (pre-selected) as high as 680 ug/L but average around 100 to 200 ug/L.

The installed system will be monitored for the next 10 months as part of an ongoing technology evaluation program. The installation was implemented by ARS Technologies, Inc (ARS) as part of a corrective measure study to assess the effectiveness of Pneumatic Fracturing/Liquid Atomized Injection (PF/LAI) and In-Situ Chemical Reduction (ISCR) emplacing a mixture of Zero Valent Iron (ZVI) powder and Adventus’ EHC bioremediation product for the treatment of subsurface Chlorinated Volatile Organic Compounds (CVOC's). 

Field operations at the Site were performed from June 19 through July 15, 2006. Field work began with installation of twelve injection boreholes with depths as great as 83 feet across a 125 ft. long by 25 ft. wide treatment area. The reactive materials were injected by ARS Technologies’ patented pneumatic technology termed “Liquid Atomization Injection” (LAI) using bulk nitrogen gas to maximize the extent and uniformity of reactive medium distribution. The gas was injected at flow rates ranging from 300 to 800 scfm using a proprietary high-pressure pneumatic injection module designed to regulate high flow rate.  The gas served to drive and disperse the EHC and ZVI powder into the formation. PF/LAI may be applied by a steady stream of nitrogen or a pulsing method in response to formation characteristics at specific intervals or depths. 

Injections were performed in discrete 3.5-ft intervals in order to isolate and concentrate the energy of the nitrogen for better distribution. Ten to fifteen injections were conducted in each of the twelve injection locations.  Over four weeks, a total of 64,877 pounds of zero-valent iron (ZVI) and 26,645 pounds of EHC (containing tailored proportions of organic material such as lactate, molasses, and complex sugars) in the form of powder were emplaced directly in the aquifer.

Mike Liskowitz, ARS Project Manager said, “We’re pleased to be working with our teaming partner Adventus here at this site. This project represents the first EHC/ZVI barrier installed using gas atomized injection of the treatment media.  This approach results in more even distribution of the treatment media within the subsurface which results in more efficient treatment of the impacted ground water”. 

A critical component of ARS’ injection process is ensuring that the reactive media is distributed effectively within the subsurface to facilitate the desired chemical reactions.  To accomplish this distribution, ARS incorporates its gas-based PF/LAI technologies for the emplacement of reactive media.  The LAI approach serves as an effective method for injecting liquids or slurries uniformly within all types of geology.  LAI relies upon the theory that it is more effective to inject gases or "aerosols" into the subsurface than it is to inject an incompressible liquid into the subsurface.  Depending upon the permeability or heterogeneities within the targeted geologic zone, PF may be integrated as a precursor to LAI of a reactive media.  PF is a patented process in which a gas is injected into the subsurface at pressures that exceed the combined overburden pressure and cohesive soil strength of the geologic matrix, and at flow rates that exceed the effective permeability of the undisturbed soil.  The result is the propagation of fractures outward from the injection well to various distances depending upon the geology.  Fracture propagation distances of 30 - 60 feet are common in rock formations. Unconsolidated materials such as silts and clays typically exhibit fracture propagation distances of 20 - 40 feet. In most geologic formations the propagation is relatively uniform around the injection well.  PF can serve as a critical component for many in-situ treatment processes since it allows for an effective permeability enhancement of the geologic matrix while reducing geologic heterogeneities within the subsurface. 

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