CAN003 – EHC Injection, ZVI
Quebec City, Quebec, Canada
ARS Technologies, Inc. and Adventus Group announced 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 was an active facility with a TCE plume that was migrating to a local river. The plume was about 2.2 km (1.5 miles) long and had three large source areas as well as a few smaller source areas. The three large source areas co-mingled to form one large plume. The geology was comprised of sands and gravels over bedrock with small localized inclusions of silts and clays. Groundwater (GW) travel times were estimated at 1.0-3.0 ft. per day. Depth to bedrock varied, but was 95-130 ft. bgs with the water table at approximately 30 ft. bgs. Concentrations in the pilot test areas (pre-selected) were as high as 680 ug/L, but averaged around 100-200 ug/L.
The installation was implemented by ARS Technologies, Inc. (ARS) as part of a corrective measure study to assess the effectiveness of Pneumatic Fracturing/Atomized Liquid Injection (PF/ALI) and In Situ Chemical Reduction (ISCR) while 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 12 injection boreholes with depths as great as 83 ft. across a 125 ft. long by 25 ft. wide treatment area. The reactive materials were injected by ARS Technologies’ patented pneumatic technology termed “Atomized Liquid Injection” (ALI) using bulk nitrogen gas to maximize the extent and uniformity of reactive medium distribution. The gas was injected at flow rates ranging from 300-800 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/ALI 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 12 injection locations. Over four weeks, a total of 64,877 lbs. of Zero-Valent Iron (ZVI) and 26,645 lbs. of EHC (containing tailored proportions of organic material such as lactate, molasses, and complex sugars) in the form of powder were emplaced directly into the aquifer.
Mike Liskowitz, ARS’ Project Manager spoke of the project: “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 groundwater.”
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/ALI technologies for the emplacement of reactive media. The ALI approach serves as an effective method for injecting liquids or slurries uniformly within all types of geology. ALI relies upon the theory that it is more effective to inject gases or “aerosols” into the subsurface than it is to inject a non-compressible liquid into the subsurface. Depending upon the permeability or heterogeneities within the targeted geologic zone, PF may be integrated as a precursor to ALI 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 ft. are common in rock formations. Unconsolidated materials such as silts and clays typically exhibit fracture propagation distances of 20-40 ft. 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.