Innovative circulation systems developed for in situ remediation

IEG GCW systems are specially designed and configured on a site-specific basis, depending on geoenvironmental and contaminant characteristics, to provide accelerated aerobic, enhanced anaerobic or sequential anaerobic to aerobic reactions to deliver more effective treatments.

By selectively applying biological, chemical, and physical processes, IEG’s soil air and groundwater circulation technologies are applicable for a wide range of contaminants, including hydrocarbons (gasoline, diesel, kerosene, fuel oils), polycyclic aromatic hydrocarbons (PAH), creosote, chlorinated solvents (trichloroethane, tetrachloroethane), pesticides and nitrates, ammonia and metals.

For complex problems, GCW technology can also be coupled with other IEG in situ process methods such as vacuum liquid recovery, bioaugmentation, bioventing, soil flushing, soil air circulation and coaxial groundwater circulation/air sparging.

Technical operation

The Groundwater Circulation Well (GCW) system creates an in situ vertical groundwater circulation cell by drawing groundwater from an aquifer formation through one screen section of a multi-screened well and discharging it through another. The sphere of influence of a GCW depends on the distance between the two screen sections and the thickness of the contaminated aquifer. The larger the circulation cell, the larger is the travel time for the circulation.

According to the required remedial strategy, two modes of operation are possible; standard and reverse flow, where groundwater is circulated around a central GCW. Under “standard” flow conditions, groundwater flows upward through the GCW. In “reverse” circulation mode, the flow of groundwater within the GCW is downward. In the latter case, groundwater in the lower half of the aquifer moves away from the well while water in the upper half of the aquifer moves toward the well. In either case, induced differences in potentiometric head establish and maintain the three-dimensional circulation cell in an ellipsoidal zone around the circulation well.

The majority of the groundwater captured by the circulation cell circulates a number of times through the GCW before being released, treated, down gradient. Due to mass conservation, the same quantity of groundwater is released by the well down gradient as is captured up gradient.

The vertical and horizontal circulation flow patterns induced by the GCW force groundwater to move through the entire aquifer within a defined and calculated circulation cell thus improving the mobilisation of contaminants by forcing flow through less permeable formation lenses. As such, groundwater serves as an in situ carrier bringing contaminants into the dissolved phase and transporting them from throughout the capture zone to the GCW system for treatment. Clean groundwater is then discharged back into the formation.

Due to its effective means of ensuring hydraulic control and its simultaneous in-situ treatment capability, the GCW may be used in sequence to act as a “virtual Permeable Reactive Barrier” (vPRB). If the width of a contaminant plume is larger than the capture zone of a single well, several GCWs may be arranged in a transverse direction to the natural groundwater flow. The distance between each system can be modelled and calculated to ensure that no groundwater passes the well barrier without being captured and treated.

Unlike conventional PRBs, where a passive permeable barrier is inserted into the aquifer, GCW is an active remediation technique because it induces high groundwater velocities around the well barrier to expedite remediation.

System’s features

The company claims that its solutions deliver significant advantages over other in situ remediation methods. They are:

IEG’s range of patented in situ systems to treat contaminated soil and groundwater include: Groundwater Circulation Well (GZB); Vacuum Vaporiser Well (UVB); Multi-function Well (SZB); Coaxial Groundwater Circulation (CGC); Vacuum Liquid Recovery (VLR); Soil Air Circulation Flow (SAC); Soil Air Venting Screen (SAV); Multi-level Sampling Well (MLSW); and Compact Stripper.