In-situ treatment of contaminated groundwater has gained acceptance in recent years because of efficiency and lower cost, when compared to pump-and-treat systems. Permeable reactive barriers in the form of reactive walls and funnel-and-gate designs are the leading-edge technologies. These methods remove or transform contaminants in a passive manner without significantly disrupting groundwater flow. Most field trials and full-scale systems have primarily been used to treat chlorinated solvent plumes.
Current reactive wall and funnel-and-gate designs have several disadvantages, including:
· The treatment of one type of contaminant, · The use of large volumes of treatment media, · High sampling costs, and · The reconstruction of the system at breakthrough.
In-situ filtration wells incorporate the advantages of permeable reactive barriers and address these disadvantages.
The in-situ filtration well is constructed of large diameter casing with inlet and outlet openings. The head difference between the upgradient and downgradient sides causes the contaminated groundwater to flow vertically up the casing. Interchangeable, retrievable filter canisters are placed inside the casing across the controlled flow path. The outlet on the downgradient side of the gate allows treated groundwater to pass into an infiltration gallery.
The design improvements include:
· Initiating a highly controlled flow path, · Using canisters and media to treat several types of contaminants, · Reducing sampling, and · Easy replacement of spent filter canisters.
The in-situ filtration well system is most applicable to areas of shallow groundwater, with an underlying low permeability unit is present and with an aquifer of moderate to low permeability and a relatively low gradient.