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Click on the numbers in sequence to see how a typical groundwater treatment system works to clean up contaminated groundwater.
1. Diagram 2. Vault 3. Wellhead
4. Pump 5. Sparger 6. Filtration
This is one of the simplest types of groundwater pump-and-treat systems. It is designed to remove volatile organic compounds (gasoline and solvent constituents) from pumped groundwater in a two-stage process: air-sparging followed by carbon filtration. Click the sequence at left to see photos and descriptions of the actual working components of this system.
Wellheads for recovery wells may be at the ground surface, or may be in basements or subsurface vaults (such as this one). Vaults are generally used when the area cannot be reworked to reroute surface activity or traffic.
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Groundwater level in this instance is very high, almost to the top of the well screen (center of picture). This well screen (a slotted PVC pipe) is installed down through the bottom of the vault to an approximate depth of 25 ft below grade. The seasonal average water table is about 6 ft below that occurring here.
The groundwater recovery pump (at left) in this example is an air-driven pump due to possible gasoline vapors (thus the need to avoid electrical equipment that could create a spark). Compressed air is fed through the small tube at the upper right of the pump, forcing water past a check valve and out the center discharge tube. The small tube fastened to the outside of the pump body senses depth of water above the pump and shuts down the pump cycle if the well goes dry.
The pumped groundwater is piped to a surge drum (at right), and allowed to overflow to a sparge drum (at left). Air is blown (sparged) through a diffuser tube in the bottom of the sparge drum. This high rate of air bubbling through the water in the sparge drum creates a situation allowing dissolved volatile organic compounds to leave the water phase and enter the air phase, where they are released to the atmosphere. Typical removals from the groundwater are between 80% and 95%. The source of air is the blower at the lower left.
The sparged groundwater, which has 80% to 95% of the volatiles removed, is allowed to drain into another surge drum (at right), and then is pumped through two charcoal-filled filtration drums (at left) to remove remaining volatiles. After filtration, the groundwater contains only very low concentrations of contaminants, and is suitable for discharge to a sanitary sewer or surface water body.
See the slide show for a coal tar site excavation.
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