Pump and Treat Technology
When contaminated groundwater is extracted from the subsurface by pumping, it needs to be treated before it is discharged. Hence this method is referred to as pump-and-treat. This is the most common form of groundwater remediation. It is often associated with treatment technologies such as Air Stripping and Liquid-phase Granular Activated Charcoal. Treatment systems are described separately.
The well design, pumping system, and treatment are dependent on the site characteristics and contaminant type. It is not uncommon to find many wells extracting groundwater at the same time. These wells may be screened at different depths to maximize effectiveness. A major component of any groundwater extraction system is a ground water monitoring program to verify its effectiveness. Monitoring the cleanup allows the operator to make adjustments to the system in response to changes in subsurface conditions.
A major issue for a pump-and-treat system is determining when to turn the system off. For contaminants regulated by the EPA, levels established under the Safe Drinking Water Act are usually the prevailing levels that groundwater has to meet. Termination requirements are based on the cleanup objectives defined in the initial stage of the remedial process, combined with site-specific aspects revealed during remedial operations.
Limitations and Concerns
Pump-and-treat systems often take a very long time (e.g., 50 -100 years) to meet cleanup goals, and in many cases they are never expected to ever achieve those goals.
Pumping depresses the groundwater level, leaving residuals sorbed to the soil. After the groundwater level returns to its normal level, contaminants sorbed onto soil become dissolved. This phenomenon is called Òrebound.Ó Rebound tests should be performed frequently in the first few years after a system is turned off, and after major rain or flooding events.
Technology Development Status
Pump-and-treat is a mature technology.
This is a common technology. See links to Remedial Process Optimization, such as http://www.clu-in.org/techfocus/default.focus/sec/Remediation_Optimization/cat/Overview/ for methodology for improving performance of pump-and-treat-based systems.