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Ms. Lori Duncan April 12, 2002 Page 5 Project 880-039.1A contamination is deep or when there is low -permeability, injecting air into the soil assists in mobilizing contaminants for extraction. Because the process involves the continuous flow of air through the soil, it often promotes aerobic biodegradation of low -volatility organic compounds that may be present. Groundwater Extraction and Treatment When contaminated groundwater is removed from the subsurface by pumping, it is typically treated to remove the contaminants prior to discharge. Hence, this method is referred to as pump -and -treat. It is often associated with treatment technologies such as air stripping and liquid -phase GAC to remove contaminants from the extracted groundwater. Although the effectiveness of pump -and -treat systems has been called into question after two decades of use, this approach remains a component of many groundwater remediation efforts and is appropriate for both restoration and plume containment. Variations and enhancements of conventional pump -and -treat include several physical, chemical, and biological augmentations to improve performance and reduce the project duration. The well design, pumping system, and treatment method are dependent on the aquifer characteristics and contaminant type. Extraction well networks typically use wells screened at different intervals based on the aquifer system characteristics and contaminant distribution to maximize effectiveness of plume control and contaminant removal. A major component of any groundwater extraction system is a groundwater monitoring program to verify its effectiveness. Monitoring the cleanup allows the operator to make adjustments to the system operation in response to changes in subsurface conditions. Using pump -and -treat to flush contaminants from dissolved product contaminated soils (solusols) is often achievable, but flushing contaminants from separate phase contaminated soils (produsols) is not often practicable because of the large mass of contaminants retained in the soil pores and as films around soil particles. IT CORPORATION SAC:\\\SACRFP 1 \COMMON\sacDP\2002\PRJ\PJ8\880\8800391 A.2ac.doc (01040000)