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' 3. CONSTRUCTION AND START-UP OF UVB SYSTEM 3.1 UVB GENERAL SYSTEM DESCRIPTION ' In October 1996, EA submitted a Groundwater Remediation System Technical Plan (EA 1996) to the San Joaquin County Public Health Services Environmental Health Division and to the ' Central Valley Regional Water Quality Control Board In this plan, EA proposed to use UVB technology to treat the groundwater and soil below the water table at the site UVB technology was designed and developed by IEGmbH of Germany as a method for the in situ treatment of ' groundwater, and was first introduced in the United States in 1992 The UVB system was selected as the remedial option, because it is more effective than the 1990 ' proposed pump and treat system in stripping petroleum hydrocarbons and does not create the need to discharge treated groundwater The UVB system has a lower capital cost than most other remedial alternatives and has minimal operation and maintenance requirements ' The UVB well is an in situ groundwater remediation system which removes petroleum hydrocarbons using a combination of physical and biological processes The UVB system ' creates a circulation cell that transports the mobile, dissolved-phase and residual-phase hydrocarbons to a central well casing for treatment The treatment methodology is primarily air stripping, and secondarily bioremediation for the light and middle range hydrocarbon fractions The UVB well has a lower compartment, screened for groundwater extraction, separated by a packer from an upper compartment, screened for groundwater infection A support pump controls the flow direction, extracting groundwater at a predetermined flow rate and transferring it through the packer into the air stripper located in the upper UVB well compartment During operation, the water level rises inside the air-tight upper UVB well compartment due to a reduced pressure generated by an above-ground blower Atmospheric air enters the well, also due to the pressure differential, through a fresh air intake pipe connected to the stripper in the upper UVB well compartment The incoming fresh air forms bubbles as it is betted through a stripper pinhole plate into the groundwater in the well casing ' The groundwater level in the well casing is also raised by an air lift effect caused by the rising air bubbles in the stripper The reduced pressure in the upper UVB well compartment accelerates ' the rise of the bubbles When the bubbles reach the air/water interface inside the well casing, they burst and allow stripped volatile organic compounds (VOCs) to be transported upward through the well shaft for off-gas treatment As the bubbles burst, the groundwater falls along the interior wall of the well, producing a significant hydraulic pressure that drives the water horizontally into the aquifer through the upper screen ' Groundwater from the aquifer flows into the lower part of the well to replace the water exiting from the upper screen A three-dimensional circulation pattern develops, with water entering the screen in the lower compartment of the well, and leaving through the upper screen W?61 71942 R01397 1 5