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1. INTRODUCTION At the request of Exxon Company, U S A (Exxon), EA Engineering, Science, and Technology (EA) has evaluated the groundwater conditions and proposes a groundwater remediation plan for ' former Exxon retail station 7-3942, located at 4444 North Pershing Avenue in Stockton, California (Figure 1) The groundwater remediation plan described in this document is based on current groundwater conditions at the site, petroleum hydrocarbon concentrations in the groundwater, and proven remediation technologies In October 1990, EA submitted a Combined Work Plan to Remediate Soil and Groundwater(EA 1990) Under this plan, EA proposed to remediate groundwater through conventional technology available at the time a groundwater extraction, treatment and reinfection system (GETS) Pursuant to the 1990 plan, EA installed the required wells for this remedial approach, but the 1 GETS was not installed, due to concern for an apparent upgradient source of hydrocarbons that could be pulled onto the site, and the necessity of adding upgradient monitoring points A soil vapor extraction system (SUES) was also proposed in EA's 1990 plan, to address the question of petroleum hydrocarbons in the soil The SVES was installed and began operation in May 1994 The system has successfully remediated petroleum hydrocarbons in the former source area beneath the site The SVES recovered petroleum hydrocarbons using four vadose zone wells screened from 10 to 30 feet below ground surface (bgs) A total of 16,000 pounds of petroleum hydrocarbons have been removed in the vadose zone by the SUES Petroleum hydrocarbons trapped in soil below the water table have not been effective) Y PP Y remediated with the SVES Based on previous site investigations (EA 1987a, 1987b, 1988a, ' 1988b, 1989a, 1989b, 1990, 1991), petroleum hydrocarbons occur at the site between 27 and 42 feet bgs. The purpose of this present groundwater remediation technical plan is to address petroleum hydrocarbons trapped in soil below the water table and optimize the remediation program at the site as a whole The soils at this depth are mainly silty clays and clayey silts ' EA proposes to use UVB (Unterdruck Verdampfer Brunnen---vacuum vaporizer well) technology to treat the groundwater and soils 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 IEG Technologies Corporation (EEG) is the exclusive U S marketer of the UVB technology 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, does not result in the lowering of the water table, 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 system extracts groundwater through a lower well screen section in the aquifer, strips volatile organic compounds from the water in a chamber within the well, and discharges the treated groundwater through an upper well screen section back into the aquifer This induced flow remediates hydrocarbons from the top to the bottom of the aquifer WP61 73942 WP1096 TX 5 1 4