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i Beacon Station No 641 September 28, 1998 Stockton California Remedial Testing Report The AST was initiated at approximately 2 30 p m after the VET had been operating for 3 3/4 hours The sparge compressor was initially operating at 12 4 pounds per square inch (PSI) and dropped to 11 PSI after 30 minutes of operation, and stabilized at approximately 7 2 PSI after 1 3/4 hours Pressure changes at wells VW-5 and VW-3 were almost immediate (15 to 30 minutes) after initiating the AST The vapor pressure in well VW-5 showed the most influence with a change from negative pressure induced by the VET to a positive 2 2 inches of water column induced by the AST The pressure data is summarized on Table 1 DO concentrations were taken on May 27, 1998 prior to the initiating of any testing and periodically during the AST These DO concentrations were measured utilizing a Hanna Instruments Dissolved Oxygen Meter DO measurements were taken in monitoring wells MW-1, MW-2, MW-4, MW-5, and VW-1 Initial DO concentrations ranged from 2 7 to 3 8 parts per million (ppm) Additional DO measurements were taken during the AST mainly during the last half of operation These measurements showed an increase in concentrations in DO in all wells measured except well MW-4 The dissolved oxygen data is summarized on Table 3 Based on observations and measurements of DO and pressure changes, it appears that an effective radius of influence for air-sparging would be approximately 20 feet utilizing well SW-1 at a sparge pressure of 7 2 PSI This radius would encompass the main portion of the dissolved hydrocarbon plume beneath the,UST cavity and western dispensers • VET / AST Discussion and Conclusions The VET perfonned indicates that soil vapor extraction will effectively remove hydrocarbons from beneath the site Based on the concentrations being extracted during the VET, the most cost-effective device for initial treatment of the airstream would be through a catalytic hydrocarbon destruction unit Following that form of treatment, at lower concentrations, the most cost-effective device would be activated carbon vessels Assuming the radius of influence to be 18 feet and that the existing vapor extraction wells will be utilized, the area that can be effectively treated by vapor extraction is shown on the Vapor Extraction Map (Figure 3) In addition, it appears that air sparging in conjunction with vapor extraction would be effective in remediating hydrocarbons in the groundwater, and the air-sparge vapor will be effectively captured b3 vapor extraction as depicted on the Air Sparge Map (Figure 4) Aquifer Pumping Test Field work was conducted on May 28 and 29 1998 Horizon conducted aquifer pumping tests by using a 4-inch diameter submersible pump to pump groundwater from monitoring well MW-5, and measuring drawdown in observation wells MW-1 MW-2, MW-4, VW-1 • and VW-7 Automated data loggers were used to continuously record water level data in observation wells MW-1, MW-2 and MW-4 Horizon's Field Methods and Procedures are included in Attachment A 1641-21 rpt 4 HORIZON ENVIRONMENTAL INC