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CALIFORNIA GEOPHYSICAL GROUP, INC. �"IO Box 578341, Modesto, CA 95357 Tel (209) 527-1247 f August 21, 1998 Fax (209) 527-4810 Public Health Services San Joaquin County ENVIRONMENTAL HEALTH DIVISION P O Box 388 304 E Weber Ave Third Floor Stockton, CA 95201 P O Box 388, Stoc on CA 95201.0388 Approved Denied ❑ RE Work Plan Conditions ��✓r.,w te Darpetro, Inc USA Service Station pa 4��' ..,! 749 E Charter Way -- , - 4 _bY_e'A1�,..0� Stockton, CA �r Site No 1060 On June 18, 1998, the EHD sent a letter requesting further work at this site On July 29, 1998 I met with Ms Carol Oz of the EHD on site to discuss future work This work plan will define the work In July 1997, we installed a vapor extraction system to remove the contamination from the vadose zone at this site To date approximately 33,900 pounds of gasoline have been removed, but there has been no great improvement of the groundwater contamination under the site Part of the reason is the fact that the water table has risen approximately 7 feet since January 1998, the water table is presently the highest it has been since January 1990 when we commenced working on this site See Figure 1 This rise in the water level has exposed the water to new contamination in the former vadose zone and has helped to keep the contamination levels high at this site The vapor extraction system is operating properly but it has not been able to remove all of the contamination In fact, much of the contamination is now below the water table where the vapor extraction system can not reach For this reason, we are planning to start an air sparging system in the old tank hole area where most of the contamination remains The sparging well was installed at the same time as the vapor extraction wells and is located in the tank hole area The sparging point is located 57 feet below the surface AIR SPARGING The air sparging system will introduce clean air into the aquifer about 23 feet below the surface of the water table The breakout pressure for the air is 10 to 11 PSI which is the pressure needed to overcome the pressure of the water column above the sparging point The well is constructed with Schedule 40 PVC pipe and it is recommended to operate at or below 15 PSI The air will be carried to the well head by a steel pipe which has a subsurface run of approximately 90 feet The sparging point is surrounded by vapor extraction wells which will capture the sparging air as it enters the vadose zone It is estimated that the sparging air will migrate about 15 feet away from the sparging point creating a sparging zone about 30 feet in diameter The capture radius of the extraction well has been found to be approximately 25 feet and the amount of air it processes is 200 cubic feet per minute The introduction rate of the sparging air will be 10 to 25 CFM This ' rate will not be too much air for the extraction system to handle See Figures 2 and 3