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vapor well near the center of the contaminant plume for remediation A vapor extraction system (VES) was installed in August 1991 and was operated under permit requirements of the San Joaquin Air Pollution Control District order number 91-61 2.3 Remediation Remediation began in 1991, and progress has been summarized in reports submitted between March 1992 and February 1993 At the end of 1992, the VES had operated for approximately 8,884 hours, and the mean hydrocarbon vapor concentration at the inlet was approximately 500 ppm From the end of 1992 to July 1993, the VES was in operation for approximately 90 percent of the time, bringing the total operational hours to 13,500 vapor Hydrocarbon or concentrations were measured at the inlet to the VES, using a Y P photoionization detector (PID), on a weekly basis to monitor the removal of hydrocarbons from the soil Vapor samples were collected on February 22 and April 28, 1993 for laboratory analysis The sample results were then correlated with the field readings This information was used to determine the volume and efficiency of hydrocarbon removal The results of the samples were described in a Quarterly Report dated July 17, 1993 2.4 Regulatory Meeting On August 20, 1993, representatives of GeoAudit met with Mr Ronald Bruno, representing Genova Bakery, and Mrs Margaret Lagono of the PHS/EHD, to discuss further assessment and remediation activities A decision was made to re-start the vapor extraction motor and monitor vapor levels closely for several days to determine whether additional benefit could be obtained by continuing to operate the system The combustion unit was re-started and operated from September 20 to September 26 and E again from November 8 to December 7, 1993 The unit was shut-off on December 7, 1993 and has not operated since Using data obtained from the air samples collected during the first half of 1993, actual concentrations of petroleum hydrocarbons were calculated to be 43% of the PID readings The last five PID readings ranged from 145 ppm to 242 ppm, this theoretically represents actual petroleum hydrocarbon concentrations of 62 ppm to 104 ppm The concentration of vapors removed from the soil at the site during the re-start period (from September to November) was not significant It appeared that the continued operation of the vapor extraction unit would not significantly enhance soil mitigation at the site We recommended that the unit be permanently disconnected and vapor extraction at the site terminated 2.5 Additional Soil and Groundwater Investigation Seven groundwater monitoring wells had previously been installed on or near the site The wells were installed to depths of 55 feet At the time of installation, groundwater depth was OwWpsl A.dn&. m,I.. 4 at—0.6ryQW7MI