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• Unocal Station No #6981 November 9, 1995 hydrocarbons, the vapor stream is discharged to the atmosphere As of January 23, 1995, when the VES was shut down, the VES had operated approximately 116 days, or 94% of the time All of the vapor extraction wells were open and used during system operation The VES was shut down in anticipation of a switch to catalytic oxidization mode Historical VES chemical analytical data are summarized in Table 1, and historical VES operational data are summarized in Table 2 CURRENT QUARTER'S ACTIVITIES Field activities conducted at the subject site during the third quarter 1995 are discussed below Monitoring and Sampling of Groundwater Monitoring Wells Groundwater monitoring wells were monitored and sampled by MPDS Services, Inc of Concord, California on July 26 and 27, 1995 Based on measurements collected by MPDS, the groundwater beneath the site appears to flow to the northeast at an approximate gradient of 0 005 (consistent with previous data) The groundwater table was • approximately one foot lower than the previous quarter Total Petroleum Hydrocarbons as gasoline (TPHg) were detected in groundwater samples from wells MW-2, MW-4, MW-5, and MW-7 at concentrations ranging from 130 to 3,300 parts per billion (ppb) Benzene was detected in wells MW-2, MW-4 through MW-8, MW-10, MW-11, and MW-13 at concentrations ranging from 0 55 to 640 ppb The Quarterly Data Report dated August 18, 1995 was submitted by MPDS to the San Joaquin County Public Health Services (SJCPHS) and California Regional Water Quality Control Board (CRWQCB). VES Operation San Joaquin Valley Unified Air Pollution Control District (SJVUAPCD) issued Authority to Construct Permit Number N-3335-2-0, dated April 27, 1995 for modification of the Baker Furnace abatement unit On May 16, 1995, the VES began operating in the catalytic mode, but could not meet the destruction efficiencies specified in the operating permit During May through September 1995, several attempts were made to meet the required 95% destruction efficiency by changing the VES operating parameters The VES was shut down after each attempt to increase destruction efficiency In addition to assessing the integrity of the mechanical operation of the abatement unit, the influent airstream was sampled for compounds that might have poisoned the catalyst, including lead 495502-5 2