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Unocal Service Station #6981 April 25, 1995 CURRENT QUARTER'S ACTIVITIES Field activities conducted at the subject site during the first quarter 1995 included monitoring and sampling of the groundwater monitoring wells by MPDS Inc of Concord, California, bi-monthly monitoring of VES operational parameters by Gettler-Ryan Inc (G-R) of Dublin, California, and monthly sampling of the VES influent and effluent vapor stream by G-R VES sampling procedures are presented in Appendix A Monitoring and Sampling of Groundwater Monitoring Wells Groundwater monitoring wells were monitored and sampled by MPDS on January 25 and 26, 1995 Based on measurements collected by MPDS, the groundwater beneath the site appears to flow toward the northeast an approximate gradient of 0 005 Total Petroleum Hydrocarbons as gasoline (TPHg) were detected in groundwater samples from wells MW-2 through MW-5 and MW-7 at concentrations ranging from 54 to 8,600 parts per billion (ppb). Benzene was detected these wells MW-2, MW-4, MW-5, and MW-7 at concentrations ranging from 2 4 to 4,100 ppb A copy of the MPDS Quarterly Data Report is presented in Appendix A Monitoring and Sampling of VES The VES consists of six vapor wells (VW-1 through VW-6) manifolded into a single vapor stream connected to a Baker Furnace thermal/catalytic oxidizer system After destruction of the extracted petroleum hydrocarbons, the vapor stream is discharged to the atmosphere The system operates under San Joaquin Valley Unified Air Pollution Control District (SJVUAPCD) Permit Number N-3335-1-0, dated October 5, 1994 Schematic representation of the VES is shown on the Process Flow Diagram (Figure 3) A copy of the SJVUAPCD permit is presented in Appendix C G-R collected samples from the VES influent and effluent vapor streams on January 9, 1995, and measured VES system parameters on January 9 and 23, 1995 VES field monitoring data are summarized in Table 1 The calculated influent flow rate from the wellfield ranged from 129 9 to 136 3 standard cubic feet per minute (scfm), and the calculated effluent flow rate ranged from 159 5 to 258 7 scfm The VES was shut down on January 23, 1995, due to an increase in supplemental fuel use and in anticipation of a switch to catalytic oxidation mode Collected vapor stream samples were submitted to the Sequoia Analytical laboratory located in Sacramento, California (ELAP #1624) Samples were analyzed for Total Petroleum Hydrocarbons as gasoline (TPHg) and Benzene, Toluene, Ethylbenzene, and total Xylenes (BTEX) by EPA Methods 50301801518020 Chemical analytical results for the VES influent and effluent vapor stream samples are summarized in Table 2 The VES Operation and Emissions Data are summarized in Table 3 Copies of the Sequoia Analytical Laboratory reports and chain-of-custody forms are presented in Attachment D 4855 02-3 2