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R603 UPDATE-10 11/09/92 Figure 4C, represents depth to ground water measurements obtained on October 8 , 1992 and utilizes the newly installed monitoring wells MW11 and MW12. Prior to obtaining the depth to ground water measurements, all the wells were surveyed by a licenced surveyor for position to one another and top of casing elevations in reference to the City of Stockton bench mark #12 , elevation 11. 741 . Previously the elevation datum used was the southwestern corner of the UST pad with an interpretive elevation of 10 feet above mean sea level, as depicted from a U. S. G. S . topographic map. Figure 4C, October 8, 1992, shows a continual decline in the ground water elevation, with a valley low forming at MW1 towards MW2 and overall flow direction to the southeast. The mound that had previously been observed at MW3 is not present, great care was made not to position the depth to water probe down the 1" pvc tubing that is in the well. Measurements obtained from MW8 were not used; no repeatable measurement could be obtained when measuring the depth to ground water at this well. 2.2 GROUND WATER QUARTERLY SAMPLING . Ground water samples have been collected since December 9 , 1988 , see Table 1 . These samples were collected by a WEGE geologist and "Chain of Custody" hand delivered on ice to a state certified testing laboratory (McLaren Analytical or Chemtech (MATRIX) Analytical Laboratories) for chemical analyses. These samples were analyzed for TPH and BTEX concentrations using EPA Methods 8015 and 602 respectively. Since diesel has never shown up in the sample results, the samples obtained on 11/27/90 and later were analyzed using EPA methods 5030 and 602 for Total Fuel Hydrocarbons and BTEX. The next quarterly sampling will occur in December, 1992 . 3 . 0 RESULTS 3. 1 PRODUCT AND RECOVERY During the initial site assessment and subsequent site visits, floating product was observed in monitor wells MW-1, MW-3 and M"w10 . Product thickAess in MW-1 has ranged from 101 . 011 to 1 . 26 ' and from 0 . 17 ' to 1 . 66 ' in MW-3 . Only a product sheen has been observed in MW10 during the March, June and September, 1991 and the March 10 , 1992 sampling. Observations made during this update status report show that MW1 is free of any floating product and MW10 and MW3 have a sheen of floating product, see Figures 5A, 5B and Table 1. These reductions in product thickness can be attributed to the on going vapor extraction at this site. The recovered gasoline is amber yellow and appears to be fresh (no apparent degradation) . PAGE 4