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ANALYTICAL METHODS AND RESULTS Laboratory Anal sis ' The groundwater samples were delivered to ATL for the analyses of TPHg and TPHd following EPA Test Method 8015 modified, and benzene, toluene, ethylbenzene and total xylenes (BTEX) and ' MTBE following EPA Test Method 8020 Well VW-2 was further analyzed to confirm the presence of MTBE following EPA Test Method 8260 The laboratory reports and chain of custody documentation are presented in Appendix B ' Analytical Results TPHg was detected In wells MW-1, MW-2, MW-3, MW-6, MW-7, MW-8, MW-11, VW-1 and VW- 2 at concentrations ranging from 300 to 17,000 gg/l TPHg was detected in downgradient well MW- I 1 at a concentration of 800 gg/l TPHg was not detected in perimeter cross gradient wells MW-4, ' MW-5, MW-9, MW-10 and MW-12 TPHd was detected In each of the wells sampled, with the exception of well MW-9, at concentrations ranging from 53 to 570 gg/l TPHd was detected at a concentration of 170 gg/l In downgradlent well MW-1 I ' Benzene was detected in each well sampled, with the exception of wells MW-5, MW-9 and MW-12 at concentrations ranging from 1 0 to 4,200 gg/l Using EPA Test Method 8020, MTBE was detected ' in wells MW-1, MW-2, MW-3, MW-6, MW-7, MW-8, MW-1 1, VW-1 and VW-2 at concentrations ranging from 5 4 to 43 gg/l Using EPA Test Method 8260, MTBE was reported in well VW-2 at a concentration of 14 µg/l (as opposed to 43 gg/I by EPA Test Method 8020) The EPA Test Method 8260 MTBE data for well VW-2 suggests that MTBE concentrations reported by EPA Test Method 8020 for well VW-2 (and other onsite wells) may be artificially high A summary of the analytical laboratory test results is presented on Table 1 Concentrations of ' petroleum hydrocarbons in groundwater are presented on Figure 3 Laboratory reports and chain-of- custody records are presented In Appendix B ' WORK IN PROGRESS Geocon performed a vapor extraction pilot test (VET) at the Stockton Yard site on August 15, 1996 ' The purpose of the VET was to evaluate the feasibility and economics of using vapor extraction to remove residual TPHg from soil beneath the site Results of the test indicate that soil vapor extraction is both technically and economically feasible The VET results will be included In a ' Problem Assessment Report/Corrective Action Plan that is currently being prepared for submittal to Caltrans separately from this quarterly groundwater monitoring report The PAR/CAP for Stockton Yard will be completed by mid-December 1996 1 Project No S8100-06-62 -3- November 27, 1996