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u t� Mr Kyle Christie Project 0805-114 04 • January 29, 1996 Page 3 GROUNDWATER MONITORING: FOURTH QUARTER 1995 EMCON was contracted by ARCO to conduct the field work at the site Field work included measuring depths to water and collecting groundwater samples for subjective and laboratory analyses EMCON used these data to evaluate the gradient and direction of groundwater flow beneath the site C:On December 7, 1995, technician from EMCON measured depths to groundwater and co ecte groundwater samples from wells MWA through MW-8, and MW-10 for subjective and laboratory analyses The remediation system was operational during the site visit Floating product or product sheen was not noted in samples from the wells (see Table 1) Sampling and analyses procedures are presented in Appendix A The wellhead elevations of the monitoring wells at the site were previously surveyed by Morrow Surveying of West Sacramento, California. The surveyed elevations and the depth to groundwater measurements, summarized in Table 1, were used to evaluate the potentiometnc surface beneath the site The groundwater flow direction on December 7, 1995, was to the east ith a hydraWLc gradiegLgf 0.001 (see Figure 3) The groundwater flow direction in the past has generally been towards the east to southeast Groundwater elevation data are presented on Figure 3 and in Table 1 Groundwater elevations increased 134 feet from the previous sampling event (August 1995) Groundwater samples collected from wells MWA through MW-8 and MW-10 were analyzed for TPHG, and benzene, toluene, ethylbenzene, and total xylene isomers using California Department of Health Services LUFT Method and Environmental Protection Agency (EPA) Method 5030/8020, respectively These samples were analyzed at Columbia Analytical Services, Inc , ui San Jose, California- The results of these analyses are summarized in Table 2 Copies of the chain-of-custody records and laboratory analysis reports are presented in Appendix B Dissolved hydrocarbons were detected in wells MW-1, MW-2, MW-5 and MW-10 TPHG concentrations ranged from below detection limits in well MW-5 to 540 ppb in well MW-2 Benzene concentrations ranged from 0 7 ppb in well MW-10 to 18 ppb in well MW-2 TPHG and benzene concentrations are shown on Figure 2 OPERATION AND MAINTENANCE OF THE REMEDIATION SYSTEM EMCON began the operation and maintenance of the remediation system in November 1994 The system consists of an air sparging-enhanced vapor extraction system with catalytic oxidation (AIREX KATOX 100). The system is connected to 3 air sparge . wells (AS-1 through AS-3) and 12 vapor extraction wells (VW-1 through VW-12) SACNN\PJ(rL7 O"8051140 4GS-95\pas 1