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Mr. Kyle Christie Project 0805-147.02 . March 12, 1996 Page 2 . GROUNDWATER MONITORING: FOURTH QUARTER 1995 EMCON was contracted by ARCO to monitor the groundwater monitoring wells installed at the site. Field work included measuring depths to groundwater 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. On December 22, 1995, a technician from EMCON measured depths to groundwater and collected groundwater samples from wells MW-1 through MW-3 for subjective and laboratory analyses. Floating product was not noted in samples from the wells (see Table 1). Sampling and analysis procedures are presented in Appendix A. The wellhead elevations of the site monitoring wells were previously surveyed by Tom O. Morrow, Inc. The surveyed elevations and the depth to groundwater measurements, summarized in Table 1, were used to evaluate the potentiometric surface beneath the site. The direction of groundwater flow on December 22, 1995, was toward the east with a hydraulic gradient of 0.003 (see Figure 3). The gradient during the initial sampling event (September 1995) was toward the east. Groundwater elevations have increased . approximately 4.27 feet since the last sampling event (September 1995). Groundwater samples from wells MW-1 through MW-3 were analyzed for TPHG using Environmental Protection Agency (EPA) Methods 5030/DHS LUFT, and BTEX using EPA Methods 5030/8020 prescribed by the state of California. These samples were analyzed at Columbia Analytical Services, Inc., in San Jose, California. The results of analyses are summarized in Table 1. Copies of the chain-of-custody records and Iaboratory analysis reports are presented in Appendix B. Results of analyses indicated that dissolved gasoline hydrocarbons were detected in the groundwater sample collected from well MW-1, but were not detected in wells MW-2 and MW-3. TPHG was detected in well MW-1 at a concentration of 730 parts per billion (ppb) and benzene was detected at a concentration of 3.5 ppb. Concentrations of TPHG and benzene are shown on Figure 2. ACTIVITIES PERFORMED DURING THE FOURTH QUARTER • EMCON performed quarterly groundwater sampling. • EMCON compiled and evaluated groundwater monitoring data. . • EMCON is preparing a Preliminary Investigation Evaluation Report (PIER). SAG\N:\PJft805\0805 t470.2AS-951,cjb:t