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' Beacon Station No.474 December 23, 1997 Stockton. 1i iAdditionalrf a Investigation RepQrt ,- oxygenated fuel additive ve compounds methanol, ethanol, tertiary butanol, MTBE, DIPE, ' ETBE, and TAME by EPA Method 8260. ' Analytical results for groundwater samples submitted from the monitoring wells detected the following concentrations: ' • Well MW-6 indicated TPHg (58,000 parts per billion (ppb)) and BTEX (16,000 ppb benzene, 7,900 ppb toluene, 1,000 ppb ethylbenzene, and 7,100 ppb xylenes). ' • Well MW-8 indicated only detectable TPHg (79 ppb). • Wells MW-7 and MW-9 indicated below the laboratory detection levels for all tested ' compounds. • All groundwater samples indicated below the laboratory detection levels for the oxygenated fuel additive compounds methanol, ethanol, tertiary butanol, MTBE, DIPE, ETBE, and TAME. ' • Monitoring wells were resampled by Doulos Environmental for the fourth quarter on November 21, 1997. These results confirm the Horizon September 30 and October I results (see Table 2 and Appendix H). 1 Laboratory results for the groundwater samples are summarized in Table 2. Laboratory ' analytical data and COC reports are included in Appendix H. ' CONCLUSIONS 1 Based on data collected during this study, the latest quarterly groundwater monitoring ' performed at the site on November 21, 1997, and historical soil and groundwater analytical results (Appendix I), Horizon concludes the following: ' • _ Soil samples collected between 50 and 65 feet bsg in boring B-5 (6 feet-south of wells" MW-2 & MW-6) indicated hydrocarbon concentrations averaging over 5,000 ppm TPHg ' and over 55 ppm benzene. This data suggests that the source of the hydrocarbons may have originated from the north end of the eastern dispenser island. 1474-12.rpt 8 HORIZON ENVIRONMENTAL INC. 1