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06 June 1997 AGE-NC Project No. 97-0327 Page 4 of 5 at concentrations as high as 5.0 parts per million(ppm). 4.3 ANALYTICAL RESULTS OF SOIL SAMPLES A total of five soil samples were submitted to a state-certified laboratory for analysis of TPH-g, TPH- d, BTEX and MTBE. The laboratory analysis did not detect TPH- , TPH-d, benzene, toluene or Y g ethylbenzene in the soil samples. However, MTBE was detected from soil samples collected in probe borings P-3 (25-feet), P-4 (30-feet) and P-5 (25-feet) at concentrations as high as 0.28 mg/kg h (milligrams per kilograms or parts per million: ppm); xylenes were detected in a soil sample collected at P-4 (30-feet) at a concentration of 0.026 ppm. Analytical results of soil samples are summarized in Table 1 -Analytical Results of Soil Samples. The laboratory report (Castle Analytical Laboratory Reference No. 1116) and chain-of-custody are l included in Appendix B. 5.0. CONCLUSIONS AND SUMMARY Based upon field and analytical data collected at the site on 12 May 1997, AGE concludes the following: • Low concentrations of petroleum hydrocarbons (MTBE and xylenes) were detected in soil samples from probe borings P-3 through P-5 at depths of 25 and 30 feet bsg. However, the concentrations of MTBE and xylenes are not much greater than the laboratory reporting limits. Therefore, it appears that soil impacted by trace levels of hydrocarbons in the UST area is limited in vertical extent to depths of approximately 25 to 30 feet bsg. • The estimated depth to ground water at the property is 70 feet bsg. • The detected xylene is well below Maximum Contaminant Level (MCL) of the California Drinking Water Standards. • Although there is no MCL standard for MTBE, there is an established Action Limit (AL) with respect'to California Drinking Water Standards. MTBE is a widely,used gasoline additive r (octane enhancer)that began to be used in California during the late 1970's and early 1980's. MTBE is very water soluble, and appears to have a very slow biodegradation rate in ground water. The detection of MTBE suggests that a release may have occurred within the last 20 years. I FJ