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• 12 March 2003 AGE-NC Project No 96-0236 Page 4 of 5 4.0. SUMMARY AND CONCLUSIONS The implications of the fourth quarter 2002 site assessment results are as follows • From field observations,no petroleum hydrocarbon odors or discoloration were noted in grab ground water samples collected from probe borings P-36, P-37 and P-38 • MTBE was not detected by laboratory analysis of ground water samples • TPH-g, benzene, ethylbenzene, fuel oxygenated compounds, EDB and 1,2-DCA were not detected in any of the above referenced P-36, P-37 or P-38 grab water samples • TPH-d was detected in grab ground water samples collected from P-36, P-37 and P-38 at concentrations ranging as high as 1,700 (µg/1), however, both CAL and MAI laboratories reported the sample chromatograms to have both non-diesel patterns and a single, unknown isolated peak The laboratories both indicated to AGE that(1)the TPH-d detections did not have typical diesel characteristics, (2) was probably"not" the result of diesel fuel, and (3) that the s Ingle 1 arge p eaks d etected i n e ach s ample c hromatogram were u nknown, b ut possibly the result of some type of plastic or pesticide (Appendix B, Appendix C) The • estimated horizontal distribution of the laboratory TPH-d detections are contoured on Figure 3 • Very low concentrations o£toluene and xylene were detected in water samples collected from P-37 and P-38 The State of Califorrua drinking water standards, adopted by the Safe Drinking Water Act,have established maximum contaminant levels(MCLs)for toluene and - xylenes at 150 µg/1 and 1,750 µg/l, respectively Concentrations of dissolved toluene and xylene detected in the P-37 and P-38 grab ground water samples were below MCLs o Laboratory and field data collected from P-36,P-37 and P-38 suggests that an unknown,non- petroleum related dissolved plume, possibly related to a plastic or pesticide, may have impacted ground water in the area bound by soil bonngs P-36, P-37 and P-38 The plume may have further been influenced by being pulled from the north-northwest due to pump- and-treat ground water extraction activities at the site 5.0 RECOMMENDATIONS Based upon data collected from the site, AGE recommends • Additional G eoprobe soil borings for collection of grab ground water samples may be warranted between P-37 and MW-4,west and south of P-37 and north of P-38 to fully assess the extent of impacted ground water • • Include EPA Method 8270 to the laboratory analysis referenced in Section 2 1 to better characterize impacted ground water detected in the area of P-36, P-37 and P-38 Advanced GeoEnvironmentai,Inc