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Ms Mary Meays Page 4 September 11, 1997 associated with historical sampling events TPH(g) was only detected in the MW-1A and MW-2A samples, the highest detections were associated with MW-1A TPH(d) was detected at low concentrations in all samples except those associated with MW-5A, the highest detections (less than 1 mg/L) were associated with MW-1A BTEX compounds were only detected in the MW-1A and -2A samples Historical trend analysis indicates that TPH and BTEX concentrations have decreased significantly over time ' As presented in Table 4, the water quality measurements do not exhibit notable trends at this time, as evidenced by comparison of post-ORC to baseline (10/96) ' conditions The dramatic increase in heterotrophic plate count in the samples collected from MW-1A and MW-2A indicates that the presence of the ORC socks appears to be enhancing microbial activity 1 ' CONCLUSIONS As in past sampling events, TPH (gasoline and diesel) and BTEX compounds were detected in ground water samples collected at the Catellus properties located at 1325 and 1515 West Weber Avenue The magnitudes of the detections are comparable to those of historical detections At both sites, the highest detections are associated with the wells located in the immediate vicinity of the former tanks Detections decrease dramatically in nearby wells, indicating that the extent of affected ground water is limited The consistency with historical results indicates that the plumes do not appear to be migrating The introduction of ORC appears to have enhanced the level of microbial activity at each site, as evidenced by the dramatic increase in heterotrophic plate count results Please feel free to contact me at (510) 946-0455 if you have any comments or questions Sincerely, ' ERM-WEST, INC �F-R�DG 0, `' A QU/��C c'& -46� No,=4 Jill A Quillen, G Project ManagerOF ' CJH/jaq/2996 00 Enclosure cc Mr James Adams, Catellus Development Corp Ms Elizabeth Thayer, CVRWQCB