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' FROM 1997.0S-1S 12 27 #177 P 02/03 <br /> MAY -15' 97(THU) 12 13 UNOCAL CERT NORTH RE TEL-510 277 2309 P 002 <br /> f PUBLIC hEALTH SERVICES <br />' R �:��V�D SANIOAQUM COUNTY x s <br /> ENVIRONMENTAL HEALTH DIl VISION <br />' LIAR - 7 1997Frnest NL Fujimoto,M. D., M-EIL, Acting Healkh Officer <br /> 3M4 fast Weber Avenue,Third Floor @ Stocktart,CA 95202 <br /> 2091468-3420 <br /> zg <br /> UNOCAL.CORPORATION FILE# ?,9=5j SS ,-- BN 997 <br /> BOB ROUST RPT ,�QA4 TRANSMITT — <br />' PO BOX 5155 <br /> SAN RAMON CA 94583 1— 2— 3-Z 4 5— 6--- <br /> RE. FORMER UNOCAL M59 SITE CODE 1213 <br /> 1665 PACIFIC AVE <br /> STOCKTON CA <br /> San Joaquin County Publio Health Services. Environmental Health Division <br />' (PHS1EHD) has reviewed your February 7, 1997 request for closure letter, <br /> Your letter states that eight years of monitoring data strongly suggests the <br /> groundwater plume is naturally attenuating The monitoring wells with 8 years of <br /> data are wells 1, 2 and 3, wells 4 and 5 have 7 years of data, wells 6 and 7 have <br /> 4 years of data and wells 8 and 9 have 2 years of data <br />' Well 1 has rarely exhibited evidence of contamination Well 2 is the most highly <br /> 9 Y <br /> contaminated well exhibiting 4200 ppb as'the current benzene level. Well 3 <br />' exhibited a flat trend from 1988 to 1990, was dry from 1990 to 1993 and after <br /> 1993 exhibited decreasing levels of benzene Well 6 has shown a definite <br /> decrease from 19 ppb benzene in 1992 to ND in 1996. Wells 7, 8 and 9 have <br />' never shown any benzene Well 5 has shown very low benzene levels <br /> sporadically. Well 4 has shown levels between .5 and 2 ppb at least annually <br /> from 1989 to 1996 <br />' The data indicate a stable and declining plume with MW-2 at the core The overall <br /> area of the plume is oriented downgradient approximately 130 feet long and 60 <br /> feet wide with an average benzene concentration of 32 ppb <br /> Remedial activities which have occurred to date include overexcavation of 1104 <br /> I cubic yards of impacted sail from an excavation under the tank pit area, and <br /> removal of 2745 lbs of gasoline and 12 lbs of benzene using a pilot vapor <br /> extraction system (VES)_ <br /> A Division of Sari Joaquin Cebuily[%jul Care Services <br /> I <br />