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FROM 1997.0S-1S 12:27 0177 P.02/03 <br /> MAY. -I3' 97(7HU) 12:12 UNi CERT NORTH REr <br /> TEL.510 2309 P. 002 <br /> PUBLIC hEALTH SERVfCES <br /> ,•P4ti. <br /> SAN JOAQUINCOUNTYRECEIVED p•� <br /> ENVIRONMENTAL HEALTHs <br /> DlV><SYQN � <br /> 1Emest M. Fujimoto, M. D. M.P.11 A <br /> LIAR 7 197 ] � cling Health Officer <br /> 394 Fast Weber Avenue,Third Floor Stockmn, CA 95202 <br /> 209/46s-342c <br /> UNOCAL.CORPORATION I'll E# 2 SS <br /> BOB BOOST RPT—QM I•RRNSM1TTAt�� 997 <br /> P O BOX 5155 1 2 3-Z4 �5 6--„ - <br /> SAN RAMON CA 94563 <br /> RE; FORMER UNOCAL#2859 SITE CODE: 1213 <br /> 1665 PACIFIC AVE <br /> STOCKTON CA j <br /> San Joaquin County Public Health Services, Environmental Health Division <br /> (PHS/EHD) has reviewed your February 7, 1997 request far 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 /> 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 1998. 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 1100 <br /> cubic yards of impacted soil 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 Sen Joaquin ly V aldi Gam 5mvicm � <br /> I <br />