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PUBLIO�HEALTH SERVICES c� <br /> SAN JOAQUIN COUNTY <br /> ENVIRONMENTAL HEALTH DIVISION 0` `X <br /> Ernest M. Fujimoto, M.D., M.P.H., Acting Health Officer4. „��P <br /> 445 N. San Joaquin Street • P.O. Box 388 • Stockton, CA 95201-0388 <br /> (209) 468-3420 <br /> C P <br /> STEPHEN POA <br /> MOBIL OIL CORPORATION <br /> 3800 W ALAMEDA AVE STE 2000 <br /> 1994 <br /> BURBANK CA 91505-4331 � � 9 <br /> RE: Former Mobil Bulk Plant SITE CODE: 1968 <br /> 500 East Grant Line Road <br /> Tracy CA 95376 <br /> San Joaquin County Public Health Services, Environmental Health Division (PHS/EHD) has <br /> completed review of the "Supplementary Site Assessment Report" dated August 10, 1994 and <br /> prepared by Alton Geoscience. PHS/EHD has the following comments for your <br /> consideration. <br /> The report included the results of the additional soil investigation requested by PHS/EHD to <br /> define the vertical and horizontal extent of the residual soil contamination. Soil borings <br /> SB 1 - SB 11 were drilled and sampled on May 9 and 10, 1994 and evidenced significant soil <br /> contamination to 19 feet below ground surface (vertically) and off site (horizontally). <br /> Concentrations of up to 8,400 ppb benzene were detected below the current groundwater <br /> level. Significant soil contamination was detected in the soil borings to the north and west of <br /> site suggesting that the horizontal extent of the soil contamination has not been defined. <br /> The report also included the result of the May 2, 1994 groundwater sampling event. Only <br /> monitoring well, AW3, continued to evidence groundwater contamination of 210 ppb TPH- <br /> diesel. <br /> Finally, the report included the recommendation that no further remedial action was warranted <br /> and that quarterly groundwater monitoring be continued. PHS/EHD concurs that additional <br /> groundwater monitoring is necessary and quarterly groundwater sampling should be scheduled <br /> immediately. However, PHS/EHD does not concur with the recommendation that no further <br /> remedial action is necessary. Significant soil contamination has been evidenced beneath that <br /> groundwater that poses a threat to the future groundwater quality beneath the site. Additional <br /> remedial alternatives must be considered besides excavation and feasibility analysis must be <br /> submitted to both the CVRWQCB and PHS/EHD for evaluation along with the calculation of <br /> the residual mass of soil contamination. <br /> A Di%ision of San Joaquin County Health Care Services <br />