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PUBLIC nEALTH SERVICES <br /> P�•V�N <br /> SAN JOAQUIN COUNTY <br /> 2�. <br /> ENVIRONMENTAL HEALTH DIVISION X <br /> Ernest M. Fujimoto, M. D., M.P.H., Acting Health Officer •` <br /> 304 E. Weber Ave., Third Floor • P. O. Box 388 • Stockton, CA D <br /> 209/468-3420 ltv <br /> DALE STEELE MW JUL U31596 <br /> CALTRANS <br /> PO BOX 2048 <br /> STOCKTON CA 95201 <br /> Re: Stockton Yard Site Code: 10193 <br /> 1604 South "B" Street <br /> Stockton CA 95205 <br /> San Joaquin County Public Health Services, Environmental Health Division (PHS/EHD) has <br /> completed review of GEOCON's "Site Investigation Report" dated April 1996, "Groundwater <br /> Monitoring Report Second Quarter 1996" dated June 18,1996 and "Site Assessment Workplan" <br /> dated June 21, 1996. PHS/EHD has prepared the following comments for your consideration. <br /> The January 1996 investigation included the drilling and sampling of four additional monitoring <br /> wells (MW9 - MW12) one vapor extraction well (VW2) and one soil boring (S63). The monitoring <br /> wells were screened from 60 to 80 feet below grade and the vapor extraction well was screened <br /> from 15 to 70 feet below grade. <br /> The volume of soil contamination was estimated at 1,500 cubic yards and a cross-section of <br /> lithological information was prepared. The mass of contaminants has not yet been determined. <br /> Groundwater results from samples collected on February 6, 1996 and April 22, 1996 continued to <br /> evidence significant groundwater contamination up to 54,000 ppb TPH-gas, 8,100 ppb benzene and <br /> 60 ppb methyl tertiary butyl ether (MTBE). <br /> The investigation report included the recommendation to install two additional monitoring wells to <br /> further define the extent of groundwater contamination evidenced in MW11. The work plan <br /> referenced above actually proposed the installation of three monitoring wells to be located <br /> approximately 100 - 120 feet north, east and south of MW11. <br /> The most recent analytical results of samples collected from MW1 1 (0.7 ppb benzene and 1.0 ppb <br /> MTBE) suggested that the eastern boundary of the plume was adequately defined. Monitoring well <br /> MW10, which defined the contamination to the south, unfortunately was not sampled in April <br /> 1996, because the well was buried under construction materials. Please verify that wells are <br /> accessible when scheduling sampling events. Additional monitoring of the contaminant plume is <br /> warranted, prior to the installation of additional monitoring wells to define the extent of <br /> contamination observed in MW11. <br /> Also, since monitoring wells associated with the investigation of 1603 B Street (MW11 and MW12) <br /> are being used to define the contamination to the west of 1604 B Street, it will be necessary to <br /> perform concurrent monitoring and to develop an integrated site map including all of the referenced <br /> wells. The most recent analytical results from these wells were obtained from samples collected in <br /> May 1994 and reported in the Ninyo & Moore report dated September 23, 1994. The results <br /> documented concentrations of benzene which exceed regulatory limits. As PHS/EHD requested in <br /> correspondence dated August 29, 1995, groundwater samples should be collected from 1603 B <br /> Street monitoring wells and the results submitted to PHS/EHD. <br /> A Division of San Joaquin County Health Care Services <br />