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y <br /> � 1 <br /> PUBIC HEALTH RVICES <br /> SAN JOAQUIN COUNTY ' <br /> ENVIRONMENTAL HEALTH DIVISION <br /> Karen Furst, M.D., M.P.H., Health Officer ; <br /> 304 East Weber Avenue,Third Floor• Stockton, CA 95202 �'FORr <br /> 209/468-3420 <br /> BRETT HUNTER DEC 2 91997 <br /> CHEVRON USA INC <br /> P O BOX 6004 <br /> SAN RAMON CA 94583-0904 <br /> RE: Chevron Service Station #9-1918 SITE CODE: 1952 <br /> 2905 West Benjamin Holt Drive in Stockton CA <br /> San Joaquin County Public Health Services, Environmental Health Division (PHS/EHD) has <br /> completed review of the Geraghty&Miller `'Addendum to Corrective Action Plan" dated <br /> October 9, 1997 and the Blaine Tech Services "Third Quarter 1997 Monitoring Report" dated <br /> October 28, 1997. PHS/EHD has the following comments for your consideration and <br /> response. <br /> The Addendum included a summary of the lateral and vertical extent of the soil and <br /> groundwater contamination,an estimate of the mass of hydrocarbons,a discussion of the <br /> feasibility and cost effectiveness of the installed SVE/air sparging remediation systems,and <br /> proposed cleanup levels. <br /> PHS/EHD has been working with Chevron on this corrective action plan for some time and <br /> believes that the information in the addendum together with the "Corrective Action Plan" <br /> dated May 29, 1997 has provided sufficient evidence of compliance with the Underground <br /> Storage Tank Regulations. However,please be informed that Chevron will be required to <br /> continue assessment of the evidenced plume and will be required to submit a subsequent <br /> addendum to the corrective action plan. <br /> PHS/EHD appreciates Geraghty and Miller's inclusion of the assumptions used to estimate the <br /> mass of contamination. PHS/EHD disagrees with the assumption that the zone of <br /> contamination was 10 feet and therefore,the calculated masses. For example,the air sparge <br /> wells which are screened in the aquifer between 25 and 30 feet below ground surface (bgs) <br /> evidenced benzene concentrations of up to 1,600 ppb and groundwater has been as shallow as <br /> 8 feet bgs. Mass calculations shall be provided quarterly with the remediation progress and <br /> monitoring report. Additionally, PHS/EHD will require the re-sampling of all the air sparge <br /> wells since they were last sampled April 1, 1997. Please contact PHS/EHD to discuss the <br /> sampling procedure for these operating remediation wells. Finally, Chevron has an operating <br /> methanol tank at this site,and PHS/EHD has not yet been provided with the results of analysis <br /> for the oxygenates which includes methanol. The samples collected from fourth quarter 1997 <br /> shall all undergo analysis for the oxygenates. Enclosed you will find PHS/EHD correspondence <br /> dated September 25, 1997 and Central Valley Regional Water Quality Control Board <br /> correspondence dated August 30, 1997, for your further information. <br /> The addendum included the Groundwater Technology cross-section that was prepared in <br /> March 1994. New geologic information has been collected,including the 10 recently drilled <br /> borings, which should be included in a cross section. The results of the soil boring drilled and <br /> sampled to characterize the vertical migration of the contamination,suggest that the <br /> contaminants may not have migrated downward to greater depths than 31.5 feet bgs. <br /> A Division of San Joaquin County Health Care Services <br />