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FILE UPY <br /> PUBLIC HEALTH SERVICES .o <br /> SAN JOAQUIN COUNTY a <br /> ENVIRONMENTAL HEALTH DIVISION <br /> Karen Furst M.D. M.P.H. Health Officer <br /> 304 East Weber Avenue, Third Floor • Stockton, CA 95202 <br /> 209/468-3420 <br /> ROBERT COCHRAN APR 17 2001 <br /> CHEVRON PRODUCTS COMPANY <br /> P O BOX 6004 BLDG L <br /> SAN RAMON CA 94583 <br /> RE: Chevron Station 9-4275 SITE CODE:' 1952 <br /> 2905 Ben Holt Drive <br /> Stockton CA 95207 <br /> San Joaquin County Public Health Services, Environmental Health Division (PHS/EHD) <br /> has reviewed the "Work Plan for Site Assessment" dated February 23, 2001, and the <br /> report "Analytical Results for Municipal Well No. 10" dated March 26, 2001, that were <br /> prepared by SECOR International Incorporated (SECOR) on behalf of the above <br /> referenced site and has the following comments. <br /> The Work Plan was written in response to a detection of methyl tertiary butyl ether <br /> (MtBE) in the City of Stockton Municipal Well No. 10 during the fourth quarter 2000 <br /> routine monitoring event. MtBE was reported in the water sample from the municipal <br /> well at a concentration of 11.0 micrograms per liter(µg/1). However, the field blank from <br /> this monitoring event also reported a detection of MtBE, at 30 µg/l. A confirmation <br /> sampling of the municipal well took place on March 2, 2001. Duplicate samples were <br /> sent to two different State certified analytical laboratories for analysis by EPA Method <br /> 8260B. Analytical results from one of the laboratories reported a detection of MtBE at <br /> 0.57 µg/I. Analytical results from the second laboratory reported that MtBE was not <br /> detected at a reporting limit of 2.5 µg/I. <br /> The Work Plan proposes to investigate the potential impact of MtBE on Municipal Well <br /> No. 10 with the advancement of ten cone penetrometer (CPT) borings and the <br /> installation of one groundwater monitoring sentry well to a depth of approximately 90 feet <br /> below surface grade (bsg). The CPT borings and the well will not penetrate the aquitard <br /> that is expected to extend from 75 to 90 feet bsg. Based on information obtained during <br /> each CPT, three to four depth discrete water samples will be collected from each boring. <br /> The samples will be analyzed for total petroleum hydrocarbons as gasoline (TPHg), <br /> benzene, toluene, ethylbenzene and xylenes (BTEX) and fuel oxygenates including <br /> MtBE by EPA Method 8260B. The information obtained from this phase of work will also <br /> be used to determine the potential mass discharge of MtBE from the facility, and in the <br /> development of a site conceptual model. <br /> A Division of San Joaquin County Health Care Services <br />