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L <br />u <br />PUBLIC HEALTH SERVICES <br />SAN JOAQUIN COUNTY <br />ENVIRONMENTAL HEALTH DIVISION ": '' .T <br />Karen Furst, M.D., M.P.H., Health Officer <br />cq. CP <br />304 East Weber Avenue, Third Floor • Stockton, CA 95202 <br />209/468-3420 FILE Copy <br />HUGO MONSANTO <br />THE EARTHGRAINS COMPANY <br />PO BOX 1830 <br />ST LOUIS MO 63118-0830 <br />MAR 2 3 1999 <br />Re: Rainbow Baking Company Site Code: 19093 <br />2651 S. Airport Way <br />Stockton, CA 95206 <br />San Joaquin County Public Health Services Environmental Health Division (PHS/EHD) <br />has reviewed the Quarterly Monitoring Report (QMR) dated July 6, 1998 prepared by <br />Philip Environmental for the above referenced site. Di -isopropyl Ether (DIPE), Benzene, <br />Toluene, Ethylbenzene, and Xylene (BTEX) contaminants were evidenced in the <br />groundwater collected from Monitoring Wells (MWs) 1 and 12 on May 21, 1998. The <br />water samples collected January 29, 1998 evidenced DIPE in MWs1, 7 and 12 and BTEX <br />in MWs1, 9, 10 and 12. <br />MW 12 is northeast of the previous location of the Underground Storage Tanks that were <br />on the property. MW8 is located southeast of MW 12. Groundwater collected from <br />MW8 was non-detectable for contaminants. MW8 has a screened interval shallower (35 <br />to 60 feet below surface grade) than MW12 which is screened from 34 to 74 feet below <br />surface grade (bsg). Historical gradient information in QMRs indicates that the ground <br />water flow direction has varied from east to northeast. According to the 1978 San <br />Joaquin County Flood Control Map the groundwater level at this site was approximately <br />80 feet bsg in that year. Non-detectable sample results from MW8 may not accurately <br />reflect downgradient groundwater conditions nor would potential contaminants below 60 <br />feet bsg be picked up by MW8. The east-northeast lateral extent of the contaminant <br />plume should be defined. Vertical definition of plume migration should be determined in <br />the east-northeast direction of the site. Vertical investigation should continue to a depth <br />of at least 80 feet bsg. <br />PHS/EHD recommends using the cone penetrometer test boring method to obtain <br />relevant lithological and hydrological data prior to the placement of any monitoring wells <br />and to evaluate contaminant migration potential at this site. <br />After the contamination plume has been defined a feasibility study comparing the cost <br />effectiveness of two site appropriate remediation methods should be submitted to <br />PHS/EHD. Air sparging remediation was proposed for this site in October 1994 by <br />Burlington Environmental, Inc. This remediation method should be re-evaluated with <br />A Division of San Joaquin County Health Care Services <br />