SITE INFORMATION AND CORRESPONDENCE FILE 1

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i I PUBLIC IntEALTH SERViNZES SAN JOAQUIN COUNTY ? a ENVIRONMENTAL HEALTH DIVISION [ ` Karen Furst, M.D., M.P.H., Health Officer 304 East Weber Avenue, Third Floor • Stockton, CA 95202 9 ' F ° tea 209/468-3420 ROGER LISTON NOV 2 51997 DARPETROINC 3450 EL CAMINO AVE CERES CA 95307 RE: Darpetro Exxon SITE CODE: 1060 749 E Charter Way Stockton CA 95206 - San Joaquin County Public Health Services, Environmental Health Division (PHS/EHD) has reviewed the November 10, 1997 Quarterly Report prepared by California Geophysical Group for the above referenced site. Monitoring wells 1 , 2 and 3 have not been tested for the presence of oxygenates. The PHS/EHD letter dated September 25 , 1997, states that all monitoring wells should be monitored for oxygenates by method 8260. The water samples from these wells, beginning with the January monitoring event, should be analyzed for oxygenates, gasoline, benzene, toluene, ethyl benzene and xylenes. A copy of the September 25, 1997, PHS/EHD letter has been enclosed for your review. Oxygenates were detected in monitoring wells 5,6, 7, 8 and 9. The MTBE detection in monitoring well 5 was not tabulated in Table 3 "Summary of Groundwater Analyses" or in Table 3B "Summary of Groundwater Analyses (oxygenates)" . Please tabulate this data appropriately. ORC compound has been placed in several wells in lieu of air sparging to aid in the vapor extraction process. Oxygen readings from 8 of the 11 wells have been included in the report, Table 3A does not indicate which wells contain the ORC compound and which wells are being monitored for oxygen dispersal from the ORC wells. PHS/EHD recommends that the table be revised to include this data. 'r In order to reduce the probability of cross contamination of wells and samples and to aid in the 'r decontamination process, wells are sampled in the customary sequence of lowest concentration to highest concentration, Based on data obtained in July of 1997 , the sample order for October should have been 11 416, 10, 9,7, 8, 5. In October the sample order was 11 1416110171 %815, The presence of 1 ppb benzene, 2 ppb toluene, .4 ppb ethyl benzene and . 5 ppb xylenes in the tubing blank taken on October 21 , 1997 indicates that decontamination procedures were inadequate. The pump blank taken on July 21 , 1997 tested positive for 52 ppb benzene, 266 ppb toluene, 79 ppb ethyl benzene, 367 ppb xylenes and 1730 ppb gasoline. The tubing blank taken on April 24, 1997 tested positive for 161 ppb benzene, 418 ppb toluene, 78 ppb ethyl benzene, 306 ppb xylenes and 2180 ppb gasoline, Equipment blanks were not taken prior to April 1997. With this quantity of contamination remaining on equipment after decontamination, cross contamination of samples may be occurring and the accuracy of the analytical results may be compromised . Although the equipment blank for October indicates lower concentrations of contaminants, PHS/EHD recommends that you run equipment blanks for every sample taken until the reliance of your decontamination procedure can be re-established. A Division of San Joaquin County Health Care Services