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Ms Marla D Guensler Exxon Company, U S A September 22, 1997 Page 2 Ground Water Saniplin2 Analytical Results Ground water samples collected from monitoring wells MW-I through MW-8 on August 20, 1997, were submitted to Sequoia Analytical for analysis of benzene, toluene, ethylbenzene, and total xylenes (BTEX-), and methyl tertiary butyl ether (MTBE) using EPA Method 8020, and total purgeable petroleum hydrocarbons (TPPR) as gasoline using EPA Method 8015 Modified The ground water sample collected from monitoring well MW-I was additionally analyzed for MTBE using EPA Method 8260 Concentrations of BTEX and TPPH as gasoline were not reported above the laboratory detection limits in the samples collected from monitoring wells MW-1 through MW-8 Detectable concentrations of MTBE were reported in monitoring wells MW-1 through MW4, MW-6, and MW-8 The detectable levels of MTBE ranged from 6 0 micrograms per Iiter (pg/L) in monitoring well MW-4 to 150 µg/L (MW-1)by EPA Method 8020 The presence of MTBE in MW I was confirmed at a concentration of 220 µg/L using EPA Method 8260 A dissolved benzene concentration map using the August 20, 1997, analytical results is presented as Figure 4 Cumulative analytical results are summarized in Table 1, and a copy of the laboratory analytical report for the August 20, 1997, sampling event is presented in Enclosure B . Schedule If concentrations of BTEX and TPH as gasoline continue to remain below the laboratory detection luzut, the proposed Remedial Action Plan dated August 20, 1997, may be modified and an addendum would then be submitted A response from the regulatory agencies has not been received regarding the Remedial Action Plan Remarks/S«natures The interpretations contained in this report represent our professional opinions, and are based in part, on information supplied by the client These opinions are based on currently available information and are arrived at in accordance with currently accepted hydrogeological and engineering practices at this time and location Other than this, no warranty is implied or intended Delta recommends that a copy of this report be forwarded to Mr Mike Infurna Ms Elizabeth Thayer San Joaquin County Environmental Health California Regional Water Quality Control Board, Division, Public Health Services Central Valley Region Post Office Box 2009 3442 Routter Road Stockton, California 95201 Sacramento, California 95827-3098