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i <br /> { <br /> Response to Letter October 18, 1990 <br /> Former Texaco Station, Manteca, California AGS 38053-2 <br /> In conclusion, it is our opinion that additional monitoring wells are not necessary at this site <br /> i <br /> at this timd. Currently, we have monitoring wells at the site in the downgradient and lateral <br /> directions of ground-water flow, and approximately 5 feet from the former tank cavity in the <br /> -water flow. Therefore, after purging each well, we are <br /> upgradient direction of ground <br /> sampling formation water from adjacent to the source of hydrocarbons, and in the lateral <br /> and downgradient directions of groundwater flow. <br /> In addition, we believe that by removing the source of hydrocarbons, we have effectively <br /> ! reduced the possibility that hydrocarbon concentrations in ground water will increase. We <br /> believe that natural degradation of the relatively low levels of hydrocarbons initially present <br /> in the ground water is occurring. During the latest sampling event, TPHg and BTEX were <br /> not detected in the water samples from the wells. Therefore, we do not believe further <br /> Y <br /> drilling is warranted to delineate dissolved gasoline hydrocarbons. Laboratory analyses <br /> detected TPHd at a concentration of 0.28 ppm in monitoring well MW-2 and 0.48 in <br /> monitoring well MW-3. It is our opinion that these levels do not warrant additional <br /> delineation or remediation. <br /> E <br /> 4 <br /> i <br /> Applied stem . ... <br /> s - .......---_ . � � ..... .............. _..................................� <br /> pp Geos� <br />