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Manteca Unified School District <br /> Soil&Groundwater Investigation eport <br /> Page 7 <br /> ' Groundwater was measured at depths of approximately 17 5 to 18 feet below grade <br /> iduring the monitoring of the wells Groundwater flow was calculated at north 25 degrees <br /> west with a gradient of 008 ft 1 ft Groundwater occurrence vanes from unconfined in the <br /> southern wells to semi- confined in the northern well where the sandy aquifer is capped <br /> by a moist silty clay <br /> 3.2 Soils Contamination <br /> Subjective evidence of hydrocarbon contamination such as petroleum staining or odors <br /> was not detected in soil samples collected from the exploratory borings Laboratory <br /> analysis of soil samples collected from the capillary fringe, water-bearing interval, and <br /> base of the bonngs did not report detectable concentrations of hydrocarbon <br /> contamination <br /> 33 Groundwater Contamination <br /> ' Trace concentrations of individual petroleum hydrocarbons were detected in all three <br /> wells with the highest concentrations detected in well MW3, located adjacent the former <br /> underground storage tank All hydrocarbon detections were well below established water <br /> quality goals for municipal and domestic use The onsite domestic well, located 150 feet <br /> to the south of the former underground storage tank did not have detectable <br /> concentrations of hydrocarbon contaminants Well construction details were not available <br /> for the onsite domestic well or irngation well <br /> 40 CONCLUSIONS <br /> Three groundwater-monitonng wells were installed in the area surrounding the former <br /> diesel tank at the Ag Shop building near the Manteca Unified School Distnct offices A <br /> water sample was also collected and analyzed from the onsite domestic well All soil and <br /> water samples collected during this phase of work were below detection limits for diesel <br /> ' (non-detect) The groundwater collected from the monitonng wells did contain traces of <br /> BTEX near detection limits and well below the state Water Quality Goals MCL levels <br /> The onsite domestic well did not contain detectable amounts of any hydrocarbon <br /> contaminants <br /> The Ag Shop is used for vehicle maintenance and evidence of fuel storage and use are <br /> present at the site Trace concentrations of fuels are probably present in the surface soils <br /> from spillage through out the site It is possible, despite all efforts to select dnlling <br /> locations that appeared free from spillage, that residual hydrocarbons were carried into <br /> the deeper soils during the drilling of the wells <br /> ' Diesel contamination was detected in three of four soil samples collected for laboratory <br /> analysis from an exploratory boring at the location of the former underground storage <br /> tank in 1998 Diesel contamination was not detected in the soil sample collected at a <br />. 1 <br /> 1 <br />