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Morita Brothers Service Station 21 November 6, 1992 <br /> ft i <br />' Groundwater was encountered at a depth of 57 feet during drilling at the interface <br /> between a slightly sandy silt and the overlying clay with minor silt However, the <br /> groundwater was measured at a depth of 54 feet during the subsequent sample <br />' collection activities This indicates that the overlying clay acts as a confining layer <br /> which produces a head to the aquifer This also may indicate that the overlying clay <br /> is an effective barrier to the vertical migration of gasoline hydrocarbons If this is <br /> the case then a very strong argument can be made that the gasoline hydrocarbons <br /> detected in the groundwater are not a result of a release from the gasoline tank at <br />' Morita Brothers, but is a result of migration from an off site source which has been <br />' confined within this water zone <br /> If gasoline hydrocarbons had migrated vertically to groundwater from the tank leak <br />' at the Morita Brothers' service station, then residual concentrations would be present <br /> within the fine grained silts and clays regardless of flucuations in the groundwater <br /> elevation No gasoline hydrocarbons have been detected in the fine grained <br /> sequence between a depth of 3€1 feet and groundwater at a depth of 57 feet <br /> Groundwater sampled from all of the monitoring wells on the Morita Brothers' <br />' property contained concentrations of the gasoline constituents in excess of the State <br /> of California Maximum Contaminant Levels The highest concentrations are in the <br /> I <br /> well at the northwest corner of the property closest to the other gasoline service <br />' station An order of magnitude lower concentrations are in the well closest to Morita <br /> Brothers' gasoline tanks This may indicate a source to the northwest of Morita <br />' Brothers from which gasoline hydrocarbons have impacted groundwater resulting <br /> in gasoline hydrocarbons being present within the groundwater at positions <br /> laterally down gradient to the current flow direction <br /> Despite total lead being detected in the three groundwater samples, soluble lead for <br /> which the MCL has been established was not detected This indicates that gasoline <br /> hydrocarbons are not responsible for the concentrations of total lead detected within <br />' the groundwater <br /> EB-g 101_3 9210-E055 RPT <br />