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1 <br /> Fuller Mobile Home Park <br />' 365 E. Louise Ave., Lathrop, California May 28, 1998 <br /> Phase HSite Characterization - Continued Page: 6 <br /> I <br />' 6.0 Groundwater Conditions <br />' The water table was approximately 10 feet below ground level as the borings were being <br /> drilled During the quarterly event on Aprd 8, 1998, subsequent water levels before <br /> sampling recorded water levels in the vicinity of 8 5 feet below ground level (Table 3) <br /> A groundwater gradient 0 0160 ft/ft was calculated (Figure 4) The direction is S63°W <br /> across the site <br /> 7.0 Conclusions and Recommendations <br /> The sod contamination "Plume" has been defined at this site A groundwater <br /> p <br /> contamination plume exists at varing depths from approximately 10' bgl to approximately <br /> 32 5' bgl at the eastern boundary of the former underground tanks The lateral and <br /> vertical extent is completely defined Only one (1) monitoring well showed some traces of <br />' contamination The groundwater gradient direction is (at the time of sampling - April 8, <br /> 1998) to the SW With the shallow water table and the exceptionally flat groundwater <br /> gradient, contaminants have been moving laterally with the variable gradients caused by <br /> pumping of wells, irrigation of nearby fields and precipitation The Dellu sand that covers <br /> the area is a very permeable sand that overlies a sandy silt (in some areas) that is in contact <br /> with the water table This is evidenced by contamination over 50 feet down gradient and <br /> over 60 feet laterally from the past gradients, and both soil and water samples have higher <br /> contamination levels to the south and west of the former tank site <br /> I The following facts support the vertical and lateral definition of both soil and <br /> groundwater <br /> I The most recent groundwater data collected indicates only Diesel contamination present at <br /> monitoring well 97 This 60 ug/L of Diesel is within the State of Califorruas allowable <br /> level of 100 ugfL All other wells tested non-detected for all analytes The water sample <br /> collected from boring B-12 at 12 5' bgl indicates 3000 ug/L of Gasoline, 4 4 ug/L of <br /> Ethyl-Benzene and 33 ug/L of total Xylenes These levels of Ethyl-Benzene and total <br /> Xylenes are well below the established allowable levels (Xylenes - 1,750 ug/L, E-Benzene <br /> 700 ug/L) The Gasoline level does exceed the allowable level of 5 ug/L <br /> The defined mass of the secondary source of petroleum hydrocarbon is calculated to be <br /> approximately 1,150cubic yards in quantity underlying the former UST location The <br /> calculated volume in gallons of petroleum hydrocarbon contamination remaining is <br /> Iapproximately 37 6 gallons <br />