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F -• <br /> F- <br /> E <br /> 4 <br /> RKLEINFELDER <br /> 1 EXECUTIVE SUMMARY <br /> i <br /> E In July 1987,East Bay Municipal Utility District(EBMUD)removed a 1,000-gallon regular <br /> i gasoline underground storage tank from its Stockton yard. The storage tank was contained <br /> in a cement vault. On July 29, 1987, Polymatrix Associates sampled soil beneath the <br /> cement vault floor near both ends of the former storage tank. Analytical results from the <br /> soil sample from the east end of the tank indicated the presence ofasa ' <br /> above the method detection limits. g hoe constituents <br /> In May of 1988, ainfelder prepared a soil and ground water assessment workplan to � <br /> assess the presence of gasoline constituents in the soil and ground water at the EBMUD <br /> Stockton facility, The workplan was prepared in direct response to a request from Cottle <br /> r° i <br /> Engineering of Antioch, California. On September 30, 1988 EBMUD received approval I <br /> from the San Joa uni <br /> q Local health District (SJI.HD) to implement the scope-of-work <br /> Gutlined in the 10einfelder workplan. In April 1989,Kleinfelder received authorization <br /> Proceed with the scope-of--work approved b the to <br /> Y 5J1�D. fn May of 1989, Kleinfelder i <br /> x drilled four exploratory soil boringsand <br /> drilled and installed three ground wale <br /> s monitoring well;. Soil samples were collected in each of the soil borings and selected <br /> samples were analyzed for *ntal hydrocarbons and benzene, toluene and xylenes <br /> EDB and or TX), <br /> organic lead. Gasohn0 constituents were detected in soils collected from borings <br /> ; near the former tank location. The second sampling was completed on October 4, 1989. <br /> Ground water monitoring wells were developed and initially x <br /> P Nally sampled approximately two <br /> weeks after completion. Ground water samples were sent ' <br /> r � to t <br /> a State certified laboratory for <br /> k t analyses. Ground water samples from the two u i <br /> p-gradient wells (MW-2 and MW-3) were <br /> none detected for total hydrocarbons and BTX However, analyses of the ground water � <br /> samples from the down-gradient monitoring.well (MW-1) detected total hydrocarbons <br /> ,300ug/l,benzene at 250 u Y at <br /> g/�ethyl benzene 30 ug/l and�rylenes at 280 ug/I from the first <br /> 3 5 L SMPHng(June 1989),and benzene at 882 u <br /> g/1,xylenes at 151 ug/i and total hydrocarbons l <br /> at 574 ug/1 from the second sampling{October 198 <br /> - -p - <br /> The general direction of ground water flow appears-to be to the southwest. Based on the ; <br /> groundwater flow direction and analytical results from ground water sample, Kleinfelder z <br /> ckrenv s that an.on-site source far.th hydrocarbons detected ir_ the ground water is <br /> , ' <br /> } ' ed. <br /> sf <br /> z, t EBMUD-001-89-001 1 <br />