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MWl and MW2 <br /> no <br /> collected from boil contamination�is ldimited Iola <br /> contamination, <br /> suggesting <br /> small area in the immediate vicinity of the former tanks. <br /> To prevent the contaminated soil remaining in the vicinity <br /> of the former tanks from acting as a continual .source of <br /> groundwater degradation, waterWork recommends re-excavation <br /> of the tank <br /> pit. It is estimated that 200 cubic yards of <br /> e ii-,nited by <br /> soil will be excavated. The excavation will <br /> tbo groundwater <br /> the building foundation and the Excavated shallow will be <br /> (approximately 12-13 feet) . om previously <br /> aerated on site, along with cuttings permit from the San <br /> installed boring/monitoring wells, <br /> Joaquin county Air pollution Control. District. Remediated <br /> soils will be backfilled into the excavation. Composite <br /> soil samples will be collected and analyzed to confirm that <br /> successful remediation of sails has occurred. Any open <br /> excavations will be contained in a perimeter security fence, <br /> to be installed for the duration <br /> icor ©therersepresentative of <br /> il remediation <br /> process. Waterwark personnel, <br /> ethe mergent esty owner will op site within bone hourble to of notification- <br /> To <br /> otifica pion.. to any <br /> To avoid exposing an open excavation during <br /> u in,�henhe rainy <br /> season, soils will be excavated in the spring aeration <br /> of contaminated soils can be completed efficiently. <br /> in interim, the former tank pit location has been covered with <br /> 6-mil plastic to prevent leaching of contaminants. <br /> 4.2 Groundwater Contamination <br /> for water samples collected frox <br /> Analytical results <br /> monitoring well MW3 recorded elevated <br /> 3 concelltrations of <br /> dissolved petroleum hydrocarbons <br /> No dissolved contaminants were detected in upgradient well <br /> Mw1, and down gradient well MW2 contained less than 5 ppb <br /> benzene, indicating the groundwater contaminant pi.ume has <br /> not migrated substantially, This interpretation is <br /> radient <br /> substantiated by the relatively flat groundwater 9 <br /> ( approximately 4ft/mile) . This southwest gradient <br /> presumably will prevent migrationof <br /> the <br /> well which is <br /> contamination toward the municipal supply <br /> located approximately 90 feet north of <br /> thcontair.ination <br /> estimation of the areal extent of groundwater <br /> is shown on Figure 5. <br /> Groundwater sampling has shown that the dissolved hydrocar- <br /> ll area adjacent to the former <br /> bon plume is limited to a sma <br /> tanks. Concentrations recorded in downcfradient well MW2 <br /> were near the State Action Level (SAL) for the only detected <br /> gasoline constituent (benzene), <br /> indicating that the dis- <br /> solved contaminants drop off rapidly along the flow direc- <br /> tion. This undoubtedly reflects the processes of dispersion <br /> 5 <br />