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California (Figure 2 The station has four Mariposa Road and Farmington Road in Stockton, {F g ) underground storage tanks (UST's), of which three are 12,000 gallon gasoline tanks and one is a 3,000 gallon diesel fuel tank (Figure 3) All four tanks appear to be located in the same tank pit excavation near the Manposa Road side of the property 2.2 Site History Three phases of site assessment have been performed at this facility The first, as part of a pre- purchase due diligence by Pacific Environmental Group, consisted of the drilling and sampling of four soil borings, one of which was completed as a groundwater monitoring well ' Groundwater was present at about 45 feet bgs Soil sample analyses from these borings indicated that there were TPH and BTEX constituents present in shallow soils and soils lust above the water table One groundwater sample contained BTEX compounds above state action ' levels The presence of petroleum hydrocarbon compounds in the soil and groundwater beneath the site ' prompted a second site assessment conducted by Applied GeoSystems This second phase of work consisted of the drilling and installation of two additional groundwater monitoring wells Groundwater sample analyses from these wells confirmed that TPH compounds were present in ' the groundwater beneath the site The direction of groundwater movement was calculated to be in a north-westerly direction As a result of these findings PHS/EHD requested that a quarterly groundwater monitoring program be initiated for this location, plus a request that all domestic groundwater wells be identified and sampled Six domestic wells were located and sampled Test results presented in a May 13, 1987 letter report prepared by Applied GeoSystems were non detect for TPH and BTEX The next quarterly sampling could not be performed because the groundwater table had declined below the bottom of the monitoring wells In the third work phase, Park replaced the three groundwater monitoring wells at the site in September, 1992 One shallow vapor extraction well was also installed during the additional site ' characterization Also performed were quarterly groundwater sampling and a vapor extraction treatability study Results from this latest work confirmed the presence of petroleum hydrocarbons in the soil and groundwater In late September, groundwater was calculated to be flowing south southeast, while in October, January and February, 1993 was flowing northeasterly Groundwater was approximately 75 feet bgs ' 2.3 Area Background ' Prior consultants have indicated that all four corners at the intersection have had operating retail gasoline service stations on them at one time or another No site assessments have been performed at any of these other corners ' An abandoned Chevron service station is present on the northeast corner This ,property is IPA 1125J2 WP 3