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' Site Background Information CHAPIN BROTHERS INVESTMENTS, INC. 1766 Monte Diablo Avenue, Stockton, California ' The site is located at the southeast intersection of Monte Diablo Avenue and Buena Vista Avenue It is our understanding that the site was operated as a gasoline service station from the late 1930's to December 30, 1990 Originally, three underground storage tanks (USTs) were present on the property However, additional tanks were added to the site between 1941 and 1975 From 1991 to the present the site has operated as a automotive repair facility The site is currently occupied by a t single L-shaped building,which houses the auto repair business The building is surrounded on the north and west by an asphalt-paved parking area ' INITIAL SITE INVESTIGATION ' In December 1990, one groundwater monitoring well(MW-1)was installed at the site,north of the former UST located on the eastern portion of the site The well was installed in response to previous work at the site which indicated that hydrocarbon impacted soil and/or groundwater may have been ' present Soil samples collected during the installation of MW-1 indicated that petroleum hydrocarbon impacted soil was present at the site, a groundwater sample from the well indicated that total petroleum hydrocarbons (TPH as gasoline) and benzene, toluene, ethylbenzene and total xylene (BTEX) were present in ground water at the site ' UST REMOVALS In August 1993, one 550-gallon waste oil UST, two 4,000-gallon gasoline USTs and two ' 8,000-gallon gasoline USTs were removed from the site The tanks were removed from the north- central portion of the property During removal,three additional 1,000-gallon USTs were discovered near the western portion of the property These tanks were apparently abandoned in place,however, ' It is our understanding that the San Joaquin County-Environmental Health Department(EHD)has no record of the abandonment Soil samples collected at the time of the tank removals indicated the presence of significant petroleum hydrocarbon impacted soil at the site 1 ASSESSMENT OF HYDROCARBON IMPACTED SOIL AND GROUND WATER ' In 1993, four soil borings were drilled at the site Two borings were located on-site and two were located off-site Three of the borings were completed as 2-inch diameter groundwater monitoring ' wells Well MW-2 was installed north of MW-1,across Monte Diablo Avenue,MW-3 was installed west of MW-1,across Buena Vista Avenue,MW-4 was installed south of MW-1,near the northeast corner of the on-site structure The fourth boring was completed as a 4-inch diameter vapor ' Advanced GeoEnvironmentel,Inc 1