|
iInterim Remedial Action Test Report,Former Unocal#0I87,Stockton,CA
<br /> August 28,2001
<br /> PREVIOUS ENVIRONMENTAL WORK
<br /> Two 1,000-gallon gasoline and one 550-gallon waste oil USTs were removed from the southeast corner of
<br /> the subject site in 1967 Data related to soil conditions beneath the USTs at the time of removal is not
<br /> available These USTs appear to have been replaced with two 10,000-gallon gasoline and one 280-gallon
<br /> waste oil USTs situated in a common excavation in front of the station building
<br /> The two 10,000-gallon gasoline and one 280-gallon waste oil USTs, associated product piping, hydraulic
<br /> lifts, and oil/water separator were removed and the station facilities demolished in January, 1992
<br /> Petroleum hydrocarbons were not detected in soil samples collected beneath the USTs, hydraulic lifts, or
<br /> oil/water separator Total Petroleum Hydrocarbons as gasoline (TPHg) and benzene were detected in one
<br /> soil sample collected from the product piping trench between dispenser islands D-1 and D-3 at
<br /> concentrations of 150 and 0 81 parts per million(ppm), respectively This trench area was overexcavated,
<br /> and a confirming soil sample collected from the base of the excavation Petroleum hydrocarbons were
<br /> not detected in this soil sample A second 130-gallon waste oil UST was removed from the eastern
<br /> portion of the property in May 1992 Petroleum hydrocarbons were not detected in the soil beneath this
<br /> UST Results of the UST removal investigation were presented in GeoStrategies (GSI) report
<br /> No 782701-1, Tank Removal Observation Report, dated September 11, 1992 Based on the data
<br /> collected during this investigation, there does not appear to be hydrocarbon-impacted soils in the vicinity
<br /> of the former UST pit south of the station building,waste oil tank, hydraulic lifts, or dispenser islands
<br /> In October 1993, GSI drilled eight on-site exploratory soil borings (U-A through U-H) in the locations of
<br /> the former USTs, the former product dispenser islands, and the former hydraulic lifts in anticipation of
<br /> site closure During this investigation, TPHg were detected in soil samples collected at 16 5 and 31 5 feet
<br /> below ground surface (bgs) from boring U-C, drilled within the former gasoline UST pit in the
<br /> southeastern corner of the site, and from boring U-D, drilled adjacent to former dispenser island D-4
<br /> TPHg concentrations ranged from 1,600 to 2,900 ppm Benzene was not detected in these soil samples
<br /> TPHg or benzene were not detected in soil samples collected from the other borings Results of this
<br /> subsurface investigation are presented in GSI report No 782702-3, Exploratory Soil Boring Report,
<br /> dated December 15, 1992
<br /> In July 1994, GSI drilled five additional on-site soil borings (U-I through U-M)and installed three on-site
<br /> groundwater monitoring wells (U-1 through U-3) This work was performed to assess the extent of
<br /> impacted soil in the southeast corner of the site and evaluate whether groundwater beneath the site had
<br /> been impacted by petroleum hydrocarbons TPHg were detected in soil samples analyzed from borings
<br /> U-J (1 7 ppm at 26 5 feet bgs), U-K (130 ppm at 41 5 feet bgs), U-3 (330 ppm at 46 5 feet bgs), U-L
<br /> (19,000 ppm at 45 5 feet bgs), and U-M (5 10 ppm at 45 5 feet bgs) Results of this subsurface
<br /> investigation are presented in GSI report No 4827 703-5, Well Installation and Exploratory Soil Boring
<br /> Report, dated September 21, 1994
<br /> GSl performed a limited environmental site assessment (ESA) of the properties in the vicinity of the
<br /> subject site The ESA identified a former station located at 448 East Miner Avenue, south of the subject
<br /> site Historical groundwater data indicate that this former station is upgradient of the subject site
<br /> Environmental information related to the soil and groundwater conditions beneath this former service
<br /> station were not obtained during the ESA Environmental data related to surrounding properties in the
<br /> • vicinity of the subject site are discussed in GSI report No 4827 04-1,Limited Phase I Environmental Site
<br /> Assessment, dated May 11, 1995
<br /> 24004209-1 2
<br />
|