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Monitoring Well Installation Report - Chevron Station #9-5775, Lodi, CA
<br />. April 7, 2000
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<br />For the wells and soil borings located in the vicinity of the former gasoline USTs, only well borings EX -1
<br />and VE -1 had detectable concentrations of TPHg up to 1,740 and 85 ppm, respectively, with the
<br />concentrations diminishing toward the base of both well borings All wells and borings in the vicinity of
<br />the former USTs had detectable concentrations of benzene and MtBE Well boring EX -1, which was
<br />drilled though the former gasoline UST pit, had benzene concentrations from 446 ppm at 16 feet bgs,
<br />diminishing with depth becoming non -detect at the base of the boring The vapor extraction well borings
<br />and soil borings surrounding the former gasoline UST pit had low concentrations of benzene up to 1 7
<br />ppm MtBE concentrations in the groundwater and vapor extraction well borings and soil borings were
<br />up to 100 ppm (at the base of well VE -1), with overall concentrations diminishing with distance from the
<br />former UST pit
<br />Groundwater Analytical Results
<br />TPHg was detected in wells MW -5 (shallow sample), MW -6, and EX -1 at concentrations of 190, 170, and
<br />51,000 ppb, respectively In the deep sample from well MW -5 collected from the screened interval at 73
<br />feet btoc, TPHg was not detected Benzene was detected in wells MW -5 through MW -7 and EX -1 at
<br />concentrations ranging from 0 72 to 39,000 ppb, with the highest concentration in well EX -1 MtBE by
<br />EPA Method 8260 was detected in all wells except well MW -7 with concentrations in the monitoring
<br />wells ranging from 3 1 to 520 ppm and a concentration in extraction well EX -1 of 720,000 ppb TBA and
<br />DIPE were not detected in any of the wells ETBE was detected in wells MW -5, MW -6, and MW -9 at up
<br />to 56 ppm, and TAME was detected in well MW -6 at 6 8 ppb Both ETBE and TAME were detected in
<br />groundwater extraction well EX -1 at concentrations of 18,000 and 6,000 ppb, respectively
<br />WASTE DISPOSAL
<br />Soil cuttings generated during drilling activities were placed on and covered with plastic sheeting at the
<br />subject site and disposal confirmation samples SP -(A -D), SP -1 (A -D), SP -2 (A -D), and SP -3 (A -D) were
<br />collected (Table 1) Approximately 13 yards of soil cuttings will be removed from the site by IWM for
<br />disposal
<br />DISCUSSION �� \
<br />Based on analytical results from soil samples collected and analyzed during this investigation, at appears
<br />that soil in the vicinity of the former gasoline USTs has the highest concentrations of petroleum /LIT
<br />hydrocarbons with TPHg, benzene, and MtBE concentrations up to 1,740, 446, and 100 ppm,
<br />respectively Hydrocarbon concentrations diminish with distance from the former gasoline UST location
<br />Based on this and the previous GR investigation (GR report #346408 04-2, Monitoring Well Installation
<br />Report, dated June 2, 1999), hydrocarbon concentrations in the vicinity of the former UST pit have been
<br />adequately defined
<br />Shallow groundwater at the site has been impacted by TPHg (up to 51,000 ppb), benzene (up to 39,000
<br />ppb), MtBE (up to 720,000 ppb), ETBE (up to 18,000), and TAME (up to 6,000 ppb) beneath the former
<br />gasoline USTs, with concentrations diminishing away from the former gasoline UST location
<br />Hydrocarbon concentration in shallow groundwater has been delineated to non -detect to the east (MW -2)
<br />and west (MW -7) To the southwest and south of the site in wells MW -8 and MW -9, TPHg and benzene
<br />are non -detect, and MtBE is present at concentrations of 3 1 and 78 ppb, respectively
<br />34640806-1
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