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SIECR
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<br /> ' were reported at 19 8 mg/kg (GP-2 at 50') and 21 1 mg/kg (GP-3 at 60') MtBE was reported in
<br /> one soil sample at a concentration of 26 5 mg/kg (GP-3 at 60') Based on the results of this
<br /> investigation, IT recommended an additional investigation to determine the vertical extent of
<br /> ' petroleum hydrocarbons in sod beyond 60 feet bgs, and the installation of additional
<br /> groundwater monitoring wells for assessment of deeper zone groundwater impacts (IT, August
<br /> 30, 2000)
<br /> On January 22, 2001, three deep on-site groundwater monitoring wells (MW-5, MW-6, and MW-
<br /> 7) were installed by IT to depths of 80 feet bgs to delineate the vertical extent of petroleum
<br /> hydrocarbons in groundwater The highest concentrations of petroleum hydrocarbons were
<br /> detected in soil samples collected between 60 and 70 feet bgs, at concentrations of TPHg, and
<br /> benzene up to 4,780 mg/kg and 55 3 mg/kg (MW-6@60'), respectively Petroleum
<br /> hydrocarbons were detected in groundwater samples collected from all three wells Maximum
<br /> concentrations of TPHg, benzene, and MtBE in groundwater were reported at 2,300 parts per
<br /> billion (ppb) (MW-6), 22 ppb (MW-6), and 16 ppb (MtBE, EPA Method 8260) Based on the
<br /> results of the investigation, IT concluded that the vertical extent of petroleum hydrocarbons in
<br /> ' soil were generally defined to a depth of 80 feet bgs IT further recommended that additional
<br /> assessment activities be performed to evaluate the lateral extent of dissolved petroleum
<br /> hydrocarbon impacts between approximately 50 and 80 feet bgs (IT, April 16, 2001)
<br /> ' On August 30, 31, and September 5, 2001, IT installed three additional on-site deep
<br /> groundwater monitoring wells (MW-8 through MW-10) at locations upgradient of the UST
<br /> complex, in the vicinity of the pump islands and downgradient of the pump islands Wells were
<br /> ' completed at depths of 79 feet (MW-8) and 80 feet bgs (MW-9 and MW-10) Petroleum
<br /> hydrocarbons were present in soil samples collected between 60 and 80 feet bgs, with
<br /> concentrations of TPHg and benzene reported up to 4,400 mg/kg and 77 mg/kg, respectively
<br /> ' TPHg was detected in groundwater from wells MW-8 through MW-10 at concentrations up to
<br /> 22,000 ppb, and benzene was detected in wells MW-9 and MW-10 at concentrations up to 600
<br /> ppb Fuel oxygenates were not detected in any soil and groundwater samples collected from
<br /> ' the site Based on the results of this investigation, SECOR recommended the installation of
<br /> additional off-site deep zone groundwater monitoring wells for further delineation of the
<br /> dissolved petroleum hydrocarbon plume between approximately 60 feet and 80 feet bgs
<br /> ' (SECOR, May 29, 2002)
<br /> Between June 6 and July 11, 2003, SECOR install four deep groundwater monitoring wells
<br /> (MW-11 through MW-14) Each of the wells was in an offsite location and the purpose of the
<br /> ' work was to delineate the lateral extent for the petroleum plume in the deeper zone Wells MW-
<br /> 11 and MW-14 were installed to a depth of 82 feet below ground surface (bgs) and screened
<br /> from 77 to 82 feet bgs Wells MW-12 and MW-13 were installed to a depth of 83 feet below
<br /> ' ground surface (bgs) and screened from 78 to 83 feet bgs TPHg, benzene, MtBE, and 1,2-
<br /> DCA were not reported in any of the soil samples analyzed with the exception of 1,2-DCA
<br /> reported at a concentration of 0 0071 mg/kg in sample MW-12@70'
<br /> The site is currently monitored and sampled on a quarterly basis Second quarter 2004
<br /> groundwater sampling reported TPHg in three of the four shallow wells at a maximum
<br /> concentration of 400 ppb, benzene in one of the four shallow wells at a maximum concentration
<br /> of 0 57 ppb, MtBE in each of the four shallow wells at a maximum concentration of 430 ppb, and
<br /> ' 1,2-DCA in two of the four shallow wells at a maximum concentration of 1 2 ppb Second
<br /> quarter 2004 groundwater sampling reported TPHg in eight of the ten deep wells at a maximum
<br /> ' concentration of 5,100 ppb, benzene in two of the ten deep wells at a maximum concentration of
<br /> Updated SCM doc 3 August 13,2004
<br /> 77CP 64409 05 0005
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