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1 S E C 0 R
<br /> ISIECOR
<br /> ' new wells was initiated on January 5, 2000 Total petroleum hydrocarbons as gasoline (TPHg),
<br /> benzene, toluene, ethylbenzene, and xylenes (BTEX), and methyl tertiary butyl ether (MtBE)
<br /> were generally not detected in the wells, with the exception of low concentrations of benzene
<br /> ' and/or MtBE (EPA Method 8260) detected in wells MW-3 and MW-4 (Table 3) Initial depth to
<br /> water was approximately 28 to 29 feet bgs The direction of groundwater flow was established in
<br /> the easterly direction, at an approximate gradient of 0 003 foot/foot Soil boring and well
<br /> completion details are included in Table 1, historical soil analytical data is included in Table 2,
<br /> and historical groundwater monitoring and analytical data are included in Table 3 p
<br /> On July 20 — 21, 2000, three Geoprobe borings (GP-1 through GP-3) were completed by IT to a 4
<br /> ' depth of 60 feet bgs to investigate the vertical extent of petroleum hydrocarbons in soil and
<br /> groundwater Petroleum hydrocarbon-impacted soil and groundwater were encountered at
<br /> depths ranging from approximately 40 to 60 feet bgs Maximum concentrations of TPHg in soil '"kX{
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<br /> were reported at 4,570 mg/kg {GP-2 at 40'} and 3,650 mg/kg (GP-3 at 60') Maximum
<br /> concentrations of benzene in soil were reported at 19 8 mglkg (GP-2 at 50') and 21 1 mg/kg
<br /> (GP-3 at 60') MtBE was reported in one soil sample at a concentration of 26 5 mg/kg (GP-3 at
<br /> ' 60') Based on the results of this investigation, IT recommended an additional investigation be
<br /> conducted to determine the vertical extent of petroleum hydrocarbons in soil below 60 feet bgs,
<br /> and the installation of additional groundwater monitoring wells for assessment of groundwater
<br /> impacts below the A monitoring zone (IT, August 30, 2000) -r
<br /> On January 22, 2001, three on-site, B monitoring zone groundwater monitoring wells (MW-5,
<br /> MW-6, and MW-7) were installed by IT to depths of 80 feet bgs to delineate the vertical extent ofR,
<br /> '• petroleum hydrocarbons in groundwater The highest concentrations of petroleum -
<br /> hydrocarbons were detected in soil samples collected between 60 and 70 feet bgs Maximum LL"
<br /> a
<br /> concentrations of TPHg and benzene were 4,780 mg/kg and 55 3 mg/kg (MW-6@60'),
<br /> ' respectively Petroleum hydrocarbons were detected in groundwater samples collected from all
<br /> three wells Maximum concentrations of TPHg, benzene, and MtBE in groundwater were 2,300
<br /> parts per billion (ppb) (MW-6), 22 ppb (MW-6), and 16 ppb (MW-7) Based on the results of the 4
<br /> ' investigation, IT concluded that the vertical extent of petroleum hydrocarbons in soil was >r ,
<br /> generally defined to a depth of 80 feet bgs However, IT 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 /> tOn August 30, 31, and September 5, 2001, IT installed three additional on-site B monitoring #
<br /> zone 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 to depths of 80 feet (MW-8 and MW-9) and 79 feet bgs (MW-10) Petroleum
<br /> hydrocarbons were present in soil samples collected between 60 and 80 feet bgs, with
<br /> ' maximum concentrations of TPHg and benzene reported at 4,400 mg/kg and 77 mg/kg,
<br /> respectively (MW-9@60') TPHg was detected in groundwater from wells MW-8 through MW-
<br /> 10 at a maximum concentration of 22,000 ppb (MW-9), and benzene was detected in wells MW-
<br /> 8 through MW-10 at a maximum concentration of 600 ppb (MW-8) Fuel oxygenates (MtBE,
<br /> EtBE, TAME, TBA, DIPE, EDB, 1,2-DCA) were not detected in any soil and groundwater
<br /> samples collected from the site Based on the results of this investigation, SECOR
<br /> recommended the installation of additional off-site B monitoring zone groundwater monitoring
<br /> wells for further delineation of the dissolved petroleum hydrocarbon plume between _
<br /> approximately 60 feet bgs and 80 feet bgs (SECOR, May 29, 2002)
<br /> Updated SCM 2005 doe 3 �
<br /> 77CP 64409 05 0005 "
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