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<br /> 7-Eleven Store#14117
<br /> Quarterly Groundwater Monitoring Report (1Q2003)
<br /> June 24, 2003
<br /> Page 2
<br /> Current Quarter Analytical Data (See Figure 3 and Table 1)
<br /> Maximum TPHg Concentrations MW-3, 22,000 ug/L r
<br /> Maximum Benzene Concentrations MW-3, 73 uglL
<br /> Maximum MtBE Concentrations MW-4, 200 uglL
<br /> Maximum TBA Concentrations MW-1, 10,000 ug/L
<br /> BACKGROUND
<br /> On July 17, 1998, three 10,000-gallon single-walled USTs were removed from the site The UST
<br /> excavation was extended to the east, and two new 10,000-gallon double-walled steel USTs were
<br /> installed The new tanks were installed in a tank pit located east of the original UST locations One
<br /> ten-inch diameter Schedule 40 PVC conductor casing was installed in the new UST pit between the
<br /> new tanks for future installation of well MW-2
<br /> On September 29 and October 2, 1998, Fluor-Daniel GTI advanced six offsite (OSGP-1 through
<br /> OSGP-6) and 11 onsite (GP-7 through GP-17) Geoprobe sod borings The offsite borings did not
<br /> contain total petroleum hydrocarbons as gasoline (TPHg), benzene, toluene, ethylbenzene, and total
<br /> xylenes (BTEX), or methyl-tert-butyl ether (MtBE) in sod above laboratory reporting limits The onsite
<br /> borings reported benzene, TPHg, and MtBE at maximum concentrations of 12 5 milligrams per
<br /> • kilogram (mg/kg) (GP-17@20'), 42,900 mglkg (GP-15@15'), and 234 mg/kg (GP-14@10'),
<br /> respectively(Fluor Daniel GTI, 1998)
<br /> On May 13 and 14, 1999, four groundwater monitoring wells (MW-1 through MW-4) were advanced
<br /> to 51 feet below ground surface (bgs) Benzene, TPHg, and MtBE in soil were reported at maximum
<br /> concentrations of 2 89 mg/kg (MW-3-15'), 429 mg/kg (MW-3-15'), and 0 119 mg/kg (MW-4-20'),
<br /> respectively(IT Corporation, 1999)
<br /> On October 30, 2001, three groundwater monitoring wells (MW-5, MW-6, and MW-7)were advanced
<br /> to 20 feet bgs TPHg, BTEX, and MtBE in soil were not detected above laboratory reporting limits,
<br /> except for 0 006 mg/kg total xylenes (MW-7@20') Selected halocarbons also reported in the soil
<br /> samples indicated possible dry cleaner plume contributions (IT Corporation, 1999) An active USA
<br /> Gasoline (former Exxon) service station is located east of the site
<br /> MONITORING AND SAMPLING PROCEDURES
<br /> The depth to water was measured in monitoring wells MW-1 through MW-7 from top of casing (TOC)
<br /> using a water level indicator to within 0 01 feet bgs Dissolved oxygen readings were also collected
<br /> from each well using a YSI Model 550A dissolved oxygen meter equipped with a down hole sensor
<br /> Well purging and sampling equipment is thoroughly cleaned prior to purging and sampling each well
<br /> The sampling procedure for each well includes measuring the water level and checking for the
<br /> presence of liquid-phase hydrocarbons (LPH), using either an electronic indicator and a clear
<br /> Teflon® bailer or an oil-water interface probe Wells not containing LPH are purged of approximately
<br /> three casing volumes of water (or to dryness) using a submersible pump or bailer The equipment
<br /> and purging methods used for the current sampling event are noted on the field data sheets included
<br /> in Attachment A During purging, temperature, pH, and electrical conductivity are monitored in order
<br /> to document that these parameters are stable prior to collecting samples After purging, water levels
<br /> • are allowed to recover to 80% of the original levels prior to collection of the water sample
<br /> Groundwater samples are collected using a disposable Teflon® bailer, placed into appropriate EPA-
<br /> 14117 03-1Q Report SECOR Intemahonal Incorporated
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