|
S E C 0 R
<br /> 7-Eleven Store #17647
<br /> Quarterly Groundwater Monitoring Report(3Q2003)
<br /> . November 25, 2003
<br /> Page 2
<br /> Current Quarter Analytical Data (See Figure 3 and Table 1)
<br /> Maximum TPHg Concentrations Not Detected, <50 u /L
<br /> Maximum Benzene Concentrations Not Detected, <0 50 u /L
<br /> Maximum MtBE Concentrations Not Detected, <0 50 u /L
<br /> Maximum TBA Concentrations Not Detected, <5 0 u /L
<br /> BACKGROUND
<br /> On December 4, 1998, two 10,000-gallon and one 6,000-gallon single-walled steel underground
<br /> storage tanks (USTs) were removed from the site Six soil samples were collected from beneath the
<br /> ends of the USTs, and two sidewall samples were collected, at the direction of SJCEHD (IT
<br /> Corporation, January 1999) Benzene was not detected above laboratory reporting limits in the soil
<br /> samples Concentrations of total petroleum hydrocarbons as gasoline (TPHg) ranged up to 1,300
<br /> milligrams per kilogram (mg/kg) at the base of the excavation, but sidewall samples did not contain
<br /> TPHg above laboratory reporting limits Concentrations of methyl-tert-butyl ether (MtBE) ranged
<br /> from 0 32 mg/kg to 1 0 mg/kg, and lead concentrations ranged up to 6 1 mg/kg On the basis of
<br /> these findings, the SJCEHD requested further assessment
<br /> On June 18, 1999, five push-probe borings (GP-1 through GP-5) were advanced to depths of
<br /> approximately 15 feet below ground surface (bgs) (IT Corporation, August 1999), at locations
<br /> adjacent to the hydrocarbon source area (former USTs/pump islands) Soil samples collected during
<br /> drilling contained up to 0 026 mg/kg MtBE, and no other detectable constituents Grab groundwater
<br /> samples contained up to 19,400 micrograms per liter (Ng/L) TPHg and 126 pg/L MtBE Site closure
<br /> was requested on the basis of these findings The SJCPHS requested groundwater monitoring well
<br /> installation, and a workplan for this activity was submitted (IT Corporation, October 1999)
<br /> On December 21, 1999, three groundwater monitoring wells (MW-1, MW-2, and MW-3) were
<br /> installed to 20 feet bgs (IT Corporation, February 2000) Benzene in soil was not detected above
<br /> laboratory reporting limits TPHg and MtBE were detected in soil up to 0 005 mg/kg to 0 0233
<br /> mglkg, respectively The highest soil concentrations were detected at depths of 15 to 20 feet bgs A
<br /> detection of dissolved tert-butyl alcohol (TBA) (111 ug/L, MW-3) is considered anomalous, as TBA
<br /> has not been detected in this well in subsequent quarterly sampling events
<br /> On March 20, 2002, two additional push-probe borings (GP-6 and GP-7) were advanced to a depth
<br /> of 20 feet bgs (IT Corporation, April 2002), as requested by the SJCEHD, to verify lateral plume
<br /> delineation Groundwater samples were collected using a Hydropunch sampler at depths of 13 feet
<br /> bgs Soil samples GP-6 @ 15' and GP-7 @ 18', and grab groundwater samples GP-6 @ 13' and
<br /> GP-7 @ 13', did not contain petroleum hydrocarbons above laboratory reporting limits
<br /> On May 7, 2003, four soil samples were collected from beneath the fuel dispensers, product lines
<br /> and in the area of a former tank sump during fuel line upgrades at the site The four soil samples did
<br /> not contain TPHg, benzene, toluene, ethylbenzene, and total xylenes (BTEX), MtBE, TBA,
<br /> diisopropyl ether (DIPE), ethyl-tert-butyl ether (EtBE), and tert-amyl-methyl ether (TAME) above
<br /> laboratory detection limits
<br /> 17647 03-30 Report doc SECOR International Incorporated
<br />
|