|
First Quarter 2002 Monitoring and Sampling Report 2
<br /> 7-Eleven, Inc,Store#17647, 1048 West Yosemite Avenue, Manteca,CA April 29 2002
<br /> Background
<br /> l' There are no active fueling facilities at this location On December 4, 1998, two 10,000-gallon and one
<br /> 6,000-gallon single-wall steel underground storage tanks(USTs)were removed from the site Six soil
<br /> ' samples were collected from beneath each end of the USTs at depths of 14 feet below grade, and two
<br /> side wall samples were collected at depths of 6 feet below grade, at the direction of SJCPHS (IT
<br /> ' Corporation, January 1999)
<br /> Soil samples collected during UST removal were analyzed for benzene, toluene, ethylbenzene, total
<br /> xylenes(BTEX), methyl-tertiary butyl ether(MTBE), total petroleum hydrocarbons as gasoline (TPH-G),
<br /> other oxygenates, and lead Benzene was not detected in the soil samples Soil TPH-G levels ranged up
<br /> to 1,300 milligrams per kilogram (mg/kg) at the base of the excavation, and sidewall samples contained no
<br /> ' detectable TPH-G Soil MTBE levels were less than 0 02 mg/kg, and soil lead levels ranged up to
<br /> 6 1 mg/kg On the basis of these findings, the SJCPHS requested further assessment
<br /> ' On June 18, 1999, five push-probe drilling points (GP-1 through GP-5)were advanced to depths of about
<br /> 15 feet below grade (IT Corporation, August 1999), at locations adjacent to and farther from the
<br /> ' hydrocarbon source area (former USTs/pump islands) Soil samples collected during drilling contained up
<br /> to 0 026 mg/kg MTBE, and no other detectable constituents Grab groundwater samples ranged up to
<br /> 19,400 micrograms per liter(ug/L) TPH-G and 126 ug/L MTBE Site closure was requested on the basis
<br /> of these findings The SJCPHS requested groundwater monitoring well installation, and a workplan for
<br /> 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 installed to
<br /> 20 feet below grade (IT Corporation, February 2000) The wells are screened from 10 to 20 feet below
<br /> ' grade at each location Soil benzene concentrations obtained during well installation were non-detectable
<br /> Soil TPH-G and MTBE concentrations ranged from 0 005 mg/kg to 0 0233 mg/kg, respectively Highest
<br /> soil hydrocarbon concentrations were detected at depths of 15 to 20 feet below grade Only well MW-3
<br /> ' contained detectable dissolved hydrocarbon concentrations benzene(0 94 ug/L), TPH-G (81 ug/L),
<br /> MTBE (108 ug/L), and TBA(111 ug/L) Dissolved DIPE, ETRE, and TAME were not detected in any of the
<br /> samples collected
<br /> Recent Assessment Activities
<br /> ' On March 20, 2002, two additional push-probe drilling points (GP-6 and GP-7)were installed to a depth of
<br /> 20 feet below grade (IT Corporation, April 2002) Groundwater samples were collected using a
<br /> ' hydropunch at depths of 13 feet below grade Soil hydrocarbon (GP-6 @ 15', GP-7 @ 18') and grab
<br /> groundwater(GP-6 @ 13', GP-7 @ 13') sample concentrations were non-detectable for gasoline
<br /> constituents
<br /> •
<br /> 1
<br /> 21766a4rpi
<br /> I
<br />
|