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Fourth
<br /> Quarter 1998 Monitoring and Sampling Repoli and Work Pian for Additional Subsurface Investigation 3
<br /> The Southland Co ration Store#19976 1399 North Main Street,Manteca CA January 29 1999
<br /> summarizes the laboratory analytical results for the soil samples collected from the UST tank pit The
<br /> samples were analyzed for benzene,toluene, ethylbenzene, and total xylenes (BTEX), methyl-tart-butyl-
<br /> ether(MTBE), total petroleum hydrocarbons as gasoline (TPH-G), following EPA method 8020/modified
<br /> 8015, and total lead by EPA method 6010 If MTBE was detected by EPA method 8020, an additional
<br /> analysis by EPA method 8260 was used to confirm its presence
<br /> ' From September 19 through 24, 1996,the tank pit was extended approximately 20 feet to the south and
<br /> excavated to a depth of 15 feet BGS to accommodate the installation of three new 10,000-gallon USTs
<br /> (Figure 2) Soils encountered during the tank removal included fine sand to silty sand to a depth of
<br /> ' approximately 10 feet BGS followed by sift, silty clay, and clayey silt with some interbedded fine sand to a
<br /> depth of 15 feet BGS Soil encountered at 15 feet BGS appeared very moist to wet but no accumulation of
<br /> groundwater was observed in the tank pit excavation or at the sample locations On September 20, 1996, a
<br /> ' total of seven sod samples were collected from the floor of the additional tank pit excavation six samples at
<br /> 13 feet BGS and one sample at 15 feet BGS Soil samples were collected using the same protocol and
<br /> analyzed for the same parameters as the samples collected beneath the USTs
<br /> ' In February 1998, SJCPHS required a work plan for further subsurface investigation of the vertical and
<br /> lateral extent of contamination at this site
<br /> On April 29, 1998, to fulfill the requirements of the SJCPHS, Fluor Daniel GTI supervised the advancement
<br /> of three geoprobe points (GP-1 through GP-3) near the underground storage tank (UST) pad and pump
<br /> island (Figure 2) Using a truck-mounted hydraulic drill and direct push techniques,discrete soil samples
<br /> were collected from each of the soil borings Soil samples were collected at 5-foot intervals beginning at 5
<br /> feet below grade
<br /> A total of 19 sod samples were submitted for laboratory analysis for BTEX, MTBE, and TPH-G using EPA
<br /> methods 8020/modified 8015 One sample from each soil boring was also analyzed for the oxygenates,
<br /> MTBE, TBA, DIPE, ETBE, and TAME using EPA method 8260
<br /> Table 1 summarizes the laboratory analytical results for the soil samples collected from the three sod
<br /> bonngs drilled April 29, 1998 The highest concentrations of benzene, MTBE and TPH-G were reported in
<br /> sample GP-3-35 at 15 milligrams per kilogram (mg/kg), 27 mg/kg and 2,600 mg/kg, respectively MTBE,
<br /> TBA, DIPE, ETBE, and TAME, using EPA method 8260 were not detected in the three samples analyzed
<br /> Soil samples taken from the UST pit and soil borings indicate the dissolved hydrocarbon source area is
<br />' between the pump island and former UST pit
<br /> Following completion of the bonngs,grab groundwater samples were collected from soil bonngs GP-1, GP-
<br /> 2, and GP-3 using disposable bailers, then decanted into 40-milliliter glass vials treated with hydrochloric
<br /> acid to preserve the samples The samples were sealed using Teflon®-septum caps, labeled, placed on
<br /> ice in an insulated container, and transported under chain-of-custody manifest to Core Laboratories The
<br /> groundwater samples were analyzed for BTEX, MTBE, and TPH-G, using EPA methods 8020/modified
<br /> 8015, and for oxygenates MTBE, TBA,DIPE, ETBE, and TAME using EPA method 8260
<br /> Table 2 summarizes the laboratory analytical results of groundwater samples collected from three soil
<br />' borings GP-1, GP-2, and GP-3 on April 29, 1998
<br /> In July of 1998, SJCPHS required a work plan for additional subsurface investigation of the vertical and
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