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r, SITE HISTORY
<br /> 1 BOYETT PETROLEUM
<br /> 419 S.Main Street
<br /> Manteca, California
<br /> On November 20 and 21, 1996, soil sampling was conducted at the site by WHF, Inc., (WHF) under the
<br /> direction of Mr, Robert McClellon of the San Joaquin County'Public Health Service, Environmental
<br /> Health Division (SJCEHD). According to WHF, on November 20, 1996, one soil sample was collected
<br /> from beneath each of the site's three existing fuel dispensers at a depth of approximately two feet below
<br /> the dispenser piping. On November 21, 1996, four discrete soil samples were collected to characterize
<br /> approximately 44 cubic yards of soil from demolition and retrofit activities stockpiled at the site. The four
<br /> discrete samples were composited into two soil samples for laboratory analyses. The soil samples
<br /> collected from both the dispenser locations and the soil stockpile were analyzed for total petroleum
<br /> hydrocarbons quantified as gasoline (TPH-G) by EPA method 8015M, and for benzene, ethyl benzene,
<br /> toluene,total xylenes(BTEX), and methyl tert-butyl ether (MTBE)by EPA Method 8020.
<br />' On October 5, 1998, WHF, in conjunction with Fisch Environmental Exploration Services, completed
<br /> two vertical soil borings, SB-1 and SB-2, to a maximum depth of-18 feet below ground surface (bgs)
<br /> proximal to the fuel dispenser island. Soil samples were collected at five-foot intervals for soil
<br /> classification. Three soil samples were collected from each boring at depth intervals of 4-6 feet, 9-11 feet,
<br /> and 16 feet. One groundwater sample was collected from each boring from a depth of 18 feet for
<br /> laboratory analyses.
<br />' 1 On August 27 and 30, 1999, WHF, in conjunction with Frontier Drilling, completed four soil borings. The
<br /> borings, which varied in total depth from 26.5 to 36.5 feet bgs, were subsequently converted into monitor
<br /> wells MW-1 through MW-4; depth to groundwater was reported to be at approximately 18 feet bgs.
<br /> Laboratory analytical results of eleven soil samples collected from the borings indicated no detectable
<br /> concentrations of petroleum hydrocarbons with the exception of MTBE, which was detected in soil
<br /> samples from the borings for MW-1,MW-3, and MW-4 at concentrations up to 200 micrograms/kilogram
<br /> (µg/kg). MTBE was detected in groundwater samples collected from MW-1, MW-3, and MW-4 at
<br /> concentrations of 2,700 micrograms per liter(µg/L), 5,700 gg/L, and 140 µg/L, respectively. Tert-butanol
<br /> (TBA) was detected in the sample collected from MW-1 at a concentration of 98 gg/L, and tert-amyl
<br /> methyl ether (TAME) was detected in the samples collected from MW-1 and MW-3 at concentrations of
<br /> 7.7 µglL and 16 gglL, respectively. Quarterly groundwater monitoring at the site began in the fourth
<br /> quarter of 1999.
<br /> iWHF prepared the Lateral Extent of Groundwater Contamination Work Plan, dated May 18, 2000,
<br /> describing proposed activities associated with the installation of four additional monitor wells intended to
<br />' define the lateral extent of groundwater contamination. At the request of the SJCEHD, WHF modified the
<br /> work plan to include use of cone penetration testing (CPT). The modified work plan was subsequently
<br /> approved by the SJCEHD on June 9, 2000.
<br />' From December 20 through 22, 2000, WHF, in conjunction with Frontier Drilling, completed four soil
<br /> borings. The borings, which varied in total depth from approximately 20 to 25 feet bgs, were
<br /> Q11hcPrniently converted into monitor wells MW-5 through MW-8: Lyroundwater death was measured at
<br /> approximately 17 feet bgs. According to a representative of the SJCEHD, aquarium sand purchased at a
<br /> pet store was used in the construction of MW-5. Soil samples were collected from each boring at five-foot
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