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SITE HISTORY
<br /> ' 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 /> 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
<br /> monitoring wells MW-1 through MW-4; depth to groundwater was reported to be at approximately 18
<br /> feet bgs. Laboratory analytical results of eleven soil samples collected from the borings indicated no
<br /> detectable concentrations of petroleum hydrocarbons with the exception of MTBE, which was detected in
<br /> soil samples from the borings for MW-1, MW-3, and MW-4 at concentrations up to 200
<br />' micrograms/kilogram (µg/kg). MTBE was detected in groundwater samples collected from MW-1, MW-
<br /> 3, and MW4 at concentrations of 2,700 micrograms per liter (gg/L), 5,700 µg/L, and 140 µg/L,
<br /> respectively. Tertiary-butanol (TBA) was detected in the sample collected from MW-1 at a concentration
<br />' of 98 tig/L, and tertiary-amyl methyl ether (TAME) was detected in the samples collected from MW-1
<br /> and MW-3 at concentrations of 7.7 µg/L and 16 gg/L, respectively. Quarterly groundwater monitoring at
<br /> the site began in the fourth quarter of 1999.
<br />' WHF prepared the Lateral Extent of Groundwater Contamination Work Plan, dated May 18, 2000,
<br /> describing proposed activities associated with the installation of four additional monitoring wells intended
<br />' to define the lateral extent of groundwater contamination. At the request of the SJCEHD, WHF modified
<br /> the work plan to include use of cone penetration testing (CPT). The modified work plan was subsequently
<br /> approved by the SJCEHD on June 9,2 00 0.
<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 /> subsequently converted into monitoring wells MW-5 through MW-8; groundwater depth was measured at
<br /> approximately 17 Leet 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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