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Flag City Chevron - 2 - 20 March 2012
<br /> 6421 Capitol Ave., Lodi, San Joaquin County
<br /> of the trench identified no impacts from CDCs. Groundwater was encountered in the
<br /> tank excavation at approximately 9' bgs. Groundwater "grab" samples collected from
<br /> the UST excavation showed maximum concentrations as: TPHg, 8,000 ug/L; total
<br /> petroleum hydrocarbons as diesel (TPHd), 1,000 ug/L; B, 230 ug/L; T, 300 ug/L;
<br /> E, 160 ug/L; and X, 860 ug/L. In April 1995, three additional grab groundwater samples
<br /> were collected from the tank pit. Maximum analytical results of the grab groundwater
<br /> samples showed: TPHg, 1,600 ug/L; TPHd, 1,400 ug/L; T, 4.2 ug/L; E, 8.9 ug/L; and
<br /> X, 73 ug/L. Benzene was not detected in any of the groundwater samples.
<br /> Approximately 1,000 cubic yards of soil generated from excavation activities were
<br /> transported off-site for disposal at a local landfill. In 1996, MW-4 replaced MW3, which
<br /> had to be destroyed due to its proximity to the UST excavation. In June 1998, three
<br /> additional monitoring wells (MW-5, MW-6 and MW-7) were installed on and off site to
<br /> assess impacts to groundwater. Analytical results for the initial sampling of the wells in
<br /> July 1998 showed maximum concentrations of TPHd and Methyl tert-Butyl Ether (MtBE)
<br /> as 280 ug/L and 14 ug/L, respectively. Analyses for TPHg and BTEX were non-detect.
<br /> In October 1998 a separate petroleum hydrocarbon release was discovered during UST
<br /> removal activities at the 3 B's Truck Stop (3 B's), which is located west of the Site
<br /> across Thornton Road. In December 1999, the Rocky's Restaurant Well (RDW-1),
<br /> located southwest of the Site, was sampled. MtBE was reported at 18 ug/L in RDW-1.
<br /> Subsequent investigations at the Site FCC and at 3 B's have been interpreted to show
<br /> that the two groundwater plumes converged at, and impacted, RDW-1, due in part to a
<br /> compromised well sanitary seal that did not properly isolate the shallow and deep
<br /> aquifer zones. As a result of the RDW-1 impact, the SJCEHD transferred the regulatory
<br /> lead to the Regional Board by letter dated 16 February 2000. On 1 March 2000, the
<br /> Regional Board Executive Officer issued Cleanup and Abatement Order (CAO)
<br /> 5-00-700 to Flag City Chevron.
<br /> In March 2000, seven soil borings (P-6 through P-12) were advanced to 5' bgs to
<br /> assess soil gas vapor concentrations near the fuel dispenser and USTs. The soil gas
<br /> survey maximum results (P-6) were TPHg, 600 ug/L; B, 05. ug/L; and MtBE, 2.5 ug/L.
<br /> One groundwater extraction well (EW-1) was installed onsite to a depth of 33.5 feet bgs
<br /> for interim remediation measures. Additionally, five cone penetrometer testing (CPT)
<br /> soil borings were advanced onsite to characterize the geologic and hydrogeologic
<br /> framework. Based on the CPT data collected, five informal hydrologic units (Attachment
<br /> 3) that are hydraulically connected were defined as First Zone (10'-35' bgs), Second
<br /> Zone (40'-60' bgs), Rocky's Upper Zone (70'-75' bgs), Secondary Aquifer Zone (90'-
<br /> 110' bgs), and the Primary Aquifer Zone (130'-150' bgs). The data show the two
<br /> groundwater plumes (Site and 3 B's) traveled through the First Zone and Second Zone
<br /> until reaching RDW-1, where the plumes were drawn down into the Rocky's Upper Zone
<br /> and the Secondary Aquifer Zone. In April 2000, groundwater "grab" samples collected
<br /> near RDW-1 showed maximum concentrations of MtBE, 280 ug/L (Second Zone); Tert-
<br /> Butyl Alcohol (TBA), 7.1 ug/L (Secondary Aquifer Zone); Methanol, 170 ug/L (Rocky's
<br /> Upper Zone); and Ethanol, 27 ug/L in the Rocky's Upper Zone.
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