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<br />The following discussion provides a brief history of previous investigations and remediation
<br />activities at this former Chevron station.
<br />2.2 Previous Investigations
<br />Gettler-Ryan, Soil Sampling During Underground Storage Tank and Piping Removal
<br />a (November 10, 1998)
<br />On August 24, 1998, the five former USTs, hydraulic hoists, dispenser islands, and associated
<br />product piping were removed by Musco Excavators. Soil samples were collected by Gettler-
<br />F_ . Ryan (G -R) beneath the USTs and product piping. Low to nondetectable concentrations of
<br />petroleum hydrocarbons were reported in soil samples collected below the used -oil UST,
<br />product lines, and hydraulic hoist. Soil samples collected beneath the eastern end of the middle
<br />-' gasoline UST (14-1/2 ft below ground surface [bgs]) contained concentrations of total petroleum
<br />_# hydrocarbons as gasoline (TPHg), benzene, toluene, and methyl tertiary butyl ether (MtBE) up
<br />to 14,000 milligrams per kilogram (mg/kg), 84 mg/kg, 1,500 mg/kg and 56 mg/kg, respectively.
<br />The area beneath the eastern end of the middle gasoline UST was excavated from 14-1/2 to 16
<br />feet (ft) bgs, and a second soil sample was collected. Concentrations of TPHg, toluene, and
<br />MtBE in this sample were reported at 880 mg/kg, 52 mg/kg, and 11 mg/kg, respectively.
<br />-' Benzene was not detected in this sample.
<br />On August 31, 1998, the area beneath the eastern end of the middle gasoline UST was over -
<br />excavated from 16 to 22-112 ft bgs. Soil samples collected from the base and the eastern wall
<br />of the excavation were reported to contain TPHg, benzene, and MtBE at maximum
<br />concentrations of 2,300 mg/kg, 4.1 mg/kg, and 330 mg/kg, respectively.
<br />G -R; Monitoring Well Installation Report (June 2, 1999)
<br />- Between January 25 and January 27, 1999, one soil boring was advanced (SB -1) and four
<br />monitoring wells (MW -1 through MW -4) were installed by V&W Drilling. Soil samples collected
<br />from the borings had reported concentrations of TPHg, benzene, MtBE, and ethyl tertiary butyl
<br />- ether (ELBE) up to 1,200 mglkg, 0.81 mg/kg, 110 mg/kg, and 1.3 mg/kg, respectively.
<br />Groundwater samples collected from the monitoring wells in February, 1999, had reported
<br />concentrations of TPHg, benzene, MtBE, EtBE, and tertiary amyl methyl ether (TAME) up to
<br />11,000 micrograms per liter (µg11), 6,800 µg11, 62,000 µg11, 2,400 µg11, and 780 Rg/1, respectively.
<br />' Well construction details are summarized in Table 1 and the boring logs are provided in
<br />Appendix B. Historical groundwater gauging and analytical data is summarized in Tables 2 and
<br />3. Historical soil analytical data is included in Table 4.
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<br />t G -R, Off-site Source Survey (November 2, 1999)
<br />} In October of 1999, G -R continuously monitored the groundwater elevations at the site over a
<br />three-day period. The results of the study indicated that groundwater elevations fluctuate in
<br />^ daily cycles corresponding to the operation of nearby City of Lodi Municipal Well 12 (Well 12),
<br />�_. located approximately 350 ft southwest of the site (Figure 2). The top of the well screen is 210
<br />95775 NFAR REPORT Final.doc 2 SECOR lntematlonal Incorporated
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