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Sent By,: BASELINE; 510 420 1707; Nov-9-99 le:29; Page 20129
<br /> was 09 mg/kg; toluene, 130 mg/kg; ethylbenzene, 210 mg/kg; xylenes, 1,500 mg/kg; and TPPH,
<br /> 14,000 mg/kg(Table 4).
<br /> A soil boring was also drilled adjacent to the former waste oil tank (prior to removal in 199 1) after
<br /> it had failed a precision leak test. Samples were collected at 11.5, 21.5, 31.5, and 36.5 feet bgs and
<br /> analyzed for TPH-diesel,TPH-gasoline, and BTEX. Petroleum hydrocarbons were not detected in
<br /> any of these soil samples near the former waste oil tank. No data were available regarding the
<br /> collection of soil samples during the waste oil tank removal (Enviros, 1997).
<br /> Groundwater monitoring of l l wells(MW-1 through MW-5,RW-1,RW-2,VEW-1 through VEW-
<br /> 4) was conducted near the former Shell site from 1992 until 1999 (Figure 7, Table 5). The
<br /> maximum groundwater concentrations rcportcd for the forma'Shcll Station wells were benzene,2.6
<br /> mg/L;toluene,8.3 mg/L;ethylbenzene,2.2 mg/L;xylenes,9.5 mg/L;MTBE 1.75 mg/L, and TPP H,
<br /> 47 mg/L (Cambria, 1999).
<br /> During the last sampling effort in April 1999,TPPH quantified as gasoline,was reported below the
<br /> laboratory reporting limits in the samples collected and analyzed. Benzene concentrations ranged
<br /> from 0.585 to 2.22 µg/L; toluene ranged from below laboratory reporting limits to 3.73 µg/L;
<br /> ethylbenzene, from below laboratory reporting limits to 2.40 µg/L; xylenes, below laboratory
<br /> reporting limits to 9.27 pg/L; and MTBE concentrations ranged from below laboratory reporting
<br /> limits to 944 pgJL (Cambria, 1999). Some halogenated volatile organic compounds (HVQCs),
<br /> including cis 1,2-dichioroethylene (cis 1,2-DCE), trichloroethylene, and chloroform/, were also
<br /> reported in groundwater samples collected in 1997(Table 6). Electrical conductivity measurements
<br /> and total dissolved solids were not measured during routine sampling efforts.
<br /> San Joaquin County is currently reviewing data from the former Shell station and data from the
<br /> Weber Block Phase II investigation for case closure.
<br /> OFF-SITE
<br /> Former ARCO Station
<br /> The City of Stockton recently purchased the adjacent former ARCO site located west of the project
<br /> f ai le.Three 12,000-gallon unleaded gasoline USTs and associated facilities were installed at the site
<br /> in 1984 and were removed in 1998-99. A waste oil tank and piping were also reportedly located at
<br /> the site(Supple, 1999) and removed. Soil and groundwater at this off-site location were impacted
<br /> by TPH-gasoline,BTEX,and MTBE as well as some chlorinated solvents and other volatile organics
<br /> (
<br /> SECOR, 1998,1999;Langevin, 1999). TPH as diesel and oil and grease were also reported above
<br /> laboratory reporting limits in soil samples collected during the removal of the waste oil'tank and
<br /> piping (Supple, 1999). ARCO will be responsible for cleaning up the property with regulatory
<br /> oversight,in addition to the plume that has
<br /> i�ated onto the Weber Block property(Brown, 1999).
<br /> corrective action schedule techni ue,
<br /> ARCO will have reasonable discretion to determine the9
<br /> method,and design with local regulatory oversight(City of SWckton, 1999). The former ARCO site
<br /> cannot be used for the construction or operation of any facility selling motor vehicle fuel and other
<br /> I� hydrocarbon substances for 25 years under the purchase agreement(City of Stockton, 1999). The
<br /> r clean-up agreement is presented in Appendix G.
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