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Valley Motors - 2 - 27 January 2014
<br /> 800 E. Main St.
<br /> Stockton, San Joaquin County
<br /> 3) In October 1990, two 5,000-gallon gasoline USTs were removed from beneath the sidewalk
<br /> adjacent to Grant Street on the western side of the Site (Figure 2). The fate of the
<br /> excavated soil is not provided in the available reports. The City of Stockton allowed the
<br /> excavation without an encroachment permit and, after the responsible party became ill and
<br /> could not continue the work, eventually backfilled the excavation with clean fill and repaired
<br /> the Grant Street sidewalk in June 1993.
<br /> 4) A waste oil tank associated with this site remains on City of Stockton property. A filler cap is
<br /> visible in the sidewalk adjacent to Main Street on the northern boundary of the Site. The
<br /> waste oil tank is not part of the Site because an August 2007 San Joaquin Superior Court
<br /> Judgment cleared the owners of Valley Motors from responsibility for removing the tank in
<br /> the sidewalk. In a letter dated 8 November 2013, Central Valley Water Board staff directed
<br /> the City of Stockton to remove the abandoned waste oil UST.
<br /> 5) Confirmation soil concentrations detected from the 1990 USTs removal were not accepted
<br /> by the SJCEHD due to the tank removal company's (Siebold Construction) use of Simple
<br /> Green, a surfactant (soap), introduced into the tank pit prior to the soil sampling. The
<br /> October 1995 preliminary soil and grab groundwater investigation reported maximum soil
<br /> concentrations as total petroleum hydrocarbons as gasoline (TPHg), 2,400 mg/kg; TPH as
<br /> diesel (TPHd), 870 mg/kg; and xylenes, 36 mg/kg. Soil data are presented in Table 1.
<br /> Maximum grab groundwater concentrations were TPHg, 1,500 micrograms per Liter(ug/L);
<br /> TPHd, 290 ug/L; benzene, 36 ug/L; toluene, 12 ug/L; ethylbenzene, 16 ug/L; and xylenes,
<br /> 77 ug/L. Chlorinated solvents; tetrachlorethene (PCE), 39 ug/L; trichloroethene (TCE),
<br /> 74 ug/L; cis-1, 2-dichloroethene (cis-1,2-DCE), 54 ug/L and trans 1,2-DCE, 22 ug/L were
<br /> also detected in groundwater but were not attributed to the gasoline USTs release.
<br /> Although the source of the solvents has not been identified, Central Valley Water Board)
<br /> staff have opened a Site Cleanup case for Valley Motors, which is not a part of this site
<br /> closure. The groundwater data are compared to the Water Quality Goals in Table 2.
<br /> 6) Ten groundwater monitoring wells, seven soil borings, and one remediation well were
<br /> completed from 1994 to 2011. Maximum groundwater monitoring results were TPHg,
<br /> 110,000 ug/L; TPHd, 9,680 ug/L; benzene, 35,90D ug/L; ethylbenzene, 4,900 ug/L; toluene,
<br /> 22,000 ug/L; xylenes, 19,000 ug/L; and methyl tert butyl ether (MTBE), 1,140 ug/L.
<br /> 7) A Soil Vapor Extraction Pilot Test removed approximately 427 pounds (70 gallons) of
<br /> petroleum fuels from November 2006 to January 2007.
<br /> 8) In December 2013 (Figure 3), maximum groundwater monitoring concentrations were TPHg,
<br /> 3,440 ug/L; benzene, 282 ug/L, toluene, 180 ug/L; ethylbenzene, 317 ug/L; and xylenes,
<br /> 328 ug/L.
<br /> 9) A Site Conceptual Model has been developed. Submission of multiple reports have resulted
<br /> in development of a comprehensive site conceptual model. Depth to groundwater varied
<br /> from 28 feet below ground surface (' bgs) in March 2013 to 44' bgs in December 1996. The
<br /> groundwater flow direction has been consistently towards the east at low gradients ranging
<br /> from 0.0005 ft/ft to 0.001 ft/ft. Horizontal and vertical characterization is provided by
<br /> monitoring wells VM-5 (south) VM-8 (north) VM-6 (east) and VM-7 (west) and boring VM-1
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