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GeoCogrcalTechn cs Inc Page 2 <br /> Sod Investigation Report <br /> Bank of Stockton <br /> Project No 443 2 <br /> June 19,1996 <br /> • <br /> 05/92 Backfilling with pea gravel completed <br /> • 06/92 MW-1 installed <br /> • <br /> 11/92 MW 2 & 3 installed <br /> • 06/93 MW 4 & 5 installed <br /> + <br /> 11/29/95 Domestic water well sampled by direction of County <br />' PHS/EHD Gasoline contaminants found in water <br />' The water well, which has been idle for some years, lies about 400 feet north of the <br /> previously known UST location As indicated above, the County PHS/EHD <br /> directed that the well be sampled as a part of a quarterly groundwater monitoring <br /> event The sampling occurred on November 29, 1995 Unexpectedly, the well water <br /> was found to contain 624 parts per billion (ppb) of gasoline range petroleum <br /> hydrocarbons (TPH-G) and elevated BTEX levels A follow-up sampling event was <br /> performed on December 7, 1995 The intent of the second sampling was to <br /> determine if hydrocarbons would still be detectable after the well had been pumped <br /> I for at least 1/2 hour The analysis of the second sample found non-detectable levels <br /> of TPH-G, and benzene in the follow-up sample was measured at 6 ppb as compared <br /> to 206 ppb in the initial sample <br /> As a result of traces of gasoline unexpectedly being found in the water well, <br /> Geological Technics proposed a review of publicly available records to help <br />' determine if there could be a second source of contamination in addition to the <br /> known tanks already subject to remedial investigation As is more fully described <br /> below, the file search revealed the former presence of additional fuel tanks which <br /> had not previously been known This discovery resulted in drilling five shallow soil <br /> borings in the vicinity of the newly discovered tank location to help determine if the <br /> former UST may have leaked <br /> The results of this investigation are provided in the following sections <br />' 2.0 RECORDS REVIEW <br />' In order to help identify possible sources of release of petroleum hydrocarbons <br /> found in the water well, the following information sources were checked <br />' • San Joaquin County Assessor's Office <br /> • San Joaquin County Surveyor's Office <br /> • San Joaquin County PHS Environmental Health Division <br /> • San Joaquin County Office of Emergency Services <br /> • San Joaquin County Fire Department <br />