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1117 Lone Palm Suite B <br /> hT Modesto California 95351 <br /> www atc-envi ro com <br /> 209 579 2221 <br /> Fax 209 579 2225 <br /> A S S O C I A T E S I N C <br /> February 14, 2002 <br /> 54 62605 0001 <br /> Ms Margaret Lagono <br /> San Joaquin County Public Health Services <br /> Environmental Health Division <br /> 304 E Weber Street, Third Floor <br /> Stockton, California 95202 <br /> Subject Monitoring Report First Quarter 2002, Former Thiemann's Service Station, 106 <br /> West Second Street, Ripon, California <br /> Dear Ms Lagono <br /> This report presents the results of quarterly groundwater monitoring and sampling performed in <br /> January 2002 by ATC Associates Inc at Former Thiemann's Service Station The site is located <br /> at 106 West Second Street in Ripon, California (Figure 1) Sampling was performed to monitor <br /> the distribution of petroleum hydrocarbons in groundwater at the site Monitoring was performed <br /> to determine the groundwater flow direction and the hydraulic gradient in the uppermost aquifer <br /> SITE HISTORY <br /> In March 1991, three underground storage tanks (USTs) were removed from the site Analysis of <br /> soil samples collected from the excavation indicated that high concentrations of petroleum <br /> hydrocarbons were present in soil beneath the tanks Groundwater was not encountered in the <br /> excavation The location of the former USTs is shown on Figure 2 <br /> In July 1993, a subsurface investigation was conducted at the site to determine the extent of <br /> petroleum hydrocarbons present in soil and to determine if groundwater had been impacted This <br /> included drilling eight soil borings and collecting soil samples Three of these borings were <br /> completed as shallow groundwater monitoring wells (MW-1, MW-2 and MW-3) Analysis of soil <br /> samples indicated that the majority of petroleum hydrocarbons in soil were present from about 10 <br /> feet below ground surface (bgs) to groundwater at a depth of approximately 29 feet bgs and <br /> within a radius of 35 feet from the former UST pit <br /> In August 1993, wells MW-1, MW-2, and MW-3 were monitored and sampled Analytical results <br /> showed that MW-1 had no measurable concentrations of petroleum hydrocarbons in the <br /> groundwater Wells MW-2 and MW-3 contained detectable levels of petroleum hydrocarbons A <br /> program of quarterly groundwater monitoring and sampling was begun in March 1994 <br /> w 1626051goanlyl I qr-2002 doe 1 <br />