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V 1117 Lone Palm Ave , Suite B <br /> Modesto, California 95351 <br /> www atc-enviro corn <br /> 209 579 2221 <br /> Fax 209 579 2225 <br /> A S S 0 C I A T E S 1 N C <br /> all <br /> August 22, 2002 RECOVED <br /> 54 62605 0001 <br /> AUG 2 7 2002 <br /> ENVIRONMENT HEALTH <br /> Ms Margaret Lagono PERMIT/SERVICES <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 - Second Quarter 2002, Former Thiemann's Service Station, <br /> 106 West Second Street, Ripon, California <br /> Dear Ms Lagono <br /> This report presents the results of quarterly groundwater monitoring and sampling performed in <br /> April 2002 by ATC Associates Inc at Former Thiemann's Service Station The site is located at <br /> 106 West Second Street in Ripon, California (Figure 1) Sampling was performed to monitor the <br /> distribution of petroleum hydrocarbons in groundwater at the site and to determine the <br /> groundwater flow direction and magnitude of 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 The <br /> investigation included drilling eight soil bonngs and collection of soil samples Three of the <br /> borings were completed as shallow groundwater monitoring wells (MW-1, MW-2 and MW-3) <br /> Analysis of soil samples indicated that the main concentration of petroleum hydrocarbons in soil <br /> occurred from approximately 10 feet below ground surface (bgs) to the groundwater surface at a <br /> depth of approximately 29 feet bgs and 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 wells MW-2 and MW-3 contained detectable levels of petroleum hydrocarbons in the <br /> 4S groundwater MW-1 had no measurable concentrations of petroleum hydrocarbons A program <br /> of quarterly groundwater monitoring and sampling was initiated in March 1994 <br /> W 162605`quart1y\2QR-2002 doc 1 <br /> ENVIRONMENTAL, GEOTECHNICAL AND MATERIALS PROFESSIONALS <br />