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1 <br /> • v ,,, 1117 Lone Palm Avenue, Suite B <br /> Modesto, CA 95351 <br /> ' http//www atcassociates com <br /> 1 209 579 2221 <br /> As80CIATBs 1 K C Fax 2O95792225 <br /> September 7, 2004 <br /> 54 62605 0001 � r <br /> r D <br /> s P 1 o 2004 <br /> Ms Vicky McCartney <br /> San Joaquin County ENV'' <br /> Environmental Health Department PERivii,/-InVICES <br /> 304 E Weber Avenue, Third Floor q 01� <br /> Stockton, California 95202 <br /> Subject Monitoring Report - Second Quarter 2004, Former Thiemann's Service Station, 106— 4 Y'- <br /> West Second Street, Ripon, California A 0 <br /> Dear Ms McCartney Cjv"' <br /> This report presents the results of quarterly groundwater monitoring and sampling performed in June &I <br /> 2004 by ATC Associates Inc (ATC) at the former Thiemann's Service Station The site is located at 106 <br /> West Second Street in Ripon, California(Figure 1) Sampling was performed to monitor the distribution <br /> of petroleum hydrocarbons in groundwater at the site and to determine the groundwater flow direction <br /> and magnitude of the hydraulic gradient in shallow groundwater <br /> • SITE HISTORY <br /> In March 1991, three underground storage tanks (USTs) were removed from the site Analyses of soil <br /> samples collected from the excavation indicated that high concentrations of petroleum hydrocarbons <br /> were present in soil beneath the tanks Groundwater was not encountered in the excavation The <br /> 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 petroleum <br /> hydrocarbons present in soil and to determine if groundwater had been impacted The investigation <br /> included drilling eight soil borings and collection of soil samples Three of the borings were completed <br /> as shallow groundwater monitoring wells (MW-1, MW-2 and MW-3) Analyses of soil samples <br /> indicated that the greatest concentration of petroleum hydrocarbons in soil occurred from approximately <br /> 10 feet below ground surface (bgs) to the groundwater surface at a depth of approximately 29 feet bgs <br /> and within a radius of 35 feet from the former UST pit <br /> In August 1993, monitoring wells MW-1, MW-2, and MW-3 were monitored and sampled Laboratory <br /> analytical results indicated that wells MW-2 and MW-3 contained detectable levels of petroleum <br /> hydrocarbons in the groundwater The sample collected from MW-1 was reported to contain no <br /> measurable concentrations of petroleum hydrocarbons A Quarterly groundwater monitoring and <br /> sampling program was initiated in March 1994 <br /> In August 1995, Smith Technology conducted a subsurface site investigation to further define the extent of <br /> contamination in groundwater at the site Smith Technology supervised the installation of monitoring wells <br /> . MW-4, MW-5, and MW-6 The three new wells were developed and sampled along with the original <br /> monitoring wells MW-1, MW-2, and MW-3 Analytical results of groundwater samples collected from the <br /> s lenvironmentai1626051quartlyl2QR-2004 doc 1 <br /> ENVIRONMENTAL, GEOTECHNICAL AND MATERIALS PROFESSIONALS <br />