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1260 Graphics Drive <br /> V Modesto California <br /> 95351 <br /> 209 579 2221 <br /> Aq ali;Q Fax 209 579 2225 <br /> . A S S O C I A T E S I N C T SU01I1PU00 <br /> I <br /> Panorddy <br /> 88E0-1D�S6 uol�IoOIS '8$C x0 <br /> 8 O d <br /> 13 PJILI-L any lagaM 3 170C <br /> NOISIAI Hl_J'd3H -1y1N3WN081AN3 <br /> June 24, 1998 <br /> 62605 <br /> Aq ale(] <br /> /V3HIVIN�IANOUIAN3 Uo0 <br /> Mr Ron Rowe lua❑ <br /> ddy <br /> San Joaquin County Public Health Services 8800-I WGIS xo9 O d <br /> Environmental Health Division aOoM 3170C <br /> 304 E Weber Street, Third Floor NOISIAI0 H <br /> Stockton, California 95202 <br /> Subject Monitoring Report Second Quarter 1998, Former Thiemann's Service Station, <br /> 106 West Second Street, Ripon, California <br /> Dear Mr Rowe <br /> This report presents the results of quarterly groundwater monitoring and sampling performed in <br /> April 1998 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 Monitoring was performed to <br /> 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 <br /> soil samples indicated that the majority of petroleum hydrocarbons in soil were present from <br /> about 10 feet below ground surface (bgs) to groundwater at a depth of approximately 29 feet bgs <br /> and within a radius of 3 5 feet from the former UST pit <br /> In August 1993, wells MW-1, MW-2, and MW-3 were monitored and sampled Analytical <br /> results 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 <br /> A program of quarterly groundwater monitoring and sampling was begun in March 1994 <br /> w 1626451quartlyl2gr-1998 doc 1 <br />