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C <br /> ff�1 <br /> First Semiannual 2012 Groundwater Monitoring Report <br /> Former-Texaco Service Station <br /> Chevron Site ID 309075 <br /> June 21, 2012 <br /> with the possible removal of the underground storage tanks (UST) and analytical data for the <br /> samples collected from monitoring.well MW-1 is not available. Pursuant to SJCEHD letter, dated <br /> November 30, 2010, soil samples were not collected from MW-1 during well installation. <br /> 5.1.6 Trends <br /> TPH-MO and TPH-DRO without SGC concentration ranges of groundwater samples collected <br /> during the first semiannual event of 2012 are generally consistent with the concentration ranges <br /> Ldetected during recent monitoring and sampling events. <br /> With the exception of MW-1, MW-6D, and the groundwater sampled on December 5, 2008 from <br /> MW-4, TPH-GRO, BTEX, MTBE, TBA, DIPE, ETBE, TAME, 1,2-DCA, EDB, and ethanol have <br /> not been detected since sampling began in 2006. Additionally, TPH-GRO concentrations in <br /> MW-1 have decreased from 4,700 pg/L to 99 pg/L_ <br /> 5.1.7 Data Gaps <br /> Information documenting the existence of five. former USTs associated with the former Texaco <br /> service station is not available. A subsurface investigation using electromagnetic technology <br /> and ground penetration radar, conducted in June 2008, concluded definitive UST signatures do <br /> not exist at the site. <br /> 5.2 Conclusions and Recommendations <br /> The TPH-MO and TPH-DRO results, without and with SGC, indicate the organic compounds <br /> being measured in groundwater beneath the site are polar compounds and refined petroleum <br /> hydrocarbons. Additionally, data 'gathered during recent semiannual monitoring and sampling_ <br /> events indicate the plume is stable. <br /> ARCADIS will prepare a No Further Action Report which will be submitted under separate <br /> rcover. <br /> L i <br /> C <br /> CI <br /> L <br /> L <br /> rg:\aproject\env\chevron\309075\6 deliverables\periodic monitoring\2012\tsa12\text\309075 1sa12 gmr fin 06212012.doc 17 <br /> Y� <br />