Laserfiche WebLink
*4..i N.410� <br /> Second Semiannual MMI Groundwater Monitoring Report <br /> Former Texaco Service Station <br /> Chevron Site ID 309075 <br /> February 28, 2012 <br /> ,r 5.1.5 Site Conceptual Model Updates <br /> There are no site conceptual model (SCM) updates. Historical analytical soil data, groundwater <br /> gradient and flow direction data, and soil boring and well construction details are presented as <br /> Tables 2, 3 and 4, respectively. Information regarding the collection of soil samples associated <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 /> `-1 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 second semiannual event of 2011 are generally consistent with the concentration <br /> ranges detected during recent monitoring and sampling events. <br /> With the exception of MW-1 and the groundwater sample collected on December 1, 2010 from <br /> MW-6D, TPH-GRO, BTEX, MTBE, TBA, DIPE, ETRE, 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 180 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 /> `r events indicate the plume is stable. <br /> d <br /> ARCADIS recommends discontinuing monitoring and sampling the wells associated with this <br /> \ site. Pursuant to State Water Resources Control Board Resolution No <br /> 2009-0081 and State Water Resources Control Board Resolution No 2009-042, this site should <br /> be considered for low-risk case closure. ARCADIS will prepare a No Further Action Report <br /> which will be submitted under separate cover. <br /> V <br /> V <br /> V <br /> g:\aproject\env\chevron\309075\6 deliverables\periodic monitoring\2011\2sa11\temppdf\text\309075 2sa11 gmr fin 02282012.doc 7 <br /> w <br />