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SITE CONCEPTUAL MODEL <br /> Prepared by Cambria Environmental Technology, Inc <br /> S 2375 West Grant Irne Road 97471967 <br /> - i <br /> Tracy,California San Joaquin County-Environmental Health Department i <br /> al i <br /> 1.1 Identify/Describe''Release Unknown: Methyl tertiary butyl ether(MTBE)was detected In groundwater <br /> Source and Volume(if known) samples collected from groundwater monitoring wells installed at this site <br /> during January 2003. MTBE has also been detected in soil beneath the fuel <br /> dispensers at the site. 7 <br /> 1.2 Discuss Steps Taken to Stop As there was.no specifically identified equipment failure, no directrepairs o <br /> Release action was taken. Product dispensers were removed and replaced i J <br /> November 2004. As.of January 2003,MTBE is no longer a component of the <br /> fuel sold at this site. <br /> s ] <br /> 2.1 Current Site Use/Status The site is currently a Shell-branded Service Station. <br /> 2.2 Soil Definition Status The vertical and lateral extent of TPHg and BTEX in soil is defined by non <br /> detect results in soil samples collected-from well borings MW-5 through MW <br /> 7, bodng.SB-1, and several soil samples collected beneath the dispensers a <br /> the site. The lateral extent of MTBE in shallow soil at the site has been <br /> defined by non-detect results in soil samples collected from well borings MW <br /> - <br /> 5 through'MW-7, and from boring SB-1. The vertical extent of MTBE in soil <br /> beneath the site is defined. Sol]tables and maps are included in Attachmen ! <br /> 1. I <br /> 1 <br /> 2.3 Separate-Phase Hydrocarbon Separate-phase hydrocarbons have never been detected beneath the site. j <br /> Definition Status. ' <br /> 2.4 Groundwater Definition.Status Groundwater analytical data suggests that the lateral and vertical extent o 1 <br /> (BTEX) TPHg and BTEX in groundwater beneath this site is delineated. TPHg an <br /> BTEX are,typically not detected in the wells at this site, and historically hav <br /> only sporadically been detected at low'levels. Groundwater analytical resul <br /> are included in Attachment 2. j <br /> 2.5 BTEX Plume Stability and As mentioned above,TPHg and BTEX are typically not detected In the wells !; <br /> Concentration Trends at this site. Accordingly,there is no TPHg or BTEX plume. j <br /> 2.6 Groundwater Definition Status The lateral extent of MTBE in shallow groundwater has not been defined <br /> (MTBE) north of the site. MTBE has been detected in downgradient wells MW-1,MW i <br /> 5, MW-6,and MW-7. However, Interstate 205 Is located immediately <br /> downgrad]ent of the site and further investigation is not feasible. MTBE has <br /> also been detected in well MW-4,located upgradient of the underground { <br /> storage tanks(USTs)and is likely indicative of an offsite source. The vertical <br /> extent of MTBE in groundwater has been defined by depth-discrete grab <br /> groundwater samples collected during the installation of a deep boring SB-1, <br /> downgradient of the USTs and dispensers at the site. No MTBE was <br /> detected in grab groundwater samples collected from 52,72,and 82 fbg. <br /> 1661 Page 1 of 3 Date Modified:3/21/2006 <br /> i <br />