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Evaluation ofNatural Attenuation_ 7500 West Eleventh Street, Tracy, CA. .Page 54 Analyte Method of Analysis Total Petroleum Hydrocarbons EPA Method 8015M (quantified as Diesel) with pre-treatment by EPA Method 3630. Total Petroleum Hydrocarbons EPA Method 8260B (quantified as Gasoline) Benzene EPA Method 8260B Toluene EPA Method 8260B Ethyl benzene EPA Method 8260B Total Xylene Isomers EPA Method 8260B Tertiary-butyl alcohol EPA Method 8260B Methyl-tertiary butyl ether EPA Method 8260B Di-isopropyl ether EPA Method 8260B Ethyl tertiary-butyl ether EPA Method 8260B Tertiary-amyl methyl ether EPA Method 8260B 10.3 Monitoring of Potable Water Quality r` No concentrations of contaminants of concern have been detected in samples recovered from any of the six wells included in the potable water supply well sampling program j that began in March 2004. The possibility that components of fuel hydrocarbons released at the Navarra site might affect groundwater in three of the six potable water supply wells is extremely remote. The wells at 7601 West Eleventh Street (Gowan Construction) and at Carmelo Business Park extract groundwater from depths that are at least 470 ft. BGS, well below the Corcoran Clay aquitard (see Section 1.4 for a discussion of the regional stratigraphy and - hydrogeology). They are hydraulically isolated from the shallow aquifer at the Navarra Site that is affected by components of fuel hydrocarbons because the bottom-most contaminant is located at a depth of no more than 35 ft. BGS. The potable water supply well at Anthony's Auto Body at 24195 South Chrisman Road is located well up the groundwater gradient from the location on the 7500 West 11th Street property where hydrocarbon fuels were released into the subsurface. Given that hydrogeologic situation, I } I contamination of that well due to conditions on the Navarra site area is also remote. sic e k