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Extended Site Characterization Report• 7500 West Eleventh Street, Tracy, CA. Page 13 failure to detect low concentrations of analytes of concern should they be present. As is documented in Table 4, this proved to be the case, with methyl-tertiary butyl ether (MTBE) detected in a sample of groundwater recovered from Well MW-10, while there were no detectable concentrations of any analytes of concern in a sample recovered from Well MW-9, located, as the SJCEHD directed, 135 ft. to the south of Well MW-10. �< The boring log and well construction information for Well MW-10 is included in Appendix A. :-: In compliance with SJC's work plan for the extended site characterization program, a small-diameter boring (PP-15) was drilled on the west side of Chrisman Road, some 465 :., ft. to the north of West Eleventh Street. Drilled to 16 ft. BGS, it penetrated beneath the groundwater table to allow assessment of groundwater quality in the area and to guide � ln' q Y selection of the location of a new groundwater-quality monitoring well. A grab sample of groundwater was recovered from the boring when it reached its total depth and the sample was immediately shipped for analysis with a requested 24-hour turn-around time. That analysis found 1,100 µg/L of diesel-range fuel hydrocarbon components, together with gasoline-range hydrocarbons and MTBE (See Table 4) in the groundwater sample. =$ The boring log is included in Appendix A. Given the concentration of diesel detected in the sample of groundwater recovered from boring PP-15, the location shown on Figure 2 was selected for Monitoring Well MW-11, which location was judged to be close to or slightly beyond the northern extremity of the plume of groundwater affected by the release of fuel hydrocarbons that occurred on the s 7500 West Eleventh Street site. As is discussed in Section 7.3.2.2, the selected location of Well MW-11 was, in fact, close to the end of the plume. Because the concentration of diesel detected in the sample of groundwater recovered from boring PP-15 was relatively high (1,100 �Lg/L), SJC's engineer and the SJCEHD field representative concluded that a second small-diameter boring should be drilled at a location intermediate between the locations of MW-10 and PP-I5. Based on information about the hydrogeology and geochemistry of the site that had been gathered and interpreted by that time, it was concluded that the optimal location for the additional .—A boring would be on the west side of Chrisman Road. However, although the location of all underground utilities in the area were known and SJC's California-licensed engineer j and the driller concurred that it would be perfectly safe to drill on that side of the road, SJCEHD's representative was unable to obtain the authorization from SJCEHD's Stockton office to proceed with the drilling at that location. Under those circumstances, i SJC's engineer directed that the boring, designated as PP-16, be drilled on the less than optimal eastern side of Chrisman Road at a Iocation the concerned utility agencies had marked a circular area, which was also free of buried utilities. That location is shown on -`f Figure 2 and the log of the boring is included in Appendix A. L. 1 sic