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1 Extended Site Characterization Report: 7500 West Eleventh Street, Tracy, CA. Page 11 <br /> To achieve those objectives, SJC drilled two exploratory borings (PP-15 and PP-16) and <br /> installed eight additional groundwater-quality monitoring wells (MW-3A, MW-3B, MW- <br /> - S through MW-11, MW-12 and MW-12A at the locations shown on Figure 2. <br /> As originally proposed by SJC at the time that the work plan for the first phase of site <br /> r characterization at the 7500 West Eleventh Street site was prepared, when appropriate, <br /> .1 the Califomia-licensed geotechnical engineer in responsible charge of the project would <br /> use visual and olfactory indicators of the presence or absence of hydrocarbons in soil <br /> cores and the details of the stratigraphy revealed in the borings to select the final <br /> locations for the push probe and well borings, the depths at which soil samples will be <br /> recovered, the total depth of the borings and the screened intervals and other construction <br /> details of the wells. 112 making these field decisions, the engineer intended to apply the <br /> principals of the observational method (Peck 1969), a founding principal of geotechnical <br /> engineering practice that was belatedly recognized by the United States Environmental <br /> Protection Agency (USEPA) as an essential element of cost-effective environmental site <br /> k==� characterization programs (United States Environmental Protection Agency 1997), but is, <br /> unfortunately, still unrecognized by many local environmental regulatory agencies. <br /> l Although SJC's plans provided for application of the best engineering practice, the <br /> funding restrictions imposed by the USTCF and their refusal to approve any project <br /> contingency expenditures (California Underground Storage Tank Cleanup Fund 2002, <br /> i 2000a and 2000b) greatly limited the engineer's options to modify the scope of the site <br /> characterization program in response to the subsurface conditions revealed as the work <br /> progressed. Despite these limitations, the engineer used the available data and his <br /> ` =< professional experience -to make modest changes in the locations of some the <br /> groundwater-quality monitoring wells installed during the extended site characterization <br /> k=: <br /> program. An additional exploratory boring (PP-16) was also drilled after a field <br /> [= conference between the engineer and Ms Rebecca Setliff, the SJCEHD representative, <br /> who agreed, based on the data from the boring and wells drilled earlier, that it was <br /> necessary to gain adequate understanding of the lateral extent of the plume of affected <br /> groundwater in the area along Chrisman Road to the north of West Eleventh Street. <br /> =_ Following are discussions on the rationale for selecting the locations of the groundwater- <br /> s quality monitoring wells installed during the fieldwork for the extended site <br /> characterization. <br /> =' 5.3.1 Vertical Extent - Affected Groundwater in Pump Island Area <br /> Two new monitoring wells, designated Well MW-3A and Well MW-3B, were located in <br /> close proximity to existing Monitoring Well MW-3. (See Figure 2 for locations.) These <br /> wells were designed to explore the vertical extent to which groundwater was affected by <br /> the releases of hydrocarbon fuels that occurred near the former pump islands on the <br /> property. <br /> r'. <br /> Well MW-3A has a total depth of 35.5 ft. and its screened interval is between 30 and 35 <br /> - ft. BGS. Well MW-3B has a total depth of 50.5 ft. and its screened interval is between 45 <br /> =i <br /> SJC <br />