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' 3 SOIL AND GROUND-WATER CHARACTERIZATION <br /> Given the ground-water monitoring data reviewed by EMCON Associates, <br /> it appears that the extent of petroleum hydrocarbon impact has been <br /> defined crossgradient by MW-11 and laterally to the north by MW-10. To <br /> evaluate the lateral extent to the south, EMCON Associates proposed <br />' installing one additional well at the location shown on Drawing 1 of the work <br /> plan (see Appendix A). This well has been designated MW-12 and is shown <br /> on Drawing 1 of this document. <br />' Well MW-13 was drilled and installed to determine whether residual <br /> petroleum hydrocarbon concentrations remained in soil beneath the former <br /> excavation, and to determine concentrations in ground water beneath the <br /> former excavation. The location of MW-13 was chosen based on the <br /> highest petroleum hydrocarbon concentrations detected in soil samples from <br />' the bottom of the excavation. In addition, EMCON Associates drilled boring <br /> 892-1. Boring B92-1 was drilled to determine whether residual petroleum <br /> hydrocarbon concentrations remained in soil beneath the former pump <br /> island (C-12) location, where petroleum hydrocarbon concentrations had <br /> been detected in a soil sample collected from the sidewall of the excavation. <br /> 1 �� <br /> 3.1 Exploratory Sol] Borings <br /> Before conducting field activities, EMCON Associates obtained a drilling and <br /> well installation permit from the San Joaquin County Department of Public <br /> Health Services, Environmental Health Division. EMCON Associates also <br />' contracted with an underground utility locating service to provide guidance <br /> in determining unobstructed exploratory boring locations. <br /> Three exploratory soil borings were drilled at the site. The three exploratory <br />' soil boring locations are shown on Drawing 1 . Boring MW-12 was drilled <br /> east of the lube pit to assess the southern extent of ground-water impact <br /> in the vicinity of the former tank complex. Boring MW-13 was drilled through <br /> the center of the former tank complex excavation to assess the impact to <br /> soil and ground water directly beneath this area. Each of these two borings <br /> was converted to a ground-water monitoring well. In addition, to assess the <br /> impact to soil at the location of the former pump island, EMCON Associates <br /> drilled exploratory soil boring B92-1 . Exploratory boring procedures are <br /> presented in Appendix B. <br /> i <br /> pjOV9010f900020.1 ag 3 - 1 Rev. 0 December 15, 1992 <br />