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._nm m gii ;:;e «.: s. IJ t I'+ i PRELIMINARY F{ DROCEOLOCFC ASSESSMENT WORK PLAN ""ti' Yoeernite Avenue,Msntaca,California Delta ProJect No.41)-88-481) Page 11 E west of the site, it is anticipated that the direction of ground water flow at the site is in a Westerly f to northwesterly direction. The direction of ground water flow will be defined following the installation of the ground water monitoring wells at the site(Section 4.1)and will be reported in the 1 Preliminary Hydrogeologic Assessment Report submitted at the conclusion of the investigation described in this work plan. I ' C PR PO EAS il. BORT AND M N[T R[NG WELL � a Because of the possible presen=ce of petroleum constituents on soils and ground water at the site, two is additional soil borings will be drilled to characterize the subsurface geology and to evaluate the Presence of petroleum constituents in the soils at the site. Both soil borings will be completed within the upper-most water-bearing zone as ground water monitoring wells. These wells together with the 1 existing monitoring well at the site will serve to establish the natural flow gradient, hydraulic characteristics of the water-bearing materials, and will provide information for determination of whether dissolved hydrocarbons and/or free product are present in ground water at the site. 4.1 Borings/Monitoring Wells 1' Previous work at the site and our experience at similar locations indicate that the area of the site most likely to have soils or ground water containing petroleum constituents would be adjacent or in close x proximity to the underground storage tanks(USTs). For this reason,two soil borings,each completed as a monitoring well will be located adjacent to or in close proximity to the tank excavation,(Figure 2). It is anticipated that well(MW-3)will serve as a down-gradient well,with monitoring wells MW- #s I and MW-2 either up- or across-gradient in relation to MW-3. s2 ;Zoll Sample Collection and Screeninji A California modified split-barrel sampler will be used to extract soil samples from the soil borings. Three six-inch-long brass tubes will be inserted into the California sampler to retain the soil sample. Upon retrieval,one brass tube will be capped, packaged, and preserved according to accepted EPA procedures for Possible chemical analysis. One sample from each sampler will be extracted and �. placed in a sealed jar until completion of drilling activities. ----------------------- --- amp es-p aced-nn jars will be brought to room temperature and the head space of each Jar wi!I be .� screened for total organic vapors utilizing a portable photoionization detector. Appendix C,Section 1.3, describes the detailed soil-screening procedures. Based on this screening information, soil samples will be selected for chemical analyses to determine the vertical extent of the presence of petroleum constituents in the soil,