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- POE � 2 MOR MIT yY� p'�µ3r• ., 4i s' }.�� sy� '`+_ a. - •'..„ N '��' ^�'er,'f_..rr a x-.., .. x a _:- M HYDROGEO,LOGTC ASSESSMENTWPRK PLAN Shell Service Station 820 west Charter Way Stockton,California Delta Project No.40-88-586 Pale e 4,,Q ,PROPOSED(1!2NITQRiNG WELLS This section describes the proposed assessment, including the depth and distribution of proposed monitoring wells. The methods used to drill and sample soils and ground water, the analytical procedures, quality assurance pian,and the site safety plan are contained in Appendix D. 4.1 Boring;Monitoring Well Locations Completion of soil borings in February 1989 confirmed the presence of hydrocarbon constituents in soils adjacent to the existing tanks and pump islands. In order to determine the distribution of these constituents in soils and ground water at the site,six soil borings are proposed(Figure 2). Each soil boring will be completed as a monitoring well. Four wells will be completed adjacent to the existing tank cluster. A well will be placed between the former and present waste oil tank locations, and another well will be placed to the west of the existing pump islands. !L2 Soil Sample Collection and Screening Soil samples will be recovered at 2.5 :o 5-foot-depth intervals using brass sample tubes within a California-modified split-barrel sampler. Appendix D, Section 1.1 describes the drilling and r- sampling techniques to be used. The brass tubes will be capped,packaged:and preserved according to accepted EPA procedures for possible chemical analysis. A sample collected adjacent to the brass tube will be sealed in a glass jar and held until completion of drilling activities. Soil samples will be classified and boring logs completed as described in Appendix D,Section 1.2. All soil samples collected in glass jars will be allowed to reach ambient surface temperature and screened for total organic vapors utilizing a AID. Appi ndix D, Section 1.3, describes the soil T screening procedure. based on this information, soil samples will be selected for chemical analysis to document the vertical extent of soil contamination in each boring. 4.3 Monitoring Well Installation. Devel22 ent, anUAmaling r The proposed monitoring wells, MW-1 through MW-6, will be constructed of 4-inch-diameter Schedule 40, flush-threaded, PVC pipe in accordance with typical construction details shown in Figure 3. The screenod interval of each monitoring well will extend approximately 10 fact below and t feet abu,.,e the water table. The actual screened intervals will be determined in the field by a Delta geologist or engineer. Design and selection of gravel pack and screen slot width will be done in accordance with methods outlined in Appendix D.Section 1.4.