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levinefficke-Recon <br /> ENGINEERS,NYOROGEOLOGISTS a MPLIEO SCIEMISTS <br /> Drilling Sequence <br /> The proposed soil boring would be drilled using a mud-rotary drilling method down to the base of <br /> the B-zone aquifer. A small diameter pilot boring would be first drilled and logged to the top of the <br /> A/B aquitard. This boring would then be overreamed to a diameter of 20 inches and a 12-inch- <br /> diameter conductor casing would be installed to the top of the A/B aquitard and grouted in place. <br /> Drilling mud generated during the A-zone drilling would be flushed out at this time and <br /> transported off site for disposal. Once the grout has set (a minimum of 12 hours), a small diameter <br /> boring would be advanced through the A/B aquitard to the top of each of the coarser-grained units <br /> identified on the existing MW-21 geophysical logs so that PIPP samples could be collected from <br /> each permeable interval. The boring would ultimately be advanced to the top of the B/C aquitard. <br /> The boring would then be geophysically logged. <br /> Based on the results of the lithologic and geophysical logging, and the PIPP sample analytical <br /> results, a final well configuration would be selected. At a minimum, one well casing would be <br /> installed to screen the lowest sand interval in the B zone. The decision to screen any or all of the <br /> overlaying sand intervals would be based primarily on the pattern of detected Hazardous <br /> Substances in groundwater from each of the discrete sands. For example, if detected concentrations <br /> vary substantially between intervals, a discretely screened well casing would be completed in each <br /> sand interval. <br /> A meet-and-confer would take place between LFR and Farr Associates to discuss the boring and <br /> laboratory data results and the subsequent recommendations for well construction. It is anticipated <br /> that selection of the final well completion intervals would be made within 24 hours of the end of <br /> drilling for the pilot hole. <br /> General Procedures <br /> The proposed MW-21 evaluation using the soil boring/PIPP approach would follow the procedures <br /> described in the Field Sampling Plan (FSP), Appendix B of the "Work Plan For Environmental <br /> Investigation, Lincoln Center, Stockton, California," dated September 23, 1996 ("the RI/FS Work <br /> Plan") and Quality Assurance Procedures Plan (QAPP), Appendix C of the RDFS Work Plan. <br /> Lithologic samples would be collected for geologic logging using a 5-foot core barrel. Selected soil <br /> samples would be collected from the vadose (upper A zone) and the A/B aquitard for physical <br /> analysis. Selected vadose zone soil samples would also be analyzed for VOCs on an accelerated <br /> turnaround schedule using EPA Method 8260A. At each anticipated coarser-grained sediment <br /> interval within the B zone, as defined on existing geophysical logs for MW-21, a PIPP sampler <br /> would be driven ahead of the drill bit so that an undisturbed groundwater sample could be <br /> collected. PIPP groundwater samples would be analyzed for VOCs on an accelerated turnaround <br /> time (12 hour) using EPA Method 8260A. <br /> Specific procedures for drilling the boring, installing the A-zone conductor casing, collecting PIPP <br /> groundwater samples, and lithologic logging are presented in Sections 2.3, 2.4, and 2.5 of the <br /> FSP. Laboratory analytical procedures for soil and groundwater samples are described in the <br /> LCM W2I-3.LTR:SRL 3 <br />