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• Corporation <br /> A Member of The 1'f G oup <br /> Mr. Marcus Pierce 3 December 5, 2000 <br /> the B-aquifer does not contain TCE at this location, it is not necessary to prevent TCE from <br /> migrating from the B-aquifer to the A-aquifer by perforating the well and sealing off the B-zone <br /> from the A-zone. Even if TCE were present in the B-aquifer at this location and not present in <br /> the A-aquifer, this well could not act as a significant conduit to TCE migration. This is because <br /> of the extremely low average vertical gradient at this location and the very small cross-sectional <br /> area of the annulus surrounding the well. The resultant TCE mass flux that would occur under <br /> these circumstances, if it occurred at all, would be extremely low. <br /> Two additional potential concerns relate to the possibility of vertical migration of methyl tertiary <br /> butyl ether(MtBE) and nitrates from the B-aquifer to the A-aquifer at the 233 Parallel Avenue <br /> location. For MtBE, the data indicate that there have been no detections in any of the domestic <br /> wells on Parallel Avenue. It is likely that the remediation occurring at the Equilon (Shell) <br /> property is effective at capturing the plume without additional migration, so it is highly unlikely <br /> that the 233 Parallel Avenue well could ever act as a conduit for MtBE. For nitrates, there are no <br /> nearby data to demonstrate that migration of nitrates from the B-aquifer to the A-aquifer at the <br /> 233 Parallel Avenue well would not occur. However,because of the significant <br /> interconnectivity of the B- and A-aquifers at other locations, as well as the extremely low <br /> vertical gradient at this location, the 233 Parallel Avenue well is not likely to be a significant <br /> conduit for nitrate migration. <br /> Based on these facts, IT recommends that the 233 Parallel Avenue well be decommissioned by <br /> pressure grouting without perforation. The subcontractor work for pressure grouting will be <br /> performed under the supervision of an IT geologist. A San Joaquin County Environmental <br /> Health Specialist will be on-site to inspect the work. <br /> If you agree with this justification, Nestle requests that you provide your written approval to <br /> implement this method of decommissioning to San Joaquin County Public Health Services, in <br /> variance to their standard requirements for well abandonment. If you have any questions or <br /> comments on this letter,please call me at(925)288-2101. <br /> Sincerely, <br /> IT Corporation <br /> Robert A. Ellgas, Ph.D. <br /> Project Manager <br /> C: Binayak Acharya,Nestle USA, Inc. <br /> Dottie Lofstrom, SJC-PHS <br /> Attachments: Table 1: Generalized Hydrostratigraphy Near 233 Parallel Avenue <br /> Table 2: Vertical Gradients between B- and A-Aquifer Zones <br /> Cross Section A-A' <br /> Isoconcentration Contour Map <br /> Boring Logs, Wells M-513 and M-5A <br />