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. - c,. memn Chevron 19- 16 January 10, 1996 Mr. Robert Matteoli California Regional Water Quality Control Board, Central Valley Region 3443 Routier Road, Suite A Sacramento, CA 95827-3098 RE: Work Plan for Additional Groundwater Assessment Corral Hollow and Grant Line Roads Site, Tracy California Dear Mr. Matteoli: Please find enclosed a copy of the proposed workplan from our consultant, Geomatrix, for additional vertical delineation of groundwater at Corral Hallow. This workplan was prepared in response to a concern mentioned by the RWQCB at a meeting with Chevron Pipe Line on May 2, 1995. At that meeting you expressed concern that additional vertical delineation of groundwater was necessary to determine possible impact to the deeper aquifer from petroleum hydrocarbons as a result of the Chevron Pipe Line release in October, 1987. We are proposing to sample the deep aquifer with a HydropunchTM' sampler at depth of 50 feet. The boring will be drilled outside the dissolved hydrocarbon plume as defined in the most recent groundwater sampling event. This occurs in the general location of the formerly abandoned monitoring well, MW-2. Upon retrieval of the deep groundwater sample, the borehole will be grouted to a depth of 25 feet and a shallow monitoring well completed. This well will replace MW-2 and provide additional groundwater data to determine if transport of dissolved hydrocarbons occurs in an easterly direction. The deep boring will be drilled to a depth not to exceed 50 feet and may be terminated at a shallower depth if a significant clay layer is penetrated. If the HydropunchTM' groundwater sample cannot be collected, a temporary well will be installed to collect the groundwater sample. We would like to perform this work in conjunction with work at other sites scheduled in January by Chevron Pipe Line in the Tracy area. Therefore, your prompt concurrence on this issue would be greatly appreciated. If you have any further questions regarding this site please contact me at (510) 842- 6930 or Karen Synowiec at Chevron Research &Technology Company (510) 242-5687.