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• • Advanced four (4) off-site soil borings (B-39 to B-42) to depths ranging from approximately 135 to 151 feet bgs using the mud rotary drilling method Soil cores were continuously recovered from the borings • Collected soil samples from the soil cores recovered from borings B-39 through B-42 for analytical purposes • Drilled and installed wells MW-10, MW-12, and MW-15 to depths ranging from approximately 105 to 109 feet bgs using 10-inch diameter hollow stem augers • Drilled and installed wells MW-13 and MW-14 to depths of approximately 68 and 70 feet bgs, respectively, using 10-inch diameter hollow stern augers Wells MW-13 and MW-14 were installed immediately adjacent to wells MW-10 and MW-15, respectively • Overdrilled well VW-15 to 90 feet bgs using 10-inch diameter hollow stem augers Following overdrilling, the borehole was grouted to surface grade with neat cement • Drilled and installed well MW-11 to approximately 109 feet bgs During drilling immediately adjacent to the well (at boring B-43), well MW-11 became damaged Well MW-11 was subsequently overdrilled and backfilled with neat cement Boring B-43 was also backfilled with neat cement Prior to implementation of field activities, drilling permits were obtained from San Joaquin County PHS/EHD and encroachment permits were obtained from the County of San Joaquin Department of Public Works (CSJDPW) and California Department of Transportation (Caltrans) Drilling locations were marked 48 hours prior to fieldwork Underground Service Alert, San Joaquin County PHS/EHD, CSJPWD, Caltrans, and ARCO were notified 48 hours prior to beginning work activities Standard field practices and procedures for all fieldwork are described in Appendix B All work was conducted under the direct supervision of a State of California Registered Geologist Copies of the drilling permits and encroachment permits are provided in Appendix C FIELD ACTIVITIES Exploratory Sail Borings A Stratus geologist was on-site to oversee Gregg Drilling and Testing, Inc of Martinez, California (C-57 #485165), complete borings B-39 through B-42 between February 17, 2004, and April 22, 2004 The initial 5 feet of each borehole was advanced with a hand auger to minimize the possibility of damaging underground utilities Borings B-39 through B-42 were subsequently advanced using the mud rotary drilling method Each boring was advanced using a 2 5-inch diameter core barrel advanced ahead of a 5-inch diameter drill bit The drilling mud consisted of water and powdered bentonite, circulated into and out of the borehole from a steel container situated immediately adjacent to the borehole On reaching the total depth, the drilling mud was removed from the subsurface and the borehole was backfilled to surface grade with neat cement Soil recovered from the core barrel was placed into core boxes and labeled according to borehole • ID and sampling interval Soils were classified on-site using the Unified Soil Classification System Soil samples were collected by hand driving a 1 25-inch by 6-inch diameter brass tube P\BI�Ano for URS161001ReWns\s 6100 ma ssm nt senLupdate dao Page 4 5 MA 7'115