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Mr.Nuel Henderson,P.G.,SJCEHD September 21,2005 ARCO Station 6100,Tracy,California Project No.U6100-15-1 Additional Site Assessment Work Plan Page 8 Task 1: Pre-field Activities Following approval of the work plan by SJCEHD personnel, the following activities will be completed: • Secure an access agreement from the off-site property owner (The Robert and Cleo Vieira Family Trust) enabling completion of soil boring (B-44 through B- 47) and monitoring well installation activities, • Obtain an encroachment permit from San Joaquin County Public Works Department (SJCPWD) and CalTrans (boring B-48), • Secure soil boring and well installation permits from SJCEHD, • Retain and schedule a licensed C-57 drilling contactor, • Update the health and safety plan for the site, • Mark boring locations and contact Underground Service Alert to locate underground utilities in the vicinity of the work site, and • Notify CRWQCB, SJCEHD, SJCPWD, CalTrans, ARCO, and the property owner of the scheduled field activities. Task 2: Field Activities Soil Borings and Sample Collection The initial five feet of each boring will be advanced with an air/water knife and vacuum extraction equipment to reduce the possibility of damaging any underground utilities that may be present near the work areas. A mud-rotary drilling rig will be used to advance four exploratory soil borings (B-44 through B-47) to a depth of approximately 120 feet bgs and one exploratory boring (B-48) to approximately 135 feet bgs. Non-petroleum based drilling mud will be used during drilling. The drilling mud will have a density greater than the density of water to prevent water from flowing into the borehole and to keep the hole from collapsing. This method of drilling has been selected primarily because of its capability of being able to drill deep (>100 feet) through difficult material, the ability to collect continuous cores for lithologic logging, and successful results from previously advanced borings B-33 through B-42. Because the use of drilling mud typically causes the sidewalls of the borehole to become semi-impermeable and often impedes the flow of groundwater, these borings will not be converted to groundwater monitoring wells. Borings B-44 through B-48 will be backfilled to surface grade with neat cement. K9Bp-Arco for URS\6100\Work Pims\a=6100-workplan 09-2005.doc