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US Ms. Lori Duncan Page 3 of 5 San Joaquin County Environmental Health Department August 27, 2004 to approximately 10 feet below first encountered groundwater off site in the downgradient groundwater flow direction. The second deep boring will be advanced approximately 30 feet past the deepest well currently on site. Groundwater monitoring wells will be installed in both boreholes. Proposed boring locations are presented on Figure 2. This workplan includes discussion of permitting; drilling and sample collection; monitoring well construction; groundwater monitoring well development, sampling, and surveying; and report preparation. A site-specific health and safety plan (HASP) will be prepared and will be available on site during field activities. Permitting and Access Agreements SJCEHD requires that permits be obtained prior to the completion of soil borings and monitoring wells. URS will submit the appropriate permit application(s) with fees to the SJCEHD prior to conducting field activities. Drilling and Sample Collection Boring locations will be clearly marked, and Underground Service Alert (USA) will be notified a minimum of 48 hours prior to commencement of field activities. In addition, the first 5 feet bgs in each boring will be cleared with an air or water knife to a diameter of 8.25 inches. Two 8 .25-inch diameter soil borings will be drilled using a hollow-stem auger (HSA) equipped drill rig. One shallow boring will be advanced approximately 10 feet past first encountered groundwater, and the second deep boring will be advanced vertically to approximately 95 feet bgs for the purpose of constructing 2-inch-diameter groundwater monitoring wells. A review of past quarterly monitoring reports indicated the depth to groundwater ranges from approximately 28 to 50 feet bgs. Groundwater flow across the site is generally eastward, ranging from northeast to southeast, with hydraulic gradients ranging from 0.002 feet/foot to 0.03 feettfoot. Soil samples will be collected at 5-foot intervals in brass liners. A URS geologist will log the soils encountered during drilling according to the Unified Soil Classification System. Soil will be field screened for the presence of volatile organic vapors using a phots ionization detector (PID). Soil samples selected for laboratory analysis will be preserved by capping both ends of the brass tubes with Teflon® tape and plastic end caps, placed in a cooler on ice, and transported to a California- certified laboratory under chain-of-custody for analysis of gasoline range organics (GRO) by EPA Method 8015B or 8260B (preparation by EPA Method 5030), benzene, ethylbenzene, toluene, xylene, (BTEX), MtBE, TBA, di-isopropyl ether (DIPE), ethyl tert-butyl ether (ETBE), tert-amyl methyl ether (TAME), 1 ,2-dichloroethane ( 1 ,2-DCA), and 1 ,2 dibromomethane (EDB), by EPA Method 8260B (preparation by EPA Method 5030). Soil sampling and laboratory procedures are described in the Quality Assurance Project Plan prepared by URS dated February 2003. Field duplicates will not be collected as part of this investigation. K:\Wprocess\J5 BP ARCO\00548\2004 well inslaa\WP 04.doc