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' GENERAL DYNAMICS Additional Investigation — A 3; SWMU21 Workplan, Revised NovemW003 3.4 Groundwater Impact of TPH-d and TPH-O&G ' Three monitoring wells (MW) are proposed for construction to assess the petroleum hydrocarbon in groundwater measured in monitoring well S-33 in March of 2003. ' Monitoring well S-36 will be constructed northwest of SWMU21, and monitoring wells S-37 and S-38 will be located down the depositional slope and down gradient of SWMU21. All monitoring wells will be drilled to an estimated depth of 50 - 60' bgs, after the boring, if possible, penetrates 10-ft below the top of the water-bearing zone. A two- inch diameter Schedule 40 polyvinyl chloride (PVC) plastic, with sufficient screen (0.010-inch slot) to span the groundwater-bearing zone will be installed in the boring. A ' filter pack (sand) will be installed from the total depth of the boring to 2-ft above the top of the well screen. 2.5 feet of hydrated bentonite pellets will be installed above the filter pack. The well will then be grouted using a concrete slurry to local grade level. Following the grouting of the well a metal Christie box, will be installed at the well head. A lockable water tight cap will be secured to the top of the 2" PVC well casing. The installation of the MW will be in accord with applicable regulatory requirements, i.e. ' permits, inspections, etc. The minimum of 24 hours will elapse between MW installation and MW development. ' An oil/water interface probe will be used to determine the depth to water and the depth to the bottom of the well casing. Monitoring wells will be developed using a rod and surge block assembly. After initial pH, conductivity and temperature parameters are ' recorded, the surge block will be installed. The rod and block assembly will be forced through the water column and then raised. Typically a well will be surged 25 times then two volumes of water will be extracted from the well casing. The parameters will again ' be collected and the complete cycle repeated three additional times. Parameters will be collected and the well purged once again for two additional volumes of water. t A minimum of 24 hours will elapse between MW development and sample collection. If possible, five (5) casing volumes of groundwater will be extracted (purged) from the MW prior to the collection of groundwater samples for analysis to maximize the possibility of ' collecting a water sample representative of the formation water. Should recharge of the well be slow, groundwater samples will be collected after sufficient groundwater accumulates in the well casing to provide the requisite volume for the requisite analysis. Groundwater samples will be collected using a Watera positive displacement pump attached to new, dedicated Y2" high density polyethylene tubing inserted into the well ' casing for purging and sample collection. Each sample will be labeled and placed in a cooled ice chest for transportation to a laboratory certified by the DTSC for analysis of TPHd and SVOCs. A completed chain of custody documenting sampling data, and analysis to be performed will accompany the samples from the field to the analytical laboratory. ' The soil cuttings and equipment decontamination liquids generated during the drilling of the borings will be properly contained pending disposal of these materials by the client. CHOW ENGINEERING, INC. 4 1