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Work Ilan for Additional Site Assessment <br /> and Interim Remediation/Feasibility Testing <br /> ARCO Facility Na.5469 <br /> Stockton,California <br /> Page 7 <br /> Following the CPT work, soil and groundwater samples will be collected from two <br /> separate borings located approximately 2 feet from the initial CPT boring. A minimum <br /> of three soil and three groundwater samples will be collected from each of the direct push <br /> borings. Additional soil samples may be collected for testing selected soil -parameters. <br /> HydropunchTm sampling equipment will be used to collect the groundwater samples at <br /> desired depth intervals, based on the continuous log generated from the CPT. The <br /> HydropunchTm sampler will be pushed to the bottom of the sampling interval using <br /> 2-inch diameter steel rods. The steel rods are subsequently retracted approximately four <br /> feet, exposing the screen, to allow for the collection of depth discreet groundwater <br /> samples. Hollow rods (approximately 1.7 inches in diameter), with a modified tip <br /> (similar to a California split spoon sampler) will be pushed into the subsurface to collect <br /> soil samples. Upon completion of sampling, the direct-push boring will be pressure <br /> grouted from the bottom of the borehole up to surface grade. <br /> Lateral Assessment--Monitoring Well Installation <br /> To characterize the lateral extent of petroleum hydrocarbon impact to soil and groundwater, <br /> three exploratory soil borings (MW-11 through MW-13) will be advanced using a drilling <br /> rig equipped with 8-inch diameter hollow stem augers. The borings will subsequently be <br /> converted to 2-inch diameter groundwater monitoring wells. The actual locations of the <br /> borings will be based on accessibility and the location of underground utilities. <br /> Wells MW-11 and MW-13 will be installed to a depth of approximately 15 feet below first <br /> encountered groundwater, which is expected to occur at approximately 38 feet bgs based on <br /> recent groundwater monitoring at the ARCO facility. Well MW-12 will be installed to a <br /> depth of approximately 75 feet bgs. Wells MW-11 and MW-13 will be screened from <br /> approximately 33 to 53 feet bgs, and well NnV-12 will be screened from approximately 64 <br /> to 75 feet bgs. The well screen will consist of 0.02-inch diameter, factory slotted PVC <br /> casing. A filter pack of LonestarT"4 #3 sand will be placed in the annular space around the <br /> well screen from the bottom of the screen to approximately 2 feet above the top of the <br /> screen. Two feet of bentonite will be placed on top of the filter pack and hydrated with <br /> clean water to provide a sanitary seal for the well. The borehole will be backfilled with neat <br /> cement up to surface grade. A traffic rated vault box will be placed over the well and a <br /> water-tight locking cap will be placed on top of the well. This well completion is similar to <br /> the existing groundwater monitoring wells. The actual well construction may be modified <br /> in the field based on conditions encountered at the time of the investigation. <br /> The initial 5 feet of each boring will be advanced with a hand auger and/or posthole digger <br /> to reduce the possibility of damaging underground utilities. Soil samples will be collected <br /> at 5-foot intervals during the advancement of the deep monitoring well and sparge well <br /> PAIARM54691Work Plan15469 wrkpin 03.2002.doc <br />