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�Nwe %MW Work Plan for Soil Excavation/Additional Assessment 3 Barbara Drake, 26485 North Thornton Rd.,Thornton,CA October 6, 1994 TASK a: SOIL AND GROUNDWATER SAMPLING Upon completion of excavation, Groundwater Technology will supervise the coring of five soil borings at the approximate locations shown on Figure 2 using a hydraulically driven (Enviro-Care TM) soil coring device. The position of the borings may be adjusted once the groundwater gradient is determined. The borings will be 2.5 Inches in diameter and cored to a depth of approximately 13-16 feet below ground surface (BGS), approximately 2-5 feet below the water table to accommodate temporary groundwater monitoring well installation. Soil samples will be collected continuously from each soil boring using a sample barrel lined with 1.75-inch diameter by 6-inch long stainless steel sampling tubes. The sample barrel is retrieved from the outer drive casing every three feet. Sampling equipment will be cleaned between each sampling interval. The 5 and 10 feet BGS sample tube from each continuously cored section will be sealed and placed on Ice in an insulated container pending delivery to GTEL Environmental Laboratories in Concord, California. Soil retained in the other tubes will be extruded and visually examined for evidence of hydrocarbon impact and lithologic description. Soil will be screened for hydrocarbon vapors using a photo-ionization detector (PID). Upon completion of the borings to the desired depth (approximately 2-5 feet below the water table), the drive casing will be pulled up 2-5 feet from the bottom of the borehole to allow groundwater to flow into the boring and to allow construction of temporary groundwater monitoring wells. The temporary groundwater monitoring wells will be constructed of 1-inch diameter schedule 40 polyvinylchloride (PVC) well casing and 0.010-inch slot well screen. Well screen will be installed 1-2 feet above and 2-4 feet below the water table at each location. The wells will be sampled using a 3/4 inch teflon bailer. Samples will be decanted to the appropriate sampling containers and placed on ice in an insulated container pending delivery to GTEL Environmental Laboratories In Concord, California. Upon completion of sampling, each borehole will be backfilled with a mixture of Type II cement and bentonite. The grout will be tremied through a pipe positioned at the bottom of the borehole prior to withdrawal of the outer drive-casing. The extremely small volume (estimated at less than 2 cubic feet) of soil cuttings generated during the sampling process will be combined with soil from the excavation in the main stockpile. Water generated during cleaning of the coring and sampling equipment will be temporarily stored on site in a Department of Transportation-approved 55-gallon drum. S Sol T - - 5z o 0053SGA.WKP(MI5C-15) LU GROUNDWATER ��:TECHNOLOGY