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------------ February 16, 1992 Working To Restore Nature BP Oil Facility No. 11195,Lathrop,California. 2.3 Monitoring Well Development pnd Sampling Well development and sampling were conducted according to the applicable guidelines of the governing regulatory agencies. A description of the general field procedures for well development and sampling is presented in Appendix B. r=� Monitoring wells MW-1 through MW-5 were developed on December 18, 1992. Prior to development,each well was examined for the presence or absence of floating product. The wells were developed until the water was relatively free of sand and silt, using either a 2-inch-diameter E plastic bailer or a submersible pump. F>=' On December 21, 1992 each well was purged of 3 to 4 casing volumes using a submersible pump, disposable bailer, and sampled. During purging and prior to sample collection, pH, specific _- conductivity, and temperature were measured and allowed to stabilize, indicating that formation `' water had entered the well. 2.4 Groundwater Level Monitoring and Well Surveyin The top of well casings in monitoring wells MW-1 through MW-5 were surveyed, and referenced ry to a San Joaquin Datum, and with an elevation above mean sea level relative to the National Geodetic Survey. The depth to groundwater in monitor wells MW-1 through MW-5 were measured from the top of the well casing to the nearest 0.01 foot, using an electronic sounder on December 21, 1992. The survey data and relative groundwater elevation measurements are rr ; presented in Table 1, while the potentiometric surface of the groundwater beneath the site is shown in Plate 3. 3.0 ANALYTICAL METHODS �r Soil and groundwater samples were analyzed at PACE Laboratories, Inc. of Novato, California, a California-certified analytical laboratory. Analyses were performed using standard test methods of the U.S. Environmental Protection Agency (EPA) and the California Department of Health Services (DHS). Selected soil samples from borings B-1 through B-4 were analyzed for purgeable fuel hydrocarbons as gasoline, equivalent to total petroleum hydrocarbons as gasoline (TPHg), using EPA Methods 5030/8015 (modified) and benzene, toluene, ethylbenzene, and total xylenes (BTEX) using EPA Methods 5030/8020 (modified). v_s� Y g • Soil samples from boring B-5 were also analyzed for extractable fuels as diesel,equivalent to = total petroleum hydrocarbons as diesel (TPHd),using EPA Methods 3550/8015, total oil and grease (TOG) using Standard Method 5520, and halogenated volatile compounds (HVCs) using EPA Method 8010. 1 • Groundwater samples from monitoring wells MW-1 through MW-4 were analyzed for TPHg using EPA Methods 5030/8015 (modified) and BTEX using EPA Methods 5030/8020 (modified). 17052.01 3 'r's