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s y, E <br /> Results of Initial Invrstigation and Work P14n December 18, 1990 <br /> ®rte ARCO Service Station No. 548, Stockton, California AGS 30004-2 <br /> Boringfiling, <br /> Applied GeoSystems was at the site on October 1 and 2, 1990, to observe Wayne Drilling <br /> Company of Lincoln, California, drill live 8-inch diameter soil borings (B-I. through B-5). <br /> The locations of the borings were selected using ARCO's Preliminary Tank Replacement <br /> Assessrrnen!guidelines. Sorin JL' w <br /> g _ as drilled approximately 2-1/2 feet from the northern <br /> edge of the tank area near the fill ends of the four product tanks;borings B-2 and 13-3 were <br /> drilled along the western and eastern edges of the tank area,respectively. Borings B-4 and <br /> B-5 were drilled in the area proposed as the new tank cavity. The locations of the borings <br /> are shown on Plate P-2. <br /> Soil samples were collected during drifting at approximately 5-foot intervals and were <br /> ® classified according to the Unified Soil 'classification ,'Y.,.-tem (Plate P=4). Descriptions of <br /> P. <br /> materials encountered are presented in the Logs of Borings(Plates P-5 through P-12). The <br /> materials consisted predominately of silt and sandy silt with fine- to medium-grained sand. <br /> i The geologist used a photoionization detector (PID) to evaluate the soil samples for <br /> hydrocarbon vapors. PID readings are also included on the Logs of Borings. The geologist <br /> " noted PID readings from the samples from borings B-I.through 13-3. Our staff geologist did <br /> f` not detect subjective evidence of gasoline hydrocarbons such as soil discoloration or obvious <br /> odor. The geologist initiated Chain;of Custody Records which accompanied the samples to <br /> the analytical laboratories. Copies of those documents are in Appendix B. <br /> Borings B=1 and B-3 were.terminated approximately 1 foot below the first encounter of <br /> ground water which was approximately 50 feet below grade_ Two consecutive soil'samples <br /> with PII)readings below 50 parts per million by volume(ppmv)were not obtained in these <br /> _� pp " d C�eoa�yslen�s <br />