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AW <br /> March 18, 1993 Working To Restore Nature <br /> • ARCO Station No 6100, Tracy, California <br /> excavated tank cavity contained concentrationFour <br /> of <br /> n <br /> totalto tanks weren <br /> #roleum hsailed n the new tank <br /> ocarbons as gasoline <br /> (TPHg) up to 7,400 parts per million (ppm) F <br /> cavity <br /> In October and November 1991, and June 1992 RESNA observed drilling of 20 soil borings <br /> (B-6 through B-25) and construction of 15 vapor-extractions wells The boring and vapor- <br /> extraction well locations are shown on Plate 2. Residual gasoline hydrocarbons were <br /> detected in soil beneath the dispenser islands, between the underground gasoline storage <br /> tanks and the dispenser islands, along the north and west side of the former gasoline tank <br /> cavity, and near the southeast corner of the site (RESNA, January 31, 1992, Report 30041-2, <br /> and November 12, 1992, Report No 30041-3) The lateral extent of residual gasoline <br /> hydrocarbons in soil was delineated at the site except for the area near the southeast corner <br /> of the site Although trace to low concentrations of gasoline hydrocarbons were detected <br /> below 70 feet bgs, the vertical extent of residual gasoline hydrocarbons in soil appeared to <br /> 1 be limited to a depth between 50 and 70 bp n location, and from <br /> surface grade to approximately 70 fee bgeneath the dispenser <br /> ds <br /> RESNA performed a vapor-extraction test at the site on October 14, 1991, using vapor- <br /> extraction wells VW-1, VW-2, VW-3, and VW-4 (RESNA, as aary 31, <br /> 19 mea sp or remove <br /> 2). The results of the test indicated that <br /> vapor <br /> extraction <br /> residual gasoline hydrocarbons from the soil <br /> CURRENT WORK <br /> Soil Borings and Va or-Extraction Well Ins#allation <br /> A geologist from RESNA was at the site December 14 through 18, and 22 and 23, 1992, to <br /> observe Jcon Exploration (Joon) of Yuba City, California, Kvilhaug Well Drilling and Pump <br /> Co , Inc (Kvilhaug) of Concord, California, and Western Strata Exploration (Westex) of <br /> West Sacramento, California, drill three 8-inch-diameter soil borings (B-26 through B-28) <br /> The boring locations are shown on Plate 2 The geologist collected soil samples during <br /> drilling at approximately 5-foot intervalswrtif ed using le laboratory analyses <br /> and manual methods and <br /> the geology beneath the site Samples were den <br /> late 3) <br /> classified according to the Unified Soil Classification li (Plates Descriptions4 through 12} eThe <br /> materials encountered are presented in Logs of Borings <br /> materials consisted predominately of silt, silty clay, and sand <br /> The borings were terminated at depths ranging from 40 to 110 feet bgs Ground water was <br /> not encountered in the borings Vapor-extraction <br /> well VW-15 was grouted ed from the butt m to <br /> • <br /> constructed in the borings Vapor-extraction <br /> 10 1231ccar 2 <br /> 30041-4 <br /> 0 <br />