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March 20, 1992 <br /> ARCO Station No 6100, Tracy, California <br /> the site The presence of hydrocarbons in soil within the tank cavity necessitated the <br /> excavation of the cavity to depths ranging from 15 to 25 feet below grade surface (bgs) Soil <br /> samples collected by Roux from the limits of the over-excavated tank cavity contained <br /> concentrations of total petroleum hydrocarbons as gasoline (TPHg) up to 7,400 parts per <br /> million (ppm) Four new doubled-walled fiberglass tanks were installed in the new tank <br /> cavity <br /> On the basis of the field and laboratory data, ARCO requested that RESNA perform an <br /> investigation of the lateral and vertical extent of gasoline hydrocarbons in soil beneath the <br /> site The tasks for performing this additional investigation are presented in RESNA's Work <br /> Plan (RESNA, August 5, 1991, Plan No 30041-2W) <br /> CURRENT WORK <br /> i Soil Borings <br /> A geologist from RESNA was at the site between October 8 through 11, 1991, to observe <br /> Jcon Exploration of Yuba City, California, drill six 8- to 10-inch-diameter soil borings (B-6 <br /> through B-11) A RESNA geologist returned to the site between November 20 through 22, <br /> and November 25 through 27, 1991, to observe Jcon drill eight additional 8-inch-diameter <br /> borings (B-12 through B-19) at the site The boring locations are shown on Plate 2 <br /> Soil samples were collected during drilling at approximately 5-foot intervals and were <br /> classified according to the Unified Soil Classification System (Plate 3) Descriptions of earth <br /> materials encountered are presented in the Logs of Borings (Plates 4 through 43) The <br /> materials consisted predominately of silt and silty clay Ground water was not encountered <br /> in any of the borings drilled to a maximum depth of approximately 116 feet bgs <br /> The borings were terminated at depths shown on the Logs of Borings Borings B-6, B-7, B- <br /> 13, B-16, and B-19 were backfilled to the ground surface with a neat cement slurry Jcon <br /> constructed vapor-extractions wells VW-1 through VW-9 in borings B-8, B-10, B-11, B-9, B- <br /> 12, B-15, B-14, B-17, and B-18, respectively Details of vapor-well construction are shown <br /> on the Logs of Borings and are discussed in more detail in Appendix A <br /> Cuttings generated during drilling were placed on plastic, covered with plastic, and left at <br /> the site until disposed of by Dillard Trucking of Byron, California A copy of the <br /> memorandum from Dillard trucking indicating disposal of the drill cuttings at Redwood <br /> Landfill is attached <br /> I 0129ccar <br /> 30041-2 2 <br /> r <br />