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Mr Michael Infurna Project 0805-114 02 January 29, 1996 Page 4 Air spargmg involves injecting pressurized air below the water surface to "strip" dissolved hydrocarbons from the groundwater to the vadose zone, where residual hydrocarbons are removed by the S VE system Air bubbles that exit the sparge well move vertically and horizontally through the saturated soil column, "stripping" dissolved hydrocarbons from groundwater Hydrocarbon vapors entrained in the air bubbles rise through the saturated zone into the vadose zone Control of off-gas in the vadose zone is accomplished using a SVE system SUPPLEMENTAL INVESTIGATION The purpose of this investigation was to install additional remedial facilities to be incorporated into the remediation treatment system On August 9 and 11, 1995, an EMCON geologist observed Woodward Drilling of Rio Vista, California, drill four soil borings (B26 through B29), which were converted to air sparge wells AS-2 and AS-3 and vapor extraction wells VW-11 and VW-12 The borings were drilled to approximately 65 to 78 feet below ground surface (bgs). Boring locations are shown on Figure 2 The au sparge wells AS-2 through AS-3 were constructed with 2 feet of 0 02 slotted screen The vapor extraction wells VW-11 and VW-12 were constructed with two slotted screen sizes Well VW-11 was constructed from approximately 55 to 70 feet bgs with 0.02 slotted screen and from 45 to 55 feet bgs with 0 10 slotted screen Well VW-12 was constructed from approximately 55 to 65 feet bgs with 0 02 slotted screen and from 45 to 55 feet bgs with 010 slotted screen During drilling activities, groundwater was encountered at approximately 55 feet bgs EMCON field procedures are described in Appendix A The geologist collected soil samples from the borings at approximately 5-foot intervals for possible laboratory analyses and to characterize the geology beneath the site. Samples were logged using visual and manual methods and classified according to the Unified Soil Classification System Sediments encountered are shown on the logs of exploratory borings presented in Appendix B Drill cuttings were stockpiled on site and covered with plastic sheeting On August 11, 1995, the geologist collected four soil samples from the stockpiled soil to be composited at the laboratory for analyses to evaluate disposal options At ARCO's request, drill cuttings were transported by Dillard Trucking of Byron, Cahfonua, to Browning-Ferns Industries in Livermore, California, for disposal. SAGW\PJM805\=511402FS-95\pas L