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I June 21, 1993 Working To Restore Nature i ARCO Service Station No 2130 was detected in samples from the five wells at concentrations ranging from ' 79 ppb (well MW-5) to 1.8,000 ppb (well MW-1); concentrations of benzene ranged from 6 5 ppb (well MW-3) to 260 ppb (well MW-1) AIR SPARGING PILOT TESTING Installation of Air SpaxXing, Wells In August 1992, a geologist from RESNA observed the drilling of four 8-inch-diameter soil borings (B-17 through B-20) by Wayne Drilling Company of Lincoln, California The r borings were terminated at depths ranging from approximately 69 5 to 73 5 feet bsg Borings logs for these drill sites will be included in the forthcoming Problem Assessment Report The borings were completed as air sparge well AS-1 (B-17) and air sparge monitoring wells • MS-1, MS-2, and MS-3 (B-18 through B-20) Dual-casing (two 2-inch-diameter) polyvinyl chloride (PVC) pipes with 0 02-inch slots were installed in each soil boring The first pipe extends below the ground-water surface and the other terminates in the vadose zone approximately 4 feet above the ground-water surface The slotted section of the PVC pipes is limited to the bottom 3 feet of each pipe Schematics of these wells are shown on Plates 4 and 5 0 The air sparge well (AS-1) groundwater pipe was installed to a depth of approximately 73 5 feet bsg or approximately 9 5 feet below the ground-water surface The sparge pipe installation depth was limited to approximately 9 5 feet below the ground-water surface due to a silty clay unit that was encountered at that depth The second pipe (vadose zone monitoring well) was installed next to the ground-water sparge pipe to within approximately 4 feet above the water surface The location of well AS-1 (approximately 6 feet from well VW-4) was designed to allow for subsequent vapor extraction and capture of sparge off-gas a 0 Air sparge monitoring wells (MS-1 through MS-3) also consist of two 2-inch PVC pipes of 30003-8 6