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Site Background Information- Ripon Farm Service ' Page 5 of 8 ' detected at maximum concentrations in samples collected from well VW-1 of 720 µg11 and 800 p g/l, respectively. Low concentrations (less then 3 pg/l) or lack of detectable BTEX compounds have been encountered in ground water samples from wells MW-1 and MW-3 through MW-8. DIPE has been detected in ground water samples from wells MW-3, MW-4, and MW-8 at concentrations as high as 17 µg/l. TBA has been detected in samples from wells MW-1, MW-2, MW-3, MW-4, MW-8, and soil vapor wells VW-1 and VW-2 at concentrations as high as 120 µg11. MTBE has been detected in samples from wells MW-1 and MW-3 at concentrations as high as 6.7 µg11. ETBE and TAME have not been detected in any of the wells sampled. TPH-d concentrations exceeded TPH-g concentrations in the samples containing both analytes. Impacted soil was present below the ground water table when remediation began,due to historically lower ground water elevations at the site during which time a portion of the unauthorized ' hydrocarbon release occurred. The former UST area was impacted by diesel fuel compounds,but is also impacted by significant concentrations of gasoline fuel compounds. The volume of soil addressed by the remediation system was estimated to be 645 cubic meters,based on the limited lateral extent of the vadose zone contamination and a depth to ground water of ' 20 feet bsg. The generalized mass of vadose-adsorbed TPH-g was approximately 65.2 lbs, or 29.58 kg, and the generalized mass of adsorbed TPH-d was approximately 77.16 lbs, or 35 kg. ' The total volume of impacted soil addressed by the remediation system was estimated to be 1,240 cubic meters,from the base of the former UST excavation to the depth of 30 feet bsg.The total mass of adsorbed TPH-g was approximately 123.5 lbs, or 56.8 kg, and the mass of total adsorbed ' TPH-d was approximately 150 lbs, or 68.2 kg. Hydrocarbon-impacted ground water in the former UST area has higher average TPH-g to TPH-d ratios(0.702- 1.852),indicating a greater contribution to ground water of TPH-g in the former UST area. SOIL AND GROUND WATER REMEDIATION On 25,26,and 27 April 2000,four air-sparge pilot borings and eleven soil vapor extraction soil pilot borings were advanced at the site; with borings IAS 1 through IAS4 completed as 2-inch diameter air sparging wells, drilled to a total depth of 25 feet bsg with a 5-foot screen interval. Two vertical ' zones of remediation wells were installed as follows: borings VW3A, VW8, and VW9A were completed as vapor extraction wells,drilled to a total depth of approximately 13 feet bsg with 5-foot screen intervals, and borings VW3 B,V W4, V W5, V W6, V W7, V W9B, V W 10, and V W 11 were Advanced GeoEnvironmental,Inc.