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Chronology <br /> 25775 Patterson Pass, Tracy <br /> Page 2 <br /> 07/20/90 Received report of 5 soil borings. Highest contamination in B1 at 30 feet. <br /> Depths of B1 through B5 were 56',41',26',31' and 31'. Survey of wells in <br /> the area completed. <br /> 11/02/90 USTs 1-5 removed. Strong gasoline odor observed from excavation. <br /> 11/7-13/90 Excavation and sampling of old and new UST locations. Excavation to 25 <br /> feet. Excavation filled with pea gravel and new USTs. <br /> 06/03/91 Received report of excavation soil sampling. TPH up to 7400 ppm at 25 <br /> feet below grade. Piping samples also showed TPH contamination up to <br /> 5700 ppm. <br /> 08/06/91 Received work plan for soil borings and vapor extraction wells. <br /> 08/19/91 Received receipts for soil transported to BFI by Dillard Trucking. <br /> 10/7-14/91 B6 through B11 drilled. B8 through B11 converted to vapor wells VW1- <br /> VW4. B9 drilled to 115 feet. <br /> 11/20-27/91 B12 through B19 drilled. B12,14,15,17,18 converted to vapor wells VW5- <br /> VW9. <br /> 3/26/92 Received report on borings and vapor extraction wells. <br /> VW1 screen 15-45 feet VW2 screen 28-58 feet <br /> VW3 screen 29-59 feet VW4 screen 30-60 feet <br /> VW5 screen 20-55 feet VW6 screen 15-45 feet <br /> VW7 screen 45-75 feet VW8 screen 54-84 feet <br /> VW9 screen 25-65 feet <br /> Deepest soil results and total depth: <br /> B6 ND at 75' TD B7 ND at 65' (75' TD) <br /> B8 9500 ppm TPH at 45' TD B9 1.8 ppm TPH at 115' TD <br /> B10 .01 ppm Benzene at 60' TD B11 .054 ppm Benzene at 60' (61' TD) <br /> B12NDat55' TD B13NDat35' TD <br /> B14 ND at 80' TD B15 .012 ppm Benzene at 45' TD <br /> B16 ND at 35' TD B17 .029 ppm Benzene at 85' (88' TD) <br /> B18 ND at 69' (70' TD) B19 ND at 45' TD <br /> Vapor extraction test performed - alternative appears feasible. Drill cuttings <br /> hauled to BFI by Dillard Trucking. Additional soil borings proposed. <br />