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Tkmx1we11&Ro1&D <br /> Previous Investigations <br /> Analysis of soil samples from beneath the UST in 1986 indicated TPH-g at up to 3,600 mg/kg. <br /> The excavation was deepened in October 1986, and January and July 1987. TPH-g was found at <br /> up to 569 mg/kg. Well MW-1, installed in October 1986 to 38.5 feet bgs, was sampled and <br /> found to contain TPH-g at 11.58 mg/1 and benzene at 1.54 mg/1. <br /> Three additional groundwater monitoring wells (MW-2 through MW-4) were installed and <br /> sampled in December 1992,to better evaluate the lateral and vertical extent of contaminated soil <br /> and groundwater. Nine soil samples were collected during the drilling of the well borings. Soil <br /> and groundwater samples were analyzed for TPH-g and BTEX. No fuel hydrocarbons were <br /> detected in the soil samples. TPH-g was detected in groundwater from wells MW-2 and MW-4 <br /> at 69 and 11 mg/l, and benzene at 0.051 and 1.1 mg/1. Groundwater from MW-1 was sampled in <br /> April 1992 and contained TPH-g at 20 mg/1, TPH-d at 1.3 mg/l, and benzene at 0.18 mg/l. <br /> • Approximately 0.25 inches of free product was observed floating on groundwater at MW-1. <br /> Monitoring wells MW-5 and MW-6 were installed and sampled in April 1994 and re-sampled in <br /> May 1994. TPH-g was found at MW-6 at 0.072 mg/l and MW-5 at<0.05 mg/1. Wells MW-2, <br /> MW-3, and MW-4 were also sampled in May 1994, and found to contain TPH-g at<0.05, 0.13, <br /> and 7.0 mg/l ug/1. MW-1 was not sampled for groundwater due to the presence of approximately <br /> 0.25 inches of free product. <br /> Seven groundwater monitoring wells are being sampled as part of an ongoing groundwater <br /> monitoring program conducted under the oversight of the SJCEHD. Two soil vapor extraction <br /> wells have been installed as part of a pilot system to treat soil and groundwater contaminated <br /> with fuel hydrocarbons (Wallace Kuhl 1999). <br /> Treadwell &Rollo performed additional site investigations in 1999. A geophysical survey in the <br /> eastern half of Area 21 was completed on 19 August 1999. Several geophysical anomalies were <br /> 15 <br /> 25970309.DGD 24 August 2000 <br />