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Treadwell&Rollo <br /> • <br /> Area 21 <br /> A 10,000-gallon capacity UST used for gasoline was removed on 3 September 1986 and found to <br /> have leaked. Soil samples collected below the UST contained TPH-g concentrations up to <br /> 3,600 milligrams per kilograms (mg/kg). TPH-g contaminated soil was excavated and residual <br /> TPH-g concentrations in sidewall samples were as high as 569 mg/kg. Well MW-1, installed in <br /> October 1986, was sampled and found to contain TPH-g at 11.58 mg/l and benzene at 1.54 mg/l. <br /> Subsequent monitoring of well MW-1 has encountered up 0.25 inches of free product floating on <br /> groundwater. Between 1992 and 1994 six additional monitoring wells have been installed at the <br /> site (Wallace Kuhl 1999). <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). Pilot testing of a soil vapor extraction system has <br /> reportedly been performed, but no remediation is currently being performed. <br /> 1.4 Baseline Public Health Evaluation <br /> Preliminary Endangerment Assessments (PEAs)were performed on all parcels in November <br /> 1999, the results of which were published in the 3 December 1999 Treadwell & Rollo Site <br /> Characterization Report. A full Risk Assessment incorporating the results of the 29 June 2000 <br /> RI has been prepared to more fully define site health risk, and is presented under separate cover. <br /> Both carcinogenic and noncarcinogenic risks from exposure to soil and groundwater were <br /> evaluated for construction and landscape maintenance workers, commercial industrial workers, <br /> and residents. A hazard index (HI) greater than 1 was considered to represent a potential threat <br /> to human health from noncarcinogens. A summed estimated total lifetime excess cancer risk of <br /> less than 1 E-06 was considered to represent an acceptable risk to residents, and a 1 E-04 to 1 E-06 <br /> for nonresidential. <br /> • <br /> 5 <br /> 25970318.PGS 15 November 2000 <br />