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2.5.3 Nature of Site Operations Historically, the MGP processes, and the quantities and characteristics of byproducts and residues generated from the former manufactured gas processes probably varied with the feedstock and reactants used. Limited information is available on the specific types and quantities of hazardous substances/wastes generated at the former Tracy MGP. At oil gas plants, lampblack was the residue typically found. COPCs found in lampblack are primarily polycyclic aromatic hydrocarbons (PAHs). Other MGP residues may include metals, spent oxide, feedstock oil, and oil sludge. Spent oxide, used to purify the gas, may have had residues containing cyanides. Feedstock oil and oil sludge (from storage tanks or vaults) may have contained hydrocarbons, PAHs, and other aromatic compounds [benzene, toluene, ethylbenzene, and xylenes (BTEX)]. In this RI/SSI, components of these residues were specifically targeted for laboratory analysis and analytical results are described further in Section 4. While MGP activities have ceased, current site operations as a storage and service center require that potentially hazardous materials such as oils associated with electrical equipment be stored and handled at the facility. These materials include, but are not limited to: 55-gallon drums of hydraulic or motor oil, new oil-filled equipment, and used equipment. 2.5.4 Previous Site Investigations A total of five investigations and one long term groundwater monitoring program have been conducted at the Site since 1986. The investigations include: a PA conducted in June 1986; three investigations associated with a gasoline UST that post dates the MGP conducted from November 1986 to January 1988; and finally a SI for the Tracy MGP Site conducted in October 1988. In addition to the 5 investigations at the Site, a long term groundwater monitoring program was conducted at the Site, in relation to the gasoline UST, from January 1988 to November 1995. Analytical results for samples collected during previous investigations are provided in the following: • Tables 2 through 5 - soil analytical results; • Table 6 - analytical results for soil gas samples; and • Tables 7 through 10 - analytical results for groundwater samples collected during these investigations and the long term groundwater monitoring program. The following subsections provide a summary description of these investigations/groundwater monitoring program. 2.5.4.1 Preliminary Assessment The PA for the Site, conducted in June 1986, consisted of a review of historical information for the former Tracy MGP and the collection of one soil sample, thought to be a background sample collected from the southern boundary of the Site. The background sample contained total PAHs at a concentration of 0.9 mg/kg, lead at 150 mg/kg and arsenic at 15 mg/kg. Mercury and cyanide were not detected in the sample (identified as "1" in the PA). Sample 1 was collected from approximately 0.5 feet bgs using steel trowels and the soil was transferred into a clean glass jar. The location of this sample, along with the historically detected COPCs in soil, is provided PARSONS 15 FINAL RI REPORT-FORMER TRACY MGP APRIL 2010