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L. �. of the plant. Duck Creek extends westward to Walker Slough, which in turn flows westward into the San Joaquin River. L. 2.5 UST HISTORY The facility historically operated five UST systems. The locations of the five former UST excavations are shown on Figure 2. The following sections summarize information pertaining to each UST system, their removal, and subsequent investigation, remediation, and monitoring ,., activities. Groundwater monitoring well construction details are presented in Table 1. Historical soil sample, groundwater well sample, and grab groundwater sample data are presented in Tables 2, 3, and 4, respectively. 4 2.5.1 Removal of UST Systems L' The following subsections summarize information pertaining to each UST system and their removal. Analytical data for soil samples collected during tank removal activities are included in Table 2. V Removal of Two 6.000 -Gallon Gasoline USTs (1987) Lr Two 6,000 -gallon gasoline UST systems were located near the southwestern comer of the main L. building. Prior to 1987, the eastem-most 6,000 -gallon gasoline UST had been taken out of service and abandoned in-place by removing the fuel and filling the tank with sand. In December 1986, the westem-most gasoline UST failed a tank integrity test. As a result of the L" December 1986 tank integrity test failure, both 6,000 -gallon gasoline USTs were excavated and removed in April 1987 under the direction of Environmental Science and Engineering (ESE). The disposition of the product and vent pipelines is not known. During the tank removal, soil L. was initially excavated to 18 feet BGS. Soil samples collected from the excavation contained total extractable petroleum hydrocarbons at concentrations up to 2,900 milligrams -per -kilogram L„ (mg/kg). The central portion of the gasoline UST pit was then excavated to 28 feet BGS. A confirmation soil sample collected from the floor of the excavation at 28 feet BGS contained total extractable petroleum hydrocarbons at 430 mg/kg (ESE, 1987). The analytical data are L- contained as an appendix in Anderson Consulting Group's (ACG) December 19, 1991 Problem Assessment Report. Approximately 450 cubic yards of soil was land -farmed with guidance from the San Joaquin Valley Air Pollution Control District (SJVAPCD). The excavation was backfilled with crushed y rock and resurfaced with asphalt (ESE, 1987). Subsequent investigation, remediation, and monitoring activities are described in Section 2.5.2. L L. SL_AIR SCM and RI WP 5