ARCHIVED REPORTS_PRELIMINARY ASSESSMENT_SITE INVESTIGATION REPORT

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2.1 AASF 2.1.1 Underground Storage Tanks The fuel storage for the AASF was originally located in three 5,000-gallon steel USTs which were installed in the early 1950s. These USTs were removed in 1990. The former USTs, shown on Figure 3, were oriented east-west and rested on a six-inch thick concrete slab. The slab still remains in place at a depth estimated to be 11 feet bgs. The fuel dispensers were originally located on the north side of the USTs. During the 1974 expansion/modernization, the dispensers were relocated 30 feet to the east. Aviation gasoline was reportedly stored in the former USTs until the early 1960s when turbine powered aircraft began replacing older piston powered planes. From approximately 1962 until 1989, JP-4 was stored in the former USTs. The three 5,000-gallon USTs were taken out of operation in 1989 and were removed in January 1990 (Wallace-Kuhl, 1993). The USTs reportedly appeared intact and not leaking at the time of removal. Five soil samples were collected from beneath the tanks at the time of removal. Analytical results reported no detectable concentrations of fuel constituents from samples 2, 3, and 5. Analytical results of sample 1 reported 1,500 parts milligrams per kilogram (mg/kg) total petroleum hydrocarbons as diesel (TPH-d) and 1,600 mg/kg TPH as jet fuel (TPH j); sample 4 contained 3,500 mg/kg TPH-d and 5,100 mg/kg TPH j. No other TPH or benzene, toluene, ethylbenzene, and total xylenes (BTEX) were reported. As soil adjacent to the USTs was impacted with petroleum hydrocarbons, an Unauthorized Release Form (No. 90-U11) was • completed and submitted to the SJPHS on January 31, 1990. Following the UST removal activities, several soils investigations were conducted to assess the limits of the petroleum impacted soil. The results of the investigations, summarized in Versar's Quarterly Groundwater Monitoring Report(Fourth Round), dated June 12, 1997, identified the majority of the contamination as limited to the soils adjacent to the former excavation. Three groundwater monitoring wells were installed(as shown on Figure 3) at the AASF in 1993 to assess the condition of groundwater beneath the former USTs, and have been monitored to the present. TPH was last detected in the wells in 1996. Detections of BTEX and methyl tertiary butyl ether (MTBE) have been infrequent, with maximum concentrations of benzene (14 micrograms per liter D.ag/L]) and MTBE (1.49 ,ug/L) detected in 1996. A summary of analytical results for water samples from the three monitoring wells is presented in Table 2. 2.1.2 Aircraft Washpad The aircraft washpad drainage and treatment system at the AASF was found to be inadequate in 1989 (West and Hansen, 1991). Washpad use flow rates exceeded the design flow rate, resulting in discharges of contaminants to surrounding soil. The washpad area was investigated in 1991, with soil found to be contaminated with petroleum hydrocarbons and solvents; an impact to groundwater was not identified. Remediation of identified impacts to soil was performed in • 1992 by excavation and disposal of impacted materials at a Class II landfill. Confirmation 2187-01/3134-1 00/MAY26'00 3