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DRAFT Geosyntec consultants 3. SUMMARY OF PREVIOUS INVESTIGATIONS Since the removal of the four USTs, three soil investigations and multiple groundwater monitoring events have been conducted to characterize the extent of residual contamination in the area(ERS, 2008). The historical investigations and analytical results are presented in Tetra Tech's Building 817-B Underground Storage Tank Site Investigation Report and ERS's UST 817E and UST 916E Site Characterization Report(ERS, 2008) and are summarized below. Figure 8 and Table 5 from ERS's UST 817E and UST 916E Site Characterization Report showing the boring locations and analytical results for the detected organic compounds and lead from these investigation are presented in Appendix B. The analytical results for soil from the 2008 investigation is also presented in Figure 2. 3.1.1 Removal of Tank USTs at 817B (1992 through 1996) UST 81713-2 was excavated and removed in 1992 under the Navy's abandoned tank program following a release of leaded gasoline. Removal of UST 81713-2 revealed extensive surface corrosion of the UST, including more than 25 small holes at the bottom of the UST. Three soil samples were collected during the excavation. The samples were analyzed for benzene, toluene, ethylbenzene, and xylenes (BTEX), total petroleum hydrocarbons as gasoline (TPHg), ethylene dibromide, organic lead, and total lead. Results of the analysis indicated that elevated concentrations BTEX and TPHg were present in the soil. Based on these results, the Navy determined that USTs 81713-1 and 81713-3 should also be removed. These USTs were removed in 1996. During the removal of these two USTs, a previously unknown UST referred to as Tank 3 was discovered and also removed. One soil sample was collected from the excavation beneath Tank 3. Composite soil samples were also collected from the excavated soil placed in roll-off bins (Bins 01-06 and SPO1 and SP02). These samples were tested for TPHg, TPH as diesel (TPHd), TPH as kerosene (TPHk), TPH waste oil, and BTEX. One soil sample from beneath Tank 3 was analyzed for total lead. A water sample taken from the excavation was sampled for TPHg, TPHk, and TPH as motor oil (TPHmo). Soil analytical results indicated that elevated concentrations of TPHg and TPHd was present beneath Tank 3. The results of composite samples indicated that lower concentrations of TPHk and TPH waste oil was present in the excavated soils. The water sample results indicated that TPHk and TPHmo were present in the water. Soil sampling locations and analytical results are summarized in Section 3.1.5 and discussed in detail in ERS's UST 817B and UST 916E Site Characterization Report(ERS, 2008). 3.1.2 1998 Initial Investigation Based on the UST removal findings, the Navy conducted an soil and groundwater investigation in 1998 to help define the lateral and vertical extent of contamination detected during the UST removal. Twenty borings were advanced at the Site,using direct-push equipment, to depths of 8 to 21.5 feet bgs. Forty-eight soil and 10 ground water grab samples were collected and analyzed for BTEX, methyl tertiary butyl ether(MTBE), oil and grease, soluble and total lead, TPHd, TPHg, and TPHmo. In July 1998, the Navy installed six shallow wells (917-1 through 917-6) to monitor groundwater. Samples were collected from the wells and analyzed for the above- Draft Soil and Soil Vapor Investigation 4 August 30,2019