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1995 Technical Memorandum on Soil Boring Investigation
Section 4 - SWMU Burn Area 1 (B-2)
Five soil borings were drilled at this former small arms ammunition burn area (Figure 4.1). Two historical trenches and a third identified by geophysical survey are located at this site. The trenches are oriented west-northwest by east-southeast.
4.1 - Geology and Hydrogeology
The surficial geology at the site consisted of up to 2 feet of brown clay, overlying 1 to 5 feet of pale yellow, highly weathered, marly limestone. Below this interval occurred hard, massive, white limestone interbedded with highly weathered, pale yellow marly limestone. The limestone becomes light gray in color towards the bottom of the soil borings (TD = 30 ft). Vugs, reworked intervals, bioturbation, high angle fractures with staining, and very small, black dendritic growths were observed in the cores (Appendix A).
As in B-1, the predominant fossils observed at B-2 were foraminifera followed by pelecypods. Between 26 and 29 ft bgl, the cores were fossiliferous, except for B2-SB4 and B2-SB5. An echinoid was observed in the B2-SB1 from 26 to 30 ft bgl. Worm burrows were observed in B2-SB5. Fractures and large solution channels were detected in several soil borings at B-2. Furthermore, there is a certain degree of connectivity of these fractures and solution cavities from boring to boring. This was observed during air coring in zones of lost circulation when air was seen blowing out a nearby borehole. A large cavity was detected in B2-SB2 when the drill stem dropped rapidly through a specific zone.
Perched groundwater was sampled in two borings (B2-SB3 and B2-SB5). Rust iron staining indicative of water movement was observed in most cores, particularly along fracture planes and vuggy zones. Calcite growths within the fractures and voids, another indication of water movement, were noted in B2-SB4. Water levels were measured between 22 and 24.7 ft bgl in B2-SB3 and at 25 ft bgl in B2-SB5. The total depth of these borings were 30 ft bgl.
4.2 - Observed Waste Material in the Borings
Thin metal wire was found in boring B2-SB4 from a depth of less than 6 ft bgl.
4.3 - Soil/Rock Analytical Results
Toluene was detected in the three northern-most soil borings from 29 to 30 ft bgl. Phthalates (common laboratory contaminants) were detected in four samples. Copper, iron, and nickel were detected in all seventeen samples. Chromium was detected in nine samples and lead in thirteen. Cadmium concentrations were qualified as nondetect. The analytical results are presented in Table B2-1.
4.4 - Groundwater Analytical Results
No VOCs or SVOCs were detected in the two water samples collected (Table B2-2). All ten metals analyzed for were detected in B2-SB3 (GW). Chemicals of concern were not detected in B2-SB5 (GW).
4.5 - Statistical Comparison with Background Metals and Risk-Based Closure Criteria
The concentrations of toluene detected in soil borings B2-SB3, -SB4, and -SB5 from 29 to 30 ft bgl were below MSC. Chromium exceeded the MSC in sample B2-SB4 (1.8-3.0 ft).
Groundwater sample B2-SB3 (GW) exceeded the MCLs for cadmium, lead, and nickel. The location and concentrations of the samples that exceeded MCLs or MSCs are shown in Figure 4.2.