[Home]
[Table of Contents] [Next Section]
Technical Memorandum on Soil Boring Investigation
Section 8 - SWMU Burn Area 28 (B-28)
Six soil borings were drilled around two trenches where molten metal, small arms ammunition, and metal ammunition parts were disposed (Figure 8.1).
8.1 - Geology and Hydrogeology
Clay was present at the surface in all soil borings except B28-SB1. The dark grayish brown to black, soft clay ranged in thickness from 2 to 5.5 feet. Gravel to cobble-size limestone fragments were mixed in with the clay. Underlying the clay is interbedded white to pale yellow, massive limestone and very pale brown, weathered, marly limestone containing abundant fossil fragments. Fossils include pelecypods, forams, gastropods, echinoids, and crinoids. Also present are some vertical fractures and a few vugs formed from dissolution around fossiliferous zones. The vugs were often lined with calcite crystals. Between 15.0 and 25.0 ft bgl, the limestone typically changed color to a light gray. The light gray limestone was massive and contained solution channels, a few vertical fractures, and large fossil fragments.
A fossil echinoderm was observed in B28-SB1 between 10 and 15 ft bgl, which correlates with the bed of echinoderms Salenia and Heteraster (Hemiaster) exposed in the bottom of nearby Salado Creek. This may be the contact between the upper and lower members of the Glen Rose Formation.
Small amounts of groundwater accumulated in B28-SB1 and B28-SB2, not enough to sample. A sufficient amount of groundwater accumulated in B28-SB3 to collect a sample. The water level in B28-SB3 was measured at 27.7 ft bgl.
8.2 - Observed Waste Material in the Borings
Based on field observations, the northern trench appeared to be approximately six inches thick as seen where it was exposed in the creek bed. Waste material included various metal parts, some appeared to have been melted, and concrete with the metal imbedded in it. Additional metal pieces, including a hinge similar to those observed on ammunition boxes, was noted in the bottom of the creek/drainage.
The northern trench appeared to have extended across the ephemeral creek/drainage. A 2 ft long piece of molten metal was observed approximately 4 ft down the west side of the creek bed/drainage. The material appeared to be the same as the remainder of the trench.
8.3 - Soil/Rock Analytical Results
Nineteen soil/rock samples were collected for chemical analysis. Table B28-1 presents the analytical results. No VOCs were detected in the samples. Phthalates were detected in four samples. Chromium was detected in eight and lead was detected in twelve of the samples. Nickel was detected in nineteen samples. All concentrations of cadmium were qualified as non-detect, except for B28-SB1 (29-30 ft).
8.4 - Groundwater Analytical Results
One groundwater sample was collected from B28-SB3 (Table B28-2). VOCs and SVOCs were not detected in the sample. Concentrations of chromium were detected.
8.5 - Statistical Comparison with Background Metals and Risk-Based Closure Criteria
Phthalates, a common laboratory contaminant, were detected in five soil samples, but TNRCC Appendix I does not include semivolatile MSC for comparison. One chromium sample , B28-SB2 (2-3 ft), exceeded comparison criteria. Figure 8.2 shows the locations and concentrations of these samples.