[Home]

[Table of Contents] [Next Section]

B-20 Remedial Investigation Report for Former Open Burn/Open Detonation Area

Section 6 - Conclusions

The purposes of the remedial investigation at the B-20 site were to determine if any UXO items remained at the site (posing an immediate threat to human health and the environment) and to determine if any chemicals had been released at the site (possibly posing a long-term danger to human health and the environment). To address the possible immediate concern, the entire site was screened for UXO items. To address the possible long-term effects, a large number of sediment, surface water, subsurface soil, and surface soil samples were collected and analyzed.

This section presents conclusions of the remedial investigation of the site. Since the conclusions to be made about contamination detected at the site depend on the cleanup standards that are being compared, these conclusions will reference cleanup levels required by risk reduction standards 1 and 2. Cleanup levels for closure under risk reduction standard 3 (RRS3) depend on the results of a risk assessment.

6.1 - Surface Soils

6.1.1   Unexploded Ordnance

Since no explosive incidents occurred during the unit's inactive years (1987 through 1995) and wildlife and cattle ranged freely across the northern pastures, this remedial investigation was planned under the general assumption that little or no UXO should be found during the site prescreening. Two possible sources for remaining UXO were considered to be items which blasted out of craters during detonation, but did not explode, and unexploded items buried in the craters.

A total of 193 UXO items were found during the site prescreening. Most of the items were fragments of ordnance containing explosive residue. Some of the items were chunks of raw explosive. The majority (162 of 193) of the items were found within the original site boundary, but a substantial portion (31 of 193) were found outside the original boundary. These additional items were found when the area to be screened was expanded to determine if any UXO items were outside of the site boundary. All UXO identified at the site was found on the ground surface. The UXO professionals indicated that this UXO probably blasted out of the craters during detonation. Ordnance detonated in a crater can be blasted several hundred feet, explaining why some UXO items were found up to 550 feet from the B-20 site. All of the UXO items are being temporarily stored at the site, awaiting disposal.

Although the entire B-20 site and much of the surrounding area was methodically swept for UXO items, vegetation at the site may have obstructed visual identification of UXO items on the surface. Due to the limitations of the UXO prescreening, it is possible that additional UXO items are located at or around the site.

6.1.2   Chemical Contamination

A total of 21 judgmental and 22 systematic surface soil samples each were collected at the site during the remedial investigation. The evaluation of contamination levels is based on a comparison with both RRS1 and RRS2 cleanup levels.

According to 30 TAC 335.554 which describes conditions which must be met to attain RRS1, contaminated media must be removed or decontaminated to background levels. A total of 18 of the 43 surface soil samples collected at B-20 exceeded background. The areas exceeding background are shown on Figure 5.17. It is estimated that roughly 34,300 cubic feet of soil (approximately 463,000 square feet to a depth of 2 feet) is contaminated above background levels. Surface soils do not meet RRS1 criteria in the following areas:

According to 30 TAC 335.555 which describes conditions which must be met to attain RRS2, contaminated media must be removed or decontaminated to levels specified in Appendix II of 30 TAC 335 or levels calculated using the methodology described in 30 TAC 335.558. Three of the 43 surface soil samples exceed MSCs listed in Appendix II. The areas exceeding MSCs are shown on Figure 5.18. It is estimated that roughly 560 cubic feet of soil (approximately 7,600 square feet to a depth of 2 feet) is contaminated above MSCs. Surface soils do not meet RRS2 criteria in the following areas:

6.2 - Subsurface Soils

6.2.1   Unexploded Ordnance

To address the possibility of buried UXO in the craters, magnetic surveys were conducted at each crater. The magnetometer was used in areas most likely to contain buried UXO (craters) rather than across the entire site due to interference caused by the large amount of scrap metals at the site. Magnetic anomalies were identified in 10 of the 15 craters, indicating that buried UXO may remain at the site within these craters. These anomalies may have been caused by buried inert metal scraps. If UXO items remain in the craters, they could become exposed after erosion caused by intense precipitation or site use.

6.2.2   Chemical Contamination

Metals levels in three borings (SB2, SB9, and SB10) exceed both RRS1 and RRS2 criteria. Since most of these samples were collected within rock and since groundwater was not encountered during drilling of these borings, it is unlikely that these metals levels will have an adverse affect on human health or the environment. Concentrations exceeding RRS2 criteria were all collected at a depth greater than 12 feet. Rock at this depth would not be encountered in the unlikely event that there were construction activities at the site in the future. Therefore, analytical results of rock samples collected at this depth would not be evaluated in a risk assessment.

6.3 - Surface Water

Since the ephemeral stream at the B-20 site drains into Cibolo Creek, which is considered to be a recharge area for the Glen Rose Formation, surface water is a pathway of concern. However, no contamination were detected in the natural surface water features at the site (the ephemeral stream and the small pond). However, surface water in three craters (8, 12, and 13) exceeded RRS2 criteria. There are no background data for surface water at CSSA.

[Next Section]