[Home]
[Report Addendum] [Next Section]
SWMU B-20 Investigation Report Addendum Section 2 - Summary of Previous Investigation Results
Environmental investigations at the site began in January 1994. Preliminary sampling and mapping was conducted at that time to provide information for RI planning purposes. The RI was conducted in November and December 1995, after the work plan for the investigation was reviewed and approved by the TNRCC and EPA. This section summarizes results of these two rounds of sampling activities.
2.1 - Preliminary Sampling Results
In January and February 1994, prior to the RI, an investigation was conducted at B-20 to obtain data for use in determining RI needs. The first objective was to map site features, including boundaries, crater locations, and surface water features. The map resulting from this preliminary effort was used to determine RI sampling locations, described in Section 2.2. No UXO was identified during the preliminary mapping.
Secondly, samples were collected from areas of possible contamination to determine appropriate analytical parameters for the RI. Samples were collected from within four craters, near one soil mound, and from the livestock pond. A total of four surface soil samples, three surface water samples, three sediment samples, and four background samples were collected and analyzed for explosives, volatile organic compounds (VOCs), semivolatile organic compounds (SVOCs), total metals, and pH.
No explosives were detected in any of the samples. Arsenic in three surface soil samples exceeded its medium-specific concentration (MSC) for soil at industrial sites (30 TAC 335, Subchapter S, Appendix I). Barium, cadmium, and lead in one surface water sample exceeded freshwater criteria (30 TAC 307). Summary data tables are included in Appendix B. A detailed discussion of the preliminary sampling results are presented in the B-20 closure plan (ES, 1994).
2.2 - Remedial Investigation (Phase I) Results
The purposes of the first phase 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 summarizes results and 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, the conclusions presented here reference cleanup levels required by RRS1 and RRS2.
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 CSSA pastures, the first phase of the RI was planned under the general assumption that little or no UXO would 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 first phase of the RI. 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.
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 ietems on the surface. The RI report concluded that additional UXO items may have remained.
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 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 number of samples exceeding RRS1 and RRS2 criteria for each analyte is listed in Table 2.1. Sampling locations and tables presenting analytical results are included in Appendix C, as well as in the RI report (Parsons ES, 1995a). Surface soils did not meet RRS1 criteria in the following areas:
|
Two small ammunition disposal areas in the northern portion of the site. |
|
|
B-21 small ammunition disposal area on the east side of the site. |
|
|
A large area in the west-central portion of the site covering as much as 20 percent of the site. |
|
|
In the immediate vicinity of sample location SS19. |
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 exceeded MSCs listed in Appendix II. The RI report 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 did not meet RRS2 criteria in the following areas:
|
Two small ammunition disposal areas in the northern portion of the site. |
|
|
B-21 small ammunition disposal area on the east side of the site. |
|
|
In the immediate vicinity of sample location SS19. |
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 metal at the site. The RI report concluded that, since magnetic anomalies were identified in 10 of the 15 craters, buried UXO may have remained at the site within these craters. The RI report also concluded that these anomalies may have been caused by buried inert metal scraps.
Chemical Contamination
Metals levels in three borings (SB2, SB9, and SB10) exceeded both RRS1 and RRS2 criteria, as listed in Table 2.2. Since most of these samples were collected within rock and since groundwater was not encountered during drilling of these borings, teh RI report concluded that it is unlikely that these metals levels would have an adverse affect on human health or the environment. Concentrations exceeding RRS2 criteria were all collected at a depth greater than 12 feet. The number of samples exceeding RRS1 and RRS2 criteria is listed in Table 2.2. Tabulated analytical results are included in Appendix C, as well as in the RI report (Parsons ES, 1995a).
2.2.3 Surface Water and Sediment
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. No contaminants 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) exceede RRS2 criteria. There are no background data for surface water at CSSA.
Sediments at one crater (crater 8) exceed RRS1 metals concentrations, but did not exceed RRS2 criteria.