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B-20 Remedial Investigation Report for Former Open Burn/Open Detonation Area
Section 5 - Remedial Investigation Results
This section presents the findings of the B-20 remedial investigation at CSSA. Findings and observations made during the initial site clearance for UXO are described in this section. Results of the magnetometer survey at each of the fifteen site craters are detailed. This section also evaluates the nature and extent of contamination in surface soil, subsurface soil, sediment, and surface water and the significance of these results. Conclusions and recommendations are presented in Section 6, and closure options and recommendations are presented in Section 7.
The purposes of the site prescreening activities were to determine if there was any UXO at the site and to clear safe access routes to each sampling location. The manner in which the site prescreening was conducted is described in Section 4.1.
A total of 193 UXO items were discovered at the site. Thirty-one of these items were discovered outside the original boundary of the site, so the extent of the area screened was expanded until no UXO was found. Each fragment of UXO found was given an item number and the location at which it was found was plotted on a site map. UXO item locations are shown in Figure 5.1. The aerial photograph in Figure 5.2 also shows where UXO items were found. There appears to be a direct correlation between the amount of vegetation and the number of UXO items.
The majority of items found at the site were parts of those ordnance types listed in Table 5.1. Many of the items are broken pieces in which explosive residues were trapped, but did not detonate. These items can be grouped into the general categories (projectiles, small bombs, etc.) listed in Table 5.2. Photographs of some of the ordnance types found are included in Appendix B.
Most of the items contained or were suspected of containing secondary explosives such as TNT, cyclotetramethylene tetranitramine (HMX), and RDX. Some small pieces of raw secondary explosives were also observed at the site. However, several items, such as fuzes, were suspected of containing primary explosives, such as lead styphnate and lead azide.
It is likely that the majority of these items were blasted out of an old crater during detonation, and were not found by CSSA EOD crews during the post-detonation sweep for unexploded items normally made as part of the 1980's operations.
For drilling clearance purposes, a magnetometer survey was conducted at each of the fifteen craters at the site in the manner described in Section 4.2. Due to interferences caused by the large amount of metallic material on and near the surface at the site, a grid survey was not recommended. Pictorial representations of anomalies observed during the magnetometer surveys at all craters are shown in Figure 5.3 Figure 5.4, Figure 5.5, Figure 5.6, Figure 5.7, Figure 5.8, Figure 5.9, Figure 5.10, Figure 5.11, Figure 5.12, Figure 5.13, Figure 5.14, and Figure 5.15.
Anomalies were detected in ten of the 15 craters at the B-20 site. In general, the more recent craters were more likely to have magnetic anomalies. Anomalies were observed in craters 1 and 2 through 9. The only historic (pre-1980's) craters to have anomalies were craters 14 and 15. The anomaly detected in crater 14, which appeared to be quite significant, stretched nearly 20 feet. However, the cause of this anomaly could not be determined by the magnetometer survey. Since there is a large amount of miscellaneous types of scrap metal at the site, the anomaly could be a large amount of small metallic objects, or one large object. As described in Section 4.2, the Foerster Ferex Mk-26 magnetometer can detect magnetic anomalies to a depth of up to 19 feet, but cannot identify the cause of the anomaly.
5.3 - Background Sample Analytical Results and Statistical Evaluation
The objective of the background sampling was to collect representative samples of each of the three soil types present at the B-20 site (Krum complex soils, Brackett-Tarrant association (Bte) soils, and Crawford and Bexar (Cb) stony soils). These soil types are described in detail in Section 2. Figure 4.4 shows the background surface soil sampling locations. Background surface soil samples SS1 through SS10 were collected during a previous investigation at CSSA (ES, 1994c). Table 5.3 summarizes the background surface soil sample analytical results.
Background Glen Rose limestone samples were collected from 10 borings drilled during a previous investigation (ES, 1994c). These results were also statistically evaluated to determine background metals concentrations in the Glen Rose Formation. Table 5.4 summarizes the background Glen Rose Formation results.
Background levels of inorganics in soils and in the Glen Rose Formation were statistically determined from the samples listed in Table 5.3 and Table 5.4, respectively. The statistical evaluation methodology is described in Section 4.15. Calculated background levels for each soil type and the Glen Rose Formation are shown in Table 5.5. Statistical evaluations were made on the metals analyzed for during the B-20 remedial investigation. These metals, which include arsenic, barium, cadmium, chromium, lead, and mercury, were considered to be possible contaminants of concern at the B-20 site.
The statistical evaluation for each metal in each soil or rock type included determining the percentage of non-detects, the distribution of the data (normal or lognormal), adjustments to the mean and standard deviation (when appropriate), and finally, the 95% upper tolerance limit. Appendix H shows each of the statistical calculations made in determining background concentrations for each metal in each soil or rock type.
Arsenic was detected in 15 of the 40 background samples. In Brackett-Tarrant association soils and Glen Rose limestone, arsenic was detected in less than 50% of the samples. Therefore, the highest concentration (including half the detection limit) was determined to be the non-parametric upper tolerance limit, which was 4.3 milligrams per kilogram (mg/kg) for Glen Rose limestone and 6.0 mg/kg in Brackett-Tarrant soils.
In Krum Complex and Crawford and Bexar soils, arsenic was detected in 50 to 60% of the samples. According to the methodology presented in Section 4.15.5 and Section 4.15.6, the data had to be adjusted for non-detect values using either Aitchinson's or Cohen's method. To determine the proper method, data from these two soil types were tested by determining correlation coefficients of censored and "detects only" data. Based on these tests, Krum complex soil data (normal distribution) and Crawford and Bexar soil data (lognormal distribution) were adjusted by the Aitchinson's method, resulting in upper tolerance limits of 9.87 mg/kg and 34.0 mg/kg, respectively.
Barium was detected in each of the background samples; therefore, the parametric tolerance limit test was performed on each dta set (Glen Rose, Brackett-Tarrant, Crawford and Bexar, and Krum) after the data distribution was determined. The distributions of barium data from each of the sets were both normal and lognormal. However, based on the Shapiro-Wilk Test of Normality, the distributions of barium in Glen Rose limestone and Krum Complex soils were more strongly normal, while the distributions in the other two soil types were more lognormal.
Statistically determined background levels of barium were 9.7 mg/kg (Glen Rose), 84.3 mg/kg (Bte), 169.7 mg/kg (Cb), and 171.4 mg/kg (Kr).
Cadmium was detected in very few background samples. Therefore, the parameteric tolerance limit test could not be performed on cadmium data from any of the three soil types or the Glen Rose limestone. Accordingly, the highest concentration (including half the detection limit) was established as the background concentration.
Non-parametric upper tolerance limits were 0.55 mg/kg (Glen Rose), 0.95 mg/kg (Bte), 2.6 mg/kg (Kr), and 3.0 mg/kg (Cb).
Chromium was detected in 38 of 40 background samples; therefore, the parametric tolerance limit test was performed on each of the data sets after the data distribution was determined. The distributions of chromium in each of the data sets, except the Krum soils data, are both normal and lognormal. Crawford and Bexar soils data and Brackett-Tarrant data have a stronger lognormal distribution, and Glen Rose data has a stronger normal distribution. The distribution of chromium in Krum soils is lognormal, but not normal.
Sine 20% of the Glen Rose chromium data was nondetect, the mean and standard deviation had to be adjusted before determining the upper tolerance limit. Based on the correlation coefficients for censored and detects-only data, the data was adjusted using Cohen's method.
Tolerance limits for chromium using normal or lognormal data, depending on the distribution, were 3.2 mg/kg (Glen Rose), 15.0 mg/kg (Bte), 43.4 mg/kg (Cb), and 50.7 mg/kg (Kr).
Lead was detected in each of the background samples. The distribution of lead data in each of the soil types was lognormal, based on the Shapiro-Wilk Test of Normality and probability plots. The distribution of lead data in the Glen Rose limestone was normal.
Tolerance limits for lead using normal or lognormal data, depending on the distribution, were 23.3 mg/kg (Bte), 69.3 mg/kg (Glen Rose), 82.4 mg/kg (Kr), and 133.0 mg/kg (Cb).
Mercury was only detected in three of the 40 background samples; therefore, the parametric tolerance interval test was not performed on mercury data. As in the case of cadmium, the highest value including half the detection limit) was determined to be the non-parametric upper tolerance limit.
Non-parametric upper tolerance limits were 0.03 mg/kg (Glen Rose, Kr, and Cb) and 0.04 mg/kg (Bte).
According to the Bexar County SCS soil survey, there are three soil types at the B-20 site: Crawford and Bexar stony soils, Brackett-Tarrant association soils, and Krum complex soil. Observations made during the field investigation generally support this classification. Soil descriptions are included in Table 4.3 and in the soil boring logs in Appendix E.
Brackett-Tarrant association (Bte) soils tended to consist of dark brown to olive brown silty and gravelly clay. These soils were located primarily in the topographically high areas of the site.
Krum complex soils consisted of very dark gray clay with high plasticity. These soils were found in the topographically low areas of the site, near the ephemeral stream.
Crawford and Bexar stony soils consisted primarily of dark brown gravelly clays. These soils were found between the Krum complex soils and the Brackett-Tarrant association soils.
Limestone bedrock was encountered during drilling of each of the ten soil borings at depths ranging from0.5 foot to 11 feet. This limestone, which extended to the total depth of each of the borings (maximum of 23.9 feet BGL), contained occasional interbedded marly zones. Grain size characterizations ranged from mudstone to wackestone, however, mudstone was the most predominant. Fossil fragments, including a pelecypod, gastropods, and a small amount of crinoid stems, were observed throughout most of the rock column. The limestone was generally white in shallow portions of the borings and graded to gray with depth.
A small solution cavity was encountered at a depth of approximately 10.5 to 12 feet in boring SB1, which was located in the bed of the ephemeral stream main channel. This was the only boring in which groundwater was encountered. Several of the other borings had remnants of solution cavities, however, these cavities were filled with calcite. Vertical and horizontal fractures were observed in several of the borings, generally at depths less than 12 to 13 feet.
The geologists logging the soil borings made a specific effort to look for evidence of the Corbula bed and the gypsum marker bed in the subsurface and on the surface. However, neither of these stratigraphic markers were found at the site. As published research shows this area of CSSA mapped within the upper Glen Rose, both field observations and research indicate that the site lies within the upper Glen Rose Formation. No evidence of faults or folding was observed at the surface of the site.
During the B-20 field investigation, groundwater was encountered in only one of the ten borings (SB1), which agrees with regional hydrogeologic publications that indicate perched zones within the upper Glen Rose Formation are quite sporadic. Boring SB1 is located in the bed of the ephemeral stream main channel. A perched zone is more likely in the bed of the stream than elsewhere on the site due to the more frequent flow of water in this area.
Based on the geology observed during drilling of ten borings, a perched groundwater zone is likely to be rare at the site. In addition, its yield is likely to be extremely low and highly dependent on precipitation.
Three types of surface water features were observed at the B-20 site during the field investigation: a small pond, an ephemeral stream comprised of a main channel and a small branch channel, and craters containing surface water.
Surface water runoff from the majority of the site drains into the main channel of the ephemeral stream on the east side of the site. The branch channel situated east of the main channel collects surface runoff from a small area north of the B-21 site. At the time of the field investigation, the branch channel and the portion of the main channel stream upgradient of the small pond shown in Figure 2.3 were dry. Based on the stream's large amount of topographic relief in its upper reaches, and the fact that the bottom of the stream in that area is exposed bedrock, these portions probably contain fast-moving water during periods of very intense precipitation. Downgradient of the small pond, the branch forms a confluence with the main channel and the stream bed slopes gently to the northeast. This area was boggy and wet throughout the investigation, and it is likely that surface water passes through this area at a very low velocity.
The small pond, located along the main channel of the ephemeral stream, is the first major area in which surface water collects. The water level of this pond is strongly influenced by precipitation. When the amount of precipitation decreased from November to December 1994, the water level of the pond dropped approximately 3 to 4 feet. Downgradient of this small pond is a larger pond, identified as the livestock pond on Figure 2.3. This pond, which is outside of the B-20 site boundary, was formed many years ago when an earthen dam was constructed.
The final type of surface water feature observed at the B-20 site is craters. Surface water was observed on at least one occasion in four craters at the site (craters 1, 6, 12, and 13). Crater 1 contained a small amount of water (less than 6 inches deep) in November 1994. Craters 12 and 13 also contained water in November 1994, but in early December, during the main sampling effort, these craters were dry. However, later in December, several days after precipitation, these two craters contained water once again. Crater 8 contained water during the entire field investigation. Surface water in these craters is a result of surface drainage in the immediate vicinity of these craters. Surface water in these craters evaporates or is absorbed into the underlying sediments and soils.
5.5 - Environmental Sample Analytical Results
Two soil samples were collected from each of ten soil borings, as described in Section 4.3.2. The soil samples wer analyzed for nitroaromatics and nitramines, arsenic, barium, cadmium, chromium, lead, and mercury. Analytical methods are described in Section 4.12. A full list of contaminants detected in the subsurface soils is given in Table 5.6.
Very low concentrations of one explosive compound, HMX, was detected in soil samples collected from soil boring SB4. Both samples collected from this borings contained HMX at a concentration below the PQL of 1.0 mg/kg. Since HMX was detected at a concentration below the PQL, the result can only be considered an estimate. Furthermore, it should be noted that the duplicate of SB4 (15.0-16.5 ft), SB100, contained no detectable HMX. All of the metals analyzed, with the exception of cadmium, were detected in one or more soil boring samples. Mercury was detected in only one sample, and lead was detected in all of the samples.
5.5.1.2 Comparison to Standard 1 Criteria
Background concentrations for the Glen Rose Formation described in Section 5.3 and listed in Table 5.4 were used to compare contaminant levels in subsurface soil and rock to standard 1 criteria. If the PQL was greater than the background value, then the PQL rather than background was used as the risk reduction standard 1 (RRS1) comparison criteria.
The low level concentrations of HMX detected in SB4 were below the PQL and therefore meet the cleanup criteria of RRS1. The arsenic or mercury concentrations exceeded background levels in three of the borings (SB2, SB9, and SB10). In SB2, the mercury concentration (0.43 mg/kg) exceeded the background concentration (0.03 mg/kg) at a depth of 14.0 to 15.0 feet below ground level. Arsenic exceeded background in SB9 and SB10. Figure 5.16 shows the borings exceeding RRS1 criteria.
5.5.1.3 Comparison to Standard 2 Criteria
Because the site is located in a remote area of a federal facility and is not currently being used for human habitation or for other purposes with a similar potential for human exposure (30 TAC 335.552), nonresidential cleanup standards listed in appendix II of 30 TAC 335 Subchapter S have been used as contamination comparison concentrations fro risk reduction standard 2 (RRS2) criteria, with a few exceptions.
All of the B-20 subsurface soil samples were collected at depths greater than 2 feet. Therefore, in accordance with 30 TAC 335.559(g), the concentrations of most contaminants in subsurface soils were compared to soil-to-groundwater cross-media protection concentrations. The only exceptions to this criteria were explosives concentrations and certain metals concentrations. Appendix II of 30 TAC 335 does not list cleanup levels for explosive compounds such as TNT, HMX, and RDX. According to 30 TAC 335.555(d)(1), if the PQL and/or background concentration for a contaminant is greater than the cleanup level, the greater of the PQL or background shall be used for determining compliance. Since the background concentrations is assumed to be 0 mg/kg for explosives compounds, the PQL was used as the cleanup level for explosives. In accordance with the same section cited above (30 TAC 335.555(d)(1)), lead levels were compared to the statistically determined background concentration. Methodology used to determine the statistical background concentration was presented in Section 4.15. In addition, cadmium concentrations were compared to the PQL, since the PQL exceeded the groundwater protection standard.
HMX concentrations detected in boring SB4 meet standard 2 cleanup criteria because they were below the PQL. Of the metals, arsenic and mercury exceeded the groundwater protection criteria for RRS2. Arsenic concentrations exceeded the cleanup standard (5.0 mg/kg) in SB9 (6.7 mg/kg in the 13.7 to 14.7 ft sample) and SB10 (7.6 mg/kg in the 14.6 to 15.6 ft sample). The mercury concentration exceeded the RRS2 cleanup level of 0.2 mg/kg in SB2 (0.43 mg/kg in the 14.0 to 15.0 ft sample). Figure 5.16 shows the borings exceeding RRS2 cleanup criteria.
Judgmental Samples. A total of twenty-one judgmental surface soil samples were collected at the site. The sampling locations were chosen based on prior knowledge of site uses and observations made during the site prescreening. Surface soil was samples (samples SS1 through SS14) within and 50 feet from seven craters to determine if site activities at the craters had affected surface soil. In addition, four surface soil samples (SS15 through SS18) were collected at three small ammunition disposal areas at the site and three samples (SS19 through SS21) were collected at locations were raw explosives were found during site prescreening. Judgmental sampling locations are shown on Figure 4.2. A summary of contaminant levels detected in the judgmental surface soil samples is given in Table 5.7.
Eight of fourteen samples (SS1 through SS14) collected from within and nearby the craters were analyzed for nitroaromatics and nitramines. No explosive residues were detected in any of these samples. All of the samples collected within and near the craters were analyzed for arsenic, barium, cadmium, chromium, lead, and mercury. Barium and lead were detected in all of these samples. The remaining metals were detected in several of the samples.
Samples SS15, SS17, SS18, and duplicate SS101 were collected from small ammunition disposal areas on site, and SS16 was collected downgradient of SS15. All four samples were analyzed for arsenic, barium, cadmium, chromium, lead, and mercury. Barium, chromium, and lead were detected in each of these samples, and arsenic and cadmium were detected in samples SS17, SS101, and SS18. Concentrations of lead were very high (120,000 to 280,000 mg/kg) in samples SS17, SS101, and SS18.
Samples SS19, SS20, and SS21 were collected at locations where raw explosives were found. Samples SS19 and SS21 were analyzed for nitroaromatics and nitramines. Sample SS20 was inadvertently analyzed for metals only. The explosive compound 2,4-TNT was detected in sample SS19 at a concentration of 374 mg/kg. No explosives were detected in sample SS21.
Systematic Samples. A total of twenty-two systematic surface soil samples were collected at the site. The sample locations were based on a 250-foot grid outline that stemmed from a randomly selected sampling location. All of the samples were analyzed for arsenic, barium, cadmium, chromium, lead, and mercury. In addition, thirteen of the samples were analyzed for nitroaromatics and nitramines. Analytical methods are described in Section 4.12.1. Systematic sampling locations are shown on Figure 4.2. A summary of the levels of contaminants detected in the systematic samples is provided in Table 5.8.
The explosive compound 1,3-dinitrobenzene (1,3-DNB) was detected in systematic sample SS27 at a concentration (0.346J mg/kg) below the PQL of 1.0 mg/kg. Explosive compounds were not detected in any of the other systematic surface soil samples. Barium and lead were detected in all of the systematic samples, and the other metals were detected in many of the samples.
5.5.2.2 Comparison to Standard 1 Criteria
Background concentrations for the three B-20 soil types (Brackett-Tarrant, Crawford and Bexar, and Krum complex) described in Section 5.3 and listed in Table 5.3 were used to compare contaminant levels in surface soil to standard 1 criteria. Each sample is compared to the background concentration of the appropriate soil type. If the practical quantitation limit (PQL) was greater than background, then the PQL rather than background was used as the standard 1 comparison criteria.
Judgmental Samples. The concentration of 2,4,6-TNT detected at SS19 exceeds the PQL, and therefore exceeds RRS1 cleanup criteria. In addition, metals at 11 of the 21 judgmental sampling locations exceed background concentrations. These locations include the three small ammunition disposal areas, and a large area in the central portion of the site. Figure 5.17 shows the areas at which contaminant concentrations exceed the RRS1 cleanup criteria. Metals concentrations at all locations except the small ammunition disposal areas were contoured to estimate the extent of surface soil exceeding background.
Systematic Samples. The concentration of 1,3-DNB detected in SS27 did not exceed the PQL, and therefore, did not exceed RRS1 cleanup criteria. Metals concentrations at 7 of the 22 systematic sampling locations exceed background levels. Barium and cadmium background levels were each exceeded at one sampling location (SS27 and SS35, respectively). Lead levels exceeded background at four locations (SS27, SS28, SS30, and SS31) and mercury exceeded background at five locations (SS23, SS30, SS31, SS34, and SS35). Metals concentrations exceeding standard 1 criteria are shown in Figure 5.17.
5.5.2.3 Comparison to Standard 2 Criteria
All surface soil samples (Judgmental and systematic) were collected at depths less than 2 feet. Therefore, contaminant concentrations, with the exception of arsenic, are compared to soil air ingestion/inhalation standards (MSCs) as prescribed by 30 TAC 335.558(g). Statistically calculated background arsenic levels were used as cleanup levels for each soil type since these concentrations exceeded the MSC (30 TAC 335.555(d)(1)).
Judgmental Samples. Similar to standard 1, the concentration of 2,4,6-TNT detected at SS19 exceeds RRS2 cleanup criteria. In addition, metals at 3 of the 20 judgmental sampling locations exceed RRS2 criteria. Areas exceeding RRS2 criteria are shown on Figure 5.18 and are limited to the immediate vicinity of SS19 and the three small ammunition disposal areas.
Systematic Samples. The concentration of 1,3-DNB detected at SS27 does not exceed RRS2 criteria because it did not exceed the PQL. None of the metals detected in the systematic surface soil samples exceed RRS2 cleanup criteria.
Five surface water samples were collected during this investigation. All five samples were analyzed for arsenic, barium, cadmium, chromium, lead, and mercury. The three samples (SW3, SW4, and SW5) collected within craters were analyzed for nitroaromatics and nitramines. Samples SW1 through SW4 were also analyzed for biological oxygen demand. Locations of the surface water sampling points are shown on Figure 4.3, and a summary of the analytical results is listed on Table 5.9.
No traces of explosives were found in the surface water samples. Barium was detected in three samples, and lead was detected in four samples. Arsenic and cadmium were only detected in SW5, which was collected from crater 13. Neither chromium nor mercury were detected in any of the surface water samples.
5.5.3.2 Comparison to Standard 1 Criteria
There are no data available on background concentrations of metals in surface water at CSSA; therefore, there are no standards to compare to for RRS1.
5.5.3.3 Comparison to Standard 2 Criteria
In accordance with 30 TAC 335.559(b), surface water analytical results are compared to standards presented in 30 TAC 307 (relating to Texas Surface Water Quality Standards). The only contaminants exceeding RRS2 criteria were lead and cadmium. Three samples (SW3, SW4, and SW5) contained lead levels above the freshwater criteria (30 TAC 307) of 0.005 mg/L. Samples SW3 and SW4 contained 0.006 mg/L and SW5 contained 0.390 mg/L of lead. The concentration of cadmium (0.05 mg/L) in samples SW5 also exceeded the freshwater criteria of 0.01 mg/L. All other metals were detected at concentrations below freshwater criteria levels. The samples exceeding RRS2 are shown in Figure 5.19.
A total of eight sediment samples were collected during this investigation. All of the samples were analyzed for arsenic, barium, cadmium, chromium, lead, and mercury. Five of the samples were analyzed for nitroaromatics and nitramines, and six of the samples were analyzed for VOCs and SVOCs. Sample locations are shown in Figure 4.3 and Table 5.10 is a summary of analytical results.
Common laboratory contaminants acetone, 2-butanone, and/or bis(2-ethylhexyl)phthalate were detected in five of the six samples analyzed. Since these are not compounds of concern at the site, their presence in the samples is attributed to laboratory contamination. VOCs and SVOCs were included in the sediment sampling program because methylene chloride and bis(2-ethylhexyl)phthalate had been detected at low concentrations during the preliminary sampling (Appendix C). Methylene chloride is another common laboratory contaminant.
The explosive compound HMX was detected in SE7 (0.670J mg/kg) and teh duplicate (SE100) of sample SE5 (0.881J mg/kg) at concentrations below the PQL of 1.0 mg/kg. Since both of these concentrations were below the PQL for the method, they should be considered estimates (flagged "J"). Barium, chromium, and lead were detected in all of the sediment samples. Arsenic, cadmium, and mercury were each detected in at least one sample.
5.5.4.2 Comparison to Standard 1 Criteria
Contaminant concentrations in sediments were compared to the background concentrations for the appropriate surface soil type. If the PQL was greater than the background concentration, then the PQL rather than the background was used as the RRS1 comparison criteria.
Since the HMX concentration detected in SE7 and the duplicate of SE5 did not exceed the PQL, they did not exceed the RRS1 cleanup criteria. Although acetone, 2-butanone, and bis(2-ethylhexyl)phthalate were detected in several of the samples, they are considered to be caused by laboratory contamination. CSSA records do not indicate disposal of any compounds or materials containing acetone, 2-butanone, or bis(2-ethylhexyl)phthalate. Cadmium, lead, and/or mercury exceeded background concentrations in SE5 and its duplicate, SE100. The samples exceeding RRS1 are shown in Figure 5.19.
5.5.4.3 Comparison to Standard 2 Criteria
Sediment sample analytical results are compared to soil/air ingestion and inhalation standards (MSCs) listed in Appendix II of 30 TAC 335, with the exception of arsenic results, which were compared to the PQL.
None of the VOCs, SVOCs, or metals detected in the sediment samples exceeded MSCs. Explosives concentrations detected in SE7 and the duplicate of SE5, SE100, did not exceed the PQL, and therefore, did not exceed the RRS2 cleanup criteria.
A groundwater grab samples was collected from the one boring (SB1) completed at the B-20 site which produced water. The sample was analyzed for nitroaromatics and nitramines, arsenic, barium, cadmium, chromium, lead, and mercury. No explosive compounds were detected in the sample. The only metals detected were barium and lead. These two metals are also the only two metals which were detected in every surface soil and sediment sample and in most of the subsurface soil/rock samples and surface water samples. Analytical results are presented in Table 5.11.
5.5.5.2 Comparison to Standard 1 Criteria
There are no background data available for groundwater at CSSA. However, due to the detection frequency of barium and lead in all samples collected at B-20, the concentrations are considered to be equivalent to background. The concentrations do not exceed maximum contaminant levels (MCLs). based on these results, groundwater at the site has not been affected by site disposal activities. Therefore, groundwater meets RRS1 criteria.
5.5.5.3 Comparison to Standard 2 Criteria
Groundwater analytical results are compared to Safe Drinking Water Act (SDWA) MCLs, in accordance with 30 TAC 335.559(d)(2), to determine if groundwater meets the criteria specified by RRS2. No explosives were detected, and none of the metals detected exceed MCLs. Since groundwater has not been affected by site disposal activities, it meets RRS2 criteria.
Six surface soil samples were analyzed for moisture content, pH, grain size, and cation exchange capacity. The moisture content is the percentage of water present in the soil. The pH measures the acidity or alkalinity of the soil. In this scale, 7 represents neutral; values greater than 7 are alkaline, and acids are values less than 7. Grain size is measured by shaking the soil through a series of sieves from larger to smaller openings, thus separating the soil by relative size. The result is provided as a percentage of the amount of soil which passed through a given sieve. For example, 27.0%-200 indicates that 27.0 percent of the soil passed through sieve #200 which is the smallest sieve (Krynine and Judd, 1957). The cation exchange capacity (CEC) is a measure of the quantity of readily exchangeable cations neutralizing negative charge in the soil. CEC is dependent on pH, ionic strength, the dielectric constant and teh composition of the soil (SSSA, 1982). This measure is useful in evaluating the soil's capacity to retain cations, its mineral composition, and general chemical reactivity (Buol et al., 1989).
The six samples were collected at random locations spread relatively evenly throughout the site. Moisture content in each sample was low to moderate, ranging from 13.0 to 26.9 percent. The alkalinity of the soils ranged from a pH of 8.18 to 8.30. This range indicates the presence of free calcium carbonate (Buol et al., 1989). Grain size was finer than the 200 sieve and ranged from 27.0 to 99.0%-200. The type of soil that passes through sieve 200 is silt and clay (Das, 1990). The CEC ranged from 1.4 milliequivalents per 100 grams (meq/100g) to 4.0 meq/100g which is fairly low according to one resource (Buol et al., 1989). Geotechnical results are summarized in Table 5.12. A copy of the geotechnical analytical report in included in Appendix G.
Three rock core samples were analyzed for horizontal permeability and porosity. Permeability is the capacity of a soil to transmit a fluid and measures the relative ease of fluid flow under unequal pressure (Driscoll, 1986). It depends on the size and shape of soil grains, the void ratio of soil, the shape and arrangement of voids, and the degree of saturation (Army, 1980). Porosity is the percentage of the bulk volume of a rock or soil that is occupied by both isolated and connected interstices (Driscoll, 1986).
Rock samples for geotechnical analyses were chosen based on location and lithology. Permeability ranged from 0.09 to 0.35 millidarcy, which is typical for silt (Das, 1990), and porosity ranged from 18.1 to 20.8 percent. These values are typical of limestone (Driscoll, 1986).