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SWMU B-28 RCRA Facility Investigation Report
Section 1 - Introduction
On May 5, 1999 an Administrative Consent Order was issued to CSSA pursuant to §3008(h) of SWDA, as amended by RCRA, and further amended by the HSWA of 1984. In accordance with the RFI requirements of the Consent Order, this report was prepared to document the environmental condition and site closure requirements of SWMU B-28 and to recommend further investigation, if necessary, or to provide documentation necessary for site closure. The main objectives of the SWMU B-28 investigation are to determine if the site meets TNRCC requirements for closure, as described in Section 1.4, and to meet requirements of the Consent Order.
This specific RFI was performed by Parsons under the U.S. Air Force AMC Contract F11623-94-D0024, Delivery Order RL33. AFCEE provided technical oversight for the delivery order. Based upon the RL33 SOW, a set of work plans to govern the fieldwork was established. These include:
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Work Plan Overview |
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Site-Specific Work Plan |
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Field Sampling Plan |
(Volume 1-4, RL33 Addendum); and |
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Health and Safety Plan |
For this RFI report, Section 1 provides the site-specific background and closure standard. Section 2 describes field actions and the closure evaluation. Section 3 summarizes the findings, evaluates attainment of the data quality objectives, provides recommendations, and certifies the site closure, if applicable. References cited in this report can be found in the Bibliography (Volume 1-1 of the Environmental Encyclopedia).
In addition to the consent order requirement to conduct an RFI, interim measures are also required to address SWMU B-28 soil that has been sifted to remove UXO. The UXO removal activities are described in this report, but activities related to the interim measures are addressed in the Soil Pile Disposition Assessment Report, currently being prepared under a separate delivery order.
1.1 - Background and Site Description
General information regarding the history and environmental setting of CSSA are provided in the CSSA Environmental Encyclopedia (Volume 1-1, Background Information Report). In the report, data regarding the geology, hydrology, and physiography are also available for reference.
1.2 - Site Environmental SettingSWMU B-28 is an area where small arms ammunition, metal ammunition parts, aerial flares, and other metal debris was disposed of in two trenches located near the northeast corner of the inner cantonment of CSSA (Figure B28-1). The exact dates of usage are unknown. Aerial photographs of CSSA dated 1934, 1957, 1962, 1966, 1973, 1978, 1985, 1991, 1996, and 1999 were reviewed in an effort to better determine when the site was used. In 1962, the site area was wooded, but in 1966, there were few trees at the site, and a gravel road led to the site from the east. However, there were no ground scars in 1966. This suggests that the site may have been used sometime between 1962 and 1966, but that grass had already returned to previously disturbed areas. In addition, the 1978 aerial photograph shows an area of bare soil in a linear pattern parallel to the road to the west of the site was visible. This may be representative of additional use of the site between 1973 and 1978.
Over the course of the RFI activities at this unit, two trenches were identified. The trenches were found to contain buried munitions and various metal ammunition parts. The northern trench measures approximately 300 feet long and 15 feet wide, and the southern trench measures approximately 100 feet long and 15 feet wide.
The site is mostly level and covered with sparse vegetation and a thin soil profile. No activities currently take place at this unit. One overhead utility line trends southeast to northwest across the site. Figure 8-1 of the Technical Memorandum on Geophysical Surveys, Well 16 Source Characterization shows the location of this utility line. Moyer Road is located immediately west of the unit.
Background information regarding the location, size, and known historical use of SWMU B-28 is also included in the Environmental Encyclopedia (Volume 1-2, SWMU B-28). Volume 1-2 also includes a Chronology of Actions and a Site-Specific Work Plan Addendum for SWMU B-28.
1.1.2.2 Potential Sources of Contamination
The potential source of contamination at SWMU B-28 is buried waste consisting of small arms ammunition, metal ammunition parts, aerial flares, and other metal debris. Excavation activities performed at the site have identified the presence of buried metal debris and small amounts of UXO. There are no records available to confirm all possible waste disposed at the site.
The site is located near the northeast corner of the inner cantonment, west of SWMU O-1 and SWMU B-19. AOC 36 overlaps the northern boundary of SWMU B-28. The area is approximately 0.1 acre in size (Figure B28-1).
1.2.1 Site Soils and Topography
The elevation of the site is approximately 1,220 feet above sea level (Figure B28-2), with a gentle slope towards the southwest. Surface runoff from the site drains to Salado Creek located approximately 200 feet southwest of the site. The site is relatively flat and vegetated with native grasses, isolated clusters of live oaks stands and juniper trees.
SWMU B-28 lies almost entirely in the Krum Complex soils, with a very small southern corner lying in the Trinity and Frio Soils (Figure B28-2). Detailed descriptions of the CSSA soil types are provided in the CSSA Environmental Encyclopedia (Volume 1-1, Background Information Report, Soils and Geology). Most CSSA soils are typically calcareous clay, ranging in depth from 4 to 60 inches and are underlain by limestone. SWMU B-28 appears to be typical with silty clay observed from 0 to 5 feet bgs, underlain by limestone.
The Upper Glen Rose is the uppermost geologic stratum in the area of SWMU B-28 (Figure B28-3). The Upper Glen Rose consists of beds of blue shale, limestone, and marly limestone, with occasional gypsum beds. Generally, it outcrops in stream valleys and at the ground surface where soils are poorly developed or eroded. Where present at CSSA, the Upper Glen Rose may be up to 150 feet thick. It is underlain by the Lower Glen Rose, which is estimated to be 300 feet thick beneath CSSA. The Lower Glen Rose is a massive, fossiliferous, vuggy limestone that grades upward into thin beds of limestone, marl, and shale. The Lower Glen Rose is underlain by the Bexar Shale (regionally known as the Hensell Shale), which is estimated to be from 60 to 150 feet thick under the CSSA area. The Bexar Shale consists of silty dolomite, marl, calcareous shale, and shaley limestone. The geologic strata dip approximately 10 to 12 degrees to the south-southeast at CSSA.
Based on current published information, there are known to be two major fault (shatter) zones at CSSA: the North Fault Zone and the South Fault Zone. SWMU B-28 is located entirely over the North Fault Zone that trends to the northeast, and transects the central portion of CSSA (Figure B28-3). Additional information on structural geology at CSSA can be found in the Environmental Encyclopedia (Volume 1-1, Background Information Report, Soils and Geology).
At CSSA, the uppermost hydrogeologic layer is the unconfined Upper Trinity aquifer, which consists of the Upper Glen Rose Limestone. Locally at CSSA, low-yielding perched zones of groundwater can exist in the Upper Glen Rose. Transmissivity values are not available for the Upper Glen Rose. Regionally, groundwater flow is thought to be enhanced along the bedding contacts between marl and limestone, however, the hydraulic connection between beds is thought to be poor. This interpretation is based on the observation that static well levels are discordant in adjacent wells completed at approximately the same elevation. Principle development of solution channels is limited to evaporite layers in the Upper Glen Rose Limestone. Groundwater discharge occurs predominantly via natural springs, seeps, and pumping. Regional groundwater flow appears to be to the southeast.
The Middle Trinity aquifer is unconfined and functions as the primary source of groundwater at CSSA. It consists of the Lower Glen Rose Limestone, the Bexar Shale, and the Cow Creek Limestone. The Lower Glen Rose Limestone outcrops north of CSSA along Cibolo Creek and within the central and southwest portions of CSSA. Principle recharge into the Middle Trinity aquifer is via precipitation infiltration at outcrops. At CSSA, the Bexar Shale is interpreted as a confining layer, except where it is fractured and faulted, therefore allowing vertical flow from the up-dip Cow Creek Limestone into the overlying, but down-dip Lower Glen Rose. Fractures and faults within the Bexar Shale may allow hydraulic communication between the Lower Glen Rose and Cow Creek Limestones. In general, groundwater at CSSA flows in a north to south direction, with some seasonal fluctuations. However, local flow gradient may vary depending on rainfall, recharge, and possibly wells pumping.
SWMU B-28 is located entirely over the northern fault zone at CSSA (see Figure B28-3). Fracture systems associated with the fault zones are thought to affect groundwater flow and to be the controlling structural feature for migration of contaminants in the vadose zone at CSSA (Volume 1-1, Background Information Report).
No site-specific information regarding groundwater is available. In 1995, shallow perched groundwater was encountered at a depth of approximately 28 feet bgs in boring B28-SB3. A sample of the perched groundwater was collected and analyzed for VOCs, SVOCs, and metals. Results are described in Section 1.3.3.
The nearest CSSA water well is Well CS-4, located approximately 1,000 feet northwest of B-28. Well CS-4 is currently used for monitoring purposes only. Groundwater levels within Well CS-4 typically range from approximately 150 to 250 feet bgs, but have been as high as 45 feet bgs during periods of significant rainfall. The nearest off-site water well is a private well located on Ralph Fair Road approximately 4,500 feet west of the site.
No creeks, streams, or ponds are located within SWMU B-28, however, Salado Creek is approximately 200 feet to the southwest of the site. Regional groundwater flow appears to be to the southeast. More information regarding the regional hydrology at CSSA is in Volume 5.
Cultural resources are prehistoric and historic sites, structures, districts, artifacts, or any other physical evidence of human activity considered important to a culture, subculture, or community for scientific, traditional, or religious purposes. The nearest site of potential archeological significance are World War II foxholes located approximately 4,600 feet to the southeast of SWMU B-28, near Gate 7.
A land use survey identifying local and possible future uses of groundwater and surface water, a water well survey, and sensitive environmental areas was conducted at CSSA. This survey was completed during December 15 and 16, 1999. The results of this survey, along with results from a more in-depth survey to identify potential receptors, points of human exposure, and possible constituent pathways is presented in Section 3 of the Technical Approach Document for Risk Evaluation (Volume 1-6).
Land within 0.25-mile of SWMU B-28 is classified as "Evergreen Forest Land" in Figure 1.1 of the Technical Approach Document for Risk Evaluation. Several buildings are present to the south of B-28. These buildings are used by CSSA primarily for storage and exposure concerns from B-28 are considered minimal. Three inactive water supply wells (Wells CS-2, CS-3, and CS-4) are located west of B-28. The nearest residential area is approximately 4,500 feet west of the unit. In addition, Fair Oaks Elementary School is over a mile from the site.
A small herd of cattle is maintained on CSSA by the USDA-ARC. The cattle roam freely throughout the Inner Cantonment and in selected areas of the North Pasture. CSSA also manages wild game species for hunting purposes. White-tailed deer, axis deer, and wild turkey all roam freely throughout CSSA. A map of deer hunting stands that overlook mechanical feeders and planted food plots is located in the Technical Approach Document for Risk Evaluation (Volume 1-6). SWMU B-28 is located approximately 900 feet southwest of hunting stand number 2.
Four water ponds/tanks are maintained at CSSA for the purpose of sport fishing. Two of the ponds are located in the northwestern and northeastern portions of the North Pasture while the other two ponds are located near the western boundary of the Inner Cantonment.
No active livestock wells or monitoring wells are located within the areal extent of SWMU B-28. The closest well is Well CS-4, approximately 1,000 feet to the northwest. The B-28 area is currently not used by CSSA.
The nearest potential habitats for local endangered species (Volume 1-1, Background Information Report, Figure 11) are 1,250 feet to the east (Black-Capped Vireo) and 5,400 feet to the east (Golden-Cheeked Warbler).
1.3.1 Mustard Gas Investigation
Environmental field actions at B-28 commenced in 1958 with concerns of mustard gas disposal in AOC 36, which overlaps the northern boundary of the site. AOC 36 was identified by CSSA records as a site that may possibly contain six 155-millimeter (mm) shells containing mustard gas, which were buried and detonated in 1942 at one location at the post. In 1958, at the request of CSSA, the shell fragments were excavated and destroyed by the U.S. Army Chemical Corps Technical Escort Detachment personnel and the burial site was determined to be free of contamination. A records review was conducted in 1997 to search for any additional records regarding possible mustard gas disposal at CSSA. Following the record search, a physical investigation was conducted in the suspected area to determine if mustard gas shells remained at the site. Several investigation methods were employed to accomplish this goal. No evidence of mustard gas or mustard gas shells was observed at AOC 36 or SWMU B-28. The complete report on the investigation and approved closure of the mustard gas site can be found in the Mustard Gas Investigation Report (Volume 3-2, AOC 36).
The records for SWMU B-28 were reviewed during the preliminary evaluation for groundwater contamination in October 1992. This records search indicated that small arms ammunition, metal ammunition parts, aerial flares, and other metal debris were disposed of in two trenches at the site. On February 3, 1995, Parsons ES conducted an EM geophysical survey, during which two geophysical anomalies potentially related to past waste management activities were identified. On February 16, 1995, Parsons ES conducted a GPR geophysical survey in the northern trench area. The GPR survey provided a strong response in areas where metal was exposed at the surface. The locations of the anomalies identified during the geophysical surveys are included on Figure B28-4.
1.3.3 Soil Boring and Groundwater Samples
Between February 27 and March 1, 1995 six soil borings (SB01 through SB06) were drilled in the B-28 disposal locations. The borings were drilled to a depth of 30 feet bgs. Soil boring locations are shown on Figure B28-4. Soil/rock samples were collected at depths of 0 to 3 feet bgs, 14-16 feet bgs, and at the boring terminus. The samples were submitted to Chemron Inc, of San Antonio, Texas, and analyzed for VOCs (SW-8260), SVOCs (SW-8270), and metals (SW-6010). Sample holding times were exceeded for the six VOC samples from borings SB01 and SB02 and therefore, these borings were redrilled in June 1995.
Analytical results for the soil boring samples indicated that no VOCs were present in the samples. Results are summarized in Table B28-1. Phthalate isomers bis(2-ethylhexyl)phthalate, butylbenzylphthalate, and di-n-butylphthalate were detected in sample SB03 (0.0-1.0 ft), SB03 (14.0-15.0 ft), SB03 (29.5-30.0 ft), SB04 (29.5-30.0 ft), and SB05 (0.0-2.0 ft). The presence of the phthalates in the samples is believed to be an artifact associated with laboratory or field sampling activities and not representative of site conditions. Additionally, cadmium and chromium were detected at levels slightly above the RRS1, or background, levels in samples SB01 (0.0-1.0 ft) and SB03 (0.0‑2.0 ft), respectively. All other constituents were either not detected or were present at concentrations below the RRS1 levels. Complete results of the soil/rock sampling activities are presented in the Environmental Encyclopedia (Volume 1-2, SWMU B-28), and in Section 8 of the Technical Memorandum on Soil Boring Investigation, Well 16 Source Characterization (Parsons ES, 1995).
During the February and March 1995 soil boring activities, one groundwater sample was collected from boring SB03. The groundwater samples was submitted to Chemron Inc. of San Antonio, Texas and analyzed for VOCs (SW-8260), SVOCs (SW-8270), and metals (SW-6010). Analytical results for the groundwater sample, summarized in Table B28-2, indicated that all constituents were either not detected or present at concentrations below their respective RRS2 standards. Although lead was not detected, the detection limit (0.03 mg/L) was greater than the RRS2 criteria (0.015 mg/L). Results of the groundwater sampling is presented in the Environmental Encyclopedia (Volume 1-2, SWMU B-28), and in the Section 8 of the Technical Memorandum on Soil Boring Investigation, Well 16 Source Characterization (Parsons ES, 1995).
In June 1995, two additional soil borings were drilled and one additional groundwater sample was collected at SWMU B-28 due to exceedances of sample holding times for samples collected during the earlier sampling event. Soil borings SB01R and SB02R were drilled in close proximity to the original borings SB01 and SB02. The borings were drilled to a depth of 30 ft bgs, and soil/rock samples were collected from the borings at depths of 0 to 3 ft bgs, 14-16 ft bgs and at the boring terminus. Samples were submitted to Chemron Inc. of San Antonio, Texas for VOC analysis (SW-8260) only. Additionally, one groundwater sample was collected from boring SB01R and submitted to Chemron for VOC analysis (SW-8260). Results of the soil and groundwater samples were below the detection limits for all constituents. Results of the resampling activities are presented in the Addendum to the Technical Memorandum on Soil Boring Investigation, Well 16 Source Characterization (Parsons ES, 1995), and are summarized in Table B28-1.
Finally, a soil gas survey was conducted at the site between June 29 and July 19, 1995. A total of 16 soil gas samples were collected at the unit, at locations shown in Figure B28-4. The samples were analyzed for PCE, TCE, DCE, and BTEX. PCE was the only compound detected in the soil gas samples and the maximum concentration detected in the samples was 0.7 μg/L. Based on the concentrations and locations of the low level detections, SWMU B-28 is not considered to be the source of VOCs in soil gas. Nearby SWMUs B-3 and O-1 are considered the sources of VOCs in soil gas in the area. The results of this survey are presented in Section 6 of the Technical Memorandum on Soil Gas Surveys (Parsons ES, 1996).
As described in Section 4.3 of the Risk Assessment Technical Approach Document (Volume 1-6), CSSA has opted to pursue closure of SWMU B-28 under the Risk Reduction Rule (30 TAC §335). If the site concentrations do not exceed background, then the site will be closed using RRS1. If the site exceeds background, then a determination will be made regarding the feasibility of cleaning the site to meet background concentrations. If the decision is made to clean the site to background, closure under RRS1 will be sought. However, if it is determined that the site cannot be closed to meet background concentrations, then the site will be closed under TRRP. A notification of intent to close sites identified to date (including the B-28) in accordance with the former RRR was sent to the TNRCC on July 12, 1999. TNRCC acceptance of this notification was received on October 5, 1999.
RRS1 requires that the site be closed following removal or decontamination of waste, waste residues, and contaminated operation system components; and demonstration of attainment of cleanup levels (30 TAC §335.554). If closure requirements under RRS1 are attained and approved by the TNRCC Executive Director, then the owner is released from the deed recordation requirement.
Since the COCs for the B-28 site are VOCs, explosives, and metals, the cleanup levels should be the RLs for VOCs and explosives, and the background levels for metals. Chlorinated VOCs and explosives are man-made chemicals, and rarely occur naturally. Background metals levels were statistically calculated for CSSA soils and the Glen Rose Limestone, and are reported in the Second Revision to the Evaluation of Background Metals Concentrations in Soils and Bedrock (Volume 2, Soils).