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SWMU B-10 RCRA Facility Investigation/Closure Report

Section 1 - Introduction

On May 5, 1999, an Administrative Consent Order was issued to CSSA pursuant to §3008(h) of the 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 has been prepared to document the environmental condition and site closure requirements of SWMU B-10 and to recommend further investigation, if necessary, or to provide documentation necessary for site closure. The main objectives of the SWMU B-10 investigation are to determine if the site meets TCEQ (formerly known at the 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 AMC Contract No. F11623-94-D0024, delivery order RL53. AFCEE provided technical oversight for the delivery order. Based upon the SOW, a set of work plans was established to govern the field work. These include:

For this report, Section 1 provides the site-specific background and closure standard. Section 2 describes field actions and the closure evaluations. Section 3 summarizes the findings, evaluates attainment of 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, Environmental Encyclopedia).

1.1 - Background and Site Description

1.1.1   CSSA

General information regarding the history and environmental setting of CSSA is provided in the Environmental Encyclopedia (Volume 1-1, Background Information Report). In that report, data regarding the geology, hydrology, and physiography are also available for reference.

1.1.2   SWMU B-10

1.1.2.1   Site Description

SWMU B-10 is located in the inner cantonment of CSSA south of SWMU B-3 and across the road from Building 43 (Figure B10-1). The site covers an area of approximately 3,700 square feet (0.09 acre). SWMU B-10 was reportedly used as an ammunition disposal area. Waste observed at the site consists of banding material and ammunition cans, and further field investigation identified mufflers, brake pads, oil filters, miscellaneous 5-gallon containers, an empty 55-gallon drum, miscellaneous machine gun parts, and an engine block. A UXO investigation did not reveal any UXO. The site is covered with native grasses. Trees are along the western boundary and a dirt road is located directly to the east. No stressed vegetation was identified. Prior to work completed as part of the current investigation, SWMU B-10 contained a 4-foot tall bunker formed of dirt and gravel, facing northeast. Corrugated tin formed a porch on the bunker. An 8-foot long by 1-foot wide area of miscellaneous metal debris was located southeast of the bunker. The metal debris included nails, hinges, and scrap metal. In the northeast corner of the site was a depression approximately 30 feet in diameter and 2 to 3 feet deep.

Background information regarding the location, size, and known historical use of SWMU B-10 is also included in the Environmental Encyclopedia (Volume 1-2, SWMU B-10). Volume 1-2 also includes a Chronology of Actions and a Site-Specific Work Plan for SWMU B-10.

1.1.2.2   Potential Sources of Contamination

Possible sources of contamination include metal debris, metallic leachate from metal debris, solvents, and fuels that may have been disposed at the site. Contaminated media could include surface and subsurface soils and possibly shallow groundwater, if present. Therefore, potential COCs associated with these wastes include metals and VOCs. Soil samples were also analyzed for total petroleum hydrocarbons during trenching activities.

1.1.2.3   Site Location

SWMU B-10 is located in the north-central portion of the Inner Cantonment directly east of AOC 36. The western boundary of SWMU B-10 borders AOC 36. The northern boundary of SWMU B-10 is approximately 100 feet south of SWMU B-3, and the southern boundary of SWMU B-10 is approximately 50 feet west of Building 43 (Figure B10-1). Numerous other SWMUs and AOCs are located to the west and south of SWMU B-10. SWMU B-10 is located 800 feet south-southeast of Well CS-16 and 1,000 feet southeast of Well CS-D. The site is located approximately 1,000 feet northwest of CS-MW2 and 1,250 feet northeast of CS-MW1. The nearest CSSA boundary is over ½-mile to the west.

1.2 - Site Environmental Setting

1.2.1   Site Soils and Topography

SWMU B-10 is covered by a single soil type, gently undulating Tarrant Association soils (Figure B10-2). Gently undulating Tarrant Association soils occur as nearly level and gently sloping areas of typical prairie and plateau topography. These soils occur primarily in areas not occupied by streams, such as the north-central area of the inner cantonment and the hills north of the inner cantonment. This soil type covers approximately 14.3 percent of CSSA. The soils are typically dark colored, very shallow, calcareous and clayey, and are best suited for native grasses and range use. Additional information on CSSA soil types is available in the Soils and Geology section of the Background Information Report (Volume 1-1) and in the Description of Soil Types and Bedrock (Volume 2). Soil samples collected as part of the excavation at SWMU B-10 were collected at depths of up to 6.5 feet bgs during trench sampling. The Upper Glen Rose Formation underlies the site but no bedrock outcrops were identified within SWMU B-10.

The elevation of SWMU B-10 ranges from approximately 1,230 to 1,235 feet above mean sea level. The ground surface slopes gently to the west-southwest towards Salado Creek.

1.2.2   Geology

The Upper Glen Rose Formation is the uppermost geologic stratum in the area of SWMU B-10 (Figure B10-3). 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 upwards into thin beds of limestone, marl, and shale. The Lower Glen Rose is underlain by the Bexar Shale facies of the Hensell Sand, 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 two known major fault zones at CSSA: the North Fault Zone and the South Fault Zone. SWMU B-10 is located within the North Fault Zone (Figure B10-3). Additional information on structural geology at CSSA can be found in the Environmental Encyclopedia (Volume 1-1, Background Information Report, Soils and Geology).

1.2.3   Hydrology

In general, the uppermost hydrologic layer at CSSA 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. Regionally, groundwater flow is thought to be enhanced along the bedding contacts between marl and limestone; however, the hydraulic conductivity between beds is thought to be poor. This interpretation is based on the observation that static well levels are discordant in adjacent wells completed in different beds. Principal 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.

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. As such, principal 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. Groundwater flow within the Middle Trinity Aquifer is toward the south and southeast, and the average transmissivity coefficient is 1,700 gpd/ft (Ashworth, 1983). In general, groundwater at CSSA flows in a north to south direction. However, local flow gradient may vary depending on rainfall, recharge, and possibly well pumping.

No site-specific information regarding groundwater is available. However, the nearest well is Well CS-16, an inactive drinking water well, located 800 feet north-northwest of SWMU B-10. Static water levels range between 78 ft BTOC (November 1998) and 316 ft BTOC (April 1995) in this well (Environmental Encyclopedia, Volume 5, Groundwater Monitoring).

The nearest surface water from SWMU B-10 is an intermittently flowing creek that flows south across AOC 38, which is west of SWMU B-10 (Figure B10-1). This intermittently flowing stream is located north and west of SWMU B-10 and the tributary joins with Salado Creek southwest of SWMU B-10. The unnamed tributary and Salado Creek are more than 500 feet from SWMU B-10. Salado Creek exits CSSA approximately one mile to the south across the southern CSSA boundary.

All the structures on-post are considered historical resources. 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 cultural resource to SWMU B-10 is Building 43, located approximately 50 feet to the east of the southern boundary of SWMU B-10.

1.2.5   Potential Receptors

A land use survey discussing local and possible future uses of groundwater and surface water, a water well survey, and sensitive environmental areas at CSSA was completed on 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).

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 the purpose of hunting. White-tailed deer, axis deer, and wild turkey all roam freely throughout CSSA. A map of deer hunting stands which overlook mechanical feeders and planted food plots is located in Figure 5.2 of the Technical Approach Document for Risk Evaluation (Volume 1-6). SWMU B-10 is located approximately 700 feet south of hunting stand number 2. Four water tanks are maintained at CSSA for the purpose of sport fishing. Two of the tanks are located in the northwestern and northeastern portions of the North Pasture, while the other two tanks are located near the western boundary of the Inner Cantonment.

1.3 - Previous Investigations

Historical records indicate that SWMU B-10 may have been used for ammunition disposal. A field investigation conducted in 1993 revealed miscellaneous metal debris at the site. In November 1995, soil gas samples were collected at SWMU B-10 in the area known as the “Area between SWMU B-3 and the Oxidation Pond.” Soil gas survey locations are shown in Figure B10-4. Each sample was analyzed for carbon tetrachloride, cis-1,2-DCE, PCE, and TCE. PCE was detected in every sample, and concentrations ranged from 0.02 μg/L to 1.6 μg/L. The maximum concentration was detected at the location E,10, which is situated approximately 75 feet east of SWMU B‑10. Carbon tetrachloride was detected in five samples and one duplicate, and concentrations ranged from 0.05 μg/L to 11 μg/L, with the maximum detected at location E,11. TCE was detected in only one sample (0.03 μg/L), approximately 250 feet southeast of SWMU B-10, and cis-1,2-DCE was not detected in any of the samples.

At location E,14, the only soil gas sample location within the SWMU B-10 boundary, 1.2 μg/L PCE and 0.07 μg/L carbon tetrachloride were detected. TCE and cis-1,2-DCE were not detected there. Results of the November 1995 survey are provided in Table 9.2 of the Technical Memorandum on Soil Gas Surveys, Section 9, Open Areas contained in Volume 5, Groundwater Investigation and Associated Source Characterization, June 1996. The PCE soil gas plumes underlying B-10 and vicinity are shown in Figure B10-4.

1.4 - Closure Standard