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Final SWMU B-15/16 RCRA Facility Investigation Report

Section 1 - Introduction

On May 5, 1999, an Administrative Consent Order was issued to Camp Stanley Storage Activity (CSSA) pursuant to §3008(h) of the Safe Drinking Water Act (SDWA), as amended by the Resource Conservation and Recovery Act (RCRA), and further amended by the Hazardous and Solid Waste Act (HSWA) of 1984. In accordance with the RCRA Facility Investigation (RFI) requirements of the Consent Order, this report has been prepared to document the environmental condition and site closure requirements of Solid Waste Management Unit (SWMU) B-15/16 and to recommend further investigation, if necessary, or to provide documentation necessary for site closure. The main objectives of the SWMU B-15/16 investigation are to determine if the site meets Texas Commission on Environmental Quality (TCEQ) requirement 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 Air Mobility Command Contract F11623-94-D-0024, Delivery Orders RL17 and RL83. The Air Force Center for Environmental Excellence (AFCEE) provided technical oversight for the delivery order. Based upon the statement of work (SOW), a set of work plans to govern the fieldwork were established. These include:

For this 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 the attainment of data quality objectives (DQOs), 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). 

1.1 - Background and Site Description

1.1.1   CSSA

Generalized facts regarding the history and environmental setting of CSSA can be found in the CSSA 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-15/16

1.1.2.1   Site Description

SWMU B-15/16 is a large area, approximately 3.3 acres, of disturbed soil and partially open trenches. [The July 1999 Current Conditions Report incorrectly reported an area of approximately 5.8 acres.] In 1993, B-15 was observed to be two large rectangular areas of settled soil and stressed vegetation. Also during this year, a field survey of B-16 indicated two trenches in which metal objects were visible on the surface partly covered by soil that had settled into the trenches. Subsequent geophysical survey results (described in Section 1.3) showed that the two SWMUs were connected, and the sites were combined.

Two large trenches trend from east to west across the site. One of them is approximately 300 feet long and 20 feet wide and the other is approximately 200 feet long and 40 feet wide. Smaller trenches as well as oblong and round dirt mounds of varying height are located south of the site. The area north of the site contains long, low, parallel mounds separated by wide depressions. Large mounds of dirt are located at each end of the southern trench and are assumed to be from its excavation. Each mound is approximately eight feet tall with a base diameter of approximately 50 feet. Two shorter dirt mounds were observed north of the northern trench.

B-15/16 is open and covered by grass both inside and outside of the trenches. Some low brush has grown up in areas around the site. Oak trees dot the western and northwestern edges of the site. A dry creek bed bounds the site to the west while a dirt access road bounds the site on the east (Figure B15/16-1).

According to interviews and records, both SWMU B-15 and B-16 were used as SWMU landfill areas for the disposal of target vehicles and weapons mounts (Parsons ES, 1993). Visible metal debris, including vehicle parts, is present in the landfill areas. 

Except for cattle and wildlife grazing, no other activities are currently performed at SWMU B-15/16.

Background information regarding the location, size, and known historical use of the site is also included in the Environmental Encyclopedia (Volume 1-2, SWMU B-15/16). This volume includes a Chronology of Actions and a Site-Specific Work Plan Addendum for SWMU B-15/16.

1.1.2.2   Potential Sources of Contamination

Historical records indicate that SWMU B-15/16 was used as a landfill area for the disposal of miscellaneous metal debris that included target vehicles and weapons mounts. Trenches present at the site contain these metal objects which are the primary source for contamination of surface and subsurface soils in the vicinity of the site. Chemicals of potential concern (COPCs) include volatile organic compounds (VOCs), explosives, and metals from materials disposed in SWMU B-15/16.

1.1.2.3   Site Location

SWMU B-15/16 is located in the east pasture, approximately 100 feet east of the boundary fence separating the inner and outer cantonment (Figure B15/16-1). The site lies approximately 150 feet north of the CSSA/Camp Bullis southern boundary fence. SWMU B-15/16 is situated between two areas of concern, AOC-48 on the north and AOC-47 on the south.

1.2 - Site Environmental Setting

1.2.1   Site Soils and Topography

As shown on Figure B15/16-2, soils in the vicinity of SWMU B-15/16 are defined as Trinity and Frio soils in the U.S. Department of Agriculture (USDA) Soil Conservation Service soil survey for Bexar County, Texas (USDA, 1991). Thickness of soils ranged from four to ten feet within the site boundary of SWMU B-15/16. Trinity and Frio soils are the main channel soils for Salado Creek and a large tributary that joins the creek in southwestern CSSA. Additional information concerning the soil types at CSSA is included in the Second Revised Evaluation of Background Metals Concentrations in Soils and Bedrock (Volume 2).

SWMU B-15/16 lies in the Salado Creek floodplain; therefore, it is topographically lower than the surrounding areas. The elevation of the site is approximately 1,170 feet above sea level, sloping gently (less than one percent grade) toward Salado Creek to the west. The northern trench at the site is open on the west side to allow for drainage into the creek bed. Dirt mounds bound the southern trench on both ends.

1.2.2   Geology

The Upper Glen Rose is the uppermost bedrock geologic stratum in the area of SWMU B-15/16 and the north pasture (Figure B15/16-3). 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 thickness of the Upper Glen Rose varies up to 150 feet in thickness. 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 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.

There are two major fault (shatter) zones at CSSA: the North Fault Zone and the South Fault Zone. SWMU B-15/16 is located approximately 350 feet south of the South Fault Zone. Additional information on structural geology at CSSA can be found in the Environmental Encyclopedia (Volume 1-1, Background Information Report, Soils and Geology).

Bedrock outcrops are found on the western portion of the site where Salado Creek dissects the limestone. Subsurface information from the nine borings drilled at the site indicates that limestone bedrock exists beneath approximately ten feet of soil and alluvium.

1.2.3   Hydrology

At CSSA, the uppermost hydrologic 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 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. 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.

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, 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. 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). 

Surface waters drain to the west into Salado Creek which runs along the western portion of the SWMU (Figure B15/16-1). The north-south trending creek exits the CSSA boundary approximately 400 feet south-southeast of the site. No site-specific information regarding groundwater is available. However, between October 1992 and June 2002, measured water levels at Well CS-1, which is located approximately 1,500 feet southwest of the site, have ranged from 101.3 feet below top of casing (ft BTOC) (November 1998) to 230.4 ft BTOC (September 2000).

1.2.4   Cultural 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 lies approximately 775 feet northeast of the site area. It consists of World War I foxholes and trenches.

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 during December 15 and 16, 1999, in accordance with the TCEQ Texas Risk Reduction Program (TRRP). 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).

Within CSSA, there is a full-time work force of approximately 100 persons working in shops and office buildings. Personnel also work outdoors throughout the facility to perform maintenance activities such as road and fence maintenance, brush clearing, and security patrols.

The USDA Agricultural Research Center (ARC) maintains a small herd of cattle on CSSA. 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 the Technical Approach Document for Risk Evaluation (Volume 1-6). SWMU B-15/16 is located approximately 1,500 feet east of hunting stand number 8. 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.

 The nearest potential habitats for local endangered species (Volume 1-1, Background Information Report, Figure 11) are approximately 840 feet southwest (Golden-Cheeked Warbler) and 2,100 feet northeast (Black-Capped Vireo).

1.3 - Previous Investigations

A surface geophysical survey using electromagnetic (EM) and ground penetrating radar (GPR) instruments was performed at SWMU B-15/16 on March 9, 1995. Three geophysical anomalies, which indicated subsurface disturbance and possible buried waste, were identified during the surface geophysical survey. The in-phase and quadrature phase conductivity data were mapped using 2 parts per thousand (ppt) and 5 milliSiemens per meter (mS/m), respectively. The grid was 200 feet long (northeast) and 100 feet wide (northwest).

Three EM anomalies were identified at the site (Figure B15/16-4). The anomalies suggest that past waste management activities may have occurred at the site. The three anomalies were assigned letters that identified each. Anomaly A trends southwest-northeast and contains both metal debris areas. The width of the anomaly is approximately 40 feet. The anomaly terminates in the area of the eastern soil mound on the southwestern boundary of the SWMU.

Anomaly B trends in an approximate east-west direction. It converges with anomaly A on the eastern end and extends to the western SWMU boundary. The approximate width of the anomaly is 52 feet. 

Anomaly C trends in a north-south direction and extends past the northern boundary of the SWMU. It converges with anomaly B on the southern end and is approximately 40 feet in width. Details of the geophysical survey conducted at SWMU B-15/16 can be found in Section 6 of the Technical Memorandum on Geophysical Surveys at High Priority SWMUs.

1.4 - Closure Standard

RRS1 requires that the site is 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 TCEQ Executive Director, then the owner is released from the deed recordation requirement.

Since the COCs for SWMU B-15/16 are VOCs, explosives, and metals, the RRS1 standards should be the reporting limits (RLs) for VOCs and explosives and the soil or rock background values for metals. 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 Soil Types (Parsons, February 2002). TCEQ approved the background metals evaluation on April 23, 2002.

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