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Final AOC 56 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 Amendments (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 Area of Concern-56 (AOC-56) and to recommend further investigation, if necessary, or to provide documentation necessary for site closure. The main objectives of the AOC-56 investigation are to determine if the site meets the Texas Commission on Environmental Quality (TCEQ) 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 Air Mobility Command (AMC) Contract F11623-94-D-0024, delivery order RL83. The Air Force Center for Environmental Excellence (AFCEE) provided technical oversight for the delivery order. Based upon the project statement of work (SOW), a set of work plans was established to govern the field work. These include:

For this report, Section 1 provides the background and site description, environmental setting, a description of previous investigations, and the target closure standard. Section 2 describes field actions and the closure evaluations. Section 3 summarizes the findings, evaluates 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, 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 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   AOC 56

1.1.2.1   Site Description

AOC-56 is a site that is suspected to have been used as a construction debris landfill. Visual observation of the site indicates an area of excavation on the western side of the site. Except for cattle grazing, no other activities are currently practiced at AOC-56. No previous investigations have been completed at AOC-56.

Background information regarding the location, size, and known historical use of the site is also included in the Environmental Encyclopedia (Volume 1-3, AOC-56). Volume 1-3 also includes a Chronology of Actions and a Site-Specific Work Plan Addendum for AOC-56.

1.1.2.2   Potential Sources of Contamination

Information obtained concerning AOC-56 indicates that the site was used as a construction debris landfill. Although the site was generally known as being used to dispose of metal debris and construction materials, it is possible that solvents or fuels, which were commonly used at CSSA, may also have been discarded in the area.

Based on prior usage at the site as a landfill, chemicals of potential concern include volatile organic compounds (VOCs), semivolatile organic compounds (SVOCs), and metals. Metals (arsenic, barium, cadmium, chromium, copper, lead, mercury, nickel, and zinc) are included due to the potential metallic nature of the waste. VOCs analysis is included in the analytical program to detect typical contaminants associated with a disposal area. SVOCs are included at this site since waste burning may have occurred. Explosives are not included in the analysis since no ammunition has been observed.

1.1.2.3   Site Location

AOC-56 is located in the southeast portion of the inner cantonment at the intersection of Bernard Road and East Outer Road and occupies an area of approximately 0.5 acres (Volume 1-3, Site Location Map). The site is generally oblong in shape with a length of approximately 400 feet in the northwest-southeast direction and a width of approximately 150 feet in the northeast-southwest direction. The AOC is approximately 100 feet east of the outer cantonment boundary. Bernard Road is the north boundary of AOC-56, and East Outer Road marks the boundary on the east side (Figure AOC56-1). There is no development upon AOC-56 except for overhead utilities and roadside drainage control.

1.2 - Site Environmental Setting

1.2.1   Site Soils and Topography

The only soil type present within the site area is the Tarrant Association, rolling, soil complex (Figure AOC56-2). Detailed descriptions of the CSSA soil types are provided in the CSSA Environmental Encyclopedia (Volume 1-1, Background Information Report, Soils and Geology). This soil type occurs over only 1.3 percent (52.1 acres) of CSSA lands. The slopes tend to have a gradient of 5 to 15 percent. The soils are dark colored, very shallow, clayey, weakly calcareous, and typically more stony than Tarrant Association, gently undulating.

The elevation of the site is approximately 1,185 to 1,200 feet above sea level, sloping gently (less than 1 percent) to the east-northeast. The site is vegetated with native grasses and oak trees.

1.2.2   Geology

The Upper Glen Rose is the uppermost geologic stratum in the area of AOC-56 (Figure AOC56-3). 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. The Upper Glen Rose is estimated to be up to 150 feet thick at CSSA. 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 (shatter) zones at CSSA: the North Fault Zone and the South Fault Zone. AOC-56 is located directly south of the southern fault zone (Figure AOC56-3). Additional information about structural geology at CSSA can be found in the Environmental Encyclopedia (Soils and Geology, Background Information Report, Volume 1-1).

1.2.3   Hydrology

In general, the uppermost hydrogeologic 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. Transmissivity values are not available for the Upper Glen Rose Formation. 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. 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. 

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, 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, with some seasonal fluctuations. 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 (Well CS-1), which is a production well that periodically contributes to the water distribution system at CSSA, is located just over ¼-mile southeast of AOC-56 on Camp Bullis. Between January 1998 and March 2000, water levels in Well CS-1 ranged from 101.3 feet below top of casing (BTOC) (November 1998) and 261.9 feet BTOC (March 2000). 

The nearest surface water body is Salado Creek which is approximately 150 feet east of AOC 56 (Figure AOC56-1). Flow in Salado Creek is intermittent. The creek exits the CSSA boundary approximately 1/8-mile southeast of AOC-56.

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 site of potential cultural significance is located approximately 1,240 feet northeast of AOC-56. The cultural resource consists of World War I, foxhole type trenches. A similar cultural resource is located approximately 1,650 feet north of AOC-56. Approximately ¼ mile to the southeast, on Camp Bullis property, are a hand dug water well and a stone house built in 1847.

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. 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 ¼-mile of AOC-56 is classified as “Commercial and Services“ and “Evergreen Forest Land” in Figure 1.1 of the Technical Document for Risk Assessment. CSSA production well CS-1 is located approximately 1,400 feet southeast of AOC-56.

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. 

A small herd of cattle is maintained on CSSA by the U.S. Department of Agriculture Agricultural Research Center (USDA-ARC). The cattle roam freely throughout selected areas of the North Pastures. 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 Figure 5.2 of the Technical Approach Document for Risk Evaluation (Volume 1-6). 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 (Figure 11, Volume 1-1 Background Information Report) are 580 feet southwest (Golden-Cheeked Warbler) and 2,200 feet north (Black-Capped Vireo) of AOC-56.

1.3 - Previous Investigations

No previous environmental investigations have been conducted at AOC-56.

1.4 - Closure Standard

As described in Section 4.3 of the Risk Assessment Technical Approach Document (Volume 1-6), CSSA has opted to pursue closure of AOC-56 under the Risk Reduction Rule (30 Texas Administrative Code [TAC] §335). If the site concentrations do not exceed background, then the site will be closed using Risk Reduction Standard 1 (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 Texas Risk Reduction Program (TRRP). A notification of intent to close sites identified to date (including AOC 56) in accordance with the former Risk Reduction Rule was sent to the TCEQ on July 12, 1999. TCEQ 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 TCEQ Executive Director, then the owner is released from the deed recordation requirement.

The contaminants of concern (COCs) for AOC-56 are VOCs, SVOCs, and metals. Since chlorinated VOCs are man-made chemicals, and rarely occur naturally, the RRS1 cleanup levels are the reporting limits (RLs). 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 evaluation on April 23, 2002.

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