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AOC 49 Delisting 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 Solid Waste Disposal Act (SWDA), 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 of Area of Concern (AOC) 49 (AOC-49) and, based on those findings, request delisting.
The investigation work was performed by Parsons under the U.S. Air Force Environmental Remediation and Construction (ENRAC) Contract F41624‑01‑D‑8544, Task Order 19 (TO 0019). The Air Force Center for Environmental Excellence (AFCEE) provided technical oversight for the task order. Based on the project statement of work (SOW), a set of work plans to govern the fieldwork was established. These include:
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Work Plan Overview (Volume 1‑1, TO 0019 Addendum); |
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Site‑Specific Work Plan(s) (Volume 1‑3, AOC‑49); |
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Field Sampling Plan (Volume 1‑4, TO 0019 Addendum); and |
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Health and Safety Plan (Volume 1‑5, TO 0019 Addendum). |
Section 1 of this report provides the site‑specific background. Section 2 describes the field activities. Section 3 summarizes the findings, evaluates attainment of data quality objectives (DQOs), and recommends delisting for AOC‑49. References cited in this report can be found in the Bibliography (Volume 1‑1 of the Environmental Encyclopedia).
1.1 - Background and Site Description
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 geology, hydrology, and physiography are also available for reference.
AOC‑49 has an area of approximately 0.03 acre (Figure AOC49‑1). The site consists of a potential trench area, measuring approximately 4 feet by 7 feet by 3 feet deep. The site was identified through site reconnaissance. No surface debris was observed at the site. Figure AOC49‑2 shows a progression of historical aerial photographs of the site from 1957 to 2003, including the 1966 aerial photograph.
1.1.2.2 Potential Sources of Contamination
No formal waste management activities were known to occur at AOC‑49, although a suspected trench was identified at the site due to a visible ground depression. Based on the presence of a suspected trench, contaminants concern (COCs) initially included volatile organic compounds (VOCs), semivolatile organic compounds (SVOCs), metals, and explosives. Subsequent work at the site revealed no evidence of waste management, so no analytical data was collected for any of the aforementioned COCs.
AOC‑49 is located in the central portion of the East Pasture at CSSA, approximately 1,000 feet from the nearest facility boundary to the east. The site is adjacent to an unnamed tributary of Salado Creek, and is approximately 1,600 feet south of Solid Waste Management Unit (SWMU) B‑25. The site is approximately 1,300 feet south of SWMU B‑26, and 1,000 feet southeast of AOC‑63 (Figure AOC49‑1).
A detailed description of the site environmental setting is provided in the CSSA Background Information Report (Volume 1‑1). A summarized description is provided in the paragraphs below.
The soils at AOC‑49 are representative of Krum Complex soils, as shown in Figure AOC49‑3. The Krum Complex soils cover approximately 20 percent of the land at CSSA and occur on slopes of 2 to 5 percent, occupying ‘foot’ slopes below Brackett and Tarrant soils. Generally, Krum Complex soils occur downslope of prairie plains and calcareous clays and silty clays, and typically are approximately 30 inches thick. Based on soil boring data from nearby sites, the Krum Complex soils at AOC-49 are from 0.5 to 10 feet thick. Detailed descriptions of the CSSA soil types are provided in the CSSA Environmental Encyclopedia (Volume 1‑1, Background Information Report, Soils and Geology).
The ground surface elevation at AOC‑49 is between 1,214 and 1,216 feet above mean sea level (msl). The ground surface slopes to an intermittent stream that runs southward on the eastern edge of AOC‑49. The stream joins Salado Creek just south of CSSA.
Prior to the field investigation, the area was cleared of cedar (Ashe juniper), and now the site is covered predominantly by grasses.
The Upper Glen Rose is the uppermost geologic strata in the area of AOC‑49 (Figure AOC49‑4). 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 thickness ranges from 0 (eroded outcrop) to 128 feet thick, with an average thickness of approximately 50 feet. It is underlain by the Lower Glen Rose, which has a thickness between 284 feet and 338 feet, with an average thickness of approximately 320 feet. 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 58 to 63 feet thick, with an average thickness of approximately 60 feet. 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.
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 hydrologic layer is the unconfined Upper Trinity aquifer, which consists of the Upper Glen Rose Limestone. Locally at CSSA, low‑yielding perched groundwater zones 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. Principal development of solution channels is limited to evaporite layers in the Upper Glen Rose Limestone. Principal recharge into the Middle Trinity Aquifer is via precipitation infiltration at outcrops. Groundwater discharge occurs predominantly via natural springs, seeps, and pumping.
The nearest monitoring well to AOC‑49 is CS‑MW17‑LGR, located approximately 1,900 feet southwest of the site. This well is sampled on a quarterly basis. Historic water levels for CS‑MW17‑LGR range from 115.70 feet below top of casing (btoc) in December 2002 to 250.89 feet btoc in December 2003. Well CS‑1, an off‑site well located directly south of CSSA, is located approximately 5,900 feet southwest of AOC‑49. This is the nearest off‑site well to AOC‑49. Static water levels in well CS‑1 have measured between 163.48 feet btoc (March 2001) and 323 feet btoc (March 2000).
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 site to AOC‑49 are former World War II training trenches that are located approximately 3,100 feet southwest.
A land use survey describing local current and possible future uses of groundwater and surface water, a water well survey, and a sensitive environmental area survey were completed at CSSA during December 1999. The results of these surveys, along with results from a more in‑depth survey to identify potential receptors, points of human exposure, and possible constituent pathways, are presented in Section 3 of the Technical Approach Document for Risk Evaluation (Volume 1‑6). Land uses on the facility are not anticipated to change in the foreseeable future.
CSSA contains mostly forested, undeveloped land, various portions of which are being managed to promote different species. Some areas are managed to maintain habitat for two endangered bird species, the Golden‑cheeked Warbler and the Black‑capped Vireo. AOC‑49 is located within 1,500 feet of potential habitat areas for both the Black‑capped Vireo and the Golden‑cheeked Warbler (Section 4, Environmental Assessment, Volume 1‑1). The native White‑tailed deer and introduced Axis deer populations are also managed, and controlled hunting is allowed. Management practices which benefit the deer and other wildlife species include maintenance of feed plots and feeding and watering stations. Other areas are managed as pastures for grazing by cattle. AOC‑49 is located southwest of deer stand number 41.
No previous investigations have been conducted at AOC‑49.