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AOC-48 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 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, an RFI report for Area of Concern-48 (AOC‑48) was completed in June 2002 to document the environmental condition of the site and site closure requirements, and to recommend further investigation. This closure report includes by reference the information presented in the AOC-48 RFI Report.
The AOC-48 RFI Report found that no contaminants exceeded background levels in surface soil but the cause of a geophysical anomaly, potentially related to waste management at the site, was unknown. The AOC-48 RFI Report recommended that test pits be excavated to determine if buried waste was causing the geophysical anomaly at the site. If buried waste was found, it and any remaining waste residue or contaminated soils were to be excavated, characterized, and properly disposed of. Following waste excavation, if any, confirmation samples would be collected to verify that all waste had been removed. The site would then be backfilled with clean soil and restored. If no waste was found, it was recommended that closure in accordance with RRS1 be pursued.
This 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 delivery order. Based upon 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 |
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Site-Specific Work Plan |
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Field Sampling Plan |
(Volume 1-4, TO 0019 Addendum); and |
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Health and Safety Plan |
Excavation activities at AOC‑48 did not reveal any evidence of waste management activities at the site. Soil samples collected at the site during the RFI investigation did not exceed RRS1 for any contaminants of concern (COCs). The site was originally registered as an AOC based on the likelihood that waste management was performed in an area with soil mounds. Since the site was not used for waste management, it should not be considered an AOC. Rather, the site should be delisted as an AOC. This report documents the excavation and sampling activities at the site and delists the site as an AOC.
For this closure report, Section 1 provides the site-specific background for AOC‑48. Section 2 describes the field actions and the delisting evaluation. Section 3 summarizes the findings and provides the delisting recommendations. 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, detailed data regarding the geology, hydrology, and physiography are also available for reference.
AOC-48 is a 2.7-acre tract located near the southeastern corner of CSSA, in the southernmost portion of the East Pasture area (Volume 1‑3, Site Location Map). The general shape of the site is 500 feet long (north-south) by 250 wide (east-west). The site consists of three north-south trending mounds. The AOC‑48 RFI Report indicated that a construction debris pile was located within the site. However, upon more careful inspection, it was found that the pile was actually within the SWMU B-15/16 boundary immediately to the south. AOC‑48 was visually identified as an area of concern due to the long linear mounds present at the site.
Former activities at AOC-48 include the suspected use of the site as a four-wheel drive/all-terrain vehicle (ATV) training area. Aerial photographs from 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 1957, bare soil was visible in a rectangular shaped area in the center of the site. Although less distinct, the outline of the bare area is still visible in aerial photos from other years (Figure AOC48‑9).
Background information regarding the location, size, and known historical use of AOC-48 is also included in the Environmental Encyclopedia (Volume 1-3, AOC-48). Volume 1-3 includes a Chronology of Actions and a Site-Specific Work Plan Addendum for AOC-48.
1.1.2.2 Potential Sources of Contamination
No waste management activities were known to occur at AOC-48. Historical aerial photographs dated between 1957 and 2003, presented in Figure AOC48-9, show some ground disturbance but it is not apparent that the disturbance was related to waste management activities. AOC-48 was identified as an area of concern due to the long linear mounds present at the site. RFI sampling did not indicate any contaminant concentration above CSSA background levels as described in Section 1.4.3. However, the source of one small geophysical anomaly identified at AOC-48 during a previous investigation was unknown, and excavation was recommended in the RFI Report to confirm that it was not buried waste.
AOC-48 is approximately 2.7 acres of undeveloped open area located near the southern boundary of CSSA, in the southwest area of the East Pasture (Figure AOC48‑8). AOC-48 is bordered on the south by SWMU B‑15/16, and on the east by a dirt access road. Salado Creek is located on the western side of AOC-48 and SWMU B‑14 is to the northwest of the site.
1.2 - Site Environmental Setting
A detailed description of the site environmental setting is provided in the CSSA Background Information Report (Volume 1-1) and the AOC-48 RFI Report (Parsons, 2002). A brief description of the setting at AOC-48 is provided in the paragraphs below.
1.2.1 Site Soils and Topography
AOC-48 rests entirely on Trinity and Frio soils (Figure AOC48-2 in the AOC-48 RFI Report). The Trinity and Frio soils cover approximately 8.8 percent (352.4 acres) of CSSA. The soils are frequently subjected to flooding, and are the main channel soils for Salado Creek and a large tributary that joins the creek in southwestern CSSA. Some areas are subject to thin sediment depositions, while other areas are scoured. Channels are poorly defined and are of small capacity. Trinity soils are 3 to 5 feet deep and composed of clayey to gravely loam. Frio soils are a dark grayish-brown clay loam, 3 to 4 feet deep. Detailed descriptions of the CSSA soil types are provided in the CSSA Environmental Encyclopedia (Volume 1-1, Background Information Report, Soils and Geology).
AOC-48 lies in a broad, relatively flat floodplain of Salado Creek (Figure AOC48-2 in the AOC-48 RFI Report). The elevation of the site is approximately 1,175 feet above sea level, sloping gently (less than 1 percent grade) to the south‑southwest. An intermittent stream joins Salado Creek near the northwestern corner of AOC-48. Except for scattered oaks and shrubs on the western edge, the site is primarily vegetated with grasses.
The Upper Glen Rose is the uppermost geologic stratum in the area of AOC‑48, as shown in Figure AOC48‑10. 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 128 feet thick at CSSA. It is underlain by the Lower Glen Rose, which is estimated to be an average of 328 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 an average of 60 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. Additional information on geology at CSSA can be found in the Environmental Encyclopedia (Soils and Geology, Background Information Report, Volume 1-1).
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. 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 and for adjacent off-post wells. 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 geographic/stratigraphic structure 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-48 on Camp Bullis. Between January 1998 and March 2004, 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. Salado Creek lies west of AOC-48 (Figure AOC48-8). This small intermittent stream exits the CSSA boundary south of AOC-48, adjacent to AOC-47.
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 500 feet northeast of AOC‑48 and consists of an area with World War I foxholes and trenches. Similar trenches are also located approximately 1,500 feet north-northwest and 2,500 feet east of AOC‑48.
A land use survey describing local, current, 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 uses on the facility are not anticipated to change in the foreseeable future.
Land within ¼‑mile of AOC-48 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-48. The closest residential area is approximately one mile to the southwest, and the nearest school is over 1.5 miles to the southwest of the site. AOC‑48 is located approximately 2,700 feet west-southwest of hunting stand number 45. With the exception of intermittent Salado Creek, no surface water bodies, or tanks, are located within ¼‑mile of AOC‑48. The nearest potential habitats for local endangered species (Figure 11, Volume 1‑1 Background Information Report) are 1,100 feet to the west (Golden-Cheeked Warbler) and 2,000 feet north (Black-Capped Vireo) of AOC‑48.
Previous investigations at AOC-48 include a soil gas survey in 1996, and geophysical survey and soil sampling in 1999 and 2000. The results of these previous investigations are described below.
Soil gas sampling was conducted at neighboring SWMU B-15/16 between August 20 and 22, 1996, and many of the sampling locations were actually within the AOC-48 boundary. A total of 54 samples were collected from 46 locations in the SWMU and in the areas directly north and south. As shown in Figure AOC48‑4, eight soil gas samples were collected within the boundary, and fourteen samples were collected north and east of the site.
An initial screening of the soil gas samples was performed in the field by scanning the exhaust from the vacuum pump with an HMX-271 explosimeter for oxygen content. Each sample was analyzed for benzene, toluene, ethylbenzene, total xylenes, cis-1,2-dichloroethene (DCE), trichloroethene (TCE), and tetrachloroethene (PCE) with an HNu model 321 gas chromatograph (GC) equipped with an electron-captor detector and a photoionization detector with a 10.2 electron volt (eV) light source. None of these analytes were detected in any of the soil gas samples collected at SWMU B-15/16 or AOC-48. Results are included in Table B-15/16-1 in the SWMU B-15/16 RCRA Facility Investigation Report.
Electromagnetic (EM) and ground penetrating radar (GPR) geophysical surveys were conducted at AOC-48 between July 26 and August 10, 1999. Prior to collecting EM or GPR data, a grid system which encompassed the areas of suspected ground disturbance was established at the site.
GPR surveys were conducted with a GSSI SIR-2 instrument to verify and further substantiate the results of the EM survey. Fifteen profiles were created with a 300 MHz antenna, thirteen in the east-west direction, and two in the north-south direction (Figure AOC48-4 in the AOC-48 RFI Report).
The geophysical surveys revealed evidence of a subsurface anomaly. When contoured, the variation in the data that were recorded during the EM survey show the linear trending dirt mounds and the linear anomaly located on the western side of the AOC. The anomaly is labeled A on Figure AOC48‑5 and Figure AOC48‑6 in the AOC-48 RFI Report. Anomaly A originates in SWMU B-15/16, and it has a linear pipeline-type signature which trends north-south.
Three surface soil samples were collected at AOC-48 in June 2000. The samples were collected at locations (Figure AOC48-11) that were based on the results of the geophysical surveys. Sample AOC48-SS01 was collected at the location of a strong geophysical anomaly, AOC48-SS02 was collected on top of the central north-south trending soil mound, and AOC48-SS03 was collected in the large shallow depression located between the linear soil mounds.
Samples were analyzed using EPA methods volatile organic compounds (VOCs) (SW‑8260B), semivolatile organic compounds (SVOCs) (SW-8270C), explosives (SW-8330), barium, chromium, copper, nickel, and zinc (SW-6010B), arsenic (SW-7060A), cadmium (SW-7131A), lead (SW-7421A), and mercury (SW-7471A).
No VOCs, SVOCs, or explosives were detected at concentrations exceeding RLs, and none of the metals levels exceeded background levels for CSSA soils. Results are summarized in Table AOC48-1 in the AOC-48 RFI Report.