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AOC 48 RCRA Facility Investigation 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 AOC 48 and to recommend further investigation, if necessary, or to provide documentation necessary for site closure. The main objectives of the AOC 48 investigation are to determine if the site meets 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 AMC Contract number F11623-94-D0024, Delivery Order RL83. AFCEE provided technical oversight for the delivery order. Based upon the project SOW, a set of work plans was established to govern the fieldwork. These include:
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(Volume 1-1, RL83 Addendum); |
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(Volume 1-3, AOC 48); |
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(Volume 1-4, RL83 Addendum); and |
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(Volume 1-5, RL83 Addendum). |
For this report, Section 1 provides the site-specific background and target closure standard. Section 2 describes field actions and the closure evaluation. 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 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 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 outer cantonment 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 and a construction debris pile. The site was visually identified during the field efforts of the SWMU B-15/16 investigation.
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, in the same location as the bare area visible in Figure AOC48-1.
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 for AOC 48.
1.1.2.2 Potential Sources of Contamination
Prior uses of AOC 48 are unknown and no activities are currently practiced there. Based on the trenches and mound at the site, chemicals of potential concern include VOCs, SVOCs, metals, and explosives. Metals (arsenic, barium, cadmium, chromium, copper, lead, mercury, nickel, and zinc) are included due to the metallic nature of potential waste. Ammunition that may have been disposed would include explosives residue; therefore, analysis for explosives was conducted. VOCs analysis is included in the analytical program to detect typical contaminants associated with a disposal area and SVOCs are included since waste burning may have occurred at the site.
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 AOC48-1). 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
1.2.1 Site Soils and Topography
AOC 48 rests entirely on Trinity and Frio soils (Figure AOC48-2). 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). Most CSSA soils are typically calcareous clay, ranging in depth from 4 to 60 inches and are underlain by limestone. While no descriptions of subsurface conditions have been gathered at this site, it is reasonable to assume that limestone bedrock exists between 6 and 8 feet bgs based on information gathered at the nearby SWMU B-15/16.
AOC 48 lies in a broad, relatively flat floodplain of Salado Creek (Figure AOC48-2). The elevation of the site is approximately 1,170 to 1,180 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 Formation is the uppermost geologic stratum in the area of AOC 48 (Figure AOC48-3). The Upper Glen Rose Formation 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 (shatter) zones at CSSA: the North Fault Zone and the South Fault Zone. The northern tip of AOC 48 is located in the South Fault Zone (Figure AOC48-3). Additional 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 hydrogeologic 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.
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. 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. Regionally, groundwater flow within the Middle Trinity aquifer is toward the south and southeast and the average transmissivity coefficient is 1,700 gpd/ft. 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, Well CS-1, which is a production well that periodically contributes to the water distribution system at CSSA, is located 1/4 mile southeast of AOC 48 on Camp Bullis. Between January 1998 and March 2000, water levels in Well CS-1 ranged from 101.3 feet 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 AOC48-1). 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 that investigated 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).
Land use within ¼-mile of AOC 48 is classified as “Commercial and Services” and “Evergreen Forest Land” in Figure 1.1 of the Technical Approach Document for Risk Assessment. Although there are no buildings within ¼-mile of the site, one well (Well CS-1) is located at this radius from the site. 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.
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. Approximately 25 people, including children, occupy seven residences on the CSSA facility.
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 that overlook mechanical feeders and planted food plots is located in Figure 5.2 Technical Approach Document for Risk Evaluation (Volume 1-6). AOC 48 is located approximately 2,700 feet west-southwest of hunting stand number 45. 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 located approximately 1,100 feet to the west (Golden-cheeked Warbler) and 2,000 feet to the north (Black-capped Vireo).
No previous environmental investigations have been performed at AOC 48.
As described in Section 4.3 of the Risk Assessment Technical Approach Document (Volume 1-6), CSSA has opted to pursue closure of AOC 48 under the Risk Reduction Rule (30 TAC §335). If the site concentrations do not exceed background, then the site will be closed using 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 TRRP. A notification of intent to close sites identified to date (including AOC 48) in accordance with the former RRR was sent to the TNRCC on July 12, 1999. TNRCC 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 TNRCC Executive Director, then the owner is released from the deed recordation requirement.
Since the COCs for AOC 48 are VOCs, SVOCs, metals and explosives, the cleanup levels should be the RLs for the VOCs, SVOCs, and explosives. 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).
The Data Verification Report for the AOC 48 analytical data included in Appendix B also contains data verification information for analytical data from other AOCs on Camp Stanley.