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Final AOC-50 RCRA Facility Investigation Report
Section 1 - Introduction
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 (AOC)-50 and to recommend further investigation, if necessary, or to provide documentation necessary for site closure. The main objectives of the AOC-50 investigation are to determine if the site meets 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 Air Education and Training Command (AETC) Contract number, F41689-96-D-0710 and delivery order (DO) number 5068. 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 fieldwork. 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, DO5068 Addendum); and |
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Health and Safety Plan |
For this report, Section 1 provides the site-specific background and 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
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-50 consists of approximately one acre of undeveloped wooded land. The site is irregularly shaped and approximately 450 feet at its widest point, which is oriented in an east-west direction (Figure AOC50-1). In the north-south direction, AOC-50 is approximately 200 feet at its widest point. A dirt road enters the site’s boundary in the northwestern corner and exits the boundary in the far northeastern portion of the AOC. The site was identified in March 1996 during the field efforts that were conducted at nearby sites Solid Waste Management Units (SWMUs) B-29 and B-30. During the initial site visit in March 1996, seventeen distinct areas of suspected waste were identified. The suspected areas consist of rust-colored material at the ground surface and in near-surface soils. During a site inspection in December 1999, potential unexploded ordnance (UXO) and other munitions scrap were located at the AOC. The remaining metal carcass of a 100-pound practice bomb was removed from the site prior to the site inspection.
In March 2001, a small trench containing household type trash measuring 75 feet long, 10 feet wide, and approximately 4 feet deep was discovered during the initial excavation activities. The date that waste was disposed in this trench is unknown; however, two soda bottles found in the trench were dated 1953.
Background information regarding the location, size, and known historical use of AOC-50 is also included in the Environmental Encyclopedia (Volume 1-3, AOC-50). Volume 1-3 also includes a Chronology of Actions and a Site-Specific Work Plan for AOC-50.
1.1.2.2 Potential Sources of Contamination
The potential sources of contamination at AOC-50 include the areas of rust-colored material on the surface, the trash-filled trench, and spent munitions and potential UXO. The rust-colored material was identified as metal waste generated from the ordnance maintenance operations conducted in Building 90. This waste material consisted of metal particles and was thought to contain nickel penetrant. However, recent information from personnel working in Building 90 indicates that this waste was generated from the Wheelabrator blast cleaning operations and does not contain nickel penetrant. Because of the metallic nature of the waste, metals are the primary contaminant of concern (COC). Volatile organic compounds (VOCs) are also COCs because they are frequently associated with waste management activities and explosives are included as COCs because spent munitions and potential UXO were discovered at the site.
AOC-50 is a one-acre tract that is located in the southeastern portion of the inner cantonment area (Figure AOC50-1). The site is approximately 100 feet south of SWMU B-29 and 200 feet south of SWMU B-30. SWMU I-1 is located approximately 200 feet northwest of AOC-50 and the CSSA perimeter fence which borders Leon Springs Villa Mobile Home Park is approximately 400 feet south of the site.
1.2 - Site Environmental Setting
1.2.1 Site Soils and Topography
The native soils at AOC-50 are Krum Complex soils (Figure AOC50-2). Krum Complex soils cover approximately 20 percent of the land at CSSA. These soils occur on slopes of two to five percent, occupying ‘foot’ slopes below Brackett and Tarrant soils. Generally, Krum Complex soils are subject to hydraulic erosion as they occur down-slope of prairie plains and receive sediments from higher elevations. Krum Complex soils are dark grayish-brown, calcareous, and typically extend to depths of approximately 30 inches below grade. Detailed descriptions of the CSSA soil types are given in the CSSA Environmental Encyclopedia (Volume 1-1, Background Information Report, Soils and Geology).
AOC-50 lies in the southwestern portion of CSSA. AOC-50 is located on a gentle, south-southwest trending slope and the site elevation is between 1,165 and 1,175 feet above sea level. A small intermittent stream bounds much of the eastern portion of the site. This stream exits CSSA through a concrete culvert and continues through the Leon Springs Villa Mobile Home Park. Surface water runoff from AOC-50 drains into the same drainage basin as the wastewater treatment plant effluent.
The Upper Glen Rose is the uppermost geologic stratum at CSSA, where present, and it outcrops southwest of AOC-50 (Figure AOC50-3). 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 Upper Glen Rose may be up to 150 feet thick. It is underlain by the Lower Glen Rose, which outcrops in the area of AOC-50 and is estimated to be 320 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 1 to 2 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 eastern portion of AOC-50 lies in the South Fault Zone, which trends in a northeast-southwest direction. Some evidence of this fault zone can be observed just north of the site in the form of open linear fractures and a small (less than 5 foot diameter) sinkhole. Additional information on structural geology at CSSA can be found in the Environmental Encyclopedia (Volume 1-1, Background Information Report, Soils and Geology).
In general, the uppermost hydrologic 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 Limestone. 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 at approximately the same elevation. Principle development of solution channels is limited to evaporite layers in the Upper Glen Rose Limestone.
The Upper Trinity aquifer is found in the Upper Glen Rose limestone, which is not present with enough vertical thickness at CSSA to contain much water. The Upper Trinity aquifer is underlain by the middle Trinity aquifer. 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. However, local flow gradient may vary depending on rainfall, recharge, and possibly well pumping.
The eastern portion of AOC-50 is located directly on the Southern Fault Zone at CSSA. Fracture systems associated with the fault zones are thought to affect groundwater flow and to be the controlling structural feature for migration of contaminants in the vadose zone at CSSA (Volume 1-1, Background Information Report, Groundwater).
No site-specific information regarding groundwater is available. However, the nearest well, Well LS-1, which
is domestic drinking water well, is located approximately 700 feet southeast of
AOC-50. Water levels are not available
for this well but other information for this well may be found in the
Environmental Encyclopedia, Volume 5.
The nearest surface water is an intermittent stream that borders the site to the east. This intermittent stream connects with the concrete drainage ditch from the wastewater treatment plant (Figure AOC50-1). The water then exits CSSA in a manmade concrete culvert that runs through the Leon Springs Villas Mobile Home Park and eventually merges with Leon Creek.
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 consists of a series of World War I-era training trenches located approximately 7,000 feet northeast of the site area, directly next to the eastern Inner Cantonment boundary. All of the structures on the installation are considered historical resources.
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 on 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).
Generally, CSSA is a controlled access facility where a security guard and perimeter fence restricts access. Within CSSA, however, 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.
Land use within ¼-mile of the site is classified as “Residential’’, “Commercial and Services”, and “Evergreen Forest Land”. Numerous homes in the Leon Springs Villas Mobile Home Park occupy the area outside CSSA within a ¼-mile of AOC-50. Well LS‑1, which is a public drinking water supply well operated by Bexar-Met, is located within ¼-mile of AOC-50.
The site and much of the area surrounding the site is wooded with live oak and ash juniper (cedar) trees. The eastern portion of the site lies in an area of potential habitat for the endangered Golden-cheeked warbler. The nearest potential habitat for the endangered Black-capped vireo is located over 1½ miles northeast of the site.
A small herd of cattle is maintained on CSSA by the United States Department of Agriculture – Agricultural Research Center (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, which overlook mechanical feeders and planted food plots, is located in the Technical Approach Document for Risk Evaluation (Volume 1-6). AOC-50 is located approximately 800 feet west southwest of hunting stand number 12. 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.
No previous investigations have been performed at AOC-50.
As described in Section 4.3 of the Risk Assessment Technical Approach Document (Volume 1-6), CSSA has opted to pursue closure of AOC-50 under the Risk Reduction Rule (RRR) (30 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 TRRP. A notification of intent to close sites identified to date (including AOC-50) in accordance with the former RRR 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 Texas Administrative Code [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 AOC-50 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). The background metals evaluation was approved by TCEQ on April 23, 2002.