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Final AOC 61-RCRA Facility Investigation/Closure Report
Section 1 - Introduction
On May 5, 1999 an Administrative Consent Order was issued to CSSA pursuant to §3008(h) of SWDA, as amended by RCRA, and further amended 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 61 and to recommend further investigation, if necessary, or to provide documentation necessary for site closure. The main objectives of the AOC 61 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 the U.S. Air Force AMC Contract 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 field work. These include:
For this RFI 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, 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
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 61
1.1.2.1 Site Description
AOC 61 is a suspected landfill site that was identified in a 1966 aerial photograph. The photograph revealed a ground disturbance covering approximately one acre in area. Vegetation appears to have returned to the area according to the 1973 aerial photograph. The location of the site shown on a 1998 aerial photograph of CSSA is presented in Figure AOC 61-1. Aerial photographs from 1966 and 1973 are shown in Figure AOC 61-2 and Figure AOC 61-3.
During the 1999 visual reconnaissance survey, the site was mostly level and covered with sparse native vegetation. The central portion of AOC 61 has exposed bedrock while a thin soil profile covers the remaining areas. Information obtained from interviews with base personnel suggest that the site was used as a temporary staging area for palletized equipment and munitions. Evidence indicates that AOC 61 has been used in the past as a burn site for cleared brush and other combustible material. Metal hinges and numerous small diameter wood screws were observed at the site, which suggests that wooden crates or storage boxes were burned. A few small arms projectiles were also discovered but are believed to have originated from RMU-3, which is located approximately 500 feet northwest of the site.
Background information regarding the location, size, and known historical use of the site is also included in the Environmental Encyclopedia (Volume 1-3, AOC 61). Volume 1-3 also includes a Chronology of Actions and a Site-Specific Work Plan Addendum for AOC 61.
1.1.2.2 Potential Sources of Contamination
AOC 61 was suspected to have been used as a landfill, however there are no records available indicating what type of waste, if any, was disposed there. The site was identified on a 1966 aerial photograph as a possible trench. Possible sources for contamination include metallic contamination from metal debris potentially disposed at the site. No significant ammunition or UXO has been observed in the vicinity of the site so explosives are not considered a likely contaminant. A small number of small arms projectiles were observed on the site but they are believed to have originated from RMU-3 which is located approximately 500 feet northwest of the site. There are a number of possible sources for contamination including VOCs, SVOCs, and metals resulting from burning activities.
1.1.2.3 Site Location
AOC 61 is located southwest of the intersection of Tenberg Road and East Outer Road (Figure AOC61-1). The site has an approximate area of 1.0 acre. The general shape of the site is approximately 290 feet long (north-south) by 120 feet wide (east-west). The AOC is over 1 mile east of the facility’s western boundary. AOC 61 is undeveloped except for overhead utilities and roadside drainage control. Livestock grazing is the only activity that currently takes place at AOC 61.
1.2 - Site Environmental Setting
1.2.1 Site Soils and Topography
The Brackett soil complex (Figure AOC61-4) dominates AOC 61. Detailed descriptions of the CSSA soil types are provided in the Background Information Report (Volume 1-1). The Brackett soils range over a large portion of CSSA and occur on slopes of 12 to 30 percent. These loamy and clayey soils are thin (about 4 inches thick), grayish-brown, and strongly calcareous. Gravel and cobblestone lithics occur at the surface and shallow subsurface. The soils can develop over soft limestone and are underlain by hard limestone, which gives the slopes a stairstep appearance. Topographic relief associated with Brackett soils is expressed as steep, cone-shaped hills with "saddles" between them. Brackett soils are nonarable and best suited to native grasses. They typically have permeabilities of 1.0-1.2 inches per hour (in./hr.) and available water values of 0.14 to 0.16 in./in.
AOC 61 is located just east of the Salado Creek floodplain. The site lies at an elevation of between 1,225 and 1,235 feet above sea level. The ground surface slopes to the west at approximately 7 percent grade.
1.2.2 Geology
The Upper Glen Rose is the uppermost geologic stratum in the area of AOC 61 (Figure AOC61-5). 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 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 61 is located approximately 1,642 feet south of the northern fault zone and 3,800 feet north of the southern fault zone. Additional information on structural geology at CSSA can be found in the Environmental Encyclopedia (Background Information Report, Volume 1-1).
1.2.3 Hydrology
At CSSA, 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. 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. In general, the 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).
AOC 61 is located more than ¼ mile south of the northern 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 (Background Information Report, Volume 1-1).
No site-specific information regarding groundwater is available. CSSA is currently installing additional monitoring wells and has recently installed Well CS-MW4-LGR. CS-MW4-LGR is located approximately 400 feet west of the site. In June 2001, the water level in CS-MW4-LGR was 57.4 ft BTOC. Well CS-MW2-LGR, which is a monitoring well, is located approximately 1,500 feet northwest of AOC 61. Between April 1996 and June 2001 water levels in CS-MW2-LGR have ranged from 70.6 ft BTOC (November 1998) to 268.9 ft BTOC (September 2000) (Volume 5, Introduction to Groundwater Monitoring Program, Table 3).
The nearest surface water body is Salado Creek which is located approximately 600 feet west of the site (Figure AOC61-1). Salado Creek is intermittent and exits the CSSA boundary approximately one mile south of AOC 61.
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 an area of World War I fox-holes and trenches located approximately 2,000 feet south of AOC 61.
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 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 within ¼-mile of AOC 61 is classified as “Commercial and Services“ and “Evergreen Forest Land” in Figure 1.1 of the Technical Document for Risk Assessment. There are no buildings, but one monitoring well, CS-MW4-LGR, was recently installed within ¼ mile of AOC 61. The well is located approximately 400 feet west 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.
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 which overlook mechanical feeders and planted food plots is located in Figure 5.2 of the Technical Approach Document for Risk Evaluation (Volume 1-6). AOC 61 is located approximately 900 feet west-southwest of hunting stand number 47 and 900 feet northeast of hunting stand number 4. Four water tanks are maintained at CSSA for the purpose of sport fishing. Two of the tanks are located in the north western and north eastern portions of the North Pasture while the other two tanks are located near the western boundary of the Inner Cantonment.
AOC 61 is located within an area designated as potential habitat for the endangered Black-capped Vireo (Volume 1-1, Background Information Report). Potential habitat for another endangered species, the Golden-Cheeked Warbler, is located approximately 3,200 feet east of the site.
1.3 - Previous Investigations
A chronology of actions at AOC 61 is located in both the AOC 61 tab of Volumes 1-3 and 3-2 of the CSSA Environmental Encyclopedia. As noted previously, AOC 61 was identified as a possible landfill on a 1966 aerial photograph. An area of exposed rock and soil was verified in this photograph. It is believed that the area was leveled and used for the storage of palletized equipment and supplies. No previous environmental investigations have been completed prior to the closure activities at AOC 61.
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 61 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 concentrations exceed 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. Notification of intent to close sites identified to date (including AOC 61) in accordance with the former Risk Reduction Rule was sent to the TNRCC on July 12, 1999. Acceptance of this notification was sent by TNRCC 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 deed recordation requirement.
Since the COPCs for AOC 61 are metals, VOCs and SVOCs, the RRS1 standards should be the soil or rock background values for metals and the RLs for VOCs and SVOCs. 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).
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