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On May 5, 1999, an Administrative Consent Order was issued to Camp Stanley Storage Activity (CSSA) pursuant to §3008(h) of the Safe Drinking Water Act (SDWA), 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 RFI report has been prepared to document the environmental condition and site closure requirements of Area of Concern-42 (AOC-42) and to recommend further investigation, if necessary, or to provide documentation necessary for site closure. The main objectives of the AOC-42 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 U.S. Air Force Air Education and Training Command (AETC) Contract Number F41689-96-D-0710, Delivery Order 5068. The Air Force Center for Environmental Excellence (AFCEE) provided technical oversight for the delivery order. Based upon the project statement of work (SOW), dated August 13, 1999 and modified May 12, 2000, a set of work plans to govern the fieldwork was established. These include:
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Work Plan Overview (Volume 1-1, DO5068 Addendum); |
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Site-Specific Work Plan (Volume 1-3, AOC-42); |
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Field Sampling Plan (Volume 1-4, DO5068 Addendum); and |
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Health and Safety Plan (Volume 1-5, DO5068 Addendum). |
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 available for reference.
AOC-42 is approximately 2.5 acres of undeveloped open area with few trees and a cover of native grasses and shrubs. The site is surrounded on the northeast, east, and south sides by a thicket of oak trees. AOC-42 is bordered on the north side by AOC-62 and on the west side by Salado Creek (Figure AOC42-1). The site was discovered during a geophysical investigation conducted in May 1995 of the “open” areas within a 2,000-foot radius of Well CS-16. The area surveyed was designated “Salado Creek” and portions of the survey include the area now defined as AOC-42. Due to geophysical anomalies detected during the Salado Creek survey, the area was subdivided into AOC‑62, AOC-42, and AOC-52. Prior uses of AOC-42 are unknown and no waste disposal activities are currently practiced there.
Background information regarding the location, size, and known historical use of AOC-42 is included in Environmental Encyclopedia (Volume 1-3, AOC-42). Volume 1-3 also includes a Chronology of Actions and a Site-Specific Work Plan for AOC-42.
1.1.2.2 Potential Sources of Contamination
Potential sources of contamination include past waste disposal activities that have taken place at nearby locations and may have taken place at AOC-42. Volatile organic compounds (VOCs) and metals may be present at the site as a result of past waste disposal activities. Explosives contamination may be present because ammunition disposal activities may have taken place at nearby solid waste management units (SWMUs). Contaminants of concern (COCs) for AOC-42 are metals, VOCs, and explosives.
AOC-42 is centrally located, in the northeastern portion of the Inner Cantonment, approximately 300 feet east of the H & I section. AOC-62 is located on the northern boundary of the site, AOC-58 and Well CS-MW2-LGR are located on the eastern side, and Salado Creek defines the western boundary of AOC-42.
1.2 - Site Environmental Setting
1.2.1 Site Soils and Topography
The native soils at AOC-42 are classified as Trinity and Frio soils (Figure AOC42-2).
The Trinity and Frio soils cover approximately 8.8 percent (352.4
acres) of CSSA, overall. The
soils are frequently flooded and are the main channel soils for Salado Creek
and a large tributary that joins the creek in southwestern CSSA.
The soils occur in narrow, long, and irregularly shaped areas.
They are flooded at least once a year after heavy rains.
Some areas are subject to thin sediment depositions, while other areas
are scoured. Channels are poorly
defined and are of small capacity.
Trinity
soils make up the majority of this soil type and are 3 to 5 feet deep, clayey
to gravelly loam. Frio soils are
3 to 4 feet deep, dark grayish-brown clay loam.
The soils are generally used as pasture, with occasional cultivation.
Additional information about the Trinity and Frio soils can be found in
the CSSA Environmental Encyclopedia
(Volume
1-1, Background Information Report, Soils and Geology).
AOC-42 is located on the bank of Salado Creek and is at an elevation between 1,200 and 1,210 feet above sea level. The site has low relief and has native grass vegetation (Figure AOC42-2). The direction of surface runoff is to the southwest, directly into Salado Creek, which is the western boundary of AOC-42.
The Upper Glen Rose is the uppermost geologic stratum in the area of AOC-42 (Figure AOC42-3). 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 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 one to two 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-42 lies on the southern edge of the North Fault Zone (Figure AOC42-3). Numerous faults with small displacements have been located north of AOC-42 using mapping, seismic, and GPR techniques. No evidence of faulting has been observed within AOC-42; however, one of the faults is inferred to cross the northern portion of the site. Additional information on structural geology at CSSA can be found in the Environmental Encyclopedia (Soils and Geology, Background Information Report, Volume 1-1). AOC-42 is located on the Cretaceous-aged Lower Glen Rose of the Trinity Group (Figure AOC42-3). The underlying bedrock does not outcrop at the site but it is exposed directly to the west in Salado Creek.
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. 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 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. In general, groundwater flow within the Middle Trinity aquifer is toward the south, southeast, and southwest, and the average transmissivity coefficient is 1,700 gpd/ft (Ashworth, 1983). However, local flow gradient may vary depending on rainfall, recharge and possibly well pumping.
AOC-42 is located partially within the northern fault zone identified 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 Resources).
No site-specific information regarding groundwater is available. However, monitoring well CS-MW2-LGR, located 100 feet east of AOC-42 and completed in the bottom portion of the Lower Glen Rose aquifer has had static water levels ranging from 70 feet bgs to 268 feet bgs (Volume 5, Introduction to Groundwater Monitoring, Table 3). The nearest surface water body is Salado Creek, which lies on the western border of AOC-42. Salado Creek is an intermittently flowing stream that continues southeast through Camp Bullis and eventually joins the San Antonio River.
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 to AOC-42 is Building 43, which is located approximately 700 feet north of AOC-42.
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).
A small herd of cattle is maintained on CSSA by United States Department of Agriculture Agricultural Research Center (USDA-ARC). The cattle roam freely 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 in the Technical Approach Document for Risk Evaluation (Volume 1-6). AOC-42 is located approximately 500 feet north of hunting stand number 3. Four water tanks are maintained at CSSA for the purpose of recreational 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.
AOC-42 is located at the western edge of a potential habitat for the Black-Capped Vireo, which is a local endangered species (Volume 1-1, Background Information Report, Figure 11, Biological Receptors). The nearest potential habitat for the Golden-Cheeked Warbler, another endangered bird species, is approximately 4,000 feet east of AOC-42.
AOC-42 was identified during investigation of potential source areas within a 2,000 foot radius of Well CS-16-LGR. At that time, the area was identified as “Salado Creek.” A geophysical survey was performed in the “Salado Creek” area in May 1995. In June and July of 1995, a soil gas survey was performed in the area. The area was later renamed AOC-42 to be consistent with the naming convention used at CSSA. A chronology of investigations at AOC-42 is located behind the AOC-42 tab of Volume 1-3 and Volume 3-2 of the Environmental Encyclopedia.
A geophysical survey was conducted in May 1995 and four geophysical anomalies were identified. The boundary of AOC-42 was not yet defined and the 1995 geophysical survey was conducted on an area designated “Salado Creek site.” Anomaly A may be associated with the trash pile present in the same area, which was subsequently designated as AOC-62. Anomaly B is a trench subsequently designated as AOC-52. Anomalies C and D may be indicative of past waste disposal trenches and were designated as AOC-42. The geophysical survey effort did not delineate the southern extent of anomalies C and D. Additional information on the geophysical survey conducted on the “Salado Creek site” is contained in Section 11.6 of the Technical Memorandum on Surface Geophysical Surveys, Well 16 Source Characterization, (Parsons ES, 1995).
A soil gas survey was conducted on the area designated “Salado Creek” in June and July 1995. Fourteen soil-gas survey samples were collected near the area now defined as AOC-42. Five of the 14 samples were collected within the boundaries of AOC-42. The soil gas samples were analyzed for chlorinated and aromatic volatile organics. Tetrachloroethene (PCE) was the only target analyte detected. PCE concentrations detected within the boundaries of AOC-42 ranged from 0.03 micrograms per liter (µg/L) to 0.15 µg/L. The maximum concentration (0.15 µg/L) was detected at soil gas survey point 20,20 located within the current boundaries of AOC-42 (Figure AOC42-4 and Figure AOC42-5). No other analytes were reported. PCE was detected outside the boundaries of AOC-42 at a concentration of 0.19 µg/L at sample point 0,40.
As described in Section 4.3 of the Risk Assessment Technical Approach Document (Volume 1-6), CSSA has opted to pursue closure of AOC-42 under the Risk Reduction Rule (30 Texas Administrative Code [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 the Texas Risk Reduction Program (TRRP). A notification of intent to close sites identified to date (including AOC-42) in accordance with the former Risk Reduction Rules 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 is 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 TCEQ Executive Director, then the owner is released from deed recordation requirement.
Since the COCs for AOC-42 are VOCs, metals, and explosives, the cleanup levels should be the reporting limits (RLs) for VOCs and explosives, and the soil or rock background values for metals. Chlorinated VOCs are man-made chemicals, and rarely occur naturally. 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). TCEQ approved the background metals evaluation on April 23, 2002.