SWMU B-26 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 the RCRA, and further amended by the HSWA of 1984. In accordance with the RFI requirements of the Consent Order, this RFI report has been prepared to document the environmental condition and site closure requirements of SWMU B-26 and to recommend further investigation, if necessary, or to provide documentation necessary for site closure. The main objectives of the SWMU B-26 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-D-0024, Delivery Order RL17. AFCEE provided technical oversight for the delivery order. Based upon the project SOW, a set of work plans to govern the fieldwork was prepared. These include:
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Work Plan Overview: |
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Site-Specific Work Plan: |
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Site-Specific Rework Plan: |
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Field Sampling Plan: |
(Volume 1-4 RL17 Addendum); and |
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Health and Safety Plan: |
For this report, Section 1 provides the site-specific background and the target closure standard. normal'>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
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.
SWMU B-26 is a low priority site where a trench was identified during a review of a 1966 aerial photograph. During a field investigation, wooden pallets were found next to the trench, and soil piles were found on either end of the trench. However, no waste materials were apparent during visual inspection of the site. Based on a records review, there is no known prior documentation of the trench or its usage by CSSA. The dates of its usage are also unknown. However, because of visible presence of the trench, SWMU B-26 was suspected of having possibly been used as a waste management site. SWMU B-26 is presently inactive.
SWMU B-26 is a rectangular area and covers approximately 0.4 acre. It is approximately 220 feet long in the north-south direction and 110 feet wide in the east-west direction. A three foot deep, 20 foot wide, 185 feet long trench runs north-south down the center of SWMU B-26. At each end of the trench, a five foot high, circular soil pile adjoins the trench. These soil piles were most likely created from materials excavated from the trench. Three linear soil piles run parallel to each side of the trench. These linear soil piles are less than an inch high and approximately one foot wide. The site boundaries are defined such that the site contains the soil piles and trench.
Background information regarding the location, size, and known historical use of SWMU B-26 is also included in the Environmental Encyclopedia (Volume 1-2, SWMU B-26). Volume 1-2 includes a Chronology of Actions and a Site-Specific Work Plan for SWMU B-26.
1.1.2.2 Potential Sources of Contamination
The previous uses of SWMU B-26 are not documented; however, it may have been used for disposal purposes. The potential COCs, therefore, are metals, VOCs, and SVOCs.
SWMU B-26 is located in the east pasture of the outer cantonment, approximately 1,000 feet from the eastern boundary of CSSA (Figure B26-1). Three additional investigation areas are located within ¼ mile of SWMU B-26. SWMU B-25 is located approximately 400 feet northwest of SWMU B-26 and AOC 63 is approximately 800 feet southwest of SMWU B-26. AOC 49 is located approximately 1,200 feet south of SWMU B-26. A road runs approximately 300 feet west of SWMU B-26. Further details regarding the site physiography may be found in Volume 1-2 (SWMU B-26).
1.2 - Site Environmental Setting
1.2.1 Site Soils and Topography
The native soils at SWMU B-26 are Krum Complex soils (Figure B26-2). 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. At SWMU B-26, the Krum soil layer ranges from 3 to 5 feet in thickness. Detailed descriptions of the CSSA soil types are provided in the Soils and Geology section of the Background Information Report (Volume 1-1).
SWMU B-26 is located on a gentle, west-trending slope that leads to an intermittent streambed located approximately 100 feet to the west. The site elevation is between 1,230 and 1,240 feet above sea level. Prior to the investigation, SWMU B-26 had been cleared of juniper ash (cedar) trees. Remaining vegetation did not appear to be stressed prior to excavation as identified on historical aerial photographs.
There are no significant changes in topography, except the trenches and soil piles described above in the immediate vicinity of SWMU B-26. Surface run-off occurs toward the west at the site. However, it is expected that any run-off intercepted by the trench would be retained within the trench.
The Upper Glen Rose is the uppermost geologic stratum in the area of SWMU B‑26 (Figure B26-3). 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. The thickness of the Upper Glen Rose is estimated to be up to 150 feet at CSSA. 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 known to be two major fault zones at CSSA: the North Fault Zone and the South Fault Zone. SWMU B-26 is located between the North and South Fault Zone. Additional information on structural geology at CSSA can be found in the Environmental Encyclopedia (Volume 1-1, Background Information Report, Soils and Geology).
At SWMU B-26, the near-surface site geology consists of 3 to 4 feet of surface soils composed chiefly of silt and clay. Upper Glen Rose Limestone was encountered at depths as shallow as 3 feet bgs. At SWMU B-26, this limestone was described as pale yellow near the surface and grading to gray with depth, highly weathered near the surface, and massive. Boring logs are included in Appendix B.
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 exist in the Upper Glen Rose. Transmissivity values are not available for the Upper Glen Rose. 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. Groundwater discharge occurs predominantly via natural springs, seeps, and pumping. Regional groundwater flow appears to be to the southeast.
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, the Cow Creek Limestone, and the Hammett Shale. 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. 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.
An intermittent stream runs southward approximately 100 feet west of SWMU B‑26. This creek feeds into the Salado Creek just south of CSSA. No site–specific information regarding groundwater is available. There are no wells within ½-mile of SWMU B-26 (Figure B26-1).
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. There are no documented cultural resources in the vicinity of SWMU B-26.
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 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 use within ¼-mile of the site is classified as “Evergreen Forest Land”. There are no buildings or residential use areas within ¼-mile of SWMU B-26. Generally, CSSA is a controlled access facility, so access is limited by a security guard and perimeter fence. The area around the site is wooded with mountain juniper and grasses. There are no CSSA wells within ½ mile of SWMU B-26 (Figure B26-1).
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 of the Technical Approach Document for Risk Evaluation (Volume 1-6). SWMU B-26 is located approximately 500 feet northwest of hunting stand number 41. Four water reservoirs are maintained at CSSA for the purpose of sport fishing. Two of the reservoirs are located in the northwestern and northeastern portions of the North Pasture while the other two reservoirs are located near the western boundary of the Inner Cantonment.
The Golden-Cheeked Warbler and Black-Capped Vireo, which are both endangered species, may potentially reside to the west and east of SWMU B-26, respectively. Both potential habitat areas are located approximately 1,500 feet away from SWMU B-26.
No previous investigations have been performed at SWMU B-26.
As described in Section 4.3 of the Risk Assessment Technical Approach Document (Volume 1-6), CSSA has opted to pursue closure of SWMU B-26 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 SWMU B-26) in accordance with the former RRR was sent to the TNRCC on July 12, 1999. TNRCC acceptance of this notification was sent 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 SWMU B-26 are metals, VOCs, and SVOCs, the RRS1 standards are the soil or rock background values for metals and the laboratory 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 Soils and Bedrock (Parsons, February 2002).
Updated January 2020