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SWMU B-26 Delisting Report
Section 1 - Introduction
On May 5, 1999, an Administrative Consent Order was issued to Camp Stanley Storage Activity (CSSA) pursuant to §3008(h) of the Solid Waste Disposal Act (SWDA), 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, an RFI report for Solid Waste Management Unit (SWMU) B‑26 was completed in August 2002 to document the environmental condition and site closure requirements, and to recommend further investigation. This report includes by reference the information presented in the SWMU B‑26 RFI Report (Parsons, 2002).
The SWMU B‑26 RFI Report recommended excavation of a test pit in the area of a suspected geophysical anomaly and proper disposal of any discovered waste. Results for five surface soil and Glen Rose Limestone samples indicated very low levels of chromium, zinc, and bis(2-ethylhexyl)pthalate (DEHP) (greater than background concentrations) in three of the Glen Rose Limestone samples. However, the concentrations of both metals were less than the Texas-specific median background concentrations. None of the analytes exceeded background levels in surface soil samples.
The work documented in this report was performed by Parsons under the U.S. Air Force Environmental Remediation and Construction (ENRAC) Contract F41624‑01‑D‑8554, Task Order 19 (TO 0019). The 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 to govern the fieldwork was established. 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, TO 0019 Addendum); and |
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Health and Safety Plan |
Excavation activities commenced at SWMU B‑26 during December 2003. As recommended in the RFI report, excavation of a test pit in the area of a suspected geophysical anomaly was conducted. Approximately 500 cubic yards (CY) of soil was excavated, inspected for waste, and replaced into the test pit after no waste was found. In addition, one sample was collected from each of the soil mounds at the site to confirm there was no contaminated material in the mounds.
Excavation activities at SWMU B‑26 did not reveal any evidence of waste management activities at the site. Soil samples collected at the site did not exceed RRS1 for any contaminants of concern (COCs). The site was originally registered as a SWMU based on the likelihood that waste management was performed in an area with trenching and soil mounds. Since the site was not used for waste management, it should not be considered a SWMU. Rather, the site should be delisted as a SWMU. This report documents the excavation and sampling activities at the site and delists the site as a SWMU. Since the site is not a SWMU, it will be referred to as B‑26 throughout the remaining portion of the report. In addition, activities at the site will be referred to as delisting activities, rather than closure activities.
For this delisting report, Section 1 provides the site-specific background for B‑26. Section 2 describes field actions and the delisting evaluation. Section 3 summarizes the findings and provides the delisting recommendations. References cited in this report can be found in the Bibliography (Volume 1-1 of the Environmental Encyclopedia).
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.
1.1.2.1 Site Description
B‑26 is rectangular in shape and covers approximately 0.4 acre. The site is approximately 220 feet long in the north-south direction and 110 feet wide in the east-west direction. A trench was identified during a review of a 1966 aerial photograph. This trench is visually apparent at the site, and is approximately three feet deep, 20 feet wide, 185 feet long, and runs north-south down the center of 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. The site boundaries are defined such that the site contains both the soil piles and trench. Figure B26‑7 shows aerial photographs of the site over time. (Figure B26‑1 through Figure B26‑6 are provided in the SWMU B‑26 RFI report.)
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, B‑26 was suspected of having possibly been used as a waste management site. B‑26 is presently inactive.
Background information regarding the location, size, and known historical use of 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 B‑26.
1.1.2.2 Potential Sources of Contamination
The previous uses of B‑26 are not documented; however, the presence of a trench and soil mounds indicate that it may have been used for disposal purposes in the past. Potential COCs include metals, volatile organic compounds (VOCs), and semivolatile organic compounds (SVOCs).
B‑26 is located in the East Pasture of the Outer Cantonment Area, approximately 1,000 feet from the eastern boundary of CSSA (Figure B26‑8). Three additional investigation areas are located within 0.25 mile of B‑26. SWMU B‑25 is located approximately 400 feet northwest of B‑26 and Area of Concern (AOC) 63 is located approximately 800 feet southwest of B‑26. AOC 49 is located approximately 1,200 feet south of B‑26.
A detailed description of the site environmental setting is provided in the CSSA Background Information Report (Volume 1-1) and the SWMU B‑26 RFI (Parsons, 2002). A summarized description is provided in the paragraphs below.
1.2.1 Site Soils and Topography
The only soil type that occurs at B‑26 is the Krum Complex. This soil occurs 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. At B‑26, the Krum soil profile ranges from 3 to 5 feet in thickness.
The topographic elevation of the site is between 1,230 and 1,240 feet above sea level. B‑26 is located on a gentle, west-trending slope that leads to an unnamed intermittent streambed located approximately 100 feet to the west. There are no significant changes in topography, except the trenches and soil piles described above in the immediate vicinity of B‑26. Grading of the site was part of the delisting activities described in Section 2.
The Upper Glen Rose is the uppermost geologic stratum in the area of B‑26 The Upper Glen Rose consists of beds of blue shale, limestone, and marly limestone, with occasional gypsum beds, averaging 50 feet thick. The Upper Glen Rose is underlain by the Lower Glen Rose (averaging 320 feet thick). The Lower Glen Rose is underlain by the Bexar Shale facies of the Hensell Sand (averaging 76 feet thick). The geologic strata dip approximately 10 to 12 degrees to the south-southeast at CSSA. The geologic setting of the site is presented in Figure B26-9.
In general 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 exist in the Upper Glen Rose. Principle recharge into the Middle Trinity Aquifer is via precipitation infiltration at outcrops. In general, groundwater at CSSA flows in a north to south direction. However, local flow gradient may vary depending on geologic/stratigraphic structure, rainfall, recharge, and possibly well pumping.
The nearest surface water feature is an intermittent stream that runs southward approximately 100 feet west of 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 0.5 mile of B‑26.
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 B‑26.
Land use within 0.25 mile of the site is classified as “Evergreen Forest Land.” There are no buildings or residential use areas within 0.25 mile of B‑26, and there are no active wells within 0.5 mile of B‑26. The nearest potential habitat for locally endangered species, the Golden-Cheeked Warbler, may exist approximately 1,500 feet to the west of the site, and habitat for the locally endangered species, the Black-Capped Vireo, may exist approximately 1,500 feet to the east of B‑26.
A summary of previous investigations is presented in the following sections. For more detailed information, refer to the SWMU B‑26 RFI Report (Parsons, 2002).
An electromagnetic (EM) geophysical survey was conducted at B‑26 in March 1996. Two anomalies were identified during the geophysical survey (see Figure B26-5 and Figure B26-6 in the B‑26 RFI Report). One anomaly was located in the central portion of the site and another anomaly in the northwest corner of the site. The anomaly near the center of the site was not visible in the in-phase component; therefore, it is not thought to be associated with buried waste. Excavation of a test pit to investigate the anomaly in the northwest portion of the site was recommended in the SWMU B‑26 RFI Report. Although investigation was not recommended for the anomaly in the central portion of the site, a soil boring was advanced at the anomaly location. The boring did not reveal evidence of subsurface waste.
Three surface soil samples (RW-B26-SS01, RW-B26-SS02, and RW‑B26-SS03) were collected at B‑26 on March 23, 2000. Sample RW-B26-SS01 was collected in the top half-foot of soil from one of the soil piles located parallel to the trench where a geophysical anomaly was identified. Sample RW-B26-SS02 was collected within the trench. Sample RW-B26-SS03 was collected from the circular soil pile adjoining the northern end of the trench. In addition, the shallowest sample collected at borings RW-B26-SB02 and RW-B26-SB03 were also surface soil samples (Figure B26-10).
All metals results for surface soil samples were below the RRS1 background concentrations. All reported VOC and SVOC concentrations were below RLs, therefore, RRS1 criteria for VOCs and SVOCs were met.
On March 23, 2000, three soil borings were completed at B‑26. Boring RW-B26-SB01 was drilled adjacent to surface sample RW-B26-SS01, within the confines of the geophysical anomaly identified in the northwestern portion of the site. Boring RW-B26-SB02 was drilled within the confines of the geophysical anomaly identified in the central portion of the site. Boring RW‑B26‑SB03 was advanced in an area south of the southern extent of the trench, between the trench and an adjacent soil pile.
For each boring location at B‑26, a sample was collected from two depths. The majority of metal results for subsurface samples were less than the associated RRS1 background concentrations. Zinc exceedances were reported at RW‑B26‑SB01 (12.5 to 13 ft), RW‑B26‑SB02 (9.5 to 10 ft), RW‑B26‑SB03 (6 to 6.5 ft), and RW‑B26‑SB03 (12.5 to 13 ft). Concentrations in these samples ranged from 11.9 milligrams per kilogram (mg/kg) to 17.5 mg/kg. The zinc background level for Glen Rose Limestone is 11.3 mg/kg, and the Texas-specific median background concentration (30 TAC 350.51(m)) is 30 mg/kg. In addition, chromium was detected at 9.7 mg/kg at RW‑B26‑SB01 (12.5 to 13 ft) and at 8.6 mg/kg in RW-B26-SB02 (9.5 to 10 ft), which both slightly exceed the Glen Rose background level of 8.1 mg/kg. The Texas-specific median background concentration for chromium is 30 mg/kg.
All samples reported VOC concentrations below RLs, therefore RRS1 criteria for VOCs were met. One SVOC, DEHP, had concentrations greater than the reporting limit (RL) of 0.7 mg/kg for three samples: RW-B26-SB01 (6 to 6.5 feet), with a reported concentration of 30.0 mg/kg; RW-B26-SB03 (6 to 6.5 feet), with a reported concentration of 52 mg/kg; and RW-B26-SB03 (12.5 to 13 feet), with a reported concentration of 2.3 mg/kg. All other SVOC concentrations were less than the RLs.
Because DEHP is not known to have ever been used by any processes at CSSA, and based on the absence of any other VOC or SVOC detections at the site, the concentrations detected in the three Glen Rose Limestone samples are strongly suspected of being associated with sampling or laboratory procedures. DEHP is a common plasticizing component of sampling and laboratory equipment.