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SWMU B-23 Closure 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 was prepared to document the environmental condition of Solid Waste Management Unit (SWMU) B‑23 and to recommend further investigation and site closure requirements. This closure report includes by reference the information presented in the SWMU B‑23 RFI Report (Parsons, 2002).
The SWMU B‑23 RFI Report recommended excavation and disposal of waste, if any was found to be present. Results for three borings sampled at SWMU B‑23 indicated concentrations of some metals and volatile organic compounds (VOCs) that exceed closure standards. The RFI Report estimated that excavation of up to 1,700 cubic yards (CY) of soil and waste material might be required. The RFI Report also recommended confirmation sampling for benzene, toluene, ethyl benzene, and xylenes (BTEX), dichlorodifluoromethane, barium, copper, lead, nickel, and zinc to confirm that the site achieved closure requirements. This report documents the closure activities at SWMU B‑23.
The closure work was performed by Parsons under the U.S. Air Force Environmental Remediation and Construction (ENRAC) Contract F41624‑01‑D‑8544, Task Order 19 (TO0019). 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, TO0019 Addendum); and |
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Health and Safety Plan |
For this closure report, Section 1 provides the site‑specific background and closure standard. Section 2 describes closure activities and closure evaluation. Section 3 summarizes the findings, evaluates attainment of data quality objectives (DQOs), and certifies the site closure. References cited in this report can be found in the Bibliography (Volume 1‑1 of the Environmental Encyclopedia).
As described in Section 4.3 of the Risk Assessment Technical Approach Document (Volume 1‑6), CSSA has opted to pursue closure of many of its sites under the Risk Reduction Rules (RRR) (30 Texas Administrative Code [TAC] §335). A notification of intent to close sites identified to date (including SWMU B‑23) was sent to the Texas Commission on Environmental Quality (TCEQ) in accordance with the RRR on July 12, 1999. TCEQ acceptance of this notification was received on October 5, 1999.
Following the RRR guidelines, if site concentrations are at or below background, and all waste and waste residue has been removed, then the site can be closed under Risk Reduction Standard 1 (RRS1). CSSA background levels are the RRS1 criteria for metals concentrations and laboratory reporting limits (RLs) are the RRS1 criteria for organic compounds. Based on the RFI sampling results at SWMU B‑23, CSSA opted to clean the site to background levels and pursue closure under RRS1. If closure requirements under RRS1 are attained and approved by the TCEQ Executive Director, then CSSA is released from the deed recordation requirement.
Due to the presence of some solid waste at the site and the occurrence of VOCs and metals concentrations above RRS1 standards, removal of waste and waste residue was recommended in the RFI Report to meet RRS1 requirements.
1.2 - 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). Data regarding the geology, hydrology, and physiography are also available for reference within the aforementioned report.
SWMU B‑23 (Figure B23‑5) contains a trench identified from a 1966 aerial photograph. Figure B23‑6 displays a chronology of aerial photographs ranging from 1957 to 2003. Figures B23-1 through B23-4 are included in the SWMU B-23 RFI Report, and in Appendix E of this document. During a field survey in September 1993, evidence of a northeast‑southwest trending trench was apparent. The trench has filled in with locally eroded sediments. The soil eroded into the trench had native grass cover. Several unidentified, half‑buried, green canisters and a large soil mound were located towards the southernmost end of the trench. Approximately 65 canisters were found, each measuring approximately 3 feet in length. All of the canisters were filled with soil. Metal banding was also littered across the surface of the trench area. Unexploded ordnance (UXO) specialists from UXB International visually surveyed the site in 1997 and suggested that the unidentified canisters were likely Jet‑Assisted Take‑Off (JATO) units. JATO units contain liquid or solid fuel and are attached to an aircraft to augment the take-off power of an aircraft’s engines. All of the fuel in the units is expended when they are used. No model numbers were present on the canisters. The exact dates of trench usage are unknown.
Background information regarding the location, size, and known historical use of SWMU B‑23 is also included in the Environmental Encyclopedia (Volume 1‑2, SWMU B‑23). Volume 1‑2 also includes a Chronology of Actions and a Site‑Specific Work Plan for SWMU B‑23.
1.2.2.2 Potential Sources of Contamination
Results of surface and subsurface soil and rock samples collected at SWMU B‑23 during the RFI indicate that some metals and VOCs concentrations exceed RRS1 standards. These analytes, including BTEX compounds, dichlorodifluoromethane, barium, copper, lead, nickel, and zinc, are considered contaminants of concern for the closure activities.
The JATO canisters and metal banding littered on the trench surface were potential sources of contamination, and additional waste was thought to possibly be buried. UXO specialists from UXB International visually surveyed the site in 1997 and found both empty and soil‑filled JATO canisters.
1.2.2.3 Site Location
SWMU B‑23 is located in the central portion of the North Pasture at CSSA. SWMU B‑23 is approximately 150 feet long by 50 feet wide with the long axis oriented northwest to southeast. It contains a small, narrow trench with soil mounded at the southernmost end. The trench is about 4 feet deep, 20 feet wide, and 120 feet long, covering approximately 2,400 square feet (less than 0.1 acre) in area. Figure B23‑5 shows the approximate site location within CSSA. (Figures B23‑1 through B23‑4 are found within the RFI Report.) The site is approximately 3,000 feet from the western boundary of the base and 2,500 feet from the northern base boundary. SWMU B‑23A is located about 200 feet to the southeast. No utilities exist at SWMU B‑23.
1.3 - Site Environmental Setting
A detailed description of the site environmental setting is provided in the CSSA Background information Report (Volume 1‑1) and the SWMU B‑23 RFI Report (Parsons, 2002).
The single soil type present within the site area is the gently undulating Tarrant association (Figure B23‑2). Tarrant association soil occurs in as nearly level and gently sloping areas of typical prairie and plateau topography. SWMU B‑23 contains little topographic relief and lies at approximately 1,320 to 1,330 feet above sea level (Figure B23‑6). The land surface within the site area slopes approximately three degrees to the southwest. Vegetation at the site consists of native grasses, shrubs, and trees.
The Upper Glen Rose Formation is the uppermost geologic stratum in the area of SWMU B‑23 (Figure B23‑7). The Upper Glen Rose Formation consists of beds of blue shale, limestone, and marly limestone, with occasional gypsum beds, averaging 50 feet thick. Generally, it outcrops in stream valleys and at the ground surface where soils are poorly developed or eroded. The Upper Glen Rose is underlain by the Lower Glen Rose (averaging 320 feet thick). The Lower Glen Rose Limestone is underlain by the Bexar Shale (regionally known as Hensell Shale, averaging 60 feet thick), and the Cow Creek Limestone (averaging 76 feet thick). The geologic strata dip approximately 10 to 12 degrees to the south‑southeast at CSSA. Additional information on structural geology at CSSA can be found in the Environmental Encyclopedia (Volume 1‑1, Background Information Report, Soils and Geology).
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 can exist in the Upper Glen Rose. In general, groundwater at CSSA flows in a north to south direction. No site‑specific information regarding groundwater is available. The nearest well, Well CS‑MWG‑LGR, which is an agricultural water supply well, is located 750 feet west of SWMU B‑23. Between September 1994 and March 2004, water levels within Well CS‑MWG‑LGR have ranged from 171.22 feet below top of casing (BTOC) (April 2003) to 316.7 feet BTOC (January 1997) (Volume 5, Introduction to Groundwater Monitoring Program, Table 3).
The nearest surface water feature to the site is a northeast‑southwest trending intermittent stream located about 1,000 feet to the south of the site area. This stream flows south, draining into Salado Creek in the Inner Cantonment.
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 burned rock midden located approximately 800 feet southwest of SWMU B‑23. The nearest potential habitat location for local endangered species is a Golden‑Cheeked Warbler habitat, which is approximately 1,200 feet west of SWMU B‑23. A Black‑Capped Vireo habitat is also located approximately 1,900 feet south of the site area (Parsons ES, 1993). There is no potential habitat for these two species associated with SWMU B‑23.
Results of the previous geophysical survey are described in Section 1.3 of the SWMU B‑23 RFI Report (Parsons, 2002). Two anomalies were identified at the site during a 1995 geophysical survey, as described in Section 1.3 of the RFI Report and as shown on Figure B23‑8. Both of these anomalies corresponded with scrap metal on the ground surface.
On August 26, 1996, a soil gas survey was performed at SWMU B‑23. Seven soil gas points were sampled for BTEX compounds, cis‑1,2‑dichloroethene (DCE), 1,1,1‑trichloroethane (TCA), trichloroethene (TCE), and tetrachloroethene (PCE) analysis. The seven soil gas points were located across the trench area, covering the entire length of the trench. Samples were collected at depths ranging from 3 to 5 feet below ground surface (bgs).
None of the seven soil gas samples reported detectable concentrations of any of the VOCs analyzed. Although the blank sample of air collected in the gas chromatograph room had a slight detection of PCE, all SWMU B‑23 soil gas survey points were reported as non‑detects (U‑flagged) for all analyzed compounds. Results are provided in Table B23‑1 of the SWMU B‑23 RFI Report, and in Appendix E of this report.
1.4.3 Surface and Subsurface Soil Samples
In order to characterize the subsurface soils surrounding the trench, three soil borings (B23‑SB01, B23‑SB02, and B23‑SB03) were drilled at SWMU B‑23 on March 2 and 3, 2000 (Figure B23‑8). Each soil boring was drilled to two feet below the estimated SWMU depth and was sampled at three discrete intervals, for a total of nine samples. B23‑SB01, B23‑SB02, and B23‑SB03 were drilled to depths of 9.5 feet bgs, 10.5 feet bgs, and 10 feet bgs, respectively. The soil borings were located in the most probable areas of contamination. One of the soil borings (B23‑SB03) was advanced near the middle of the trench, where metal banding was present. The other borings, B23‑SB01 and B23‑SB02, were advanced in the southernmost end of the trench, near the green canisters and the soil mound identified during the field survey effort. Samples collected were analyzed for semivolatile organic compounds (SVOCs), VOCs, metals, and explosives.
Metals concentrations exceeded CSSA soil or rock background levels in four of the nine samples collected at SWMU B‑23. At B23‑SB01 (0.5‑1 foot), copper was detected at 103.3 milligrams per kilogram (mg/kg), exceeding the soil background of 23.2 mg/kg. At B23‑SB02, barium was detected at 23.63 mg/kg in the samples collected between 5.5 and 6 feet bgs, and zinc was detected at 17.35 mg/kg in the sample collected between 10 and 10.5 feet bgs. Finally, at B23‑SB03 (9.5‑10 feet), barium, lead, nickel, and zinc concentrations slightly exceeded background levels. Background levels for barium, lead, nickel, and zinc in Glen Rose Limestone are 10.0 mg/kg, 5.5 mg/kg, 6.8 mg/kg, and 11.3 mg/kg, respectively.
BTEX compounds were detected above RRS1 RLs criteria in four samples collected from B23‑SB01 and B23‑SB02. The highest concentrations were detected at B23‑SB02 (0.5‑1 foot). In that sample, benzene was reported at a concentration of 0.0262 mg/kg, ethylbenzene at 0.0073 mg/kg, toluene at 0.0286 mg/kg, and m,p‑xylenes at 0.0091 mg/kg. The RLs for benzene, ethylbenzene, toluene, and m,p‑xylenes were 0.002 mg/kg, 0.003 mg/kg, 0.005 mg/kg, and 0.007 mg/kg, respectively.
Finally, the compound dichlorodifluoromethane was detected above RRS1 criteria in each of the samples collected from B23‑SB03. The sample collected from 0.5‑1.0 feet bgs had a reported concentration of 0.0145 mg/kg, the 5.0‑5.5 feet bgs sample contained 0.049 mg/kg, and the sample collected from 9.5‑10 feet bgs contained 0.0319 mg/kg dichlorodifluoromethane. The RL for dichlorodifluoromethane is 0.005 mg/kg.
No SVOCs or explosives were detected in any of the samples analyzed; therefore, RRS1 criteria have been met for these compounds. Table B23‑2 of the RFI Report contains a summary of the compounds detected, as well as the comparison criteria for each compound. Refer to Section 2.2 of this report for a discussion of confirmation sample results associated with the aforementioned exceedances.