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Final AOC-38 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 report for Area of Concern (AOC)-38 was completed in April 2002 to document the environmental condition and site closure requirements, and recommend further investigation. This closure report includes by reference the information presented in the AOC‑38 RFI Report (Parsons, 2002).
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 (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, TO0019 Addendum); and |
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Health and Safety Plan |
For this closure report, Section 1 provides the site-specific background and describes the selected closure standard. Section 2 describes closure activities. Section 3 summarizes the findings, evaluates attainment of data quality objectives (DQOs), provides recommendations, 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 AOC‑38) 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.
If site concentrations are at or below background, and all waste and waste residue have been removed from a site, then the site can be closed under Risk Reduction Standard 1 (RRS1) in accordance with the RRR guidelines (30 TAC §335.554). 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 AOC‑38, CSSA opted to pursue closure under RRS1. If closure requirements under RRS1 are attained and approved by the TCEQ Executive Director, then the owner is released from the deed recordation requirement.
There were no known uses of AOC‑38 for waste disposal and no waste products were apparent. However, a geophysical anomaly, possibly associated with waste management, was identified during the RFI. Further investigation of this anomaly to determine if it was caused by buried waste was recommended in the AOC‑38 RFI Report along with waste removal, if present, 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). In that report, data regarding the geology, hydrology, and physiography are also available for reference.
The site covers approximately 35 acres located within the floodplain of two unnamed tributaries of Salado Creek which run through AOC‑38. This open pasture area is used for cattle grazing only. As shown in Figure AOC38-6, the site is situated south of North Outer Road, in the northeast portion of the Inner Cantonment. (Figures AOC38-1 through AOC38‑5 are provided in the AOC‑38 RFI Report.) Well CS‑16 is located immediately northeast of AOC‑38. The general dimensions of the site are 1,400 feet (east‑west) by 1,100 feet (north‑south). The site is bounded by a fence line and paved road to the north and east, trees to the west, and Salado Creek to the south.
One livestock well (Well CS-4) is located in the southwest portion of AOC‑38. The livestock well is inactive, but it is included in the quarterly groundwater monitoring program at CSSA. A livestock corral exists in the northeast corner of AOC‑38. Some agricultural equipment, including metal cones, are sometimes stored on the site, just to the west of the corral. A six-inch underground water supply line runs through the northwestern portion of the site. This water line is inactive.
During the installation of a fiber optic communications line in July 2000, a trench containing expended munitions was encountered in the northwest corner of the site. This area (approximately one acre) of AOC‑38 was separated from the previously defined area of AOC‑38 and designated solid waste management unit (SWMU) B‑71. The area of SWMU B‑71 is now excluded from the AOC‑38 investigation and closure. Additional information regarding investigation at SWMU B‑71 is located in Volume 1-2, Solid Waste Management Units.
A 1995 report (Section 11.2 of the Technical Memorandum on Surface Geophysical Surveys) indicated that a burn area containing metal wire, wood, rock, and ashes was situated in the north-central portion of the site. This area appeared to be a location where debris (wood, barb wire, etc.) was washed down into the site area during a flood event and was subsequently burned in place to eliminate the debris pile.
Additional background information regarding the location, size, and known historical use of AOC‑38 is included in the Environmental Encyclopedia (Volume 1-3, AOC‑38). Volume 1-3 also includes a Chronology of Actions and a Site-Specific Work Plan for AOC‑38.
1.2.2.2 Potential Sources of Contamination
No formal waste management activities were known to occur at AOC‑38, and historical aerial photographs dated between 1957 and 2003 show no evidence of waste management activities or other ground disturbance, as shown in Figure AOC38‑7. The AOC‑38 area was first identified as an area of concern when groundwater contamination was detected in nearby Well CS-16. The source of this contamination was unknown at that time, and all surrounding areas were identified as possible areas of concern. These areas were included in a soil gas survey conducted in 1995 to identify potential sources of groundwater contamination found at Well CS‑16. At that time, the site was known as the “South Pasture.”
Only low levels of chlorinated volatile organic compounds (VOCs) were detected in soil gas at AOC‑38 (Figure AOC38-8). A maximum concentration of 3.1 micrograms per liter (μg/L) of tetrachloroethene (PCE) and 0.21 μg/L of trichloroethene (TCE) were detected (as described in Section 8, Technical Memorandum on Soil Gas Surveys, Parsons ES, 1996). Because concentrations were very low and because no VOCs were detected above RLs in 60 surface soil samples collected at the site in 2000, it is concluded that the source of the soil gas plume in the vicinity of Well CS-16 originates from waste management units other than AOC‑38. However, the source of one small geophysical anomaly identified at AOC‑38 during a previous investigation was unknown, and excavation was recommended in the RFI Report to confirm that it was not buried waste. In addition, removal and disposal of a small amount of surface metal debris was necessary to meet RRS1 closure requirements.
AOC‑38 is located near the approximate center of CSSA, in the northernmost portion of the Inner Cantonment area. AOC‑38 is approximately 2,700 feet from the nearest facility boundary to the west. The site is immediately southwest of Well CS-16 at the intersection of North Outer Drive and Moyer Road. The boundaries of AOC‑38 are North Outer Drive to the north, Moyer Road to the east, and Salado Creek to the south. As shown in Figure AOC38‑6, there are numerous other AOCs and SWMUs located to the north, east, and south of AOC‑38, including AOC‑35, AOC‑36, AOC‑39, AOC‑40, SWMU B‑11, SWMU B‑28, and SWMU B‑71. RRS1 closure of several of the nearby sites has been approved by TCEQ. Closed sites in the area of AOC‑38 include AOC‑35, AOC‑36, AOC‑39, AOC‑40, AOC‑43, SWMU B‑1, SWMU B‑5, SWMU B‑7, and SWMU B‑19.
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 AOC‑38 RFI Report (Parsons, 2002) and a summarized description is provided in the paragraphs below.
1.3.1 Site Soils and Topography
The majority of soil at AOC‑38 is classified as Trinity and Frio soil, located along the two unnamed tributaries which flow toward Salado Creek. The soil occurs in narrow, long, and irregularly shaped areas, and is frequently flooded. In addition to Trinity and Frio soil, Krum Complex soil, and Crawford & Bexar stony soil occur in smaller areas adjacent to the Trinity and Frio soil. The elevation of the ground surface at AOC‑38 is approximately 1,230 feet above sea level, with the surface sloping toward Salado Creek which drains north to south across AOC‑38.
The Upper Glen Rose (UGR) is the uppermost geologic stratum in the area of AOC‑38. The UGR consists of beds of blue shale, limestone, and marly limestone, with occasional gypsum beds, averaging 50 feet thick. The UGR is underlain by the Lower Glen Rose (LGR) (averaging 320 feet thick). The LGR is underlain by the Bexar Shale unit of the Hensell Sand (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.
At CSSA, the uppermost hydrogeologic layer is the unconfined Upper Trinity Aquifer, which consists of the UGR Limestone. Locally at CSSA, low-yielding perched zones of groundwater can exist in the UGR. Principle development of solution channels is limited to evaporate layers in the UGR Limestone. Groundwater discharge occurs predominantly via natural springs, seeps, and pumping, and fracture systems associated with the fault zones may affect groundwater flow. No evidence that groundwater from the UGR is discharging to natural springs or seeps in the vicinity of AOC‑38 was reported during field investigations. Regional groundwater flow appears to be to the south and southeast.
One inactive livestock well (Well CS‑4) is located in the southwest portion of AOC‑38. The livestock well is inactive, but it is included in the quarterly groundwater monitoring program at CSSA. The depth to water at CS‑4 has varied greatly since monitoring began in 1992. Water levels have ranged from 45 feet below top of casing (November 1998) to 266 feet below top of casing (February 1996) in Well CS-4. Between December 1999 and September 2000, the well was dry. Periodic sampling of CS-4 has usually indicated low concentrations of VOCs (Below the MCL). However, during the June 2004 sampling event, PCE and TCE were detected at 5.1 μg/L PCE and 15 μg/L TCE. Well CS‑16, which is an inactive drinking water well, is located approximately 100 feet northeast of AOC‑38. Well CS‑D is located approximately 100 feet to the north of AOC‑38. TCE, PCE, and cis‑1,2‑dichloroethene (DCE) concentrations above MCLs have been detected in Wells CS‑16 and CS‑D.
The nearest surface water bodies are two intermittent tributaries which enter AOC‑38 across the northern boundary and from the northeastern corner along Moyer Road. These intermittently flowing tributaries flow across AOC‑41, ‑37, ‑35, ‑36, and ‑66 prior to entering the boundary of AOC‑38. Both of these tributaries are usually dry except for periods following a heavy rain. The tributaries merge within the south-central portion of AOC‑38 and continue to flow south to join Salado Creek within the CSSA boundary. More detailed hydrology information for AOC‑38 is included in the AOC‑38 RFI Report (Parsons, 2002).
There are no historical structures or buildings within the boundaries of AOC‑38. The nearest potentially significant cultural resource is Building 43, located 525 feet east of AOC‑38. Former cantonments are located within 1,700 feet of the site to the west and 1,400 feet to the south.
A survey of land use, local and possible future uses of groundwater and surface water, water wells, and sensitive environmental areas was completed for the CSSA facility in December 1999. The results of this survey, along with results from a more in-depth survey designed to identify potential receptors, points of human exposure, and possible constituent pathways are presented in Section 3 of the Technical Approach Document for Risk Evaluation (Volume 1-6).
One inactive well, CS-4, is located in the southwest corner of AOC-38. Several inactive wells are located within 0.25 mile of AOC‑38, including wells CS‑D, CS‑2, CS‑3, and clusters CS‑MW16, CS‑MW1, and CS‑MW2. Four water reservoirs are maintained at CSSA for the purpose of fire protection and 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. None of the water reservoirs are within 0.25 mile of AOC‑38 and none receive surface water discharge from AOC‑38. The nearest residential area is approximately 0.3 mile to the west, but the nearest school is over a mile to the northwest. More detailed information on potential receptors and AOC‑38 is included in the AOC‑38 RFI Report (Parsons, 2002).
In 1995, due to the proximity of the northern boundary of AOC‑38 to Well CS‑16, investigations were performed in an effort to identify potential source areas for contamination at Well CS‑16. Prior to being designated AOC‑38, this area was referred to as the “South Pasture.” The “South Pasture” survey in spring 1995 included soil gas sampling and an electromagnetic (EM) geophysical survey. In 2000, surface soil samples were collected to confirm that no surface contamination was present at the site. The results of these previous investigations are described in the following paragraphs.
An EM-31 geophysical survey was conducted at the site in March 1995. Grid points were staked at 100-foot intervals with data transects conducted at 50-foot intervals in both north-south and east-west directions. Both apparent conductivity and in-phase electromagnetic (EM) readings were collected at 2‑foot intervals along each transect. Five anomalies were detected during the survey; however, all but one were attributed to underground/overhead utilities, geophysical equipment aberrations, or surface metal debris including barbed wire. The location of the one remaining anomaly, Anomaly A, is shown on Figure AOC38‑8. A 1.5-inch diameter metal pipe was located on the western end of Anomaly A which may have affected the EM readings in this area. In addition, metal agricultural equipment (metal cones) were stored just to the east of the anomaly location. Results of the 1995 geophysical survey are also provided in Section 11.2 of the Technical Memorandum on Surface Geophysical Surveys for the Well 16 Source Characterization (Parsons ES, 1995).
In an effort to further identify the source of this anomaly, field personnel walked the area in August 2001. At the north end of Anomaly A, a partially-buried portion of a barbed wire fence, presumably washed down during a precipitation event, was found. If this fence part was on the ground during the 1995 geophysical survey, it may have been the cause of the suspected anomaly, together with the 1.5‑inch diameter pipe which remains on site today.
In July 1995, 26 soil gas samples were collected within or near AOC‑38, in the “South Pasture” area.. Each sample was analyzed for benzene, toluene, ethylbenzene, and xylenes (BTEX), total hydrocarbons, DCE, TCE, and PCE. PCE was detected in every sample, at concentrations ranging from only 0.02 μg/L to 3.1 μg/L. The maximum concentration was detected at the location identified as “South Pasture 110,40,” which was situated in the northeast corner of AOC‑38. No other analytes were detected. Results of the July 1995 survey are provided in Table 9.1 of the Technical Memorandum on Soil Gas Surveys (Parsons ES, 1996).
In November 1995, 95 additional soil gas samples were collected in the “South Pasture” area and analyzed for DCE, TCE, PCE, and carbon tetrachloride. These additional samples were collected to provide additional information within the area surveyed in June 1995, as well as to extend the survey area to the south and west. During the second survey, TCE was detected at 10 locations at concentrations ranging from 0.02 μg/L to 0.21 μg/L. PCE was detected at 81 locations at concentrations ranging from 0.01 μg/L to 2.6 μg/L; the maximum PCE and TCE concentrations were detected at “South Pasture 80,-40,” in the southeast corner of AOC‑38. Results of the November 1995 survey are provided in Table 9.2 of the Technical Memorandum on Soil Gas Surveys. Figure AOC38‑8 shows PCE soil gas contours, including both the 1995 and 1999 soil gas data. Higher concentrations follow the fault trends, which are postulated to provide a conduit for contamination from known VOC source areas SWMUs B-3 and O-1, located to the northeast of AOC‑38.
Sixty surface soil samples (AOC38‑SS01 through AOC38‑SS60) were collected in January 2000, and analyzed for selected VOCs (method SW‑8260B) by O’Brien & Gere Laboratory in Syracuse, New York. Based on the soil gas survey results, analytes included 1,1‑DCE, cis-1,2-DCE, trans‑1,2‑DCE, PCE, and TCE. The samples were collected from the top two feet of soil adjacent to grid points from the soil gas survey. Soil sampling locations are shown on Figure AOC38‑8.
None of the analytes were detected above their respective RLs, and therefore concentrations meet RRS1 closure requirements. Very low levels of PCE were detected in three samples, SS36, SS39, and SS58, collected in the southeast corner of the site, but these concentrations were below the RL. Concentrations of PCE ranged from 0.0005 milligrams per kilogram (mg/kg) to 0.00016 mg/kg , which is also well below the reporting limit of 0.007 mg/kg for PCE.