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AOC 41 No Further Action 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 Resource Conservation and Recovery Act (RCRA), and further amended by the Hazardous and Solid Waste Amendments (HSWA) of 1984. This report documents the field activities at Area of Concern (AOC) 41 (AOC‑41). This No Further Action (NFA) report includes by reference the information presented in the AOC‑41 Soil Gas Survey Results Report (Parsons, 1999).
AOC‑41 was originally a 5.9 acre area that was evaluated during an investigation to identify potential source areas for volatile organic compound (VOC) contamination at CSSA monitoring well CS‑MW16 (Well CS‑16). However, in 2003, during delineation of soil contamination at neighboring solid waste management unit (SWMU) B‑8, it was determined that metals contamination associated with SWMU B‑8 extends partially within AOC‑41. The purpose of this report is to re‑define the boundary of AOC‑41, and close the reduced acreage area.
The NFA 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 task 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 |
For this NFA report, Section 1 provides the site‑specific background and describes the NFA criteria. Section 2 describes the previous field activities and the NFA evaluation, summarizes the findings, and evaluates attainment of data quality objectives (DQOs). 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‑41) 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.
Initially, it was thought that AOC‑41 would be closed under Risk Reduction Standard 1 (RRS1) which requires compound-specific analytical data for closure certification. Based upon the revised site boundary for AOC‑41 and the results of historic field activities (soil gas and geophysical survey data), no compound‑specific data are necessary.
TCEQ can approve a NFA for sites that meet the following criteria: 1) historical aerial photographs do not show any ground disturbance, waste disposal, etc., 2) magnetometer data or other geophysical data from the site do not indicate the presence of geophysical anomalies, 3) no apparent, observed, or documented waste management activities were known to occur at the site, and 4) contaminants at the site have only been analyzed using non compound‑specific test or field screening techniques, such as soil gas survey data.
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, detailed data regarding the geology, hydrology, and physiography are also available for reference.
1.2.2 AOC‑41
The site currently covers approximately 2.5 acres, but previously covered approximately 5.9 acres. Metals results of samples collected in May 2003 showed that the southern boundary of SWMU B‑8, where investigation work is still in progress, should be extended further south into the area that was formerly designated AOC‑41. The adjustment of the SWMU B‑8 and AOC‑41 boundaries caused SWMU B‑8 to increase in acreage and AOC‑41 to decrease in acreage. The old and new site boundaries for SWMU B‑8 and AOC‑41 are shown on Figure AOC41‑3. (Figure AOC41‑1 and Figure AOC41‑2 are included in the AOC‑41 Soil Gas Survey Report.)
Currently, AOC‑41 is only used for cattle‑grazing. An intermittent unnamed tributary of Salado Creek flows to the north and west of the site. As shown on Figure AOC41‑3, the site is situated north of North Outer Road, just north of the 8‑foot tall chain link fence between the Inner Cantonment and the North Pasture.
1.2.2.2 Potential Sources of Contamination
Waste management activities are known to have occurred at SWMU B‑8, but none are known to have occurred within the reduced AOC‑41 boundary. Investigation activities at AOC‑41 were initiated in 1995 due to its proximity to the soil gas plume associated with Well CS‑16. In May 1995, a geophysical survey was conducted in all open areas within a 2,000‑foot radius of Well CS‑16. Three geophysical anomalies were identified in the area designated “North Pasture”, later renamed AOC‑41. [Note: In the geophysical survey conducted later in May/June 2003, these three anomalies were determined to be north of the reduced acreage AOC‑41 boundary, and within the boundaries of SWMU B‑8.] Soil gas data were collected at AOC‑41 during June/July 1995 and December 1999 to determine if a source of chlorinated VOCs exists in the AOC‑41 area. The results shown in Figure AOC41-7 indicated there is not a VOC source at AOC‑41. As shown on Figure AOC41‑4, historical aerial photographs of AOC‑41 dating back to 1957 do not show any evidence of waste disposal activities or other disturbances.
1.2.2.3 Site Location
AOC‑41 is located adjacent to the southern edge of the North Pasture Area, directly east of AOC‑37 and directly south of SWMU B‑8 (Volume 1‑3, Site Map). As shown on Figure AOC41‑3, numerous other AOCs and SWMUs surround AOC‑41, including SWMU B‑5, SWMU B‑2, AOC‑40, AOC‑37, and AOC‑66. RRS1 closure of several nearby sites has been approved by TCEQ. Closed sites in the vicinity of AOC‑41 include SWMU B‑1, SWMU B‑5, SWMU B‑10, SWMU B‑19, SWMU O‑1, AOC‑35, AOC‑36, AOC‑38, AOC‑40, and AOC‑43. In addition, AOC‑37 and AOC‑66 which were also identified as potential source areas for the well CS-16 VOC contamination, have been granted No Further Action (NFA) closure.
The site is situated about 4,500 feet from the western boundary of the North Pasture/CSSA boundary and just north of the northern boundary of the Inner Cantonment area.
1.3 - Environmental Setting
A detailed description of the environmental setting at CSSA is provided in the Background Information Report (Volume 1‑1). A brief description of the setting at AOC‑41 is provided in the paragraphs below.
1.3.1 Site Soils and Topography
The only soil type occurring at AOC‑41 is the Krum Complex, shown on Figure AOC41‑5. These soils generally cover streambeds and floodplains, occur on slopes of 2 to 5 percent, and occupy ‘foot’ slopes below Tarrant and Brackett soils. Because these soils form down‑slope of prairie plains and receive sediments from higher elevations, they are subject to hydraulic erosion.
The topographic elevation of AOC‑41 is approximately 1,250 feet above mean sea level (msl). An unnamed intermittent tributary to Salado Creek runs to the north and west of the site, but it only contains water during or after a rainfall event.
Throughout CSSA, the uppermost geologic stratum is the Upper Glen Rose, shown on Figure AOC41‑6. 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 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 hydrologic 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. Transmissivity values are not available for the Upper Glen Rose. Regionally, based on potentiometric data, groundwater flow is understood to be enhanced along the bedding contacts between marl and limestone; however, the hydraulic conductivity between beds is expected to be poor. Principal development of solution channels is limited to evaporite layers in the Upper Glen Rose Limestone. Principal recharge into the Middle Trinity Aquifer is via precipitation infiltration at outcrops. Groundwater discharge occurs predominantly via natural springs, seeps, and pumping.
The nearest monitoring well to AOC-41 is the CS‑16 cluster, approximately 220 feet southwest of AOC‑41. The construction of Well CS‑16 was modified in July 2002 and renamed CS‑16‑LGR; CS‑MW16‑CC was installed at a later date. These wells are sampled on a quarterly basis. The latest available groundwater analytical testing data (December 2004) indicate that groundwater from Well CS‑16‑LGR contains tetrachloroethene (PCE), trichloroethene (TCE), and cis‑1,2‑dichloroethene (cis‑1,2‑DCE) at concentrations equal to or exceeding maximum contaminant levels (MCLs). Between November 1998 and December 2004, water levels in Well CS‑16 ranged from 61.50 feet below top of casing (BTOC) to 316.88 feet BTOC.
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 site (41BX1172) is a prehistoric open campsite exhibiting a small burned rock midden that is located approximately 850 feet northwest of the area. The nearest historical structure is an above ground storage magazine (I-291), which is located approximately 2,050 feet southeast of AOC‑41.
A land use survey studying local current and possible future uses of groundwater and surface water, a water well survey, and a sensitive environmental area survey were completed at CSSA in December 1999. The results of these surveys, along with results from a more in‑depth survey 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). AOC‑41 is mostly used for cattle grazing as part of the North Pasture. Land uses on the facility are not anticipated to change, so the land use will most likely stay the same.
CSSA contains mostly forested, undeveloped land, various portions of which are being managed to promote different species. Some areas are managed to maintain habitat for two endangered bird species, the Golden‑cheeked Warbler and the Black‑capped Vireo. However, the AOC‑41 area is not located within an area identified as potential habitat for these species (Section 3 of the Technical Approach Document for Risk Evaluation, Volume 1‑6). The native White‑tailed deer and introduced Axis deer populations are also managed, and controlled hunting is allowed. Management practices which benefit the deer and other wildlife species include maintenance of feed plots, feeding and watering stations, and clearing of Ashe juniper to improve habitat. Other areas are managed as pastures for grazing by cattle.
1.4 - Previous Investigation Results
Surface geophysical surveys were performed in 1995 at SWMUs and AOCs at CSSA as part of a contaminant source characterization study. As the source of groundwater contamination was not known, part of the investigation was characterization of potential source sites. Geophysical surveys were performed within a 2,000‑foot radius of Well CS‑16 to locate areas potentially related to past waste disposal activities. One of the areas within the 2,000‑foot radius was AOC‑41, which was known at that time as the “North Pasture” area.
The 1995 geophysical survey identified three anomalies that were initially considered to be within the AOC‑41 boundary. In subsequent investigations, the three anomalies, labeled A, B, and C, were determined to be north of the reduced acreage AOC‑41 boundary, and within the revised SWMU B‑8 boundary (see Figure AOC41‑7). Anomaly A was subtle and was not related to known surface/subsurface features. Anomaly B was the largest and thought to be related to underground metal piping or fragments. Anomaly C was associated with a burn pit at the site. In addition, an abandoned underground 4‑inch diameter metal water pipe was identified trending northeast‑southwest in the western portion of the former AOC‑41 boundary. Exposed portions of the pipe were observed during the 1995 investigation; however, intrusive investigation of the anomalies was not conducted at the time of the survey. The pipe has since been excavated and removed.
Soil gas surveys were performed at CSSA in 1995 and 1999 in the continued effort to identify possible source areas for the chlorinated hydrocarbon contamination in the groundwater at Well CS‑16 (Parsons, 1999). A detailed description of the methodology is included in the Environmental Encyclopedia (Volume 3‑1). Between the two surveys, 51 soil gas samples were collected within the former AOC‑41 site boundary (11 samples in 1995 and 40 samples in 1999). Samples were analyzed for PCE, TCE, cis‑1,2‑ DCE, and BTEX compounds (benzene, toluene, ethylbenzene, m/p/o‑xylenes). Sample analyses were performed on site at a field laboratory established within the CSSA Environmental Office. See Figure AOC41‑7 for sample locations.
During the June/July 1995 soil gas survey, PCE was detected in 10 of the 11 samples at concentrations of 0.01 to 0.07 micrograms per liter (mg/L). However, these results were flagged “B” based on the detection of PCE in blanks, indicating the results were inconclusive. During the 1999 soil gas survey, PCE was detected at the southwestern corner of the site at sampling locations 1 and 11. Both samples had reported PCE concentrations of 0.02 mg/L. See Figure AOC41‑2 in the AOC‑41 Soil Gas Survey Results Report (Parsons, 1999) for a concentration contour map of the 1999 PCE soil gas findings in the vicinity of AOC‑41.
The results of the investigations near Well CS‑16 suggest that AOC‑41 is not a source for VOC contamination at the well. Soil gas survey data in the area show that the main portion of the PCE plume associated with Well CS‑16 terminates just north of the northern boundary of the Inner Cantonment. VOC detections in the southwest corner of the site were likely the result of lateral migration of soil gas from known offsite source areas and not the result of on-site waste disposal. AOC‑41 is north of the Inner Cantonment boundary. The soil gas survey data for AOC‑41 is available in Table AOC41‑1 of the AOC‑41 Soil Gas Survey Results Report.
1.5 - Recent Investigation Results
In May/June 2003, an additional geophysical survey was conducted in the areas of SWMU B‑8 and AOC‑41. The initial focus of the survey was SWMU B‑8, but the survey was expanded to encompass all of the open pasture area that included SWMU B‑8 and AOC‑41. Sixteen total anomalies were investigated in the area, five of which were located within AOC‑41. Intrusive investigation results showed that these anomalies consisted of wire, nails, 30‑caliber casings, a 50‑caliber casing, and a piece of metal scrap. These anomalies were small and encountered at depths no greater than 18 inches. The results of the survey are presented in the Environmental Encyclopedia (Volume 3‑1, SWMU B‑8 RCRA Facility Investigation Addendum Report). The locations of the anomalies are shown in Appendix B.
Also in May 2003 as part of further investigation of SWMU B‑8, additional surface soil samples were collected in the area to delineate the lateral extent of metals contamination occurring at the SWMU. The findings showed that metals concentrations in excess of RRS1 closure standards are present at SWMU B‑8 and extend into the former AOC‑41 boundary. Figure B8-6 in the SWMU B-8 RCRA Facility Investigation Addendum Report shows sampling locations concentrations. Based on these findings, the site boundaries were revised to expand the area of SWMU B‑8 and reduce the area of AOC‑41 so that the metals contamination is encompassed within SWMU B‑8. Because of the SWMU B‑8 boundary adjustment, each of the geophysical anomalies revealed during the May 1995 geophysical survey at AOC‑41 now lie within SWMU B‑8.