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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. This report documents the closure activities at Area of Concern (AOC) 66. This closure report includes by reference the information present in the AOC 66 Soil Gas Survey Results Report (Parsons, 1999).
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:
Work Plan Overview
Site-Specific Work Plan
Field Sampling Plan
(Volume 1-4, TO 0019 Addendum); and
Health and Safety Plan
For this closure report, Section 1 provides the site-specific background and describes the selected closure standard. Section 2 describes the closure actions and the closure evaluation, summarizes the findings, 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 66) 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 (30 TAC �335.554), if site concentrations are at or below background, and all waste and waste residue have 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 other contaminants of concern. Based on the RFI soil gas survey results at AOC 66, 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.
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.
1.2.2.1 Site Description
The site covers approximately 15 acres located within the floodplain of an unnamed tributary of Salado Creek, and it is used for cattle-grazing only. As shown in Figure AOC66-3, 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. (Figure AOC66-1 and Figure AOC66-2 are included in the AOC 66 Soil Gas Survey Results Report.)
1.2.2.2 Potential Sources of Contamination
No formal waste management activities are known to have occurred at AOC 66. However, due to this area�s proximity to Well CS-16 and a soil gas plume identified just to the south in 1995, the AOC 66 area was identified as an area of concern. A soil gas survey was conducted in 1999 to determine if a source of chlorinated volatile organic compounds (VOCs) exists in the AOC 66 area. Figure AOC66-4 shows aerial photographs dated between 1957 and 2003. No waste disposal areas or other disturbed areas are evident in these photographs.
1.2.2.3 Site Location
AOC 66 is located along the southern edge of the North Pasture Area, directly north of AOC 38 (Volume 1-3, Site Map). As shown in Figure AOC66-3, there are numerous other AOCs and solid waste management units (SWMUs) located to the south, east, and north of AOC 66, including AOC 37, AOC 41, SWMU B-8, and SWMU B-2. RRS1 closure of several of the nearby sites has been approved by TCEQ. Closed sites in the area of AOC 66 include AOC 35, AOC 36, AOC 39, AOC 40, AOC 43, SWMU B-1, SWMU B-5, SWMU B-7, and SWMU B-19.
The site is situated about 1,750 feet from the western boundary CSSA and directly north of the northeast corner of the Inner Cantonment Area.
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 66 is provided in the paragraphs below.
1.3.1 Site Soils and Topography
There are several soil types occurring at AOC 66 (Figure AOC66-5). The Trinity and Frio soil type covers the majority of AOC 66, down the center of the area. Trinity and Frio soils occur in creek beds that are frequently flooded. The topographic elevation of the site area is approximately 1,240 feet above mean sea level (MSL). Drainage within AOC 66 is to the center and then south in the area, toward an unnamed tributary of Salado Creek, which runs down the middle of the area.
The Brackett-Tarrant Association also occurs at AOC 66, on the western boundary of the area. The soils are formed on hills with 8 to 30 percent slopes and consist primarily of soils that developed over limestone. At CSSA, this soil type is found north of the Inner Cantonment, in the North Pasture. The slopes of ridges are Tarrant soils which are clayey, calcareous, and very dark grayish-brown. The Brackett soils are light grayish-brown and calcareous. Tarrant soils make up 65 percent of the association and Brackett make up 20 percent. The soils are not suited to crops, and stones and topography make the use of machinery difficult (USDA, 1991).
Also found at AOC 66 are the Krum Complex soils. 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. In AOC 66, the Krum Complex soils line the east and west boundaries of the Trinity and Frio soil type.
The Lewisville silty clay is a minor soil found at the CSSA complex. In AOC 66, it lies to the east of the Krum Complex. It typically occu�pies long, narrow, sloping areas separating nearly level terraces from upland soils. Surface soils are dark grayish-brown and about 20 inches thick.
Finally, the Tarrant association can be found at AOC 66 surrounding the Lewisville type. At CSSA, the Tarrant soils occur along the outer edges of the Salado Creek floodplain. The soils are thin and form over hard, fractured limestone. The surface layer is usually about 10 inches thick and is a dark grayish-brown, calcare�ous, clay loam with scattered gravel and cobblestones within, and on the surface layer.
Throughout the CSSA, the uppermost geologic stratum is the Upper Glen Rose Formation, as shown in Figure AOC66-6. 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 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, 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 in different beds. Principle 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 cluster is CS-MW16 cluster, located approximately 95 feet south of AOC 66. This well is sampled on a quarterly basis. The latest available groundwater analytical testing data (March 2004) indicates that groundwater from Well CS‑16-LGR contains tetrachloroethene (PCE), trichloroethene (TCE), and cis‑1,2‑dichloroethene (DCE) at concentrations equal to or exceeding maximum contaminant levels (MCLs). Prior to June 2002, former water supply Well CS-16 was an open borehole completed through the Glen Rose, Bexar Shale, and Cow Creek Formations. Water levels in Well CS-16 ranged from 78.58 feet below top of casing (BTOC) (November 1998) to 316.88 feet BTOC (April 1995). The construction of Well CS-16 was modified in July 2002, resulting in Well CS-16-LGR, and one additional well, CS‑MW16-CC, was installed. Water levels in Well CS-16-CC have ranged from 218.25 ft BTOC (September 2003) and 241.86 ft BTOC (March 2004).
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 is a prehistoric open campsite exhibiting a small burned rock midden that is located approximately 1,800 feet northwest of the area. The nearest historical structure is Building 43, which is located approximately 1,100 feet south of AOC 66.
A land use survey describing local current and possible future uses of groundwater and surface water, a water well survey, and sensitive environmental areas at CSSA was completed on 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 uses on the facility are not anticipated to change in the foreseeable future. AOC 66 is mostly used for cattle grazing as part of the North Pasture.
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 66 area is not located within an area identified as potential habitat for these species (Section 4, Environmental Assessment, Volume 1-1). 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 radium of Well 16 to locate areas potentially related to past waste disposal activities. One of these areas within the 2,000-foot radius was AOC 66, which was known at that time as the �North Pasture� area.
The site was identified as an area of concern in 1995 due only to its proximity to known contamination at Well 16, not due to any records of waste management in the area, indications of ground disturbance in historic aerial photographs, nor visible evidence of waste management at the site.
No EM anomalies were detected on either the apparent conductivity or the in-phase data in the North Pasture (AOC 66) area. The variations in conductivity data appear to reflect changes in thickness of soil cover overlying limestone bedrock.
Soil gas surveys were performed at CSSA in 1999 in the continued effort to identify possible source areas for the chlorinated hydrocarbon contamination present in groundwater at well CS-16 (Parsons, 1999). A detailed description of the methodology is included in the Environmental Encyclopedia (Volume 3-1). One hundred samples were collected at AOC 66 and were analyzed for BTEX compounds (benzene, toluene, ethylbenzene, m/p/o-xylenes), tetrachloroethene (PCE), trichloroethene (TCE), and cis-1,2-dichloroethene (DCE). The soil gas samples were analyzed on-site at a field laboratory established within the CSSA Environmental Office. See Figure AOC66-1 included in the Environmental Encyclopedia for sample locations.
TCE was detected in only one sample, AOC66-81, at a concentration of 0.04 �g/L. The TCE detection was co-located in the same sample as the highest PCE detection for the survey.
PCE was detected at 19 locations and ranged in concentration from 0.01 to 0.16 �g/L. The highest concentration occurred in the duplicate sample analysis from AOC66-81. PCE was detected at a concentration of 0.10 �g/L or above at three locations. The concentrations of PCE detected in the soil gas were generally spotty, with more than a third of the reported detections occurring along the boundary with AOC 35. At the outer cantonment fence line, the PCE concentrations in soil gas appear to be consistent with previous results that indicated low concentrations of PCE extending from AOC 35 into the north pasture. Overall, the concentration and frequency of PCE detections in the North Pasture were very low and not as pervasive as in the Inner Cantonment area, and suggests that the suspected groundwater contamination source does not extend into the North Pasture. The isolated occurrence of PCE at locations AOC66-61 and AOC66-81 could be related to gas migration focused along fractures or faults to these locations.
The recent and previous data collected at this site suggest that this site does not contain a source of VOC contamination. The soil gas survey data for AOC 66 is presented in Table AOC66-1 and illustrated in Figure AOC66-2 of the AOC 66 Soil Gas Survey Results Report.
The results of this soil gas survey combined with results from previous soil gas surveys performed on the land adjacent to AOC 66 show that the PCE plume terminates as it approaches the southern boundary of the North Pasture. The PCE results from all soil gas surveys conducted in the area were consolidated and the concentration gradients are illustrated in Figure AOC66-7.