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AOC 56 RFI 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 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) 56 was completed in October 2002 to document the environmental condition of the site and site closure requirements, and to recommend further investigation. This closure report includes by reference the information presented in the AOC‑56 RFI Report.
The AOC‑56 RFI Report recommended excavation and disposal of waste and waste residue at the site. The RFI report estimated 7,400 cubic yards of soil and waste material would require removal from the site, and confirmation sampling for arsenic, barium, cadmium, chromium, copper, lead, mercury, nickel, zinc, volatile organic compounds (VOCs), and semivolatile organic compounds (SVOCs) was to be conducted to confirm that the site achieved closure requirements. This report documents the closure activities at AOC‑56.
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
Closure activities at AOC‑56 were conducted January through April, 2004. As recommended in the RFI report, excavation and disposal activities were conducted. More than 3,800 cubic yards of waste and waste residue were excavated and removed from the site. Confirmation sampling was also conducted to verify that contaminant concentrations met closure requirements.
For this closure report, Section 1 provides the site-specific background and closure standard. Section 2 describes the closure actions and the 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 AOC‑56) 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 VOCs, explosives, and other contaminants of concern. Based on the RFI sampling soil gas survey results at AOC‑56, 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 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.
AOC‑56 is a site that was used as a solid waste landfill. Prior to closure activities visual observation of the site indicated an area of excavation on the western side of the site. Except for cattle grazing, no other activities are currently practiced at AOC‑56.
Background information regarding the location, size, and known historical use of the site is also included in the Environmental Encyclopedia (Volume 1-3, AOC‑56). Volume 1-3 also includes a Chronology of Actions and a Site-Specific Work Plan Addendum for AOC‑56.
1.2.2.2 Potential Sources of Contamination
Information obtained concerning AOC‑56 indicated that the site had been used as a construction debris landfill. Although the site was generally known as being used to dispose of metal debris and construction materials, it is possible that solvents or fuels, which were commonly used at CSSA, may also have been discarded in the area.
Based on prior usage at the site as a landfill, chemicals of potential concern included VOCs, SVOCs, and metals. Metals (arsenic, barium, cadmium, chromium, copper, lead, mercury, nickel, and zinc) are included due to the potential metallic nature of the waste. VOCs analysis is included in the analytical program to detect typical contaminants associated with a disposal area. SVOCs are included at this site since waste burning may have occurred. In addition, during closure excavation activities, ordnance-related scrap was encountered. Therefore, explosives were additional chemicals of concern.
AOC‑56 is located in the southeast portion of the Inner Cantonment at the intersection of Bernard Road and East Outer Road and it occupies an area of approximately 0.5 acres (Figure AOC56‑11). The site is generally oblong in shape with a length of approximately 400 feet in the northwest-southeast direction and a width of approximately 150 feet in the northeast-southwest direction. The AOC‑is approximately 100 feet east of the outer cantonment boundary. Road F-4 is the north boundary of AOC‑56, and East Outer Road marks the boundary on the east side (Figure AOC56‑11). There is no development upon AOC‑56 except for overhead utilities and roadside drainage control.
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‑56 RFI Report (Parsons, 2002). A brief description of the setting at AOC‑56 is provided in the paragraphs below.
1.3.1 Site Soils and Topography
The only soil type present within the site area is the Tarrant Association, a rolling soil complex (see Figure AOC56‑2 in the AOC‑56 RFI Report). Detailed descriptions of the CSSA soil types are provided in the CSSA Environmental Encyclopedia (Volume 1‑1, Background Information Report, Soils and Geology). This soil type occurs over only 1.3 percent (52.1 acres) of CSSA lands. The slopes tend to have a gradient of 5 to 15 percent. The soils are dark colored, very shallow, clayey, weakly calcareous, and typically more stony than Tarrant Association, gently undulating.
The elevation of the site is approximately 1,185 feet above sea level, sloping gently (less than 1 percent) to the east-northeast. The site is vegetated with native grasses and oak trees.
The Upper Glen Rose is the uppermost geologic stratum in the area of AOC‑56, as shown in Figure AOC56‑12. The Upper Glen Rose consists of beds of blue shale, limestone, and marly limestone, with occasional gypsum beds. Generally, it outcrops in stream valleys and at the ground surface where soils are poorly developed or eroded. The Upper Glen Rose is estimated to be up to 128 feet thick at CSSA. It is underlain by the Lower Glen Rose, which is estimated to be 320 feet thick on average beneath CSSA. The Lower Glen Rose is a massive, fossiliferous, vuggy limestone that grades upwards into thin beds of limestone, marl, and shale. The Lower Glen Rose is underlain by the Bexar Shale facies of the Hensell Sand, which is estimated to be 60 feet thick under the CSSA area. The Bexar Shale consists of silty dolomite, marl, calcareous shale, and shaley limestone. 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 (Soils and Geology, Background Information Report, Volume 1‑1).
In general, the uppermost hydrogeologic layer at CSSA 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 Formation. 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 of differing static water levels in adjacent wells completed in different beds. Principle development of solution channels is limited to evaporite layers in the Upper Glen Rose Limestone. In general, groundwater at CSSA flows in a north to south direction. However, the local flow gradients may vary depending on rainfall, recharge, and possibly well pumping.
The Middle Trinity aquifer is unconfined and functions as the primary source of groundwater at CSSA. It consists of the Lower Glen Rose Limestone, the Bexar Shale, and the Cow Creek Limestone. The Lower Glen Rose Limestone outcrops north of CSSA along Cibolo Creek and within the central and southwest portions of CSSA. As such, principle recharge into the Middle Trinity aquifer is via precipitation infiltration at outcrops. At CSSA, the Bexar Shale is interpreted as a confining layer, except where it is fractured and faulted, therefore allowing vertical flow from the up-dip Cow Creek Limestone into the overlying, but down-dip Lower Glen Rose. Fractures and faults within the Bexar Shale may allow hydraulic communication between the Lower Glen Rose and Cow Creek Limestones. Groundwater flow within the Middle Trinity aquifer is toward the south and southeast and the average transmissivity coefficient is 1,700 gpd/ft (Ashworth, 1983). In general, groundwater at CSSA flows in a north to south direction, with some seasonal fluctuations.
No site-specific information regarding groundwater is available. However, the nearest well (Well CS‑1), which is a production well that periodically contributes to the water distribution system at CSSA, is located just over ¼-mile southeast of AOC‑56 on Camp Bullis. Between January 1998 and March 2004, water levels in Well CS‑1 ranged from 101.3 feet below top of casing (BTOC) (November 1998) and 261.9 feet BTOC (March 2000).
The nearest surface water body is an unnamed tributary to Salado Creek which is approximately 150 feet east of AOC‑56 (Figure AOC56‑11). Flow in Salado Creek and its tributaries is intermittent. The creek exits the CSSA boundary approximately 1/8‑mile southeast of AOC‑56.
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 site of potential cultural significance is located approximately 1,240 feet northeast of AOC‑56. The cultural resource consists of World War I foxhole-type trenches. A similar cultural resource is located approximately 1,650 feet north of AOC‑56. Approximately ¼ mile to the southeast, on Camp Bullis property, reside a hand dug water well and a stone house built in 1847.
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 during 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.
Land within ¼-mile of AOC‑56 is classified as “Commercial and Services” and “Evergreen Forest Land” in Figure 1.1 of the Technical Document for Risk Assessment. CSSA production Well CS‑1 is located approximately 1,400 feet southeast of AOC‑56.
Within CSSA, there is a full-time work force of approximately 100 persons working in shops and office buildings. Personnel also work outdoors throughout the facility to perform maintenance activities such as road and fence maintenance, brush clearing, and security patrols.
A small herd of cattle is maintained on CSSA by the U.S. Department of Agriculture Agricultural Research Center (USDA-ARC). The cattle roam freely throughout selected areas of the North Pastures. CSSA also manages wild game species for the purpose of hunting. White-Tailed deer, Axis deer, and wild turkey all roam freely throughout CSSA. A map of deer hunting stands which overlook mechanical feeders and planted food plots is located in the Figure 5.2 of the Technical Approach Document for Risk Evaluation (Volume 1‑6). Four water tanks are maintained at CSSA for the purpose of sport fishing. Two of the tanks are located in the northwestern and northeastern portions of the North Pasture while the other two tanks are located near the western boundary of the Inner Cantonment.
The nearest potential habitats for local endangered species (Figure 11, Volume 1‑1 Background Information Report) are 580 feet southwest (Golden‑Cheeked Warbler) and 2,200 feet north (Black‑Capped Vireo) of AOC‑56.
An RFI was conducted at AOC‑56 between 1999 and 2000. As outlined in the Environmental Encyclopedia Site‑Specific Work Plan (Volume 1‑3, AOC‑56), the objectives of the RFI were to conduct a geophysical survey and to collect surface soil samples. After identifying any geophysical anomalies, three grab surface soil samples were collected at a depth of six inches below surface grade based upon the locations of the anomalies. Each sample was analyzed for VOCs, SVOCs, and metals.
Electromagnetic (EM) and ground penetrating radar (GPR) geophysical surveys were conducted at AOC‑56 in August 1999. Prior to collecting EM or GPR data, a grid system was established at the site which encompassed the areas of suspected ground disturbance.
GPR surveys were conducted with a GSSI SIR‑2 instrument to further investigate the information obtained by the EM survey. Four GPR profiles were created in the northeast-southwest direction and eight were created in the northwest-southeast direction. A 300 mega-hertz (MHz) antenna with a range setting of 90 ns was used for all profiles.
Both the in-phase component and the quadrature phase component of the EM survey revealed anomalies in the northwestern and central portions of the AOC. Two anomalies were also noted near the southeastern portion of the site. The in-phase portion revealed several anomalous areas which may be related to waste management activities. Figure AOC56-13 in this report and Figure AOC56‑5 in the AOC‑56 RFI Report show these anomalies which are located in areas mentioned above and labeled A through D. Anomalies A and B are thought to be related to waste management activities because of the magnitude and aerial extent of the anomalies. In-phase readings ranged from 0 to 18 ppt and quadrature phase readings ranged from –80 to 20 mS/m in these areas. Many smaller, less conspicuous anomalies exist between anomalies A and B on the in-phase contour map (Figure AOC56‑5 in the AOC‑56 RFI Report). These anomalies are also thought to be related to waste management activities because they coincide with areas of disturbed subsurface as revealed in the quadrature phase portion of the survey (Figure AOC56‑6 in the AOC‑56 RFI Report).
Anomaly C, which is located on both Figure AOC56‑5 and Figure AOC56‑6 is possibly related to an old rail line that may have crossed the site at this location and not to waste management activities. Evidence of the rail line includes the linear mound that trends in a nearly north-south direction across the southeastern portion of the site, an abundance of non-indigenous river gravel that may have been used as ballast, and several rail spikes found during the initial visual reconnaissance survey. All rail spikes observed while preparing the geophysical survey grid were removed before conducting the actual survey. In-phase readings near anomaly C ranged from 0 to -10 ppt while quadrature phase readings ranged from 10 to 70 mS/m.
Anomaly D, which is located in the northern portion of the AOC‑and visible in both the in-phase and the quadrature phase portions of the survey, could be related to road construction activities and not waste management activities. The location of the anomaly places it nearly on the road and away from the excavated interior portion of the AOC‑where the other geophysical anomalies were detected. In-phase readings near anomaly D ranged from 0 to -16 ppt while quadrature phase readings ranged from –70 to 30 mS/m.
GPR surveys were conducted to further investigate the information obtained by the EM survey. The four profiles included in the AOC‑56 RFI Report (Figure AOC56‑7, Figure AOC56‑8, Figure AOC56‑9, and Figure AOC56‑10) represent the typical 300 MHz antenna survey profiles that were produced at AOC‑56.
GPR profile 7, which trends southeast-northwest, indicated multiple reflectors (approximately 1‑3 feet bgs) in the western portion of the profile (Figure AOC56‑7). These multiple reflectors coincide with the location of EM anomaly A and indicate that past waste management activities (possible buried trash) may have been carried out at AOC‑56. GPR profile 8, which trends northwest-southeast, shows where the bedrock has been excavated in the western portion of the profile (Figure AOC56‑8). Profile 8 also shows disturbed subsurface conditions in the vicinity of EM anomaly A and clearly shows a subsurface reflector 1 to 3 feet in depth in the vicinity of EM anomaly C. GPR profile 9, which trends from the southeast to the northwest, shows the contrast between the relatively undisturbed subsurface conditions in the southeastern portion of the site and the disturbed area in the northwestern portion (Figure AOC56‑9). GPR profile 12, which trends northeast-southwest, indicates multiple subsurface reflectors at an approximate depth of 1 to 3 feet bgs. The disturbed subsurface area corresponds with the area around anomaly A (Figure AOC56‑10).
Three surface soil samples, AOC56‑SS01 through AOC56‑SS03, were collected in January 2000 as part of the AOC‑56 RFI investigation. Sample locations were biased towards any anomalies discovered in the geophysical surveys, and are shown in Figure AOC56‑13.
Samples were analyzed using EPA methods SW8260B (VOCs), SW8270 (SVOCs), SW6010B (barium, chromium, copper, nickel, and zinc) SW7060A (arsenic), SW7131A (cadmium), SW7421A (lead), and SW7471A (mercury).
All samples reported VOC and SVOC concentrations below RLs, therefore RRS1 criteria for VOCs and SVOCs were met (Table AOC56‑1 in the AOC‑56 RFI Report). The following compounds were reported in the soil samples at concentrations below the RLs: chloroform, toluene, benzo(a)anthracene, benzo(a)pyrene, benzo(b)fluoranthene, benzo(g,h,i) perylene, bis(2-ethylhexyl)phthalate, chrysene, fluoranthene, indeno (1,2,3‑cd) pyrene, phenanthrene, and pyrene.
RRS1 closure criteria for metals require the reported values for metals be compared to the soil background values. Zinc and lead concentrations were detected at concentrations slightly above the background levels in samples AOC56‑SS01 (0-0.5 ft). Lead was detected at a concentration of 88.32 milligrams per kilogram (mg/kg) and zinc at 97.75 mg/kg (Table AOC56‑1). Background levels for lead and zinc are 84.5 mg/kg and 73.2 mg/kg, respectively. All other metals concentrations were below CSSA background levels.