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Final AOC 65 RCRA Facility Investigation 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 Safe Drinking Water Act (SDWA), as amended by the Resource Conservation and Recovery Act (RCRA), and further amended by the Hazardous and Solid Waste Act (HSWA) of 1984. In accordance with the RCRA Facility Investigation (RFI) requirements of the Consent Order, this RFI report has been prepared to document the environmental condition and site closure requirements of Area of Concern-65 (AOC-65) and to recommend further investigation, if necessary, or to provide documentation necessary for site closure. The main objectives of the AOC‑65 investigation are to determine if the site meets Texas Natural Resource Conservation Commission (TNRCC) requirements for closure, as described in Section 1.4, and to meet requirements of the Consent Order.
This specific RFI was performed by Parsons under the United States (U.S.) Air Force Air Mobility Command (AMC) Contract F41689-96-D-0710, Delivery Orders 5068 and 5084. Air Force Center for Environmental Excellence (AFCEE) provided technical oversight for the delivery order. Based on the AOC-65 pre-defined Statement of Work (SOW), work plans were established to govern the fieldwork. These include:
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(Volume 1-1, DO5068 and DO5084 Addendums); |
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(Volume 1-3, AOC 65); |
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(Volume 1-4, DO5068 and DO5084 Addendums); and |
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(Volume 1-5, DO5068 and DO5084 Addendums). |
For this report, Section 1 provides the site-specific background and target closure standard. Section 2 describes field actions and the closure evaluation. Section 3 summarizes the findings, evaluates attainment of data quality objectives, provides recommendations, and certifies the site closure, if applicable. References cited in this report can be found in the Bibliography (Volume 1-1 of the Environmental Encyclopedia).
1.1 - 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.
1.1.2 AOC 65
AOC-65 consists of Building 90 and potential source areas associated with Building 90. AOC-65 includes two sub-slab, concrete-lined vaults, one on the west side and one in the middle of the interior of Building 90. A metal vat was installed in the western vault prior to 1966 and removed in 1995. This vat was used for cleaning ordnance materials inside Building 90 with the use of chlorinated liquid solvents, such as tetrachloroethene (PCE) and trichloroethene (TCE). In 1995, after removal of the former solvent vat, a metal plate was welded over the concrete vault, and PCE and TCE solvents were replaced with a citrus-based cleaner system, which is located on top of the metal plate. Uses of the second vault, located within the middle of the interior of Building 90, are not known. It was backfilled and capped with concrete at an unknown date. Building 90 continues to be used for weapons cleaning and maintenance. AOC-65 also includes the area extending outside Building 90 along the associated building drain lines and ditches. Initially, AOC-65 was limited to the confines of the former solvent vault housed within Building 90; however, recent investigations (Draft Soil Gas Survey Technical Report, Parsons ES, August 2001) suggested that the AOC-65 boundaries should be expanded to include affected areas.
Background information regarding the location, size, and known historical use of the site is also included in the Environmental Encyclopedia (Volume 1-3, AOC-65). This volume included a Chronology of Actions and a Site-Specific Work Plan Addendum for AOC-65.1.1.2.2 Potential Sources of Contamination
Building 90 is used to clean and maintain weapons used at CSSA. Prior to 1995, PCE and TCE were used in these processes within in the former metal vat in Building 90. The vat was removed in 1995, and the sub-slab vault was welded shut and is currently inactive. No cracks or migration pathways are visible, but solvent staining is evident in the low areas at the bottom of the vat. Through a records search and questioning of long-term staff involved with AOC-65, CSSA has made a good faith effort to determine the source of contamination. CSSA, as the generator of potential investigation and remedial wastes, cannot determine that the contamination resulted from a release of solvent from the former vat because documentation regarding a source of contamination, contaminant, or waste is unavailable or inconclusive. A potential PCE/TCE source area associated with AOC-65 is a drain line from Building 90. The drain line is currently tied in to the building storm gutter system. Floor cleanings and wash-down wastes, such as from steam cleaning, are potentially the cause of contamination observed near the drain line outfall located to the west of Building 90. The potential chemicals of concern (COCs) are: volatile organic compounds (VOCs), semi-volatile organic compounds (SVOCs), total petroleum hydrocarbons (TPHs), polychlorinated biphenyl (PCB), and metals.
AOC-65 consists of Building 90 and potential source areas associated with Building 90, which is located along the southwestern side of CSSA (Figure AOC-65-1). Building 90 is located approximately 130 feet east of the CSSA western perimeter, approximately 160 feet south of Tompkin Road, which is on-post, and approximately 120 feet from Ralph Fair Road, the nearest off-post road. Building 90 is approximately 580 feet long (north-south) by 80 feet wide (east-west) (Figure AOC-65-1).
Nearby AOCs include AOC-68 and -67, which are immediately adjacent to Building 90, and AOCs-57 and -45, which are approximately 450 feet east and northeast of AOC‑67, respectively. SWMU B-31 is approximately 600 feet east-southeast of Building 90.
1.2 - Site Environmental Setting
1.2.1 Site Soils and Topography
The Crawford and Bexar stony soils dominate in the area of AOC-65 (Figure AOC-65-2), although there is significant evidence that soils have been reworked for construction of Building 90 and associated asphalt-covered parking. Detailed descriptions of all CSSA soil types are given in the CSSA Environmental Encyclopedia (Volume 1-1, Background Information Report, Soils and Geology). The Crawford and Bexar stony soils occur in broad, nearly level to gently undulating areas with slopes of 0 to 5 percent. The soils are thin, stony, very dark gray to dark reddish brown, noncalcareous clay, and are typically less than 1 foot thick.
AOC-65 is at an elevation of approximately 1,220 feet above sea level, on land that slopes gently (less than 2 percent grade) to the southeast. Based on this, run-off would be expected to generally flow in the southeast direction. However, because of man-made drainage ditches on the west side of AOC-65, drainage from the area within Building 90 where the vat was formerly located would be expected to follow the drainage ditches. These drainage ditches lead to the formerly used railroad track spur 100 feet east of and across the road from Building 90 (Figure AOC-65-1). Ultimately, overflow from this spur would flow into “W” Tank located 1,250 feet from AOC-65; however, transport of water directly from AOC-65 into “W” Tank has not been witnessed to date.
AOC-65 is sited over the Lower Glen Rose limestone (Figure AOC-65-3). An excavated area containing bedrock exposure at the northwest corner of Building 90 confirms that the subsurface bedrock is the Lower Glen Rose limestone. The Lower Glen Rose is estimated to be 300 feet thick beneath CSSA. The Lower Glen Rose is a massive, fossiliferous, vuggy limestone that grades upward 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 from 60 to 150 feet thick under the CSSA area. The Bexar Shale consist of silty dolomite, marl, calcareous shale, and shaley limestone. The geologic strata dip approximately 10 to 12 degrees to the south-southeast at CSSA.
There are two major fault (shatter) zones at CSSA: the North Fault Zone and the South Fault Zone. The south fault zone lies approximately 2,100 feet south of the site. (Figure AOC-65-3). Another fault, projected from U.S. Geologic Survey (USGS) data collected at Camp Bullis and CSSA, is shown as running through Building 90 in Figure AOC-65-3. A fault was identified by Parsons personnel in the bedrock outcropping on the west side of Building 90. Investigations into faulting in the area of Building 90 are ongoing (AOC-65 Treatability Test Plan, Draft). These investigations, using resistivity surveys, will help define the location of the fault projected from the USGS data, as well as other potential faults in the area. Additional information on structural geology at CSSA can be found in the Environmental Encyclopedia (Background Information Report, Volume 1-1).
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. Principal 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, local flow gradient 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, principal 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, which may allow vertical flow from the up-dip Cow Creek Limestone into the overlying, but down-dip Lower Glen Rose. Because the Bexar Shale is a confining layer, fractures and faults within the Bexar Shale would provide potential 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 (Background Information Report files, Groundwater Resources, Volume 1-1, Environmental Encyclopedia)
Fracture systems associated with the fault zones are thought to affect groundwater flow and to be the controlling structural feature for migration of contaminants in the vadose zone at CSSA (Background Information Report, Volume 1-1 Environmental Encyclopedia).
There
are no streams in the vicinity of AOC-65 (Figure AOC-65-1). Natural
drainage from the land surrounding AOC-65 would be expected to be primarily by
overland flow, with rapid infiltration into the underlying formation. However, man-made drainage ditches influence the drainage pattern in the area of
AOC-65. Drainage away from Building 90 in the area that formerly
contained the metal vat, as well drainage from the building gutters, is
channeled to a north-south drainage ditch on the west side of AOC-65. Effluent from this ditch is discharged into ditches on the north side of
Building 90 which empties into a 0.7 acre railroad track spur approximately
100 feet east of Building 90. Overflow from the spur is expected
to travel south toward “W” tank, located 1,250 feet southeast of AOC-65. However, run-off has never been observed to drain directly from Building 90 into
“W” tank.
Other features that may be influencing aquifer recharge in the Building 90/AOC-65 area include utility trenches. One such feature may be an abandoned electrical line trench located approximately 100 feet west of Building 90/AOC-65. Preliminary resistivity survey data from this area suggest the trench retains considerable amounts of moisture after rain events.
No site-specific information regarding groundwater was available prior to this study. However, wells CS-MW-8-LGR, CS-MW-8-CC, CS-MW-10-LGR, CS-MW-10-CC, and CS-MW-6-LGR, CS-MW-6-BS, and CS-MW-6-CC will provide groundwater information in the area around AOC-65 (Figure AOC-65-1). The MW-6 well cluster is located 450 feet north of AOC-65; the MW-7 cluster is 850 feet southeast of AOC-65; and the MW-8 cluster is 500 feet south of AOC-65. VOC concentrations were within RLs and MCLs for samples collected in June and September 2002. Some samples collected from the Lower Glen Rose wells in December 2002 showed exceedences of the RLs and the MCLs of PCE and TCE. In these wells, PCE ranged from non-detect (ND) to 2.5 µg/L and TCE from ND to 0.51 µg/L (Quarterly Groundwater Monitoring Report, June 2001, Quarterly Groundwater Monitoring Report September, 2001, and Quarterly Groundwater Monitoring Report, December, 2001).
There were no active drinking water or livestock wells on CSSA grounds within ½ mile of AOC-65 (Volume 1-1, DO5084 Work Plan Addendum, and Volume 1-4, RL83 Sampling and Analysis Plan Addendum 3, Cluster Well Drilling, Installation, and Development). The nearest on-post wells, CS-5 and CS-6, are over ¼ mile from AOC-65 and both have been plugged and abandoned. The nearest off-post wells, LS-7, LS-2, RFR-10, and RFR-9, are all located approximately ¼ mile from AOC-65. These offsite wells are west and south of AOC-65 (Environmental Encyclopedia, Volume 5).
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, as per the State Historic Preservation Officer (SHPO) at CSSA. AOC-65 is located within Building 90, which is adjacent to Buildings 91 and 92. Buildings 90-1 and 90-2 are adjacent to Building 90. These buildings are over 50 years old and are examples of Cold War era architecture. Any work that could impact the structural integrity of Building 90 requires consultation with the SHPO.
A land use survey of local and possible future uses of groundwater and surface water, a water well survey, and sensitive environmental areas survey at CSSA were completed on December 15 and 16, 1999, in accordance with the TNRCC Texas Risk Reduction Program (TRRP). Results of these surveys, along with results from a more comprehensive 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-65 is located in the southwest corner of CSSA. Off-post land use within ½ mile of AOC-65 is primarily residential. The area south of the facility is densely populated with trailer homes located on small lots. The nearest residence is located approximately 3,170 feet away from Building 90. No on-post or drinking water supply wells occur within ½ mile of AOC-65. However, off-post supply wells LS-6, LS-7, LS-2, RFR-10, and RFR-9 are located within ½ mile of AOC-65. Building 90, which comprises the majority of AOC-65, remains an active industrial facility.
The nearest potential habitats for local endangered species (Volume 1-1, Background Information Report) are 2,200 feet south-southeast (golden-cheeked warbler) and 7,900 feet northeast (black-capped vireo). Native grasses and oak trees dominate vegetation surrounding Building 90. A small herd of cattle is maintained on CSSA by the U.S. Department of Agriculture’s (USDA)-Agricultural Research Center (ARC). The cattle roam freely throughout the Inner Cantonment and in selected areas of the North Pasture.
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 Technical Approach Document for Risk Evaluation (Volume 1-6). AOC-65 is located approximately 1,500 feet west of hunting stand number 12. Five water tanks are maintained at CSSA for the purpose of recreational fishing. Two tanks are located in the northwestern and northeastern portions of the North Pasture, one is located in the upper portion of the East Pasture, and the other two tanks are located near the western boundary of the Inner Cantonment. The nearest tank, “W” Tank, is located approximately 1,250 feet southeast of AOC-65.
The previous investigations performed at AOC-65 are described in Volume 3-3, AOC-65 of the CSSA Environmental Encyclopedia. As noted, PCE and TCE were used in a below-grade metal vat inside Building 90. The vat was removed in 1995, but there is concern that soils beneath the vault that housed the vat may be contaminated with PCE and TCE from prior use of these chemicals in Building 90.
A soil gas survey was performed in January and February 2001 to assess the potential for VOC migration in the soils in and around AOCs-57, -67, and -65 (Draft Soil Gas Survey Technical Report, Parsons ES, August, 2001). Sampling was performed at these AOCs using a 100 foot sampling grid. The sampling grid was tightened to 25 feet where the results indicated potential contamination was present. A total of 203 samples were collected from soils around the exterior of Building 90, with sampling depths ranging from 0.5 feet to refusal (maximum depth, 4.5 feet below ground surface [bgs]). An additional 40 samples were collected from underneath Building 90, including two former vat areas and associated drain lines. Sampling depths under Building 90 ranged from 1.0 to 2.5 feet.
The soil gas survey tested for BTEX compounds (benzene, ethylbenzene, toluene o-xylene, and m,p-xylene), , cis-1,2-DCE, trans-1,2-DCE, PCE, TCE, and vinyl chloride (VC). Of these, PCE, TCE, cis-1,2-DCE and trans-1,2-DCE were detected at AOC-65 during the survey.
PCE was detected in a soil gas plume that encompasses the entire area under Building 90, as well as in the area west and southeast of the building (Figure AOC-65‑4). PCE was detected in 67 of the exterior samples and all 40 samples from under the interior of Building 90. The PCE soil gas concentrations under Building 90 were generally higher (1.05 to 24,800 μg/L) than those in the soil outside Building 90 (0.07 to 1,590.0 μg/L). The highest PCE concentrations occur in the same location as the TCE plume; however, the extent of the PCE soil gas plume is greater than that of the TCE soil gas plume. PCE concentrations were highest (8,350 to 24,800 μg/L) in the area adjacent to the former metal solvent vat within AOC-65.
A localized soil gas TCE plume with a lateral extent of approximately 80 feet was indicated outside and under Building 90. The maximum TCE concentration detected was 8.56 μg/L, with concentrations under the building less than that immediately outside. This plume was found under the former vat area, extending to the soils exterior to Building 90.
Cis-1,2-DCE and trans-1,2-DCE were detected in only two samples, both located within the TCE soil gas plume limits. The concentrations for these compounds range from 0.05 to 0.88 μg/L.
As described in Section 4.3 of the Risk Assessment Technical Approach Document (Volume 1-6), CSSA has opted to pursue closure of AOC-65 under the Risk Reduction Standard One (RRS1) (30 Texas Administrative Code [TAC] §335). If the site concentrations do not exceed background, then the site will be closed using RRS1. If the site exceeds background, then a determination will be made regarding the feasibility of cleaning the site to meet background concentrations. If the decision is made to clean the site to background, closure under RRS1 will be sought. However, if it is determined that the site cannot be closed to meet background concentrations, then the site will be closed under TRRP. A notification of intent to close sites identified to date (including AOC-65) in accordance with the former RRS was sent to the TNRCC on July 12, 1999. Acceptance of this notification was received on October 5, 1999.
RRS1 requires that the site be closed following removal or decontamination of waste, waste residues, and contaminated operation system components; and demonstration of attainment of cleanup levels (30 TAC §335.554). If closure requirements under RRS1 are attained and approved by the TNRCC Executive Director, then the owner is released from the deed recordation requirement.
Since the COCs for AOC-65 are VOCs, SVOCs, TPH, PCB, and metals, the cleanup levels should be the background concentrations for metals, and RLs for the remainder of the compounds.