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Final AOC-67 RCRA Facility Investigation Report

Section 1 - Introduction

On May 5, 1999 an Administrative Consent Order was issued to CSSA pursuant to �3008(h) of the SWDA, as amended by the RCRA, and further amended by the HSWA of 1984. In accordance with the RFI requirements of the Consent Order, this report has been prepared to document the environmental condition and site closure requirements of AOC-67 and to recommend further investigation, if necessary, or to provide documentation necessary for site closure. The main objectives of the AOC-67 investigation are to determine if the site meets TNRCC requirements for closure, as described in Section 1.4, and requirements of the Consent Order.

This specific RFI was performed by Parsons under U.S. Air Force AMC Contract F41689-96-D-0710, Delivery Orders 5068 and 5084. AFCEE provided technical oversight for the delivery order. Based on the AETC pre-defined SOW, a set of work plans to govern the fieldwork was established. These include:

For this RFI report, Section 1 provides the site-specific background and closure standard. Section 2 describes field actions and closure evaluation. Section 3 summarizes the findings, evaluates attainment of data quality objectives (DQO), provides recommendations, and certifies the site closure, if applicable. References cited in this report can be found in the CSSA Environmental Encyclopedia (Volume 1-1, Bibliography).

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 67

1.1.2.1   Site Description

As part of its operations, CSSA performed waste management activities at selected locations throughout the installation. AOC-67 is located adjacent to Building 90-1, which is associated with the bluing operations for ordinance materials, and Building 90, which is used for ordinance maintenance (Figure AOC-67-1). AOC-67 consists of a drainage ditch, part of which is covered by a concrete pad. The concrete pad sat under a 1,250-gallon above ground storage tank (AST). This tank, removed in approximately 1997, was used to contain rinsate from floor cleaning activities in Building 90. 

Because of the proximity of AOC-67 Building 90 and Building 90-1, liquid solvents including PCE and TCE may also have been placed in the tank. Environmental investigations described in this report were directed to address possible soil contamination associated with previous handling and storage of floor rinsates and solvents in the area. Ongoing activities at Building 90 and Building 90-1 include weapons cleaning and maintenance, but the use of chlorinated solvents in Building 90 was discontinued in 1995.

Background information regarding the location, size, and known historical use of the site is also included in the Environmental Encyclopedia (Volume 1-3, AOC-67). Volume 1-3 includes a Chronology of Actions and a Site-Specific Work Plan Addendum for AOC-67.

1.1.2.2   Potential Sources of Contamination

Cleaning fluids and rinsate from Building 90-1 were stored in an AST at AOC-67. Although the AST was removed, the rinsate once stored in the AST presents a possible source of contamination in the immediate vicinity of AOC-67.

Another potential source of contamination near AOC-67 is a PCE plume identified in the soils, soil gases, and shallow monitoring wells (up to 35 feet deep) around Buildings 90 and 90-1 (Soil Gas Survey Technical Report, Parsons ES, 2001, and AOC-65 RFI Investigation Report, Draft). The perimeter of the PCE soil gas plume is approximately 35 feet west of AOC-67. PCE and TCE were formerly used at CSSA to clean weapons and were stored in a metal vat located inside Building 90. The most recently used vat was removed from operation in 1995. An alternative citrus-based cleaner replaced PCE and TCE at CSSA in 1995. The potential for solvent migration from Building 90 to be co-mingled with any releases from AOC-67 is remote. 

Finally, AOC-68 (Building 90-2), located approximately 60 feet southwest of AOC-67 and in a nearby swale adjacent to Building 90, is the location of a rarely used wheelabrator. Surficial hardened metal debris is present on the ground at the site.

Based on these the activities in the area of AOC and the lack of records regarding chemicals placed in the AST, the potential COCs for AOC-67 are: VOCs, SVOCs, TPHs, and metals.

1.1.2.3   Site Location

AOC-67 is located adjacent to Building 90 along the southwest side of CSSA (Volume 1-3, Site Location Map). AOC-67 consists of a tank pad that previously formed the foundation for the AST, and an associated drainage ditch located approximately 50 feet east of Building 90-1. The actual dimensions of the AOC boundary are approximately 60 feet by 30 feet (Figure AOC67-1). Building 90 is located approximately 130 feet east of the CSSA western boundary and approximately 160 feet south of Tompkins Road. A human and ecologically sensitive receptor survey was conducted at CSSA; results are presented in Section 3 of Volume 1-6, Risk Assessment Technical Approach Document.

Nearby AOCs include: AOC-68 (approximately 40 feet south of AOC-67), AOC-65, (approximately 75 to 175 feet southwest of AOC-67), AOC-45 approximately 780 feet southeast of AOC-67, and AOC-57, approximately 480 feet east-northeast of AOC-67. SWMU B-31 is approximately 600 feet east-southeast of AOC-67.

1.2 - Site Environmental Setting

1.2.1   Site Soils and Topography

The Crawford and Bexar stony soils complex is the native soil type at AOC-67 (Figure AOC67-2). Detailed descriptions of the CSSA soil types are given elsewhere in the CSSA Environmental Encyclopedia (Volume 1-1, Background Information Report). They occur in broad, nearly level to gently undulating areas with slopes of 0 to 5 percent. The soils are stony, very dark gray to dark reddish brown, noncalcareous clay, about 8 inches thick. Bexar soils range from a cherty clay loam to gravely loam. The soils are suited for native grass, such as Texas winter grass, little bluestem, sideoats grama, and buffalo grass. AOC-67 lies at an elevation of approximately 1,220 feet above sea level, sloping gently (less than 2 percent grade) to the southeast.

Natural surface run-off would be expected to flow predominantly toward the southeast; however, because a southward-draining ditch crosses AOC-67, surface run-off possibly enters the drainage ditch instead (Figure AOC67-1). This ditch runs parallel to Building 90 and empties via a pipe under the road into a long thin basin that runs parallel to Buildings 90-1 and 90-2, across the road and approximately 100 feet east of AOC-67 (Figure AOC67-1). Overflow from the basin follows a ditch to W Tank, located 1,250 feet from AOC-67. However, transport of water from AOC-67 into W Tank has not been witnessed to date.

1.2.2   Geology

AOC-67 is sited over the Lower Glen Rose limestone (Figure AOC67-3). Inspection of exposed bedrock in an excavated area 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 upwards into thin beds of limestone, marl, and shale. The Lower Glen Rose is underlain by the Bexar Shale facies of the Hensell Sand, estimated to be from 60 to 150 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.

Two major fault (shatter) zones have been identified at CSSA: t he North Fault Zone and the South Fault Zone. The south fault zone lies approximately 2,100 feet south of the site (Figure AOC67-3). A small fault, projected by the USGS from data collected at Camp Bullis, is shown running through Building 90 in Figure AOC67-3. A fault has been 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 current investigations, using resistivity surveys, should elucidate the location of the fault projected by the USGS as well as other potential faults in the area. Additional information on structural geology at CSSA can be found in the CSSA Environmental Encyclopedia (Volume, 1-1, Background Information Report).

1.2.3   Hydrology

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, ground water 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, 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 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. CSSA Environmental Encyclopedia (Volume 1-1, Background Information Report).

AOC-67 is located approximately 2,100 feet north of the Southern Fault Zone at CSSA (Figure AOC-67-3). A small fault, projected by the USGS from data collected at Camp Bullis, is shown in Figure AOC67-3 running through Building 90. A fault has been 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, should elucidate the location of the fault projected from the USGS data, as well as other potential faults in the area of Building 90. 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. CSSA Environmental Encyclopedia (Volume 1-1, Background Information Report). 

There are no streams in the vicinity of AOC-67 (Figure AOC67-1). Natural drainage from the land surrounding AOC-67 is primarily by overland flow, with rapid infiltration into the underlying formation. However, a southward-draining ditch crosses AOC-67, and surface run-off may be expected to accumulate in this ditch. The drainage ditch runs south, parallel to Buildings 90-1 and 90-2 and adjacent to the road, and water is transferred, by a pipe that passes under the road, into an approximately 0.7 acre basin approximately 100 feet east of AOC-67. It is unlikely that any drainage from AOC-67 is discharged into any naturally occurring surface water body, such as a creek because none are present downslope or in the anticipated direction of drainage from the ditch. 

No site-specific information regarding groundwater was available prior to this study. However, recently installed wells MW8-LGR, MW8-CC, MW10-LGR, MW10-CC, MW6-LGR, MW6-BS, and MW6-CC will provide groundwater information in the area around AOC-67 (Figure AOC67-1), as will the monitoring wells installed at AOC-65. The MW6 well cluster is located 275 feet north of AOC-67, the MW7 cluster is 790 feet southeast of AOC-67, and the MW8 cluster is 700 feet south of AOC-67. None of the wells in the vicinity of AOC-67 exceeded RLs for VOCs in the June or September sampling events (Quarterly Groundwater Monitoring Report, June 2001, and Quarterly Groundwater Monitoring Report, September 2001). Four groundwater samples were collected from the shallow monitoring wells installed around AOC-65 during or soon after the well installation. No wells are within 200 feet of AOC-67. The groundwater samples all contained PCE associated with the contamination at AOC-65 (AOC-65 RFI Facility Investigation, Draft). 

There are no other active on-post supply wells located less than � mile from AOC-67. Prior to field activities at AOC-65 (Volume 1-1, DO5084 Work Plan Addendum) and well installation activities at CSSA (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 � mile from AOC-67, and both have been plugged and abandoned. The nearest off-post wells, LS-7, LS-2, RFR-10, and RFR-9, are all located over � mile from AOC-67. These offsite wells are west and south of AOC-67. CSSA Environmental Encyclopedia (Volume 5, AOC-67). 

1.2.4   Cultural Resources

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-67 is located adjacent to Buildings 90, 90-1, and 90-2, which are immediately adjacent to Buildings 91 and 92. These buildings are over 50 years old and are examples of Cold War era architecture. Any work that could impact the structural integrity of these buildings requires SHPO approval.

1.2.5   Potential Receptors

A land use survey identifying local and possible future uses of groundwater and surface water, a water well survey, and a sensitive environmental areas survey at CSSA were completed on December 15 and 16, 1999. 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-67 is located in the southwest corner of CSSA. Off-post land use in this area is primarily residential. The area south of the facility is more densely populated relative to the average density for San Antonio, with trailer homes located on small lots. The nearest residence is located 500 feet from Building 90. On-post cluster wells, installed for monitoring purposes, are located within � mile of AOC-67. The MW6 well cluster is located 275 feet north of AOC-67; the MW7 cluster is 790 feet southeast of AOC-67, and the MW8 cluster is 700 feet south of AOC-67. No off-post or other on-post supply wells occur within a 1/4 mile of AOC-67; however off-post wells LS-7, LS-2, RFR-10, and RFR-9 are located within � mile of AOC-67.

The nearest potential habitats for local endangered species (Volume 1-1, Background Information Report) are approximately 2,100 feet east-southeast (golden-cheeked warbler) and 7,800 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 (USDA)-Agricultural Research Center (ARC). The cattle roam freely throughout the Inner Cantonment of CSSA and in selected areas of the North and East 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 Technical Approach Document for Risk Evaluation (Volume 1-6). AOC-67 is located approximately 1,300 feet northwest of hunting stand number 12. 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 tank, �W� tank, is located approximately 1,250 feet southeast of AOC-67. 

Previous investigations performed at AOC-67 are described in the CSSA Environmental Encyclopedia (Volume 1-3, AOC-67). As noted, an AST installed on the concrete pad at AOC-67 was used to store rinsate from Building 90-1. The AST was removed in 1997, but no data were collected to confirm that AOC-67 had not been contaminated by activities in the surrounding area. 

A soil gas survey was performed in January and February 2001 to assess the potential for VOC contamination in the soil in and around AOCs 57, 65, 68, and 67 (Soil Gas Survey Technical Report, Parsons ES, 2001). Sampling was performed on a grid that covered the AOCs, with grid spacing ranging from 25 to 100 feet, depending on the detection of VOCs within the area of the survey. A total of 203 samples was collected from soils around the exterior of Building 90, with sampling depths ranging from 0.5 feet to refusal (maximum depth, 4.5 feet bgs). Forty samples were collected inside Building 90, including the pit area and associated drain lines. The soil gas survey tested for TCE, PCE, cis-1,2-DCE, trans-1,2-DCE, BTEX, vinyl chloride (VC), toluene, o-xylene, and m,p-xylene, and benzene. Approximately 40 samples were collected within a 200 foot radius of AOC-67.

No VOCs were detected in the soil gas samples collected within the boundaries of AOC-67; however, PCE, TCE, cis-1,2-DCE, and trans-1,2-DCE were all detected within 200 feet of AOC-67, at Building 90 and AOC-65. 

A localized TCE soil gas plume with a diameter of approximately 80 feet was identified approximately 200 feet southwest of AOC-67, in soils on the west side of Building 90, with a maximum concentration of 8.56 �g/L. Cis-1,2-DCE, and trans-1,2-DCE were detected in two samples located within the TCE plume. The concentrations for these compounds range from 0.05 to 0.88 �g/L. 

A PCE soil gas plume that came within 35 feet of AOC-67 was detected underneath and around Building 90, occurring predominantly to the west and southeast of the building. PCE was detected in 23 of the 40 samples collected within 200 feet of AOC-67. The highest reported concentration of PCE (24,800.0 �g/L) occurred under the former metal vat area in AOC-65, which is approximately 200 feet from AOC-67 (Figure AOC67-4). The PCE concentrations under Building 90 are generally higher (1.05 to 24,800.0 �g/L) than those in the soils outside Building 90 (0.07 to 1,590.0 �g/L). The concentrations of the samples nearest to AOC-67 were all less than 1 �g/L.

1.4 - Closure Standard

As described in Section 4.3 of the Risk Assessment Technical Approach Document (Volume 1-6), CSSA opted to pursue closure of AOC-67 under the Risk Reduction Standards (RRS) (30 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 may potentially be closed under TRRP. A notification of intent to close sites identified through June 1999 (including AOC-67) 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-67 are VOCs, SVOCs, TPHs, and metals, the cleanup levels are the background concentrations for metals, and RLs for the organic compounds. The background concentrations for metals are taken from the Second Revision of the Evaluation of Background Metal Concentrations in Soils and Bedrock at Camp Stanley Storage Activity. The soil background concentrations taken from this report may be used for comparison to samples collected from anywhere within CSSA. 

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