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SWMU B-13 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 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 SWMU B-13 and to recommend further investigation, if necessary, or to provide documentation necessary for site closure. The main objectives of the SWMU B-13 investigation are to determine if the site meets 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 U.S. Air Force AMC Contract F11623-94-D-0024, Delivery Order RL17. AFCEE provided technical oversight for the delivery order. Based on the project SOW, a set of work plans were established to govern the fieldwork. These include:

For this report, Section 1 provides the site-specific background and closure standard. Section 2 describes field actions and closure evaluations. 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   SWMU B-13

1.1.2.1   Site Description

SWMU B-13 was used as a construction waste disposal site for the post Engineering/Public Works Department during an unknown time period. The site was identified during a records review in 1993 and the site boundaries were mapped during a field investigation of the site on March 17, 1996. Of three historical aerial photographs of CSSA dated 1966, 1973, and 1986, the SWMU B-13 area appears most disturbed in the 1986 photograph. Construction rubble, bricks, rebar, and railroad ties were identified in the rubble piles at the site. The half buried nature of the rubble piles, combined with the uneven nature of the hillsides, implied that more waste is buried at the site. Most hillsides at CSSA are covered with a very thin soil layer with sparse grass and exposed limestone bedrock. The hillsides at B-13 were not observed to be consistent with the surrounding areas, as the SWMU area contained grass cover with no exposed bedrock throughout the area. The basal depth of the fill could not be ascertained. The site covers approximately three acres of land. Weathered, empty M16 magazines were found near the bricks and fill on the exposed bedrock in the southeast corner of the site. No UXO was identified during field investigations.

Background information regarding the location, size, and known historical use of SWMU B-13 is included in the Environmental Encyclopedia (Volume 1-2, SWMU B-13). Volume 1-2 also includes a Chronology of Actions and a Site-Specific Work Plan Addendum for SWMU B-13.

1.1.2.2   Potential Sources of Contamination

Historical records indicate that SWMU B-13 was used as a landfill area for large pieces of scrap metal and weapons (Parsons, 1993b). Metal debris was covered with sand and compacted; however, erosion has resulted in debris being exposed at the surface. The large pieces of metal located near the ground surface are interpreted as the primary source for contamination of surface and subsurface soils at the site. Potential COCs at SWMU B-13 include VOCs, SVOCs, and metals.

1.1.2.3   Site Location

SWMU B-13 is located in the southern tip of the Inner Cantonment Area of CSSA (Figure B13-1, based on the 1998 aerial photograph). It comprises two hills divided by a wide drainage area. It is approximately 500 feet north of the southern boundary of CSSA and covers about 3 acres in area (Volume 1-2, Site Location Map). The site boundary trends along the natural hillsides and drainage areas, forming a crescent shape. Bedrock is exposed at the top of the hillsides, indicating the lateral extent of alluvial fill. The hilltops are therefore not part of the disposal area and are not included in the SWMU. A dirt road bounds the southern edge of the site.

SWMU B-29 and AOC 50 are located approximately 600 feet west of SWMU B-13. SWMU B-30 and SWMU I-1 are located approximately 800 feet west of SWMU B-13.

1.2 - Site Environmental Setting

Two soil types occur within the SWMU B-13 boundary: Krum Complex soils in about 85 percent of the site (Figure B13-2), and Crawford and Bexar stony soils in the remaining 15 percent. The Krum Complex soils are on slopes between 2 and 5 percent and occupy "foot" slopes below Tarrant and Brackett soils. The Krum soils receive sediments and runoff from higher elevation soils and are highly prone to water erosion if unprotected. The surface soil is dark grayish-brown or very dark grayish-brown, calcareous, and approximately 30 inches thick. The soils developed from slope alluvium of the limestone prairies. Crawford and Bexar stony soils occur as broad, nearly level to gently undulating areas with slopes of 0 to 5 percent. The Crawford soils are stony, very dark gray to dark reddish-brown, noncalcareous clay, and are about 8 inches thick. Large fragments of chert and limestone occur on the surface and within the soil profile. Bexar soils range from cherty clay loam to gravelly loam. Detailed descriptions of CSSA soil types are provided in the CSSA Environmental Encyclopedia (Volume 1-1, Background Information Report, Soils and Geology).

SWMU B-13 is composed of a dry creekbed together with two hillsides located east and west of the creekbed. The hillsides slope steeply towards the creekbed. The creekbed gently slopes to the south where it widens. The referenced creekbed is an intermittently flowing stream and is not a navigable or jurisdictional waterway of the United States. The ground surface elevation of the site area is approximately 1,200 feet above sea level. The site vegetation is predominantly grasses. Bedrock outcrops are present within the creekbed and on the hilltops.

The Upper Glen Rose is the uppermost geologic strata in the area of SWMU B-13 (Figure B13-3). 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. Where present at CSSA, the thickness of the Upper Glen Rose is estimated up to 150 feet thick at CSSA. It is underlain by the Lower Glen Rose Limestone, which 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, which is estimated to be up 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.

Based on published information, there are two known major fault (shatter) zones at CSSA: the North Fault Zone and the South Fault Zone. The site is located within the southern-most fault zone area within CSSA (Figure B13-3). Additional information on structural geology at CSSA can be found in the Environmental Encyclopedia (Volume 1-1, Background Information Report, Soils and Geology). Soil borings drilled at the site indicate an average depth to limestone of 3 to 8 feet below ground surface at SWMU B-13 (see Appendix B). SWMU B-13 contained an area suspected at first of being a sinkhole; however, field investigation revealed that the depression was actually a scraped out area associated with excavation activities that was later backfilled with debris.

1.2.3   Hydrology

At CSSA, the uppermost hydrogeologic layer is the unconfined Upper Trinity aquifer, which consists of the Upper Glen Rose Limestone. 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. Groundwater discharge occurs predominantly via natural springs, seeps, and by groundwater pumping. Regional groundwater flow appears to be to the southeast.

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. In general, groundwater at CSSA flows in a north to south direction, with some seasonal fluctuations. However, local flow gradient may vary depending on rainfall, recharge, and possibly well pumping.

SWMU B-13 is located within the South (Shatter) Fault Zone at CSSA. 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 (Volume 1-1, Background Information Report, Soils and Geology).

The nearest surface water body is a small, unnamed ephemeral stream that runs through the northwestern portion of the site area (Figure B13-1). This small stream exits the CSSA boundary approximately 1,600 feet southwest of SWMU B-13. It eventually merges with Leon Creek south of CSSA.

No site-specific information regarding on-post groundwater is available. Off-post well LS-1 is situated approximately 1,120 feet southwest of SWMU B-13. Off-post wells LS-2, LS-3, LS-7, HS-1, HS-2, HS-3, and HS-4 are located within ¾–mile of SWMU B-13.

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. No potential sites of cultural importance are close to SWMU B-13. The nearest cultural resource at CSSA is a stone house built in 1847 located about ¼-mile west of SWMU B-13. In addition, World War I era fox-hole type trenches are located approximately 6,200 feet northeast of the site area (Parsons ES, 1993). A hand-dug water well (Well CB-30) is located at neighboring Camp Bullis, at a location approximately ¼-mile east of SWMU B-13. 

1.2.5   Potential Receptors

A land use survey discussing local 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 use surrounding CSSA is primarily residential. The closest residential property to SWMU B-13 is located 400 feet to the south. The area south of the facility is fairly densely populated, with trailer homes located on small lots. Homes are only sparsely scattered along most of the western boundary; however, there is undeveloped off-site land that has potential for additional residential development.

Off-site well LS-1 is located within 1,120 feet of SWMU B-13. No VOCs have been detected above RLs for LS-1. Several other active off-site wells in Leon Springs Villa and Hidden Springs Estates are located within ¾ mile of SWMU B-13. All these wells are completed in the Lower Glen Rose or the Cow Creek Limestones. Groundwater elevations are not known for these wells, and little analytical data are available. Low levels of PCE have been detected in LS-7.

The nearest on-site well, Well CS-MW10-LGR, is located 2,000 feet east of SWMU B-13. The water level for Well CS-MW10-LGR was 60.58 ft BTOC in December 2001. The well is completed to 396 feet bgs, into the Lower Glen Rose Formation.

A small herd of cattle is maintained on CSSA by the USDA 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 that 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). SWMU B-13 is located approximately 100 feet southeast of hunting stand number 12. Four water reservoirs are maintained at CSSA for the purpose of sport fishing. Two of the reservoirs are located in the northwestern and northeastern portions of the North Pasture while the other two reservoirs are located near the western boundary of the Inner Cantonment.

The site area is located within a potential habitat of the Golden-Cheeked Warbler, a local endangered species (Volume 1-1, Background Information Report, Figure 11). Vegetation consists mainly of grasses, except in the creekbed area where the ground is bare. Portions of the eastern hillside have also been cleared of vegetation. A few large oak trees are present along the eastern hillside.

1.3 - Previous Investigations

No previous investigations have been performed at SWMU B-13. The site was identified during the 1993 EA.

1.4 - Closure Standard

As described in Section 4.3 of the Risk Assessment Technical Approach Document (Volume 1-6), CSSA has opted to pursue closure of SWMU B-13 under the Risk Reduction Rule (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 will be closed under TRRP. A notification of intent to close sites identified to date (including SWMU B-13) in accordance with the former Risk Reduction Rule was sent to the TNRCC on July 12, 1999. TNRCC 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 SWMU B-13 are VOCs, SVOCs and metals, the RRS1 standards should be the RLs for VOCs and SVOCs, and the soil or rock background values for metals. Background metals levels were statistically calculated for CSSA soils and the Glen Rose Limestone, and are reported in the Second Revision to the Evaluation of Background Metals Concentrations in Soils and Bedrock (Parsons, February 2002).

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