[Home]

[RFI/Closure Report] [Next Section]

SWMU B-1 RCRA Facility Investigation/Closure 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 RFI report has been prepared to document the environmental condition and site closure requirements of B-1 and to recommend further investigation, if necessary, or to provide documentation necessary for site closure. The primary objective of the SWMU B-1 investigation is to determine if the site meets TNRCC requirements for closure, as described in Section 1.4.

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 upon the project SOW, a set of work plans to govern the fieldwork was established. 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

1.1.1   CSSA

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-1

1.1.2.1   Site Description

SWMU B-1 is a 3-acre tract located in the North Pasture of CSSA (Figure B1-1). Native grasses cover the approximate western two-thirds of the site and thick brush and trees cover the remaining eastern third. SMWU B-1 is a medium priority site at CSSA where incendiary materials were reportedly burned in 1954. However, there are no known records regarding site use. Currently, SWMU B-1 is not used. An investigation of historical aerial photographs shows that between 1966 and 1973 the site was cleared of the trees that were on the western portion of the site.

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

1.1.2.2   Potential Sources of Contamination

Incendiary materials were reportedly burned at SWMU B-1 in 1954. Potential COCs identified during the initial investigation included metals, SVOCs, and VOCs.

1.1.2.3   Site Location

The site is located approximately 850 feet north-northwest of Well CS-16 and approximately 750 feet north of Well CS-D. The nearest CSSA boundary is approximately 3,300 feet to the west. SWMU B-1 is rectangular in shape and oriented in a northwest-southeast direction. The boundaries of the site are approximately 600 feet long and 400 feet wide. It is bounded on the east by a barbed wire stock fence and a dirt road passes through the approximate center in the same northwest-southeast orientation. An unnamed tributary of Salado Creek is located approximately 300 feet west of the site. AOC 66 is located approximately 200 feet to the south, AOC 43 and SWMU B-7 are located approximately 600 feet to the northeast, SWMU B‑2 is 150 feet to the east, and SWMU B-8 and AOC 41 are approximately 900 feet southeast of SWMU B-1.

1.2 - Site Environmental Setting

1.2.1   Site Topography and Soils

Four soil types occur at SWMU B-1: the Krum complex soils, gently undulating Tarrant Association soils, the Trinity and Frio soils, and Lewisville soils (Figure B1-2). The Krum Complex soils 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 downslope of prairie plains and receive sediments from higher elevations, they are subject to hydraulic erosion. These soils are dark grayish-brown, calcareous, and approximately 30 inches thick. The Krum Complex soils comprise about 20 percent of CSSA.

The gently undulating Tarrant Association soils are located in the eastern portion of the site. Tarrant Soils occur along the outer edge of the Salado Creek floodplain. They are thin (approximately 10 inches), dark-colored, calcareous, clayey, and form over hard, fractured limestone. Two types of Tarrant soils occur at CSSA: gently undulating and rolling. The gently undulating Tarrant Association soils cover approximately 14.3 percent of CSSA and occur on prairie and plateau topography. 

Lewisville soils are located in a small portion of the east side of the site. Lewisville soils typically occupy long, narrow, sloping areas separating nearly level terraces from upland soils. Lewisville soils cover only one percent of CSSA.

The Trinity and Frio soils cover the remainder of the site. Trinity and Frio soils occur in the main channel for Salado Creek and a large tributary creek that joins Salado Creek in southwestern CSSA. Some areas are subject to thin sediment deposition, while other areas are scoured. Trinity soils can be up to 3 to 5 feet thick and are clayey to gravely loam, while Frio soils are clayey loams that may be up to 3 to 4 feet thick. The Trinity and Frio soils comprise approximately 8.8 percent of CSSA.

Additional information about these and other soils that occur at CSSA can be found in the CSSA Environmental Encyclopedia (Volume 1-1, Background Information Report, Soils and Geology).

SWMU B-1 is located on a west-trending, very gentle slope and is situated at an elevation of between 1,240 and 1,250 feet above sea level. There are no changes in topography in the immediate vicinity of SWMU B-1, and there are no ditches or trenches in the immediate vicinity of SWMU B-1. Salado Creek, an intermittent stream, is located approximately 250 feet west of SWMU B-1. 

1.2.2   Geology

The Upper Glen Rose is the uppermost geologic stratum in the area of SWMU B-1 (Figure B1-3). 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 Upper Glen Rose may be up to 150 feet thick. It is underlain by the Lower Glen Rose, 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 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.

Based on current published information, there are two known major fault (shatter) zones at CSSA: the North Fault Zone and the South Fault Zone. SWMU B-1 is located north of the two fault zones (Figure B1-3). Additional information on structural geology at CSSA can be found in the Environmental Encyclopedia (Volume 1-1, Background Information Report, Soils and Geology). Boring logs from soil borings drilled at the site indicate that limestone was encountered at depths ranging from two to six feet below ground surface (Appendix B).

1.2.3   Hydrogeology

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. 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 water levels in adjacent wells often differ. 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 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 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. However, local flow gradient may vary depending on rainfall, recharge and possible well pumping.

Shallow perched water was discovered in the two soil borings drilled in the southeastern portion of the site. The water was encountered at a depth of approximately 26 feet in both borings. No other information regarding ground water is available for SWMU B-1. As described previously, the nearest wells are CS-16 and CS-D. Between May 1994 and June 2001, water levels in Well CS-16 have ranged from 78.58 feet BTOC (November 1998) to 316.88 feet BTOC (April 1995). In neighboring Well CS-D, water levels have ranged from 56.79 feet BTOC (November 1998) to 261.88 feet BTOC (September 2000).

As described in Section 1.2.2, Salado Creek is located approximately 250 feet west of SWMU B-1. In this area, Salado Creek only contains surface water for brief periods immediately after precipitation events. This creek flows to the southeast and exits the southeast portion of CSSA. 

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. A burned rock midden, located approximately 985 feet north of SWMU B-1, is the nearest cultural resource. 

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).

There is no housing adjacent to SWMU B-1. The nearest residential area is approximately 2,700 feet to the west of SWMU B-1. Generally, CSSA is a controlled access facility, so a security guard and perimeter fence limit access. However, wildlife, such as deer and turkey, may use the area surrounding SWMU B-1 for foraging and rest. A potential habitat for two species, the Golden-Cheeked Warbler and the Black-Capped Vireo, lies approximately 100 feet north of SWMU B-1.

The USDA-ARC maintains a small herd of cattle on CSSA. 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 Figure 5.2 in the Technical Approach Document for Risk Evaluation (Volume 1-6). SWMU B-1 is located approximately 1,275 feet northwest of hunting stand 2. Of the five ponds/tanks at CSSA, four are maintained 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.

1.3 - Previous Investigations

Due to its proximity to Well CS-16, several previous investigations have been conducted at SWMU B-1. These investigations, which included a geophysical survey, soil boring samples, and groundwater grab sampling, were conducted as part of the effort to identify sources of groundwater contamination detected at Well CS-16.

1.3.1   Surface Geophysical Survey

EM and GPR geophysical surveys were performed at SWMU B-1 in February 1995 as part of the Well CS-16 source characterization study. Results of these surveys are described in detail in Section 2 of the Technical Memorandum on Surface Geophysical Surveys (Parsons ES, 1995a).

EM readings were taken for both east-west and north-south orientations. During data collection, the EM-31 instrument was monitored to verify that no significant variations in the instrument readings occurred between stations. No EM anomalies were observed at B-1. There is a gradual increase in apparent conductivity to the west, which is interpreted to be caused by increasing soil thickness to the west.

A GPR survey was conducted at B-1 using the GSSI SIR-3 system. GPR data was collected along east-west transects separated by 100 feet. Over the majority of the site, the GPR profiles did not have the required resolution to detect subsurface stratigraphic changes. Indications of the limestone bedrock were observed along the east side of the site where there is only a thin section of soil overlying the limestone. The inability of GPR to detect subsurface stratigraphic changes is attributed to the clay soil present at the site.

1.3.2   Soil Boring Sampling

On February 21 and 22, 1995, three soil borings (B1-SB1, B1-SB2, and B1-SB3) were advanced, and three samples were collected from each boring. The locations of the borings are shown in Figure B1-4. The samples were submitted to Chemron Laboratory of San Antonio, Texas for analysis of metals, VOCs, and SVOCs. Because holding times on the VOC samples collected from B1-SB1 were missed, B1-SB1 was re-drilled (B1-SB1R) on June 13, 1995, and VOC samples were collected and analyzed by Chemron Laboratory.

Results of the 1995 sampling event are summarized in Table B1-1. Phthalate isomers were detected above RRS1 criteria in seven of the ten samples, although no other SVOCs were detected. No VOCs were detected, and no metals were detected above background levels. Although cadmium was not detected in any of the samples, the detection limit was greater than the background value for cadmium in Glen Rose Limestone. The background levels were statistically calculated for Glen Rose Limestone and are located in the Second Revision to the Evaluation of Background Metals Concentrations in Soils and Bedrock (Parsons, February 2002). RRS2 standards have also been included in Table B1-1.

1.3.3   Groundwater Sampling

Perched groundwater was encountered in two borings at SWMU B-1, although only one boring (B1-SB3) produced enough water to sample. A decontaminated Teflon^® bailer was lowered with new nylon rope to collect a grab sample from the open borehole, which was drilled to a depth of 30 feet bgs. The sample was tested for VOCs, SVOCs and metals by Chemron. No VOCs or SVOCs were detected. All metals concentrations were below MCLs, as summarized in Table B1-2. However, the PQL for lead was higher than the MCL. 

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-1 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-1) in accordance with the former RRR 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.

Based on the results of the 1995 investigation, remaining COCs are bis(2-ethylhexyl)phthalate, butylbenzylphthalate, and di-n-butylphthalate. The cleanup levels for these three compounds are the RLs.

[Next Section]