For this RFI 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

1.1.1   CSSA

General information regarding the history and environmental setting of CSSA are 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.

1.1.2.1   Site Description

SWMU B-22 is the location of a former artillery shell burn area. The exact dates of usage for the area are unknown. None of the aerial photographs of the site (dated 1966, 1973, 1986, and 1991) included in the EA showed evidence of disturbance at the site. SWMU B-22 covers approximately 5.2 acres. The site area contains very little topographic relief and is sparsely vegetated. Native grasses are the dominant vegetation present at the site. No surface debris/waste or signs of past burning activities were noted during field operations.

Background information regarding the location, size, and known historical use of the site is also included in the Environmental Encyclopedia (Volume 1-2, SWMU B-22). Volume 1-2 includes a Chronology of Actions and a Site-Specific Work Plan for SWMU B-22.

1.1.2.2   Potential Sources of Contamination

Potential sources of contamination at SWMU B-22 include metallic leachate from disposal of artillery shells and the explosives associated with the artillery shells. Based on observations at other CSSA SWMU locations, the burning activities may have consisted of placing the shells in trenches for burning, although remnants of trenching activities were not noted during field operations.

1.1.2.3   Site Location

SWMU B-22 is located in the western portion of the North Pasture and the northern portion of the North Pasture floodplain. The site area lies approximately 1,000 feet from the western base boundary and approximately 4,000 feet from the northern base boundary. The site area is bounded by a tree line to the west, a dry creek bed to the north, and an ephemeral stream to the east, causing the site area to take on an irregular shape (Figure B22-1).

1.2 - Site Environmental Setting

Two soil types, Krum Complex soils and Trinity & Frio soils (frequently flooded), are present within the site area. The Krum Complex soils constitute approximately one third of the SWMU area, dominating the western portion of the SWMU. The Trinity & Frio soils occupy the central and eastern portions of the SWMU area (Figure B22-2). Soils composing the SWMU area are typically calcareous clay, extending to approximately 0.5-2.0 feet below ground surface (bgs). Detailed descriptions of the various soil types present at CSSA are located in the CSSA Environmental Encyclopedia (Volume 2, Description of Soil Types and Bedrock). Although no descriptions of subsurface conditions have been gathered at this site, it is reasonable to assume that bedrock occurs within five feet of the land surface based on investigations conducted in neighboring areas.

The site contains very little topographic relief and lies approximately 1,260 feet to 1,280 feet above sea level (Figure B22-2). The land surface within the site area dips gently (less than 2.5) to the east-southeast. The broad floodplain area in which SWMU B-22 is situated has been maintained as an open field.

The bedrock underlying the site consists of Upper Glen Rose Limestone material. The Upper Glen Rose is the uppermost geologic strata in the area of SWMU B-22 and the north pasture (Figure B22-3). 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. The thickness of the Upper Glen Rose is estimated to be up to 150 feet at CSSA. 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 (regionally known as the Hensell Shale), 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.

There are two major fault (shatter) zones at CSSA: the North Fault Zone and the South Fault Zone. SWMU B-22 is located north of both the North and South Fault Zones. 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. Transmissivity values are not available for the Upper Glen Rose. 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 within different beds. Principal development of solution channels is limited to evaporate layers in the Upper Glen Rose Limestone. Groundwater discharge occurs predominantly via natural springs, seeps, and pumping.

The Upper Trinity aquifer is found in the Upper Glen Rose Limestone and is underlain by the Middle Trinity aquifer. 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 at 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.

No site-specific information regarding groundwater is available. Two off-site water supply wells (FO-7 and FO-8) and one inactive agricultural well (CS-G) are located within a 1,700 foot radius of SWMU B-22, as shown in Figure B22-1. The inactive agricultural well is owned and operated by CSSA. The groundwater in CS-G is produced from a depth of approximately 300 feet below grade, which is associated with the Lower Glen Rose of the Middle Trinity aquifer system. The two water supply wells are owned and operated by the Fair Oaks Water System. The groundwater in the two water supply wells is produced from a depth of approximately 525 feet below grade, which is associated with the middle Glen Rose and Cow Creek Members of the Lower Trinity aquifer system. Water from Wells FO-7 and FO-8 is used for domestic purposes.

The nearest surface water features include a dry creek bed that bounds the north of the site area and an ephemeral stream that bounds the eastern edge of the site area. The surface water features merge at the northeastern edge of the site and drain southward to Salado Creek in the South Pasture (Figure B22-2).

All of the structures on the installation are considered historical 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. The nearest cultural resource, a burned rock midden, is located approximately 800 feet east of the site area.

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 are presented in Section 3 of the Technical Approach Document for Risk Evaluation (Volume 1-6).

Land within 0.25 mile of SWMU B-22 is classified as evergreen forest land in Figure 1.1 of the Technical Approach Document for Risk Evaluation. There are no buildings within 0.25 mile of the site, but a pond known as the Drop Zone tank is located approximately 600 feet north of the site area (Figure B22-1).

As described in Section 1.2.3, two active off-base water supply wells are located slightly over 0.25 mile of the site.

A small herd of cattle is maintained on CSSA by the USDA-ARC. 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). SWMU B-22 is located approximately 750 feet north of hunting stand number 22.

The nearest potential habitat for local endangered species is a potential Black-Capped Vireo habitat located approximately 1,000 feet southeast of the site. A potential Golden-Cheeked Warbler habitat is located approximately 2,200 feet east of the site area (Parsons ES, 1993).

1.3 - Previous Investigations

In February and March 1995, an EM survey was performed using a Geonics EM-31 instrument along east-west transects spaced at 50-foot intervals. The dimensions of the surveyed area were 600 feet long (north-south) by 600 feet wide (east-west). The EM conductivity and in-phase contour maps are shown on Figure 7.2 and Figure 7.3 of the Technical Memorandum on Geophysical Surveys (Parsons ES, 1995c). No anomalies were detected at B-22 during the survey and, thus, there is no indication of any subsurface disturbance. Slightly higher conductivity values (up to 58 ms/m) observed in the western portion of the site reflect presumed thicker soil cover in the higher elevation area of the site.

1.4 - Closure Standard

As described in Section 4.3 of the Risk Assessment Technical Approach Document (Volume 1-6), CSSA has opted to close most of its sites 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 standards, then the site will be closed under TRRP. A notification of intent to close sites identified to date (including SWMU B-22) 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.

Since the COCs for SWMU B-22 are VOCs, explosives, and metals, the cleanup levels should be the RLs. Chlorinated VOCs are man-made chemicals, and rarely occur naturally. CSSA background metals levels were statistically calculated for each soil type and the Glen Rose Limestone, and are reported in the Second Revision to the Evaluation of Background Metals Concentrations in Soil Types (Parsons, February 2002).