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 SWMU B-31 and to recommend further investigation, if necessary, or to provide documentation necessary for site closure. The main objectives of the SWMU B-31 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 AMC Contract F11623-94-D-0024, delivery orders RL17 and RL33. AFCEE provided technical oversight for the delivery order. Based upon the project SOWs, 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 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   SWMU B-31

1.1.2.1   Site Description

SMWU B-31 is an area where, at an unknown date, a PVC sanitary pipeline was installed and backfilled with sand believed to contain spent ammunition. The spent shot is thought to have been generated in the Building 90 test firing room. SWMU B-31 is defined as the sanitary sewer pipe bedding material. The pipe consists of 8-inch PVC, and is an active sanitary sewer pipeline. 

Background information regarding the location, size, and known historical use of SWMU B-31 is also included in the Environmental Encyclopedia (Volume 1-2, SWMU B-31). Volume 1-2 also includes a Chronology of Actions and a Site-Specific Work Plan for SWMU B-31.

1.1.2.2   Potential Sources of Contamination

SWMU B-31 is a site where sand suspected of containing spent ammunition was reportedly backfilled around an underground pipeline. The potential constituents of concern (COCs) are metals and explosives. The ammunition typically contains high levels of lead.

1.1.2.3   Site Location

SWMU B-31 is a 0.05 acre tract of land located in the Inner Cantonment of CSSA (Figure B31-1). The nearest CSSA boundary is approximately 250 feet to the west. SWMU B-31 is an approximate 560 feet long and 40 feet wide rectangle area, oriented north-northwest. The below-grade PVC sewer line is situated along the center of the long axis associated with the site area. The sand backfill extends approximately three feet below ground surface, and is approximately two feet wide. A facility road crosses the northern portion of SWMU B-31. An embankment parallels the west side, and a tree line trends parallel to the east side. Building 92 is located adjacent to SWMU B-31.

Several SWMUs and AOCs are located in the proximity of SWMU B-31. AOC 45 is less than 100 feet east of SWMU B-31, AOC 57 is approximately 285 feet north, AOC 65 is 540 feet northwest, AOCs 67 and 68 are approximately 600 feet northwest, and SWMUs I-1, B-29, and B-30 are approximately 1,140 feet southeast of SWMU B-31.

1.2 - Site Environmental Setting

1.2.1   Site Soils and Topography

The native soils at SWMU B-31 are Krum Complex soils (Kr) (Figure B31-2). Urban soils compose the backfill materials associated with the sewer line. Krum Complex soils cover approximately 20 percent of the land at CSSA. These soils occur on slopes of two to five percent, occupying ‘foot’ slopes below Brackett and Tarrant soils. Generally, Krum Complex soils are subject to hydraulic erosion as they occur downslope of prairie plains and receive sediments from higher elevations. Krum Complex soils are dark grayish-brown, calcareous, and typically are approximately 30 inches thick. At SWMU B-31, the Krum soils are from 2 to 3.5 feet thick. Additional information about the Krum Complex soils and other soils that occur at CSSA can be found in the CSSA Environmental Encyclopedia (Volume 1-1, Background Information Report).

SWMU B-31 is located on a very gentle south-trending slope at an elevation between approximately 1,190 and 1,200 feet above sea level. The site surface consists of soil and sparse, grassy vegetation. There are no significant changes in topography in the immediate vicinity of SWMU B-31, with the exception of a small embankment along the western length of the site. The direction of run-off is south-southeast in the area of SWMU B-31.

1.2.2   Site Geology

The Lower Glen Rose Formation is the uppermost geologic stratum in the area of SWMU B-31 (Figure B31-3). The Lower Glen Rose is estimated to be in excess of 300 feet thick at CSSA and consists of 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 varies 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-31 is located south of the North Fault Zone, and is approximately 1,500 feet north of the South Fault Zone (Figure B31-3). Additional information on structural geology at CSSA can be found in the Environmental Encyclopedia (Background Information Report, Volume 1-1).

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. Areas containing the Upper Glen Rose Limestone are located to the north and east of SWMU B-31 (Figure B31-3). 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 within 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.

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. The majority of recharge into the Middle Trinity aquifer occurs via precipitation and surface water infiltration at outcrops. At CSSA, the Bexar Shale is interpreted as a confining layer, except in areas where it is fractured and faulted. Fractures and faults facilitate vertical flow from the up-dip Cow Creek Limestone into the overlying, but down-dip Lower Glen Rose. These 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 to the south and southeast and the average transmissivity coefficient is 1,700 gpd/ft (Ashworth, 1983). 

No site–specific information regarding groundwater is available. Recently, a cluster well, including CS-MW7-LGR and CS-MW7-CC, was installed approximately 100 feet to the west of SWMU B-31. In September 2001, the depth to groundwater in Well CS-MW7-LGR was 68.5 feet BTOC, and in Well CS-MW7-CC it was 94.6 feet BTOC. Three off-site wells are located approximately 2,500 feet from SWMU B-31: LS-1 is south, RFR-9 is northwest, and RFR-10 is southwest of SWMU B-31. Well LS-7 is approximately 2,200 feet southwest of SWMU B-31. No water bodies or streams are located in the vicinity of SWMU B-31 (Figure B31-1).

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. Several historic buildings are located near SWMU B-31, as shown on Figure B31-1. Building 91 and Building 92 are less than 200 feet west of the SWMU B-31, and Building 90 is located approximately 400 feet northwest of SWMU B-31.

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 a sensitive environmental area survey were completed for the CSSA facility on December 15 and 16, 1999. The results of this survey, along with results from a more in-depth survey designed 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).

SWMU B-31 is located in the southwest corner of CSSA (Figure B31-3). Off-base residential housing and off-base residential wells are approximately 1,500 feet south of SWMU B-31. Generally, CSSA is a controlled access facility, so access is limited by a security force and perimeter fence. As described in Section 1.2.3, a monitoring well cluster (CS-MW7-LGR and CS-MW7-CC) is located approximately 100 feet west of SWMU B-31. The closest off-site wells are located over 2,000 feet from SWMU B-31.

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 Technical Approach Document for Risk Evaluation (Volume 1-6). SWMU B-31 is located approximately 1,500 feet northwest of hunting stand number 12. Four ponds are maintained at CSSA for the purpose of sport fishing. Two of the ponds are located in the northwestern and northeastern portions of the North Pasture while the other two ponds are located near the western boundary of the Inner Cantonment. The golden-cheeked warbler, an endangered species, may potentially reside within 2,000 feet of SWMU B-31.

1.3 - Previous Investigations

No previous investigations have been performed at SWMU B-31. The site was identified during the 1993 EA.

1.4 - Closure Standard

As described in the Section 4.3 of the Risk Assessment Technical Approach Document (Volume 1-6), CSSA has opted to pursue closure of SWMU B-31 under the TNRCC Risk Reduction Rule (RRR) (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 B-31) in accordance with the former Risk Reduction Rule was submitted 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-31 are metals and explosives, the RRS1 standards should be the RLs for explosives, 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 Soil and Rock (Parsons, February 2002). TNRCC approved the background metals evaluation on April 23, 2002.