2.1 - Facility Description

CSSA is located in northwestern Bexar County, approximately 19 miles northwest of downtown San Antonio in south-central Texas (Figure 2.1). The installation consists of 4,004 acres immediately east of State Highway 3351 (Ralph Fair Road), and is approximately 0.5 mile east of Interstate Highway 10 (Figure 2.1).

CSSA is a restricted-access installation with inner cantonment lands to the southwest and outer cantonment areas to the east and north. Operation buildings and storage magazines are located within the inner cantonment. Outer cantonment land is primarily undeveloped open range. The eastern boundary of CSSA and part of its northern and southern boundaries are contiguous with the Camp Bullis Military Training Reservation. The surrounding area to the west is primarily rural and zoned for residential use. Some residential development is also present west, northwest, and southwest of the installation. The location of SWMU O-1 at CSSA is shown in Figure 2.2.

2.2 - Site Background and History

The primary mission of the installation is receipt, storage and issuance of ordnance materiel, as well as quality assurance testing and maintenance of military weapons and ammunition. Operations at CSSA require the use of both hazardous and non-hazardous materials and generate both solid and hazardous waste.

The Ordnance Maintenance Branch (OMB) is responsible for small arms refurbishing and maintenance operations including degreasing, fingerprint removal, and bluing. A process flow diagram for OMB is shown in Figure 2.3. Small arms arrive at the facility and are unpacked. Depending on the condition of the weapons, they are cleaned in dip tanks using a mineral spirit solvent or PCE. Next, the arms are reworked and routed to the bluing operation if necessary. After reworking, they are washed, test fired, and cleaned with cleaner-lubricant-protector (CLP) or WD-40. The arms are then processed through a series of dip tanks which consist of fingerpint removal operation, solvent rinse and volatile corrosion inhibitor (VCI), and finally packed for storage.

The bluing operation or nickel penetrate process is performed in building 90-1; this is an eight-step successive process for small arms metal components. In the process, small arms parts are placed in racks and dipped in and out of tanks by means of an overhead hoist. Tank overflow and drainage was collected in a floor drain which emptied to an exterior 1000-gallon storage tank. Tank-collected waste liquids/sludges were removed and deposited into SWMU O-1 when it was an active unit. Frequency of delivery to the unit varied with the level of bluing activity. Figure 2.4 shows a process flow diagram for the bluing operation. A detailed description of the bluing operation and the waste generated from this operation is included in the Environmental Assessment of CSSA (Parsons ES, 1993).

SWMU O-1, also referred to as the oxidation pond, was reportedly constructed in 1975 (CSSA, 1992). The pond was also reported with measurements of about 42 feet by 60 feet with a depth of 2.5 feet and was lined with vinyl plastic. Wastes from Building 90-1 (spillage, clean-out, etc.) were trucked to the unit from an exterior 1,000-gallon settling tank. In 1982, an estimated 24,000 gallons were contained in the oxidation pond (CSSA, 1992).

The Texas Department of Health conducted sampling efforts of the oxidation pond material (liquid and sludge) in April 1984. The samples were delivered to Brooks Air Force Base (AFB) for analysis. Results from this sampling event indicated that the material was nonhazardous for metal concentrations; however, no data were available to assess the PCE contamination.

In 1985, Red River Army Depot (RRAD) prepared a "recommended procedure" for closure of SWMU O-1 (RRAD, 1985). During the fall of 1985, the oxidation pond was bulldozed destroying the pond liner and filled with surrounding soils (CSSA, 1992). No records are available to indicate that disposal of the contained sludge or residue occurred before destruction of the liner.

2.3 - Geology and Hydrogeology

Based on the initial exploratory borings, soils in the main SWMU O-1 area consist of gravelly and silty clays with marly limestone and caliche fragments near the surface, progressing with depth to competent limestone. At CSSA, the upper Glen Rose formation is defined as the first competent limestone encountered. The upper Glen Rose primarily consists of alternating resistive and nonresistive beds of limestone and marly limestone. At SWMU O-1, the top of this limestone formation is encountered at depths to 4 to 5 feet below ground surface (bgs). Soils in the SWMU O-1 area are classified as Tarrant association, gently undulating.

The locations of the initial exploratory borings drilled at SWMU O-1 are shown in Figure 2.5. A representative cross-section of the SWMU O-1 trench, which was developed from the lithologic logs from borings drilled at the site, is presented in Figure 2.6.

A soil mechanical analysis was performed on soil samples collected from the site as part of the laboratory benchscale test. Based on the soil analysis, the soil at SWMU O-1 site can be classified as brown sandy clay with fine gravel. The parameters, which are relevant for the performance of the electrokinetic study in the soil, are the soil type and its hydraulic permeability. Soil characteristics of sandy clay with a very low hydraulic conductivity (2.35 x 10-8 cm/s), indicates that it is suitable for the application of the electrokinetic process.

2.4 - Previous Investigations

2.4.1   General Overview

Several investigations have been conducted to assess groundwater contamination detected in Well 16 located north of SWMU O-1. Most of these investigations have focused on identifying possible source areas that have contributed to the contamination of the groundwater. The results of previous studies are discussed in this section, and Section 6 (Conclusions and Remedial Alternatives ) of the "Groundwater and Associated Source Characterization Report" (Parsons ES, 1996a). A general overview is presented below.

Chlorinated hydrocarbons were first detected in Well 16 in 1991 at concentrations above drinking water standards, prompting investigations of the possible contaminant source areas. Source characterization began with surface geophysical surveys performed during January through March 1995 at seven potential source areas. A large anomalous area, shown in Figure 2.7, was detected at SWMU O-1 during the electromagnetic (EM) and ground penetrating radar (GPR) surveys.

Based on this geophysical data, four soil borings were drilled within SWMU O-1 to investigate the portions of each area exhibiting apparent geophysical anomalies. Results of analytical data gathered from the investigation indicated levels of PCE, chromium, and cadmium above background level concentrations. Locations of these borings are shown in Figure 2.5. The other six potential source areas were investigated; however, for this report only SWMU O-1 is addressed.

A subsequent soil gas survey of SWMU O-1 during the summer and fall of 1995, identified PCE concentrations as high as 80,000 parts per billion volume (ppbv). Depths of sampling were 1.0 to 3.5 feet bgs. Distribution of PCE in soil gas at the oxidation pond in 1995 is shown in Figure 2.8. During November 1995, additional surface soil sampling was accomplished near soil boring OX-SB2, at which time an observation of a piece of liner at 1.5 feet below ground level (bgl) was noted. This observation indicated that the liner was not intact since being bulldozed in 1985; however, an investigation into the state of the liner was conducted during January 1996.

The presence of chlorinated hydrocarbons implicates SWMU O-1 as a potential source area for the contamination detected in Well 16. The location of SWMU O-1 relative to Well 16 is shown in Figure 2.9 which also includes the location of the other six potential source areas.

2.4.2   Soil Sampling Results from Previous Investigations

Volatile Organic Compounds

 Because of laboratory deficiencies in methods used for quantifying volatile organic compounds (VOCs) present in samples analyzed by SW-8260A, data generated during the previous investigations are considered screening data only. This data does not meet quality standards and, thus, is not considered for determining quantity and extent of VOC contamination.

Screening data provides analyte identification and quantification, although the quantification may be relatively imprecise. Screening data Quality Assurance/Quality Control (QA/QC) elements include:

Inorganic Compounds

The analytical data generated for metals are considered valid from the previous investigations and used to determine site characteristics, as appropriate. The analytical results for metals indicate chromium, and cadmium above background level concentrations. For the purpose of comparison, Tarrant Association background levels are used for the fill soil, since it is likely that the fill was taken from the area of and around the site. Metals levels for the fill or Tarrant Association soil samples are within the normal range of background concentrations at CSSA in all samples collected during the previous investigations except cadmium and chromium. In soil boring #2 (OX-SB2 0 to 2 feet bgs) (see Figure 2.5) the detected concentrations of chromium , and cadmium (730 mg/kg [milligrams per kilogram] and 4.8 mg/kg, respectively), were significantly greater than the calculated maximum background concentration for CSSA soils. Arsenic, barium, copper, lead, mercury, nickel, and zinc were detected at concentrations less than those defined as background. The natural concentrations of metals at CSSA are greater than the levels provided in the TNRCC risk reduction rules, so it is appropriate to use the background levels to determine whether metal concentrations detected are indicative of contaminated backfill material or naturally occurring conditions of the soils at SWMU O-1.

2.4.3   1996 Liner Integrity Investigation

A liner integrity investigation was initiated in January 1996. The investigation was to attempt to dig a test pit above any intact existing liner. Upon initiating the integrity investigation it was apparent that the liner was indeed destroyed. Strips of liner material no larger than 2 feet by 4 feet were found. The investigation continued with the excavation of approximately 80 cubic yards of soil to a depth of 3.5 feet bgs in an attempt to collect data or provide evidence of any potential limestone fractures. Table 2.1 provides the results of analytical measurements conducted during the investigation. The excavated soil was placed near the excavated area, of which approximately 19 cubic yards of "hot soils" was placed into a plastic-lined bermed laydown area. Figure 2.10 shows the approximate location of the excavation area, the bermed "hot soils" laydown area, and the location of the remaining excavated soil.

During the spring and summer of 1996, the excavated soil was replaced into the excavated area and an additional soil gas sampling effort was completed within the SWMU O-1 area. The resulting PCE soil gas distribution map is shown as Figure 2.11. A photograph of the "hot soils" laydown area is shown in Appendix D.

2.4.4   1997 Initial Electrokinetic Location Investigation

The location of the field test unit for the planned electrokinetic treatability study was selected based on analytical data and field observations gathered during the spring of 1997. Three trenches, shown in Figure 2.12, were excavated during April of 1997, in an attempt to locate the "hot soils" containing the highest concentrations of cadmium, chromium, and PCE. Soil samples were gathered from each of these excavated trenches to identify "hot" spots, which would be suitable for the planned treatability study. Table 2.2 provides the results of analytical measurements conducted during the investigation. Ideally, the location of the planned field test unit would be within an identified "hot" spot and be relatively free of large caliche fragments. Based on the analytical and observation data, the location of the field test unit was chosen and is shown in Figure 2.13.

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