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B-20 Remedial Investigation Report for Former Open Burn/Open Detonation Area
Section 2 - Site History and Background
2.1 - Installation Description and History
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 4,004.18 acres immediately east of State Highway 3351 (Ralph Fair Road), approximately 0.5 mile east of Interstate Highway 10.
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 igloo 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 land on which CSSA is located was used for ranching and agriculture until the 1900s (Army, 1990). During 1906 and 1907, six tracts of land were purchased by the U.S. Government and designated the Leon Springs Military Reservation. The reservation was used for maneuvers by Army and National Guard units, and the lands included campgrounds and calvary shelters.
In October 1917, the installation was redesignated Camp Stanley. U.S. involvement in World War I spurred extensive construction of temporary cantonments and installation support facilities. In 1931, Camp Stanley was selected as an ammunition depot, and construction of standard magazines and igloo magazines began in 1938 (Army, 1990). Camp Stanley was transferred to the jurisdiction of the Red River Army Depot (RRAD) in 1947. In addition to ammunition storage, CSSA lands were used to test, fire, and overhaul ammunition components.
Presently, the primary mission of CSSA is receipt, storage, issue , and maintenance of ordnance materiel, as well as quality assurance testing and maintenance of military weapons and ammunition (Army, 1971). CSSA also has an agreement with the United States Department of Agriculture (USDA) Agricultural Research Service which permits cattle grazing on CSSA lands. Military personnel or other parties are allowed to hunt wildlife on a restricted basis in the outer cantonment area. Although RRAD is proposed for realignment, no changes to the CSSA mission and military activities are expected in the future.
The B-20 unit is a 33.5-acre field (acreage determined during investigation surveys) surrounded by wooded areas in the northeastern portion of CSSA (Figure 2.2). The area is vegetated with grasses and cedar shrubs. Gravel roads form the south,west, and north boundaries of the site. Site boundaries and other features are shown in Figure 2.3.
B-20 site features include an inactive bunker west of the western gravel road, a standpipe used once for static firing of a rocket motor and a junction box in the central portion of the site (Figure 2.3). Broken aboveground conduit is currently visible in the central-southeast area of the site. Fifteen craters (1 through 15) have been identified in the northern and central portions of the site. Five mounds in the eastern portion of the site are soil from the B-20 site that was piled for ready use in covering explosives prior to detonation (verbal communication, CSSA employee Mr. Howard Sampson, supervisor of B-20 activities from 1982 to 1987).
Inert scrap metal is scattered across the entire site. CSSA demolition experts have indicated that inert metal fragments are common for the type of shallow pit demolition procedures followed at B-20. Metal fragments are also found outside the boundary of the site.
Due to its proximity to the B-20 site (Figure 2.3), B-21 was incorporated into the B-20 investigation. The B-21 site was a disposal area for small arms ammunition, containing shells, shot, and sand originating from building 90 and the rifle range (ES, 1993b). The B-21 area measures approximately 50 feet by 15 feet. Two similar small arms ammunition disposal areas were observed within the B-20 site. These areas measure approximately 60 feet by 10 feet and 20 feet by 8 feet. It is not known when this ammunition was disposed at the B-20 and B-21 sites. The three small arms ammunition disposal areas are shown in Figure 2.3. A photograph of the B-21 site is included in Appendix B, photo number 6.
According to a 1950 memorandum on file at CSSA, CSSA started using the B-20 area for demolition activities on March 4, 1946 (CSSA, 1950). According to this memorandum, approximately 200 tons per year of ammunition were destroyed at the site from 1946 to 1950. No other records regarding early use of the B-20 site are known to exist.
Interviews with CSSA personnel indicated that no one at CSSA in the 1950s or 1960s still works there. The B-20 operations included detonation of conventional explosive ordnance and other ordnance items, static firing of one rocket motor nose down using the existing standpipe, disposal of scrap metal from detonation activities, and disposal of small arms ammunition.
Explosive weights detonated each year since November 1980 were obtained by CSSA explosive experts from existing records and calculations. No records or personnel interviews indicate the amount or type of explosives destroyed at B-20 prior to 1980. From November 1980 through 1983, and in 1985, no explosives were detonated. In 1984, 24,022 pounds of explosives were detonated, with a maximum single weight of 185 pounds. In 1986 and 1987, 9,867 and 4,320 pounds of explosives, respectively, were destroyed. During each of those years, the maximum weight per explosive device was less than 150 pounds.
CSSA standard operating procedures (SOPs) for explosive demolition were established by explosive experts working at CSSA. To provide the SOP summary, Parsons ES interviewed Mr. Howard J. Sampson on January 26, 1994, and reviewed the B-20 SOPs of March 28, 1986. Mr. Sampson was supervisor of B-20 demolition operations from 1982 to 1987. Procedures for demolition prior to 1980 are not documented.
The detonation procedures were broken into five SOPs:
Receiving and unloading;
Charging demolition pits or pads;
Destruction by detonation;
Site inspection and destruction of duds; and
Locating lost or broken detonating cord, lead lines, or demolition shots.
These operations are described in detail in the SOPs, which are appended to the B-20 partial facility closure plan (ES, 1994a). All demolition activities at CSSA in the 1980s took place at the B-20 site.
There are two general groups of craters at which demolition activities took place. Craters 1 through 9 have been identified by Mr. Sampson as pits that were used in the 1980s. Craters 10 through 15, which are located near the north boundary of the site, were used prior to Mr. Sampson's employment at CSSA. Each crater has a diameter of approximately 30 feet, with the exception of craters 14 and 15 which are 20 feet wide by 60 feet long. Craters 10 through 15 are generally shallower and more difficult to identify than the more recent craters. Figure 2.4 shows aerial photographs taken at the site in 1966, 1985, and 1990. The area in which craters 10 through 15 are located appears disturbed in the 1966 aerial photograph, but vegetation is returning to the area in the 1986 photo. This suggests that this area was used prior to 1966.
According to Mr. Sampson, up to seven of the nine pits (craters 1 through 9) were used for each demolition job in the 1980s. For each job, the pits were carefully excavated with a backhoe. Approximately 1,100 pounds of explosives, at roughly 150 pounds per explosive device, were unloaded in up to seven pits. Material to be destroyed was placed in each pit with detonating cord or timers, then covered with 6 to 8 feet of soil kept at the site for this purpose. The explosives were usually laid nose to fin to ensure that contact was kept between them. Each pit filled with ordnance materiels and soil was referred to as a "shot." Each shot was individually detonated after all personnel left the site. After an approximate waiting period, the pits were checked for duds. If present, the duds were destroyed in a similar manner.
The type and size ranges of explosives known to have been destroyed at B-20 are listed in Table 2.1. CSSA compiled this list from their explosive experts because CSSA records do not indicate items disposed. Included are small arms ammunition, cannon and mortar ammunition, grenades, rockets from 2.75 to 5 inches, mines, and simulators. Detonation material includes charges of trinitrotoluene (TNT), tetryl, plastic composition compounds, pentaerythrite tetranitrate (PETN) detonating cord, blasting caps, fuzes, and firing devices. According to Mr. Sampson, most of the destroyed material, including ammunition and grenades, dated from the Korean War era.
Compounds of concern at the B-20 site, including explosives noted in CSSA records, are listed in Table 2.2. The list of explosives was compiled by CSSA demolition experts. This table indicates all potential contaminants known or throught to be disposed of in the B-20 area. The list includes composition explosives, TNT and its derivatives, cyclonite (RDX) and its biodegradation components, which phosphorous, lead azide, lead styphnate, and nitroglycerin.
Explosives used in ordnance are divided into two classes, distinguished according to their sensitivity (U.S. Military Academy, 1966). Primary high explosives are extremely sensitive to shock, friction, or heat, and detonate when ignited. Secondary high explosives are relatively insensitive to shock and usually burn, rather than detonate, when ignited in small quantities. Very small quantities of primary high explosives are used to initiate detonation in secondary high explosives. Primary high explosives include lead azide, lead styphnate, and nitroglycerin. All of the other explosive compounds listed in Table 2.2 are secondary high explosives.
CSSA is located in south-central Texas on the Balcones Escarpment. Northwest of the installation, the terrain slopes upward to the Edwards Plateau; to the southwest, the terrain slopes downward to the Gulf Coastal Plains. This results in a modified subtropical climate, predominantly marine during the summer months and continental during the winter months. Summers are hot with daily temperatures above 90ºF over 80 percent of the time, and winters are mild with below freezing temperatures occurring on an average of only about 20 days per year. Temperature extremes have ranged from 0ºF to 108ºF.
CSSA is situated between a semi-arid region to the west and the coastal area of heavy precipitation to the southeast. Average annual rainfall is approximately 29 inches. Precipitation is fairly well distributed throughout the year, with the heaviest amounts occurring in May and September. Approximately 61 percent of the rainfall occurs over the period from April through September and is primarily due to thunderstorms. During this period, large amounts of precipitation may fall in a short period of time. Most of the winter precipitation occurs as light rain or drizzle; however, thunderstorms accompanied by a heavy rain have occurred in all months of the year.
CSSA is characterized by a rolling terrain of hills and valleys in which nearly flat-lying limestone formations have been eroded and dissected by streams draining primarily to the east and southeast. Physiography of the B-20 site is influenced by native topography, the underlying geology, and artificial terrain modifications caused by explosive demolition and earth-moving activities. Fifteen craters resulting from demolition activities at the B-20 site range in depth from approximately 1 to 6 feet below grade.
Resistive limestone beds outcrop as topographic highs, but none of these beds form buttes or mesas. Rather, the predominant physiographic features are hills and "saddles" which lead to stream valleys. Topographic relief across CSSA ranges from about 1,100 feet to 1,500 feet above mean sea level (MSL). Elevations at the B-20 unit range from 1,360 feet above MSL on the west, to about 1,300 feet above MSL on the east.
Sinkholes are present at CSSA, primarily in areas where porous and fractured limestone formations are exposed. However, no sinkholes were observed or encountered during drilling activities at the B-20 site.
2.3.3 Drainage and Surface Water
River and stream dissection of limestone is the major surface feature at CSSA and the B-20 site. Most major rivers and streams originating in the Edwards Plateau to the northwest of CSSA tend to follow northwest-southeast regional fracture patterns. Drainage from CSSA generally flows in a southerly direction into Salado Creek and Leon Creek, with a small portion in the northeast draining into Cibolo Creek. Approximately 75 percent of CSSA is in the Salado Creek watershed, 15 percent in the Cibolo Creek watershed, and 10 percent in the Leon Creek watershed. All of these streams are intermittent at CSSA. The B-20 site is located within the Cibolo Creek watershed, approximately 1.5 miles south of Cibolo Creek.
Drainage at the B-20 site is generally to the northeast in two runoff channels (Figure 2.3) within the Cibolo Creek watershed. The larger channel begins just north of the gravel road at the southern site border, drains into a small pond, and continues northeast to the livestock pond. The surface area of the pond is less than one acre. An earthen dam exceeding 6 feet in height causes the collection of surface water in the livestock pond. The smaller channel runs northeast along the eastern site boundary until it branches into the larger channel. Both channels are ephemeral, and the ponds are dry during periods of little to no precipitation. Due to higher elevations north, west, and south of the site, these two channels receive all site runoff.
During period of intense precipitation, some of the craters on site also contain water. Crater 8 contained water throughout the field investigation at B-20. Craters 1, 12, and 13 contained water in November 1994; but during B-20 sampling activities in early December 1994, these craters were dry. In late December 1994, craters 12 and 13 once again contained water. during the field effort, the depth of water in these craters did not exceed two feet. Observations made during the field investigation are further described in Section 5.4.4.
Generally, soil types at CSSA are dark-colored, gravelly clays and loams. According to the USDA Soil Conservation Service (SCS) soil survey for Bexar County, Texas, soil types at the installation include Brackett-Tarrant association, Brackett soils, Crawford and Bexar stony soils, Krum Complex (Kr), Lewisville silty clay, Tarrant association, and Trinity and Frio soils (USDA, 1966). Figure 2.5 shows the soil types occurring at CSSA.
The soil horizon at the B-20 site is typically thin, ranging from 0.5 to 6 feet in thickness across the site. Only the Brackett-Tarrant association, Crawford and Bexar stony soils, and Krum Complex occur at B-20. These three soil types are described in detail below.
2.3.4.1 Brackett-Tarrant Association
Brackett-Tarrant association soils occur on hills in the west-central and northern portions of the B-20 site. Typically, Tarrant soils are on the tops and the upper sides of ridges, just above Brackett soils. Both soil types are underlain by Glen Rose limestone. Tarrant soils consist of a clayey, very dark grayish-brown, calcareous surface layer which is up to approximately 10 inches thick. Various amounts of limestone gravel occur within the profile. Brackett soils consist of grayish-brown, gravelly clay loam. Brackett soils are lighter colored, less clayey, and less stony than Tarrant soils. Brackett soils are also strongly calcareous.
2.3.4.2 Crawford and Bexar Stony Soils
Crawford and Bexar stony soils occur in the north-central and southeastern portions of the B-20 site on broad, level to gently undulating areas. Both Crawford and Bexar soils are moderately deep. The Crawford type soils have a dark grayish-brown to dark reddish-brown surface layer that is generally 12 to 16 inches thick. The subsurface layer is a blocky, reddish-brown, noncalcareous stony clay that developed over broken limestone. The pH of typical Crawford soils ranges from 7.5 to 8.0 (USDA, 1966). The Bexar soils are dark reddish-brown, cherty clay loams or gravelly loams. The slope range for Bexar soils is 0 to 8 percent. Bexar soils are redder, less clayey, and more cherty than Crawford soils. The pH of typical Bexar soils range from 6.0 to 6.5 (USDA, 1966).
The Krum complex soils are located in infrequently flooded streambeds such as those in the eastern and northeastern areas of B-20. Typically, these soils occupy foot slopes between Tarrant and Brackett soils. These soils receive runoff and additional sediments from higher lying soils. Krum complex soil is dark grayish-brown, calcareous, and ranges from silty clay loam to gravelly clay. The pH of typical Krum clay is 8.0 (USDA, 1966).
The oldest and deepest rocks known in the area are Paleozoic-age (225 to 570 million years ago) schists of the Ouachita structural belt. Overlying the Paleozoic strata are Cretaceous sediments which were deposited as onlapping sequences on a submerged marine plain. Table 2.3 summarizes the stratigraphy about the Cretaceous system.
The Trinity Group Travis Peak Formation is the deepest Cretaceous-age formation. The Travis Peak Formation attains a maximum thickness of about 940 feet and is divided into five members, in ascending order: the Hosston Sand, the Sligo Limestone, the Hammett Shale, the Cow Creek Limestone, and the Hensell Sand (locally known as the Bexar Shale).
Overlying the Trinity Group is the Glen Rose Formation. The Glen Rose Formation is exposed at the surface at most of CSSA and the B-20 site (TWDB, 1983). Figure 2.6 shows the outcrop locations of the Glen Rose members at CSSA and the surrounding area. The Glen Rose Formation represents a thick sequence of shallow marine shelf deposits that have been arbitrarily divided into an upper and lower member (see below). This formation is sometimes considered to be a confining unit below the Edwards aquifer (USGS, 1985). The B-20 site and surrounding area are situated on the upper member of the formation (TWDB, 1983). Erosion of the alternating resistant and nonresistant beds causes the "stairstep" topography of the region.
The upper Glen Rose consists of beds of blue shale, limestone and marly limestone with occasional gypsum beds (Hammond, 1984). Based on well log information, the thickness of the upper member reaches 500 feet in Bexar County. The thickness of this member at CSSA has not been determined, but is estimated from well logs to be between 20 and 150 feet.
A widespread fossil stratigraphic marker known as the Corbula bed (a bed of small clamshells 3 to 5 millimeters in diameter) is the dividing boundary between the upper and lower members of the Glen Rose Formation (Whitney, 1952). Furthermore, a gypsum bed has been identified close to the Corbula bed. During this investigation at the B-20 site, the Corbula bed contact between the upper and lower members of the Glen Rose Formation and the gypsum bed were not encountered (see Section 5.4.2 for other observations made during the field investigation). The lower Glen Rose, underlying the upper Glen Rose, consists of a massive fossiliferous limestone, grading upward into thin beds of limestone, marl, and shale (TWDB, 1983). The lower member, according to area well logs, is approximately 300 feet thick in the CSSA area.
Predominant structural features in the area are two sets of regional vertical fractures, the regional dip, and the Balcones fault zone (escarpment). The regional fractures are a result of faulting in the Cretaceous sediments and in the deeper Paleozoic rocks (USGS, 1992). The two sets of fracture patterns trend northwest-southeast and northeast-southwest across the region. The regional dip of the formations is to the east and southeast at a rate of about 100 feet per mile near the fault zone in Bexar and Comal Counties, but decreases to 10 to 15 feet per mile northwest of CSSA (TWDB, 1983).
The Balcones fault zone is a series of high-angle normal faults that generally trend northeast and southwest. The faulting is a result of structural weakness in the underlying Paleozoic rocks and subsidence in the Gulf of Mexico basin to the southeast. The downdrop blocks outcrop as younger strata from northwest to southeast across the fault zone. Total displacement in northwest Bexar County is approximately 1,200 feet. Numerous minor northwest-southeast-trending faults are associated with the major faulting along the Balcones fault zone. The minor faults are laterally discontinuous and have small displacement.
The B-20 site is located about 6 miles north and west of the Balcones fault zone (ES, 1993a). No faults or sinkholes were observed at the B-20 site during the field investigation. Some vertical and horizontal fractures were observed at depths less than 12 to 13 feet in several borings drilled during this investigation.
There are three aquifers in the Cretaceous-aged rock strata underneath CSSA: the upper, middle, and lower Trinity aquifers (ES, 1993a). Most production and monitoring wells at CSSA are completed in the middle Trinity aquifer. This aquifer is promoted by solution-enhanced permeable fractures and is the primary source of potable water at CSSA. The middle Trinity aquifer encompasses the lower member of the Glen Rose Formation and the upper part of the underlying Travis Peak Formation. The water level of the middle Trinity appears to be seasonally variable. Depths of water in CSSA well I, located about 500 feet northeast of the B-20 site and completed in the middle Trinity aquifer, ranged from approximately 219 feet BGL in May 1994 to 277 feet BGL in December 1994. This aquifer is described in detail in the "Hydrogeologic Report for Evaluation of Groundwater Contamination at Camp Stanley Storage Activity, Texas" (ES, 1993a).
The upper Trinity aquifer is located within the upper member of the Glen Rose Formation. The upper Glen Rose is exposed over much of the B-20 site. Recharge to the upper Trinity aquifer is from direct precipitation on the outcrop of the upper member of the Glen Rose Formation and stream flow losses. Movement of groundwater in the upper Trinity aquifer is restricted to lateral flow along bedding planes between marl and limestone, where dissolution has enhanced the permeability of the limestone. During drilling at the B-20 site, groundwater was encountered in one of the soil borings (SB1) within a zone of interbedded marl and limestone (see Section 5.4.3). The occurrence of groundwater in this aquifer is sporadic and dependent on precipitation and secondary porosity features, indicating that beds within this aquifer are perhaps not hydraulically connected by avenues of vertical permeability. The upper Trinity aquifer is under water table conditions, it is generally of poor quality, and most wells achieve only low production (TWDB, 1983).
2.4 - Summary of Prior Investigation Results
In February 1994, prior to the remedial investigation, an investigation was conducted at the B-20 site to obtain preliminary data on site features and possible contaminants for use in determining remedial investigation needs. CSSA and RRAD, with the agreement of EPA Region VI RCRA Enforcement, Texas Section, prepared a "Phase I sampling plan" and conducted the preliminary investigation in accordance with this plan.
The first objective of the preliminary investigation was to map B-20 site features, including boundaries, crater locations, and surface water features. The map prepared during the preliminary investigation was used to determine sampling locations for the remedial investigation. No UXO was identified during the preliminary mapping.
Secondly, samples were collected from areas of possible contamination to determine appropriate analytical parameters for the remedial investigation. Samples were collected from within four craters, near one soil mound, from the small pond, and from the livestock pond. A total of four surface soil samples, three surface water samples, three sediment samples, four background soil samples, and associated qulaity assurance/quality control (QA/QC) samples were collected. Samples were analyzed for explosives (EPA SW-846 method 8330), volatile organic compounds (SW-8240), base/neutral/acid extractable semivolatile organic compounds (SW-8270), pH (water only), and total metals (SW-6010).
No explosives were detected in preliminary surface soil, surface water, or sediment samples. Arsenic in three surface soil samples exceeded its medium-specific concentration (MSC) for soil at industrial sites (30 TAC 335, Subchapter S, Appendix I). Barium, cadmium, and lead in one surface water sample exceeded freshwater concentration criteria (30 TAC 307). Summary data tables are included in Appendix C. A detailed discussion of the preliminary investigation and results was presented in the B-20 closure plan (ES, 1994a).