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SWMU B-33 RFI 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 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-33 and to recommend further investigation, if necessary, or to provide documentation necessary for site closure. The main objectives of the SWMU B-33 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 U.S. Air Force AMC Contract F11623-94-D-0024, Delivery Orders RL17 and RL33. AFCEE provided technical oversight for the delivery orders. Based upon the SWMU B-33 pre-defined SOW, a set of work plans were established to govern the fieldwork. These include:
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Work Plan Overview |
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Site-Specific Work Plans |
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Addendum; |
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Amendment for Data Quality Rework; |
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Field Sampling Plan |
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Waste Analysis Plan |
(Volume 1-4, RL33 Addendum); and |
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Health and Safety Plan |
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 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.
1.1.2.1 Site Description
SWMU B-33 consists of bedding material for an approximately 325-foot section of water supply pipe that leads from a cutoff valve north to Building 45. The water supply pipe taps into a larger 6-inch water main which trends east-west through an empty field. Sand containing projectiles from the Building 90 test range were reportedly used as bedding material for the water supply line at SWMU B-33. Sand and spent projectiles were uncovered in areas along the pipe, especially toward the south end of the pipe bedding. Sand and spent ammunition jackets were also present at the surface where the water supply line entered Building 45.
Background information regarding the location, size, and known historical use of SWMU B-33 is also included in the Environmental Encyclopedia (Volume 1-2, SWMU B-33). Volume 1-3 also includes a Chronology of Actions and several Site-Specific Work Plan Addenda for SWMU B-33.
1.1.2.2 Potential Sources of Contamination
Spent projectiles within bedding sands are the primary source of contamination at SWMU B-33. However, ammunition formerly stored at Building 45 may also have had the potential to contaminate the site. Therefore, both metals and explosives are considered potential sources of contamination at the site.
1.1.2.3 Site Location
SWMU B-33 is a 0.5-acre tract that is located in the south-central portion of CSSA, in the central portion of the inner cantonment area (Volume 1-2, Site Location Map). The general shape of the pipe trench containing the bedding material is approximately 325 feet long (north-south) by 2 feet wide (east-west) by 3 feet deep. SWMU B-33 is approximately 3,600 feet from the nearest facility boundary to the west and is located on the south corner of Building 45. The physical boundaries of SWMU B‑33 are identified by railroad tracks and Building 45 to the north, a road to the east, and fields of native grasses to the west and south. A small equipment storage shed is located directly above the central portion of SWMU B-33 (Figure B33-1).
Building 45, located north of SWMU B-33 is used to load and unload ammunition to and from transport vehicles. The ammunition is temporarily stored in Building 45 and then transported to the earthen-covered storage magazines for storage and eventual shipment off-post.
1.2 - Site Environmental Setting
1.2.1 Site Soils and Topography
SWMU B-33 lies near the western edge of the Salado Creek valley (Figure B33‑2). The elevation of the site is approximately 1,210 to 1,220 feet above sea level. Surface water runoff from the area south of the railroad tracks drains to the southeast toward Salado Creek. North of the railroad tracks, the site drains into the drainage channel, which parallels the tracks. A large open field covered in native grasses is south of the equipment storage shed. At the storage shed the site is covered in gravel. From the railroad tracks to Building 45, SWMU B-33 is covered with native grasses. No stressed vegetation has been observed at the site.
SWMU B-33 is covered predominantly with Krum Complex soils, with Brackett soils on the northern portion of the site. Brackett soils occur on hills with 12 to 30 percent slopes and consist primarily of loamy and clayey, grayish-brown soils that are strongly calcareous. Lying within and on the very shallow surface layer (about 4 inches thick) are gravel and cobblestones. Brackett soils are considered to have good to fair drainage with a permeability of 1.0 to 1.2 inches per hour. At SWMU B-33, Brackett soils make up approximately 25% of the surface, with Krum Complex soils covering the remainder. Krum Complex soils are found on slopes between 2 and 5 percent and occupy “foot” slopes below Tarrant and Brackett soils. The surface soil is dark to very dark grayish-brown, calcareous and approximately 30 inches thick. Krum Complex soils are considered to have good to fair drainage and a permeability of 0.8 to 1.0 inches per hour. Three soil borings drilled in May 1997 confirm that bedrock at the site occurs at approximately between 3 and 4.5 feet below ground surface. Detailed descriptions of the CSSA soil types are provided in the CSSA Environmental Encyclopedia (Volume 1-1, Background Information Report, Soils and Geology).
The Lower Glen Rose Formation is the uppermost geologic stratum in the area of SWMU B-33 (Figure B33-3) and 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 Formation 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 (Figure B33-3). SWMU B-33 is located between the North and South Fault Zones, more than 3,000 feet from the each of the zones. 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 confirm that bedrock at the site occurs between approximately 3 and 4.5 feet below ground surface.
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 well levels are discordant in adjacent wells completed in different beds. Principle development of solution channels is limited to evaporite layers in the Upper Glen Rose Limestone. In general, groundwater at CSSA flows in a north to south direction. However, local flow gradient may vary depending on rainfall, recharge and possibly well 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, 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. 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).
Fracture systems associated with the fault zones are thought to affect groundwater flow and to be the controlling structural feature for migration of contaminants in the vadose zone at CSSA (Volume 1-1, Background Information Report, Soils and Geology). However, SWMU B-33 is located more than 3,000 feet from the fault zones identified at CSSA; therefore potential contaminant migration beneath the site should not be affected by fracture systems (Figure B33-3).
No site-specific information regarding groundwater is available. However, the nearest wells (CS-MW4 and CS-MW19), which are monitoring wells completed in the Lower Glen Rose, are located approximately 1,800 feet northeast and 1,500 west of SWMU B-33 respectively. Water levels for CS-MW4 have been recorded at a high of 36.47 feet bgs in September 2001 and a low of 156.10 feet bgs in June 2002. Historic water levels for CS-MW19 are not available because the well was installed in August 2002.
The nearest surface water body is Salado Creek. SWMU B-33 is located on the western edge of the Salado Creek valley (Figure B33-1). The Salado Creek flows southeast from SWMU B-33 and exits the CSSA boundary approximately 1.5 miles downstream. SWMU B-33 is traversed by a west to east trending creek (Figure B33-2). This creek is ephemeral, experiencing flow only in association with precipitation events.
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. All of the structures at CSSA are considered historical resources. The historic structure nearest SWMU B-33 is Building 45, located directly north and northeast of the site. The nearest cultural resources are World War I training trenches located approximately 1,000 feet southeast of the site.
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 on 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).
SWMU B-33 is located adjacent to Building 45. The next nearest occupied building is approximately 1,400 feet west of the site and the nearest groundwater supply well (CS-10) is approximately 2,800 feet west of SWMU B-33.
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, which overlook mechanical feeders and planted food plots is located in Figure 5.2 of the Technical Approach Document for Risk Evaluation (Volume 1-6). SWMU B-33 is located approximately 1,050 feet north of hunting stand number 13. Four water reservoirs are maintained at CSSA for the purpose of sport fishing. Two of the reservoirs are located in the northwestern and northeastern portions of the North Pasture, while the other two reservoirs are located near the western boundary of the Inner Cantonment. SWMU B-33 is not in the water shed of any reservoir located on CSSA.
No previous investigations have been carried out at SWMU B-33.
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-33 under the Risk Reduction Rule (30 TAC §350). 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-33) in accordance with 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.
The COCs for SWMU B-33 are metals and explosives. Since elevated levels of these COCs would indicate potential contamination at the site, the cleanup levels should be the RLs for explosives and the soil or rock background values for metals. Background metals levels were statistically calculated for soil 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). TNRCC approved the background metals evaluation on April 23, 2002.