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SWMU B-11 RCRA Facility Investigation 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 RFI report has been prepared to document the environmental condition and site closure requirements of SWMU B-11 and to recommend further investigation, if necessary, or to provide documentation necessary for site closure. The primary objectives of the SWMU B-11 investigation are to determine if the site meets TNRCC requirements for closure, as described in Section 1.4, and to meet the requirements of the Consent Order.
This specific RFI was performed by Parsons under the U.S. Air Force AMC Contract F11623-94-D0024, Delivery Order RL53. AFCEE provided technical oversight for the delivery order. Based upon the project SOW, a set of work plans to govern the fieldwork was established. These include:
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Work Plan Overview |
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Site-Specific Work Plan |
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Field Sampling Plan |
(Volume 1-4, RL53 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 the closure evaluation. 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.
The site covers an area of approximately 0.92 acres and was reportedly used as a solid waste disposal area for an unknown period of time during which ammunition, scrap metal, and construction debris were discarded there. Ammunition boxes, arms packing crates, and construction debris were found during the initial field survey in 1993. Other types of waste visible at the western end of the site include cedar stumps, concrete rubble, wooden posts, tires, asphalt, and metal debris. No UXO has been observed at the site.
As shown in Figure B11-1, the site is situated directly on the bank of Salado Creek. Figure B11-1 is based on the aerial photograph from 1998. The terrain at the site is very rough, due to erosion and trenching activities. Waste material consisting of concrete rubble, wooden posts, tires, asphalt, and metal debris is exposed within the bank.
Immediately south of the bank is a partially filled trench which trends northwest-southeast. The approximately 325 foot long trench is up to 15 feet deep on the west end and grades upwards to the east. The trench is 25 feet wide at the southeastern end and increases in width to 100 feet wide at the northwestern end of the trench. To the west of the trench is a small mound of soil, presumably the material excavated to create the trench. Waste is partially buried on the east end of the trench, where the ground surface is very hummocky.
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-11). Volume 1-2 includes a Chronology of Actions and a Site-Specific Work Plan Addendum for SWMU B-11.
1.1.2.2 Potential Sources of Contamination
Possible sources of contamination are metal debris, explosive residue from UXO, and solvents and fuels which may have been used to burn trash. Contaminated media could include surface and subsurface soils, and possibly shallow groundwater, if present. Surface water in the intermittently flowing Salado Creek, north of SWMU B-11, could be affected.
SWMU B-11 is located in the north-central portion of the Inner Cantonment Area directly south of AOC 38 (Figure B11-1). It is situated less than 50 feet west of Moyer Road. Numerous other AOCs and SWMUs are located to the east of SWMU B-11.
The site is situated about 1400 feet from the northern boundary of the Inner Cantonment Area and approximately 425 feet northeast of monitoring well CS-MW1 (Volume 1-2, Site Location Map). The nearest CSSA boundary is over 0.5 mile to the west.
1.2 - Site Environmental Setting
1.2.1 Site Soils and Topography
The only soil type occurring at SWMU B-11 is the Trinity and Frio soil type as shown in Figure B11-2. Trinity and Frio soils occur in creekbeds which are frequently flooded. As shown in the logs for soil borings drilled at the site in March 2000 (see Appendix B), soils were encountered to a depth of up to five feet. Soils consisted of a top 1 to 2 foot layer of silt, underlain by 3 to 4 feet of clay. Detailed descriptions of the CSSA soil types are provided in the Soils and Geology section of the Background Information Report (Volume 1-1).
In general, the topographic elevation of area around the site is approximately 1,220 feet MSL. The 10-foot contour interval does not show the topographic relief at the creek. At SWMU B-11, the top of the creek bank is approximately 7 to 8 feet higher than the creek bed, which lies along the northern edge of the SWMU. The bank is steep and rough. Within SWMU B-11, therefore, drainage is to the north into Salado Creek which flows to the south-southeast.
The Upper Glen Rose is the uppermost geologic stratum in the area of SWMU B-11 (Figure B11-3). 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 where soils are poorly developed or eroded. The thickness of the Upper Glen Rose is estimated to be up to 150 feet thick 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 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.
The Upper Glen Rose Formation underlies the site but no bedrock outcrops are present within SWMU B-11. The uppermost geologic materials consist of 0.5 to 2 feet of loose brown to dark grayish-brown silt and sandy silt (Trinity and Frio soil). Below this layer is 2 to 3 feet of white to pinkish-white hard and soft clay. The Upper Glen Rose, which was comprised of packstone and wackestone, was encountered at approximately 5 feet bgs in all but one of the boreholes. Wackestone was found at 3 feet bgs in borehole B11-SB03. Voids were encountered in borings B11-SB03 through B11-SB05 at depths of between 7.5 and 10 feet bgs. A void was also encountered in B11-SB01 between 2 and 5 feet bgs. At borings SB03 through SB05, drilling was terminated when the void was encountered for safety reasons and to prevent loss of drilling equipment downhole. Boring logs are provided in Appendix B.
Based on current published information, there are known to be two major fault (shatter) zones at CSSA: the North Fault Zone and the South Fault Zone. The site is located within the northwest-southeast trending North Fault Zone (Figure B11-3). This fault (shatter) zone has been mapped with a width between 2,000 to 3,000 feet, and consists of multiple normal faults with small throws of displacement. Additional information on structural geology at CSSA can be found in the Environmental Encyclopedia (Soils and Geology, Background Information Report, Volume 1-1).
At CSSA, the uppermost hydrogeologic 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; however, no perched groundwater was encountered in the SWMU B-11 borings. 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 at approximately the same elevation. 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 pumping. Regional groundwater flow appears to be to the southeast.
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. 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. 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 groundwater information is available. The nearest well is monitoring well CS-MW1 located 425 feet to the southwest of SWMU B-11 (Figure B11-1). Water levels within well CS-MW1 have ranged from 44 feet BTOC (November 1998) to 251 feet BTOC (April 1996). The nearest offsite well is Well FO-22, a domestic water supply well, located 4,125 feet to the northwest of SWMU B-11.
The nearest surface water feature is the intermittently flowing Salado Creek, which lies along the northern boundary of the site and flows in a southeasterly direction (Figure B11-1). This creek exits the CSSA boundary over one mile southeast of SWMU B-11 and merges with the San Antonio River south of CSSA.
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 historical structures comprised of warehouses and bunkers located approximately 200 feet to the south. A prehistoric stone midden is located approximately 4,700 feet to the north in the Outer Cantonment Area. Cultural resources consisting of WWI training trenches are located approximately 1,200 feet to the southeast.
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).
Land within 0.25mile of the SWMU B-11 is classified as “Evergreen Forest Land“ to the north, east, and west, and “Commercial and Services” to the south in Figure 1.1 of the Technical Approach Document for Risk Assessment. Numerous igloos and five buildings used for storage are located within 0.25-mile south and southeast of the site.
No active water supply wells or livestock wells are located within 0.25 mile of the site. The closest well is monitoring well CS-MW1, approximately 400 feet to the southwest. Other wells within 0.25 miles of SWMU B-11 are Wells CS-2, CS-3, CS-4, CS-16, and CS-D, and these wells are currently used for monitoring purposes only. The land at SWMU B-11 is not used for any activities, and no utilities cross the site.
A small herd of cattle is maintained on CSSA by 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). Hunting stands 1, 2, and 3 are all located approximately 1,500 feet from SWMU B-11. A wildlife feed crop plot is located immediately south of the site. Four water tanks are maintained at CSSA for the purpose of sport fishing. Two of the tanks are located in the northwestern and northeastern portions of the North Pasture while the other two tanks are located near the western boundary of the Inner Cantonment.
The nearest potential habitat for local endangered species is black-capped vireo habitat that lies over 0.5-mile to the north of the site in the Outer Cantonment Area (Parsons ES, 1993).
An EM geophysical survey was performed at SWMU B-11 in April 1995. The EM survey was conducted along north-south transects spaced at 25-foot intervals. There were two anomalies identified at B-11 in the southeastern portion of the site. These anomalies were caused by cultural disturbances, namely the proximity of the fenceline to certain transects in that area. No other EM anomalies were observed at B-11. Therefore, the geophysical survey results do not indicate the presence of subsurface anomalies potentially related to past waste management activities. Results of the 1995 geophysical survey are also provided in Section 4 of the Technical Memorandum on Surface Geophysical Surveys at High Priority SWMUs (Parsons ES, October 1995).
Soil gas surveys were also performed at CSSA in 1995 in an effort to identify possible source areas for the chlorinated hydrocarbon contamination present in groundwater at well CS-16 and other CSSA wells. A large area bounded by North Outer Road to the north and Moyer Road to the east was included in the soil gas survey due to its proximity to Well CS-16. At the time of the survey, this area was identified as the “South Pasture.” The majority of this survey area is now known as AOC 38. However, one soil gas point (South Pasture 60,-60) sampled as part of the South Pasture survey is located within SWMU B-11 and several soil gas points are near SWMU B-11 (see Section 2.2.2).
PCE was detected at South Pasture 60,-60 and South Pasture 60,-70 at concentrations of 0.28 and 0.51 mg/L, respectively. At South Pasture 60,-50 2.4 µg/L of PCE was detected. Additional information about the South Pasture soil gas survey can be found in Section 9.1 of Appendix F of the Groundwater and Associated Source Characterization Report (Parsons ES, 1996) and a PCE soil gas plume map depicting the results of the 1995 survey is provided in Section 2.2.2.
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-11 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 concentrations, then the site will be closed under TRRP. A notification of intent to close sites identified to date (including SWMU B-11) 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-11 are VOCs, explosives, and metals, the cleanup levels should be the RLS for VOCs and explosives, and established background levels for metals. VOCs rarely occur naturally, and explosives are man-made chemicals. 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 Types (Parsons, February 2002). The background report is was approved by TNRCC on April 23, 2002.