[RFI/Closure Report] [Next Section]
On May 5, 1999 an Administrative Consent Order was issued to Camp Stanley Storage Activity (CSSA) pursuant to §3008(h) of the Solid Waste Disposal Act (SWDA), as amended by the Resource Conservation and Recovery Act (RCRA), and further amended by the Hazardous and Solid Waste Amendments (HSWA) of 1984. In accordance with the RCRA Facility Investigation (RFI) requirements of the Consent Order, an RFI report for Solid Waste Management Unit (SWMU) B-11 was completed in August 2002 to document the environmental condition of the site and site closure requirements, and recommend further investigation. This closure report includes by reference the information presented in the SWMU B-11 RFI Report (Parsons, 2002).
The SWMU B-11 RFI Report recommended excavation and disposal of waste at the site. Results for five borings sampled at SWMU B-11 indicated levels of arsenic, barium, chromium, cadmium, nickel, and zinc slightly above CSSA specific background levels.. The RFI report estimated 2,300 cubic yards (yd3) of soils and waste material would require removal at the site and confirmation sampling for arsenic, barium, chromium, cadmium, nickel, and zinc were to be conducted to confirm that the site achieved closure requirements. This report documents the closure activities at SWMU B-11.
The closure work was performed by Parsons under the U.S. Air Force Environmental Remediation and Construction (ENRAC) Contract F41624-01-D-8544, Task Order 19 (TO 0019). The Air Force Center for Environmental Excellence (AFCEE) provided technical oversight for the delivery order. Based upon the project statement of work (SOW), a set of work plans to govern the fieldwork was established. These include:
Work Plan Overview (Volume 1-1, TO 0019 Addendum);
Site-Specific Work Plan (Volume 1-2, SWMU B-11);
Field Sampling Plan (Volume 1-4, TO 0019 Addendum); and
Health and Safety Plan (Volume 1-5, TO 0019 Addendum).
Closure activities at SWMU B-11 were conducted during November and December 2003. As recommended in the RFI report, waste and waste residue were excavated and disposed off-site. In all, 3,078 yds3 of material were excavated and removed from the site. Confirmation sampling was also conducted to verify that arsenic, barium, chromium, cadmium, nickel, and zinc levels were below background concentrations. This list of analytes was based on metals exceeding CSSA background levels in RFI samples.
For this closure report, Section 1 provides the site-specific background and closure standard. Section 2 describes the closure actions and the closure evaluation. Section 3 summarizes the findings, evaluates attainment of data quality objectives (DQOs), provides
recommendations, and certifies the site closure. References cited in this report can be found in the Bibliography (Volume 1-1 of the Environmental Encyclopedia).
As described in Section 4.3 of the Risk Assessment Technical Approach Document (Volume 1-6), CSSA has opted to pursue closure of many of its sites under the Risk Reduction Rules (RRR) (30 Texas Administrative Code [TAC] §335). A notification of intent to close sites identified to date (including SWMU B-11) was sent to the Texas Commission on Environmental Quality (TCEQ) in accordance with the RRR on July 12, 1999. TCEQ acceptance of this notification was received on October 5, 1999.
Following the RRR guidelines, if site concentrations are at or below background, and all waste and waste residue has been removed, then the site can be closed under Risk Reduction Standard 1 (RRS1). Background levels are the RRS1 criteria for metals concentrations and laboratory reporting limits (RLs) are the RRS1 criteria for organic compounds. Based on the RFI sampling results at SWMU B-11, CSSA opted to clean the site to background levels and pursue closure under RRS1. If closure requirements under RRS1 are attained and approved by the TCEQ Executive Director, then the owner is released from the deed recordation requirement.
Due to the presence of waste at the site, as well as due to metals concentrations above background levels detected in RFI samples, removal of waste and waste residue was recommended in the RFI Report to meet RRS1 requirements.
1.2.1 CSSA
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, detailed data regarding the geology, hydrology, and physiography are also available for reference.
1.2.2 SWMU B-11
1.2.2.1 Site Description
The site covers approximately 0.92 acres and was used as a solid waste disposal area for an unknown period of time. As shown in Figure B11-6, the site is situated directly on the south/southwest bank of Salado Creek. (Figures B11-1 through B11-5 are provided in the RFI Report.) Figure B11-7 shows the site over time. Prior to closure activities, the terrain at the site was very rough due to erosion and trenching activities.
Prior to site closure activities, a partially-filled trench trending northwest-southeast was identified on the southern bank of Salado Creek. The trench was approximately 325 feet long, up to 15 feet deep on the west end, and graded upward to the east. The trench was approximately 25 feet wide at the southeastern end and increased in width to almost 100 feet wide at the northwestern end of the trench. To the west of the trench was a small mound of soil, presumably the material excavated to create the trench. Waste was partially buried on the east end of the trench, where the ground surface had a mounded appearance. Ammunition boxes, arms packing crates, and construction debris were found at the site during the initial field survey in 1993.
Additional background information regarding the location, size, and known historical use of the site can also be found 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.
1.2.2.2 Potential Sources of Contamination
The possible source of contamination at SWMU B-11 was buried solid waste, including construction and roofing debris, wire scrap, concrete, burnt wood, and parachutes, all of which were discovered during the November 2003 site excavation activities.
1.2.2.3 Site Location
SWMU B-11 is located in the north-central portion of the Inner Cantonment Area directly south of area of concern (AOC)-38 (Figure B11-6). 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 1,400 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.
A detailed description of the site environmental setting is provided in the CSSA Background Information Report (Volume 1-1) and the SWMU B-11 RFI Report (Parsons, 2002). A summarized description is provided in the paragraphs below.
The only soil type occurring at SWMU B-11 is the Trinity and Frio soil type. Trinity and Frio soils occur in creek beds that are frequently flooded. The topographic elevation of the site area is approximately 1,220 feet above mean sea level (MSL). Drainage within SWMU B‑11 is to the north towards Salado Creek.
The Upper Glen Rose (UGR) Limestone Formation is the uppermost geologic stratum in the area of SWMU B-11, as shown in Figure B11-8. The UGR consists of beds of blue shale, limestone, and marly limestone, with occasional gypsum beds, averaging 50 feet thick. The UGR is underlain by the Lower Glen Rose (LGR) (averaging 320 feet thick). The LGR is underlain by the Bexar Shale (BS) (regionally known as Hensell Shale, averaging 60 feet thick), and the Cow Creek (CC) (averaging 76 feet thick). The geologic strata dip approximately 10 to 12 degrees to the south-southeast at CSSA.
At CSSA, the uppermost hydrogeologic layer is the unconfined Upper Trinity Aquifer, which consists of the UGR. Locally at CSSA, low-yielding perched zones of groundwater can exist in the UGR; however, no perched groundwater was encountered in the SWMU B‑11 borings. Principle recharge into the Middle Trinity Aquifer is via precipitation infiltration at outcrops. Groundwater discharge occurs predominantly via natural springs, seeps, and pumping. Regional groundwater flow appears to be to the southeast.
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 B11‑6). When flowing, Salado Creek is an active recharge area for the Middle Trinity Aquifer. 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 World War I 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).
No active water supply wells or livestock wells are located within 0.25 mile of the site. The closest well is the cluster monitoring well CS-MW1, approximately 400 feet to the southwest. The depth to groundwater at well CS-MW1-LGR has ranged from 44.0 feet below top of casing (ft BTOC) (November 1998) to 251.55 ft BTOC (September 2000). Other wells used for monitoring only that are within 0.25 miles of SWMU B-11 include CS‑2, CS-3, CS-4, CS-16, and CS-D. The land at SWMU B‑11 is not used for any activities, and no utilities cross the site. 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). More detailed information on potential receptors at SWMU B-11 is included in the SWMU B-11 RFI Report (Parsons, 2002).
Investigations at SWMU B‑11 began in 1995 when geophysical and soil gas surveys were conducted in an effort to identify possible sources of contamination at nearby well CS‑16, which is approximately 1,100 feet to the north of SWMU B‑11 and is impacted by volatile organic compounds (VOC). Waste was observed at the ground surface at SWMU B‑11 during these surveys. Subsequently, in 2000, soil borings were drilled and sampled at the site. The results of these previous investigations are summarized in the paragraphs below.
1.4.1 Geophysical Survey
An electromagnetic (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 in the southeastern portion of SWMU B‑11. These anomalies were caused by cultural disturbances, namely the proximity of the fence line to certain transects in that area. No other EM anomalies were observed at SWMU B‑11. The geophysical survey results did not indicate the presence of subsurface anomalies potentially related to past waste management activities. However, there was some visible waste present on the surface and the ground surface was very uneven, indicating previous disturbance, and this indicated that buried waste was likely present. 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).
1.4.2 Soil Gas Survey
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 (Figure B11-6). 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 more sampling points are near SWMU B-11.
Very low concentrations of tetrachloroethene (PCE) were detected at South Pasture 60,‑60 (0.28 micrograms per liter [µg/L]) and South Pasture 60,‑70 (0.51 mg/L). At South Pasture 60,‑50, a concentration of 2.4 µg/L PCE was detected. South Pasture 60,-70 is located just south of the eastern end of SWMU B‑11, while South Pasture 60,‑50 is located just north of the eastern end of SWMU B‑11. 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 Figure B11‑4 of the SWMU B‑11 RFI Report (Parsons, 2002). Based on the very low PCE concentrations in soil gas at the site, it is concluded that PCE at SWMU B‑11 is associated with the soil gas plume emanating from the nearby SWMU B‑3 and O‑1 source areas, and not the result of a VOC release at the site.
1.4.3 Soil Borings
On February 28 and 29, 2000, five soil borings were drilled to characterize subsurface soils at SWMU B‑11 (B11‑SB01 through SB05). The boring locations are shown in Figure B11‑4 of the SWMU B‑11 RFI Report (Parsons, 2002) and in Figure B11‑9 of this report. The borings were placed in areas considered to have the highest probability of contamination based on visual observations of surface conditions. Three samples were obtained from each boring; one soil sample was taken from the surface, one from near the middle of the boring, and one at total depth. Boring depths ranged from 8.5 to 20 feet below ground surface (bgs). Lithologic descriptions from the boring logs indicate silt and clay was encountered overlying limestone and marl, identified as the UGR.
Samples collected above the bedrock were obtained using a decontaminated hollow-stem auger and split-spoon sampler. Rock samples were obtained by air core using a decontaminated core barrel. The analytes for the soil samples collected at SWMU B-11 were VOCs (SW-8260B), arsenic (SW-7060A), barium (SW-6010B), cadmium (SW-7131A), chromium (SW‑6010B), copper (SW6010B), lead (SW-7421), mercury (SW-7471A), nickel (SW‑6010B), zinc (SW-6010B), and explosives (SW-8330). A total of five soil and 11 Glen Rose Limestone (Upper) samples (including one duplicate) were submitted for analysis. All analytical results for samples collected from B11-SB01 through B11-SB05 are provided in Table B11‑1 and Appendix A of the SWMU B‑11 RFI Report.
1.4.3.1 Soil Results
The shallowest sample collected at each of the five boring locations was a surface soil sample. The only RRS1 exceedances in soil samples were at B11-SB01 (0.5-1 ft) and B11-SB04 (0.5-1 ft). At SB01, zinc was detected at 74.91 milligrams per kilogram (mg/kg), which slightly exceeded the background concentration of 73.2 mg/kg. At SB04, chloroform was detected above the RL; however, chloroform was also detected in the blank associated with this sample. Methylene chloride was detected above the RL of 0.005 micrograms per kilogram (µg/kg) in four of the five soil samples, at concentrations ranging from 0.0110 µg/kg to 0.0321 µg/kg; however, methylene chloride was also detected in the blank sample and it iscommonly associated with sampling equipment or laboratory equipment contamination. No explosives were detected in any of the samples, and no other metals or VOCs exceeded RRS1 levels in the soil samples.
1.4.3.2 Limestone Results
Arsenic, barium, chromium, nickel, and zinc levels each slightly exceeded RRS1 comparison criteria (site background levels) in one Glen Rose Limestone sample collected for the investigation. Barium (43.41 mg/kg), chromium (8.2 mg/kg), nickel (8.14 mg/kg), and zinc (15.33 mg/kg) levels exceeded RRS1 criteria in sample B11‑SB03 (4.5-5.0 feet). Background concentrations for these analytes are 10 mg/kg barium, 8.1 mg/kg chromium,
6.8 mg/kg nickel, and 11.3 mg/kg zinc. Arsenic slightly exceeded the RRS1 level in sample B11-SB01 (19.5-20.0 ft.), where a concentration of 3.91 mg/kg was detected.
Although the RFI report indicated that the cadmium concentration at B11-SB02 (9.5‑10.0 feet) was 0.5 mg/kg, a value, which exceeds the CSSA background level of 0.1 mg/kg, this value was found to be incorrect during further review of the data. The correct concentration, as reported in the laboratory analytical report, is 0.05 mg/kg, which is below the CSSA background concentration.
Methylene chloride, a common lab contaminant, was detected at levels above the RL in 10 of the 11 Glen Rose Limestone (Upper) samples submitted. The highest detected concentration of methylene chloride, 0.0417 µg/kg, occurred in sample B11‑SB02 (9.5 ‑ 10.5 feet). Chloroform was detected above the RL in samples B11‑SB04 (4.5-5.0 feet) and B11‑SB05 (8.0-8.5 feet); however, chloroform was also detected in the blank associated with these samples. Dichlorodifluoromethane (freon) was detected of 0.0106 µg/kg, slightly exceeding the RL of 0.005 µg/kg, in sample B11‑SB01 (9.5-10.0 feet).